Trace fossils: concepts, problems, prospects

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TRACE FOSSILS CONCEPTS, PROBLEMS, PROSPECTS

TRACE FOSSILS CONCEPTS, PROBLEMS, PROSPECTS Edited by WILLIAM MILLER, III Geology Department Humboldt State University Arcata, CA, USA

AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY

OXFORD TOKYO

PARIS

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, The Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK

First edition 2007 Copyright ß 2007 Elsevier B.V. All rights reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email: [email protected]. Alternatively you can submit your request online by visiting the Elsevier web site at http://elsevier.com/locate/permissions, and selecting Obtaining permission to use Elsevier material Notice No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN-13: 978-0-444-52949-7 ISBN-10: 0-444-52949-7

For information on all Elsevier publications visit our website at books.elsevier.com

Printed and bound in Italy 07 08 09 10 11

10 9 8 7 6 5 4 3 2 1

Contents

The Cincinnati School 23 Conclusions 28 Acknowledgements 29 References 29

Introduction: A User’s Guide— William Miller, III xiii List of Reviewers Contributors

xvii

xix

Memorial to Roland Goldring (1928–2005)— John E. Pollard xxi

3. Edward Hitchcock and Roland Bird: Two Early Titans of Vertebrate Ichnology in North America

I

S. GEORGE PEMBERTON, MURRAY K. GINGRAS,

THE HISTORICAL BACKGROUND OF ICHNOLOGY

AND JAMES A. MACEACHERN

Introduction 32 The Ichnology of the Connecticut Valley 33 Roland Bird and the Discovery of Sauropod Tracks 41 Conclusions 49 Acknowledgements 49 References 49

1. The Wadden Sea, Cradle of Invertebrate Ichnology GERHARD C. CADEÉ AND ROLAND GOLDRING

Introduction 03 The Early Beginnings of Ichnology 03 The Role of Experiments 04 Research in the Wadden Sea 04 Ichnology Elsewhere in the Wadden Sea The Promotion of Ichnology 08 Conclusions 10 Acknowledgements 10 References 10

08

4. The Ichnofacies Paradigm: A Fifty-Year Retrospective JAMES A. MACEACHERN, S. GEORGE PEMBERTON, MURRAY K. GINGRAS, AND KERRIE L. BANN

2. The Antecedents of Invertebrate Ichnology in North America: The Canadian and Cincinnati Schools

Introduction 52 The Rise of the Ichnofacies Concept Continental Ichnofacies 55 Softground Marine Ichnofacies 58 Substrate-Controlled Ichnofacies 68 Using the Ichnofacies Paradigm 74 Acknowledgements 75 References 75

S. GEORGE PEMBERTON, JAMES A. MACEACHERN, AND MURRAY K. GINGRAS

Introduction 14 The Early Canadian School

15

v

53

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CONTENTS

Acknowledgements References 131

II CONCEPTS, METHODS, THEORY, AND CONNECTIONS TO THE EARTH AND BIOLOGIC SCIENCES

MARKUS BERTLING

82

6. Taphonomy of Trace Fossils CHARLES E. SAVRDA

Introduction 92 Trace Fossil Preservation in Soft Mud 93 Preservation in Heterolithic Softground Successions 98 Preservation in Coarse-Grained Substrates 101 Preservation in Firmgrounds 103 Preservation in Hard Substrates 104 Preservation in Woodgrounds 105 Ichnofossil-Lagersta¨tten 106 Conclusions 107 Acknowledgements 107 References 107

7. Uses of Trace Fossils in Genetic Stratigraphy JAMES A. MACEACHERN, S. GEORGE PEMBERTON, MURRAY K. GINGRAS, KERRIE L. BANN, AND LYNN T. DAFOE

Introduction 110 Substrate-Controlled Ichnofacies 113 Substrate-Controlled Ichnofacies and the Role of Autocyclicity 119 Ichnological Applications to Genetic Stratigraphy 120 Conclusions 130

8. The Application of Trace Fossils to Biostratigraphy ROBERT B. MACNAUGHTON

5. What’s in a Name? Nomenclature, Systematics, Ichnotaxonomy Introduction 81 Treating Names of Trace Fossils: Nomenclature Classifying Trace Fossils: Systematics 82 Naming Trace Fossils: Ichnotaxonomy 83 Conclusions 90 Acknowledgements 90 References 91

130

Introduction 135 Limitations and Advantages of Trace Fossils in Biostratigraphy 135 Characteristic Applications of Trace Fossils in Biostratigraphy 136 Other Potentially Useful Ichnotaxa 145 Toward Reliable Trace-Fossil Biostratigraphy 146 Concluding Discussion 146 Acknowledgements 147 References 147

9. Trace Fossils and Marine Benthic Oxygenation CHARLES E. SAVRDA

Introduction 149 Oxygen-Related Ichnocoenoses (ORI) 149 Manifestation of ORI in Vertical Sequences 151 Case Study—Cretaceous Bridge Creek Limestone 153 Potential Limitations and Future Directions 154 Conclusions 156 Acknowledgements 156 References 156

10. Climatic Control of Marine Trace Fossil Distribution ROLAND GOLDRING, GERHARD C. CADEÉ, AND JOHN E. POLLARD

Introduction 159 Constraints on Recognition of Climatic Control of Trace Fossils 160 Ichnology of Certain Crustaceans 161 Spatangoid Echinoid Ichnology 164 Discussion on Modern Distributions of Infaunal Echinoids and Ophiomorpha-Forming Crustaceans 164 Ophiomorpha and Spatangoid Trace Fossils 165

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CONTENTS

A New Type Ichnospecies for Zoophycos 224 Ichnogenus Zoophycos Massalongo 1855 226 Conclusions 228 Acknowledgements 230 References 230

Other Trace Fossils of Possible Climatic Significance 168 Conclusions 169 Acknowledgements 170 References 170

11. Climatic Controls on Continental Trace Fossils STEPHEN T. HASIOTIS, MARY J. KRAUS, AND TIMOTHY M. DEMKO

Introduction 172 Distribution of Organisms and their Traces—Ichnofossils 173 Soil Formation and Palaeosols 175 Soil-Water Balance: Linking Soil, Biota, and Climate 176 Climate 177 Ichnopedologic Associations as Climate Indicators: Organism Behaviors and Palaeosols 181 Predictions of Ichnopedologic Associations of Palaeoclimate 184 Conclusions 192 Acknowledgements 193 References 193

14. Ichnofacies, Ichnocoenoses, and Ichnofabrics of Quaternary Shallow-Marine to Dunal Tropical Carbonates: A Model and Implications H. ALLEN CURRAN

Introduction 232 Ichnology of Carbonate vs. Siliciclastic Environments 233 The Geologic and Ichnologic Setting: Bahamas and South Florida 234 Ichnocoenoses of the Skolithos Ichnofacies 234 Ichnocoenoses of the Psilonichnus Ichnofacies 241 Conclusions 245 Acknowledgements 246 References 246

15. Deep-Sea Ichnology: Development of Major Concepts 12. The Trace-Fossil Record of Vertebrates STEPHEN T. HASIOTIS, BRIAN F. PLATT, DANIEL I. HEMBREE, AND MICHAEL J. EVERHART

Introduction 196 Vertebrate Ichnology: Concepts and Methods Locomotion Traces: Trails, Tracks, and Trackways 197 Burrows and Nests 205 Feeding Trace Fossils 211 Hominid Trace Fossils 214 Future Directions 215 Acknowledgements 216 References 216

13. Zoophycos and the Role of Type Specimens in Ichnotaxonomy DAVIDE OLIVERO

Introduction 219 An Enigmatic Fossil 219 The Type Specimen 224

197

ALFRED UCHMAN

Introduction 248 Age of Fucoids 248 From Algae to Worms: Towards Consistent Ichnotaxonomy 249 Morphological Classifications 250 What Worms are Doing: Fossil Behaviour 250 Environmental Distribution of Trace Fossils and the Ichnofacies Concept 252 Colonization, Bioturbation and Ichnofabric Concepts 253 Substrate 257 Trophic Level 258 Changes Through Geological Time and Evolutionary Aspects 259 Deep-Sea Fine-Grained Non-Turbiditic Sediments 261 Neoichnology 262 Further Perspectives 262 Acknowledgements 263 References 263

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CONTENTS

16. Continental Ichnology: Fundamental Processes and Controls on Trace Fossil Distribution

Conclusions 338 Acknowledgements References 340

340

STEPHEN T. HASIOTIS

Introduction 268 The Continental Realm 269 Terrestrial and Aquatic Biota: Tracemaker Classification and Behavior 276 Synthesis: Continental Ichnocoenoses 279 Conclusion: Two Distinct Parts but One Ichnology 282 Acknowledgements 283 References 283

17. Invertebrate Ichnology of Continental Freshwater Environments ´ NGANO LUIS ALBERTO BUATOIS AND MARIÁ GABRIELA MA

Introduction 285 Continental Ichnofacies 285 Ichnology of Fluvial Systems 287 Ichnology of Lacustrine Systems 299 The Ichnofabric Approach to Freshwater Ichnofaunas 307 Applications of Ichnology in Sequence Stratigraphy of Continental Successions 310 Marine vs. Nonmarine 315 Freshwater Ichnofaunas in Marginal Marine Environments 316 Acknowledgements 316 References 316

19. Early History of Symbiosis in Living Substrates: Trace-Fossil Evidence from the Marine Record LEIF TAPANILA AND A.A. EKDALE

Introduction 345 Bioclaustrations as Fossilized Behavior 346 Criteria for Distinguishing Bioclaustrations 347 Bioclaustrations in Context with Other Sessile Associations 349 Early Fossil Record of Bioclaustrations 349 Diversity Trends in the Paleozoic 351 Conclusions 354 Acknowledgements 354 References 354

20. Macroborings and the Evolution of Marine Bioerosion MARK A. WILSON

Introduction 356 Commonly Bored Hard Substrates 357 Most Common Marine Macroboring Taxa 357 History of Macroboring Through the Phanerozoic 363 Conclusions 365 Acknowledgements 365 References 365

18. Traces of Gastropod Predation on Molluscan Prey in Tropical Reef Environments

21. Microborings and Microbial Endoliths: Geological Implications

SALLY E. WALKER

GUDRUN RADTKE, AND KLAUS VOGEL

Introduction 324 Overview of Potential Trace Fossils Attributed to Predatory Reef Gastropods 325 Note on Classification, Ranking Treatment of the Gastropod Groups, and Oichnus 325 Shell-Drilling and Shell-Rasping Families and their Potential Trace Fossil Record 325 Gastropod Predators that Wedge Chip-And-Break, and Abrade Shells 333 Predatory Gastropods that Engulf Prey, Produce Toxins and Acidic Secretions, and Promote Corrosion of the Shell or Shell Blisters 336

Introduction 368 Preparation and Study of Microbial Endoliths and Microborings 368 Diversity and Geological Significance of Microbial Euendoliths 369 Microbial Endoliths and Microborings in the Fossil Record 373 Distribution and Environmental Ranges of Microbial Endoliths 375 Ichnological Treatment of Microborings 376 Vertical Distribution of Phototrophic Microbial Euendoliths 378

INGRID GLAUB, STJEPKO GOLUBIC, MARCOS GEKTIDIS,

ix

CONTENTS

Technical Uses of Trace Fossils in Gravity and Piston Cores 423 Conclusions 425 Acknowledgements 426 References 426

Conclusions 378 Future Research 378 Acknowledgements 379 References 379

22. Stromatolites: A 3.5-Billion-Year Ichnologic Record RUSSELL S. SHAPIRO

25. Theoretical and Experimental Ichnology of Mobile Foraging KAREN KOY AND ROY E. PLOTNICK

Why Stromatolites are Trace Fossils 382 The Complexity of Form 382 Models of Formation 383 How Stromatolites have been Used in the Past as Trace Fossils 385 Utility as Trace Fossils 386 Conclusions 388 Acknowledgements 388 References 388

23. Trace Fossils in Evolutionary Paleoecology

Introduction 428 Ichnofossils: Recording Behavior 429 What is Foraging? 430 Foraging Phases 430 Controls on Foraging 431 Resource Detection 432 Movement Related to Foraging 433 A Model for Mobile Foraging 434 Applications to Ichnology 438 Implications for the Early Evolution of Trace Fossils 438 Acknowledgements 439 References 439

´ NGANO AND LUIS ALBERTO BUATOIS MARIÁ GABRIELA MA

Introduction 391 Ediacaran Ecosystems 392 The Cambrian Explosion 394 The Ordovician Radiation 396 Colonization of Brackish Water Environments Continental Ichnofaunas Through the Phanerozoic 400 Conclusions 403 Acknowledgements 403 References 403

26. Material Constraints on Infaunal Lifestyles: May the Persistent and Strong Forces be with You 398

PETER A. JUMARS, KELLY M. DORGAN, LAWRENCE M. MAYER, BERNARD P. BOUDREAU, AND BRUCE D. JOHNSON

Introduction 442 The Materials 445 The Processes 447 Discussion 453 Conclusions 456 References 456

III ADVANCES, FRESH APPROACHES, AND NEW DIRECTIONS 24. Importance and Usefulness of Trace Fossils and Bioturbation in Paleoceanography ¨ WEMARK LUDVIG LO

Introduction 413 Trace Fossils 414 Bioturbation 419

27. Complex Trace Fossils WILLIAM MILLER, III

Introduction: What are Complex Trace Fossils? 458 The Concept of Complexity Applied to Biogenic Structures 459 Classification 461 Interpretation 462 Conclusions 463 Acknowledgements 465 References 465

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CONTENTS

28. A Constructional Model for Zoophycos DAVIDE OLIVERO AND CHRISTIAN GAILLARD

Introduction 466 Main Characteristics 466 Construction of the Lamina 467 The Construction of Lamellae 469 Construction of Lobes 473 Conclusions 476 Acknowledgements 476 References 476

Material and Methods 510 Bioturbation Activity of Macroscopic Burrowers 510 Meiobenthic Trace Fossils 511 Preservation of Soft-Bodied Meiobenthos Taphonomic History 514 Tidality in the Epicontinental Germanic Basin? 515 Conclusions 515 Acknowledgements 516 References 516

513

29. Arthropod Tracemakers of Nereites? Neoichnological Observations of Juvenile Limulids and their Paleoichnological Applications

RICHARD G. BROMLEY, MAX WISSHAK, INGRID GLAUB, AND

ANTHONY J. MARTIN AND ANDREW K. RINDSBERG

ARNAUD BOTQUELEN

Introduction 478 Nereites and Its Makers: Previous Hypotheses 479 Traces of Juvenile Limulus polyphemus: A Neoichnological Analog for Nereites 480 Nereites and Its Makers Reconsidered 486 Ontogeny and Ichnodiversity 488 Conclusions 488 Acknowledgements 488 References 488

30. Macaronichnus isp. Associated with Piscichnus waitemata in the Miocene of Yonaguni-jima Island, Southwest Japan

32. Ichnotaxonomic Review of Dendriniform Borings Attributed to Foraminiferans: Semidendrina igen. nov.

Introduction 518 History 518 The Dual Nomenclature 519 Details of Morphology 520 Biological Interpretation 520 Recent Distribution and Ecological Aspects 525 Stratigraphic Record 525 Possible Precursors 526 Creation of a New Ichnofamily, Dendrinidae Conclusions 527 Appendix: Systematic Ichnology 528 Acknowledgements 529 References 529

NOBUHIRO KOTAKE

33. Ecological and Evolutionary Controls on the Composition of Marine and Lake Ichnofacies

Introduction 492 Geologic Setting 493 Piscichnus waitemata Filled with Macaronichnus isp. 494 Discussion 498 Conclusions 500 Acknowledgements 500 References 500

MOLLY F. MILLER AND DAVID S. WHITE

31. Meiobenthic Trace Fossils as Keys to the Taphonomic History of Shallow-Marine Epicontinental Carbonates DIRK KNAUST

Introduction 502 Location and Geologic Setting Sedimentology 503

503

Introduction 531 Seilacher’s Model of Control and Distribution of Behavior: Ichnofacies 532 Factors Controlling Marine Ichnofacies 532 Ecologically and Ichnologically Important Aspects of Lakes 534 Benthic Animals in Lakes vs. the Ocean 536 Comparison of Marine vs. Lacustrine Ichnofacies 540 Implications and Significance 541 Conclusions 542 Acknowledgements 542 References 542

527

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CONTENTS

34. Trace Fossils in an Archaeological Context: Examples from Bison Skeletons, Texas, USA DIXIE L. WEST AND STEPHEN T. HASIOTIS

Introduction 545 Archaeological Setting and Previous Analyses 546 Approach and Method 547 Ichnology—Architectural and Surficial Morphology, Tracemaker, and Discussion 547 Invertebrate Traces 547 Human Modifications 555 Weathered Bone 558 Discussion and Conclusions 559 Acknowledgements 560 References 560

35. Ichnofacies of an Ancient Erg: A Climatically Influenced Trace Fossil Association in the Jurassic Navajo Sandstone, Southern Utah, USA A.A. EKDALE, RICHARD G. BROMLEY, AND DAVID B. LOOPE

Introduction 562 Geologic Setting 563 Organism Traces in Dunes Trace Fossils 564

Trace Makers 568 Paleoecologic Interpretations 568 Paleoclimatic Implications 569 Entradichnus Ichnofacies 570 Conclusions 572 Acknowledgements 573 References 573

36. Endobenthic Response through Mass-Extinction Episodes: Predictive Models and Observed Patterns JARED R. MORROW AND STEPHEN T. HASIOTIS

Introduction 575 Background 576 Endobenthic Ecosystems and Extinction 577 Predictive Models of Endobenthic Response 579 Observed Endobenthic Responses Across Mass-Extinction Intervals 581 Discussion—Hypothesized and Empirical Endobenthic Ecosystem Responses Compared 592 Directions for Future Research 594 Acknowledgements 594 References 595

564 Index

599

Introduction: A User’s Guide William Miller, III

ICHNOLOGY AT THE BEGINNING OF THE TWENTY-FIRST CENTURY

following Seilacher’s initial concepts. This kind of activity continues to dominate trace fossil research. Growing gradually and less conspicuously along side the nomenclatural approach has been a more analytic perspective. This involves the fundamental business of trying to determine the trace-producing organisms, comparisons with modern trace producers and modern environments, functional interpretations of structures, computer modeling, and novel approaches to the interpretation of paleoethologic, physiologic and physicochemical properties of biogenic structures of all kinds. The one aspect that has never been adequately developed is theory. I am not sure that the nomenclatural systems developed 50 years ago really qualify as biologic theory; this kind of development may have to wait until connections to behavioral ecology and evolutionary theory have been more completely and plausibly established, and is likely to grow more readily from the analytic side of ichnology. I will be quick to add that the traditional nomenclatural approach has worked very well in getting the modern enterprise of ichnology up and on its feet, has made possible the systematic documentation needed before generalizations could be attempted, and has secured important and reliable applications to sedimentary geology. So, it might be better to say that the biologic side of ichnology is where theory development has lagged—it depends on whether one sees trace fossils primarily as sedimentary structures or as ethologic records. Most modern workers have always considered them to be both, but most have emphasized connections to sedimentology and stratigraphy. Now, skip forward to the beginning of the twentyfirst century, and we see ichnology as one of the most active branches of paleontology (or sedimentary geology, if you prefer), with no signs of slowing down.

We have been describing and attempting to interpret trace fossils, more or less effectively, for over a century. One could point to several times in the history of paleontology or sedimentary geology when ichnology, as a separate discipline, appears to take shape for the first time. This is largely a matter of when the various early practitioners were active. I will leave it to the historians of our discipline to nail down all the exact dates, key figures and origins of ideas. A concise historical sketch can be found in the introduction to Ekdale et al. (1984). It is clear from this brief account, and from the longer essay by Osgood (1975) and especially the excellent historical chapters that follow, that the origins of ichnology are varied but that the discipline takes on its modern methodologic and conceptual aspects in the 1950s and 1960s. In anglophone countries, this development is usually associated with a ‘founder’ (Dolf Seilacher, signaled especially by a series of extremely influential articles: e.g., 1953, 1962, 1964, 1967a,b) and a ‘founding document’ (Ha¨ntzschel, 1962, 1975)—at least for invertebrate ichnology. Vertebrate and plant trace fossil researchers would tell the story a bit differently (see the essays that follow). But most of the central concepts and methods start to circulate and become widely applied or discussed at about this time. During the next five decades, the work of ichnology was largely nomenclatural, not simply limited to the naming and revision of ichnotaxa, but involving the classification and naming of ichnofacies, applying and modifying behavioral classification, and involving the documentation of whole assemblages of different ages and depositional contexts—in many instances

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INTRODUCTION: A USER’S GUIDE

We have a sense of where we have come from, a good idea of what works and does not work, and a whole host of notions about the potential growing points of ichnology. This book should provide a picture of how things stand at the beginning of the new century, and where ichnology may go next.

PURPOSE OF THE BOOK This collection of historical sketches, reviews of central concepts and previous work, and chapters describing ongoing research is intended primarily as a progress report on the state of ichnology at the beginning of the twenty-first century. It will also serve as a kind of stepping stone or developmental landmark: a collection of chapters in the ‘line of descent’ from the books and edited volumes that I think mark the beginning of the modern, international ichnology that we practice today (most significantly represented in the English language by Ha¨ntzschel, 1962, 1975; Osgood, 1970; Frey, 1975; Basan, 1978; McCall and Tevesz, 1982; Ekdale et al., 1984; Miller et al., 1984; Curran, 1985; Bromley, 1990, 1996; Ekdale and Pollard, 1991; Maples and West, 1992; Donovan, 1994; Lockley and Hunt, 1995)—a discipline that continues to expand in different directions with new volumes appearing every year (e.g., Pemberton et al., 2001; Hasiotis, 2002; Miller, 2003; McIlroy, 2004; Webby et al., 2004; and more in press) and its own special journal (Ichnos). Trace Fossils: Concepts, Problems, Prospects will also be useful to new ichnologists as a starting place: the source of inspiration, ideas and methods that will fuel future research and possibly launch new careers. Established researchers could use this collection of chapters as a way to check the progress of their own particular brand of ichnology or to keep tabs on what other researchers in the discipline are doing. And I hope scientists in other fields will take notice, and see the many potential connections to their parts of geology and biology. Ichnology as a scientific discipline is more vibrant than ever, has consolidated past accomplishments into a strong conceptual and methodologic framework, and continues to push outward with new discoveries, revisions, applications and connections. This volume contains not only the results of our discipline’s accomplishments to date, but also some clear incentives for future growth. The book is divided into three parts. The first part consists of historical sketches of the development of

ichnology, reviewing background information that is rarely brought out and recognizing older researchers who were never adequately acknowledged. The second contains chapters concerning concepts and practice, indicates connections to other disciplines in the earth and biologic sciences, and conveys a sense of the accomplishments and potential of ichnology. The last part is a mix of chapters that explore new territory, describe novel approaches, and serve as examples of ongoing work. There is something here for novice and veteran, outsider and insider, and for the biologists and the geoscientists.

THANKS WHERE THANKS ARE DUE Projects such as this one are impossible without the cooperation of dedicated, well-informed and experienced reviewers willing to spend their valuable time helping to ensure the quality of the contributions. To all the reviewers I extend my sincere thanks; but to those who reviewed several chapters, I owe a great debt. All are listed in the section that follows. A few reviewers, however, deserve special recognition for working on more than one chapter or for giving advice at critical stages in the development of this book: Richard Bromley, Al Curran, Tony Ekdale, Murray Gingras, John Huntley, Molly Miller, Ron Pickerill, Sally Walker and Andreas Wetzel. My friend and mentor, Molly Miller, must be singled out here, because of special help given when it was desperately needed. I thank John Pollard for providing the Memorial to Roland Goldring, to whom this volume is most appropriately dedicated. I believe Roland would have liked very much what we have done here, and would have considered the chapters well crafted, interesting and useful. The editors at Elsevier were immensely helpful and not a little tolerant of my ideas and goals. Femke Wallien invited me to undertake this project in the first place, and gave valuable advice about organization and production. She, and her assistant Tonny Smit, helped me to get the project underway. More recently, Tirza van Daalen and her assistant Pauline Riebeek have guided the book through the final stages of assembly to publication. Their help and advice are much appreciated. Finally, I thank the authors—especially the ones who took the deadlines as seriously as I did—for a remarkable set of chapters. I think we really can get a sense of how things stand in ichnology at the beginning of the twenty-first century from this collection of work. Moreover, we see how trace fossil

REFERENCES

research is carried out, how the central ideas and concepts have been developed and applied, which problems have persisted despite decades of work, and some good indications of where the discipline is heading.

References Basan, P.B. (Ed.) (1978). Trace Fossil Concepts, Society of Economic Paleontologists and Mineralogists, Short Course 5, 181 pp. Bromley, R.G. (1990). Trace Fossils: Biology and Taphonomy, Unwin Hyman, London, 280 pp. Bromley, R.G. (1996). Trace Fossils: Biology, Taphonomy and Applications, 2nd edition. Chapman and Hall, London, 361 pp. Curran, H.A. (Ed.) (1985). Biogenic Structures: Their Usefulness in Interpreting Depositional Environments, Society of Economic Paleontologists and Mineralogists, Special Publication 35, 347 pp. Donovan, S.K. (Ed.) (1994). The Palaeobiology of Trace Fossils, Wiley, Chichester, 308 pp. Ekdale, A.A. and Pollard, J.E. (Eds.) (1991). Ichnofabric and Ichnofacies. Palaios, 6, pp. 199–343. Ekdale, A.A., Bromley, R.G. and Pemberton, S.G. (1984). Ichnology: Trace Fossils in Sedimentology and Stratigraphy, Society of Economic Paleontologists and Mineralogists, Short Course 15, 317 pp. Frey, R.W. (Ed.) (1975). The Study of Trace Fossils: A Synthesis of Principles, Problems, and Procedures in Ichnology, Springer-Verlag, New York, 562 pp. Ha¨ntzschel, W. (1962). Trace fossils and problematica. In: Moore, R.C. (Ed.), Treatise on Invertebrate Paleontology, Part W, Geological Society of America and University of Kansas, pp. W177–W245. Ha¨ntzschel, W. (1975). Trace fossils and problematica. In: Teichert, C. (Ed.), Treatise on Invertebrate Paleontology, Part W, Supplement 1, Geological Society of America and University of Kansas, pp. W1–W269. Hasiotis, S.T. (2002). Continental Trace Fossils, Society of Economic Paleontologists and Mineralogists, Short Course Notes 51, SEPM, Tulsa, Oklahoma, 132 pp.

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Lockley, M. and Hunt, A.P. (1995). Dinosaur Tracks, and other Fossil Footprints of the Western United States, Columbia University Press, New York, 338 pp. Maples, C.G. and West, R.R. (Eds.) (1992). Trace Fossils, Paleontological Society, Short Course 5, 238 pp. McCall, P.L. and Tevesz, M.J.S. (Eds.) (1982). Animal–Sediment Relations: The Biogenic Alteration of Sediments, Plenum, New York, 336 pp. McIlroy, D. (Ed.) (2004). The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis, Geological Society of London, Special Publication 228, 490 pp. Miller III, W. (Ed.) (2003). New Interpretations of Complex Trace Fossils. Palaeogeography, Palaeoclimatology, Palaeoecology (Special Issue), 192, 343 pp. Miller, M.F., Ekdale, A.A. and Picard, M.D. (Ed.) (1984). Trace Fossils and Paleoenvironments: Marine Carbonate, Marginal Marine Terrigenous and Continental Terrigenous Settings. Journal of Paleontology, 58, 283–597. Osgood Jr., R.G. (1970). Trace fossils of the Cincinnati area. Paleontographica Americana, 6, 281–444. Osgood Jr., R.G. (1975). The history of invertebrate ichnology. In: Frey, R.W. (Ed.), The Study of Trace Fossils, Springer-Verlag, New York, pp. 3–12. Pemberton, S.G., Spila, M., Pulham, A.J., Saunders, T., MacEachern, J.A., Robbins, D. and Sinclair, I.K. (2001). Ichnology and Sedimentology of Shallow to Marginal Marine Systems: Ben Nevis and Avalon Reservoirs, Jeanne d’Arc Basin, Geological Association of Canada, Short Course Notes 15, 343 pp. ¨ ber die Seilacher, A. (1953). Studien zur Palichnologie. I, U Methoden der Palichnologie. Neues Jahrbuch fu¨r Geologie und Palaöntologie Abhandlungen, 96, 421–452. Seilacher, A. (1962). Paleontological studies on turbidite sedimentation and erosion. Journal of Geology, 70, 227–234. Seilacher, A. (1964). Biogenic sedimentary structures. In: Imbrie, J. and Newell, N.D. (Eds.), Approaches to Paleoecology, Wiley, New York, pp. 296–316. Seilacher, A. (1967a). Bathymetry of trace fossils. Marine Geology, 5, 413–428. Seilacher, A. (1967b). Fossil behavior. Scientific American, 217, 72–80. Webby, B.D., Mańgano, M.G. and Buatois, L.A. (Eds.) (2004). Trace Fossils in Evolutionary Palaeoecology: Proceedings of Session 18 (Trace Fossils) of the First International Palaeontological Congress, Sydney, Australia, July 2002. Fossils and Strata, 51, 153 pp.

List of Reviewers

Ken Aalto Kerrie Bann Dave Bottjer Jane Brockman Richard Bromley* Luis Buatois David Burnham Gerhard Cadeé Bill Chaisson Paul Copper Al Curran* Rick Devlin Mary Droser Tony Ekdale* Christian Gaillard Marcos Gektidis Elizabeth Gierlowski-Kordesch Murray Gingras* Susan Goldstein Steve Hasiotis John Huntley* So¨ren Jensen Alan Kohn Michal Kowalewski Heinz Kozur Lisa Levin James MacEachern

Rob MacNaughton Gabriela Mańgano Tony Martin Ken McKinney Bob Metz Molly Miller* Liz Nesbitt Davide Olivero Paddy Orr Tim Palmer Lisa Park Bill Phelps Ron Pickerill* Andy Rindsberg Francisco Rodriguez-Tovar Ray Rogers Steve Rowland Chuck Savrda Ju¨rgen Schneider Leif Tapanila John Taylor Alfred Uchman Sally Walker* Andreas Wetzel* Paul Wignall Mark Wilson

*Reviewed more than one chapter.

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Contributors

Kerrie L. Bann (52, 110) Ichnofacies Analysis, Inc., 9 Sienna Hills Court SW, Calgary, Alberta T3H 2W3, Canada Markus Bertling (81) Geological and Palaeontological Institute, University of Mu¨nster, Corrensstra. 24, D-48149 Mu¨nster, Germany Arnaud Botquelen (516) UFR Sciences & Techniques, Paleóntologie, University of Brest, C.S. 93837, F-29238 Brest, France Bernard P. Boudreau (441) Department of Oceanography, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada Richard G. Bromley (516, 560) Geological Institute, University of Copenhagen, Oester Voldgade 10, DK-1350 Copenhagen K, Denmark Luis Alberto Buatois (284, 390) Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada Gerhard C. Cadeé (3, 158) Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, Texel, The Netherlands H. Allen Curran (231) Department of Geology, Smith College, Northampton, Massachusetts 01063, U.S.A. Lynn T. Dafoe (110) Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Timothy M. Demko (171) Department of Geological Sciences, University of Minnesota—Duluth, 229 Heller Hall, 1114 Kirby Drive, Duluth, Minnesota 55812, U.S.A. Kelly M. Dorgan (441) School of Maine Sciences, University of Maine, Orono, Maine 04469, U.S.A. A.A. Ekdale (344, 560) Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112-0111, U.S.A.

Michael J. Everhart (195) Sternberg Museum of Natural History, Fort Hays State University, Hays, Kansas 67601, U.S.A. Christian Gaillard (465) UMR 5125 CNRSPaleóenvironnements et Paleóbiosphe`re, UFR Sciences de la Terre, Universite´ Claude Bernard Lyon 1, 69622 Villeurbanne cedex, France Marcos Gektidis (367) GeologischPalaöntologisches Institut, Johann Wolfgang GoetheUniversita¨t Frankfurt, Senckenberganlage 32-34, 60325 Frankfurt, Germany Murray K. Gingras (14, 32, 52, 110) Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Ingrid Glaub (367, 516) GeologischPalaöntologisches Institut, Johann Wolfgang GoetheUniversita¨t Frankfurt, Senckenberganlage 32-34, 60325 Frankfurt, Germany Roland Goldring (3, 158) Deceased Stjepko Golubic (367) Biological Science Center, Boston University, Boston, Massachusetts 02215, U.S.A. Stephen T. Hasiotis (171, 195, 267, 543, 573) Department of Geology, University of Kansas, 1475 Jayhawk Blvd., Lawrence, Kansas 66045-7613, U.S.A. Daniel I. Hembree (195) Department of Geological Sciences, 316 Clippinger Laboratories, Ohio University, Athens, Ohio 45701, U.S.A. Bruce D. Johnson (441) Department of Oceanography, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada Peter A. Jumars (441) School of Marine Sciences & Darling Marine Center, University of Maine, 193 Clark’s Cove Road, Walpole, Maine 04573, U.S.A. Dirk Knaust (501) Statoil ASA, N-4035 Stavanger, Norway

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CONTRIBUTORS

Nobuhiro Kotake (491) Department of Earth Sciences, Faculty of Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan Karen A. Koy (427) Department of Earth and Environmental Sciences, University of Illinois—Chicago, 845 West Taylor Street, Chicago, Illinois 60607, U.S.A. Mary J. Kraus (171) Department of Geological Sciences, University of Colorado, Campus Box 399, 2200 Colorado Ave., Boulder, Colorado 80309, U.S.A. David B. Loope (560) Department of Geosciences, University of Nebraska, Lincoln, Nebraska 68588-0340, U.S.A. Ludvig Lo¨wemark (412) Department of Geosciences, National Taiwan University, P.O. Box 13-318, Taipei 106, Taiwan James A. MacEachern (14, 32, 52, 110) Department of Earth Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada Robert B. MacNaughton (134) Geological Survey of Canada, Natural Resources Canada, 3303 33rd Street NW, Calgary, Alberta T2L 2A7, Canada Marıá Gabriela Mańgano (284, 390) Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada Anthony J. Martin (477) Department of Environmental Studies, Emory University, Atlanta, Georgia 30322, U.S.A. Lawrence M. Mayer (441) School of Marine Sciences, Darling Marine Center, University of Maine, Walpole, ME 04573, U.S.A. Molly F. Miller (529) Department of Earth and Environmental Sciences, 2301 Vanderbilt Place, Vanderbilt University, Nashville, Tennessee 37235, U.S.A. William Miller, III (xiii, 457) Department of Geology, Humboldt State University, 1 Harpst Street, Arcata, California 95521, U.S.A. Jared R. Morrow (573) Department of Geological Sciences, 5500 Campanile Dr., 237 GMCS, San Diego State University, San Diego, CA 92182-1020, U.S.A. Davide Olivero (218, 465) UMR 5125 CNRSPaleóenvironnements et Paleóbiosphe`re, UFR Sciences de la Terre, Universite´ Claude Bernard Lyon 1, 69622 Villeurbanne cedex, France

S. George Pemberton (14, 32, 52, 110) Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Brian F. Platt (195) Department of Geology, University of Kansas, 1475 Jayhawk Blvd., Lawrence, Kansas 66045-7613, U.S.A. Roy E. Plotnick (427) Department of Earth and Environmental Sciences, University of Illinois—Chicago, 845 West Taylor Street, Chicago, Illinois 60607, U.S.A. John E. Pollard (xxi, 158) School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester M13 9PL, United Kingdom Gudrun Radtke (367) Hessisches Landesamt fu¨r Umwelt und Geologie, Rheingaustr. 186, 65203 Wiesbaden, Germany Andrew K. Rindsberg (477) Geological Survey of Alabama, P.O. Box 869999, Tuscaloosa, Alabama 35486-6999, U.S.A. Charles E. Savrda (92, 148) Department of Geology and Geography, Auburn University, Auburn, Alabama 36849-5305, U.S.A. Russell S. Shapiro (381) Department of Geological and Environmental Sciences, California State University, Chico, California 95929, U.S.A. Leif Tapanila (344) Department of Geosciences, Idaho State University, Pocatello, Idaho 83209-8072, U.S.A. Alfred Uchman (247) Institute of Geological Sciences, Jagiellonian University, Oleandry 2a, 30-063 Krako´w, Poland Klaus Vogel (367) Geologisch-Palaöntologisches Institut, Johann Wolfgang Goethe-Universita¨t Frankfurt, Senckenberganlage 32-34, 60325 Frankfurt, Germany Sally E. Walker (323) Department of Geology, University of Georgia, Athens, Georgia 30602, U.S.A. Dixie L. West (543) Natural History Museum and Biodiversity Research Center, University of Kansas, Dyche Hall, Lawrence, Kansas 66045, U.S.A. David S. White (529) Hancock Biological Station, Murray State University, 561 Emma Dr., Murray, Kentucky 42071, U.S.A. Mark A. Wilson (355) Department of Geology, The College of Wooster, Wooster, Ohio 44691-2363, U.S.A. Max Wisshak (516) Institute of Palaeontology, University of Erlangen, Loewenichstr. 28, D-91054 Erlangen, Germany

Memorial to Roland Goldring (1928–2005) John E. Pollard School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester M13 9PL, UK

early issues of Palaeontology (Goldring, 1958; Amos et al., 1960). In 1956, Roland moved to become an assistant lecturer at St Andrew’s University, Scotland; then in 1959 he was appointed to a lectureship at Reading University. From here Roland published his first article on ichnology, ‘Trace Fossils of the Baggy Beds of North Devon’ (Goldring, 1962) which became a classic study as it combined the use of trace fossils with sedimentology of shallow marine sandstones– fields he continued to research for the next four decades. In 1962, the new sedimentology laboratories were opened at Reading as Postgraduate Research Institute for Sedimentology (P.R.I.S) and Roland invited Dolf Seilacher to present his scheme of ichnofacies as an inaugural address. This address and Seilacher’s subsequent lecture to the Palaeontological Association at the Geological Society on behaviour of trilobites deduced from trace fossils opened the eyes of several younger palaeontologists and sedimentologists to the potential of trace fossils. During the 1960s Roland continued to research and publish on trace fossils and shallow marine sandstones, visiting Australia to examine the Ediacara Series (Goldring and Curnow, 1967) and preparing his Geological Society Memoir on sedimentology of the Baggy Beds (Goldring, 1971). Ichnology articles varied from reviews on deltaic and shallow marine deposits (Goldring, 1964), to limulid undertracks (Goldring and Seilacher, 1971) and burrowing of Micraster in the Chalk (Goldring and Stevenson, 1970) in the landmark volume Trace Fossils (Crimes and Harper, 1970). In 1969, Roland visited the U.S.S.R. for six weeks on behalf of the Royal Society to meet Professor R.F. Hecker and report on the state of palaeontology and sedimentology in the U.S.S.R. He was one of the

Roland Goldring (Figs. 1 and 2), the senior British ichnologist, died on August 30, 2005 from a heart attack while cycling to the University of Reading. In appreciation of his many contributions to ichnology, sedimentology and palaeontology, particularly fossil–sediment relationships over five decades, this book is dedicated to his memory. The selected publications cited and listed below reflect the breadth and development of Roland’s interests in his long academic career. Although born in London on June 28, 1928, Roland grew up in the coastal town of Westward Ho! in North Devon before returning to London for secondary education at Royal Commercial Travellers’ Schools at Pinner, Middlesex. After school and National Service in the army (1946–1948), Roland proceeded to Bristol University, graduating with an Honours B.Sc. in Geology in 1952. He then studied for a Ph.D. in Bristol (1952–1955) on palaeontology and stratigraphy of Devonian and Carboniferous rocks of the North Devon coast under the supervision of Professor Scott Simpson, who had studied the type section of the Devonian of the Eifel region before the Second World War under Professor Rudolf Richter. In 1955–1956, Roland held a post-doctoral research associateship jointly between universities of Bristol and Frankfurt am Main. As a rare British researcher in Germany at that time he met many of the leaders of the research schools at Frankfurt and Wilhelmshaven, such as Rudolf Richter, Walter Ha¨ntzschel, Wilhelm Scha¨fer, and younger researchers Dolf Seilacher and Hans-Eric Reineck, becoming familiar with the new concepts of sedimentology, aktuogeology and aktuopalaeontology. Much of Roland’s early palaeontological work on Upper Devonian and Lower Carboniferous trilobites and brachiopods was published in German journals (Goldring, 1955, 1957a,b) and later in the

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MEMORIAL TO ROLAND GOLDRING (1928-2005)

FIGURE 1 Roland preparing for fieldwork in Saudi Arabia in 2003.

first British geologists to visit Russia in that part of the cold war period. Roland Goldring’s research fields broadened in the 1970s as although he continued some work on Devonian rocks and trace fossils including those in Poland (Goldring and Kazmierczak, 1974) and Germany (Goldring and Langenstrassen, 1979), he moved into the study of Tertiary estuarine sedimentation and ichnofaunas in southern England with his students at P.R.I.S. (Goldring et al., 1978;

Goldring and Alghamadi, 1999). During this decade he received the Lyell Fund of the Geological Society (1970), served as editor of Palaeontology (1966–1975) and Vice-President of the Palaeontological Association (1973–1975). His breadth of interest and experience continued in the 1980s including ichnology of the flysch (Crimes et al., 1981) and event beds (Goldring and Aigner, 1982; Frey and Goldring, 1992), but later focused on preparation of his text book Fossils in the Field (1991). This book presented

SELECTED PUBLICATIONS CITED ABOVE

FIGURE 2

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Roland (right) on winter fieldwork in the UK in 1999.

his unique perspectives on palaeontology and fossil–sediment relationships, particularly in field analysis and was successful enough to need a second edition less than a decade later (1999a). By the late 1980s, Roland’s reputation as an ichnologist and sedimentologist led to him becoming involved in the analysis of trace fossils and bioturbation in the wealth of hydrocarbon cores obtained from North Sea oilfields and preparation of an atlas of ichnofabrics of the Fulmar Formation for a major oil company (Goldring and Pollard, 1988). This fed his enthusiasm for ichnofabric analysis and development of such new techniques as the ‘ichnofabric constituent diagram’ (I.C.D.) (Taylor and Goldring, 1993) and a series of articles and presentations at symposia (Goldring et al., 1991; Pollard et al., 1993). Roland organised several trace fossil symposia (Palaeontological Association, Reading, 1980; International Palaeoecological Congress, Lyons, 1983; Lyell Meeting, London, 1992) and he attended most of the International Ichnofabric Workshops between 1991 and 2003. Despite his retirement from his academic post as Reader in Geology at University of Reading in 1993, Roland remained extremely enthusiastic and active in ichnology research, both in Mesozoic and Tertiary rocks in England (Goldring and Pollard, 1995;

Goldring, 1996, 1999b; Goldring et al., 1998, 2005a) and abroad with visits to Mongolia (Goldring and Jensen, 1996), China (Bin et al., 1998) and Malta (Goldring et al., 2003). He also developed and applied his teaching skills and the uses of ichnofabric analysis (Goldring, 1995; Taylor et al., 2003), particularly assisting in short courses taught to the oil industry in the UK, France, Norway and even Saudi Arabia (Goldring et al., 2005b). Roland’s unabated enthusiasm, wide interests and meticulous research are shown not only by his coauthorship of two chapters in this volume, but also that at the point of his untimely death he had eight articles in press or in revision in which he was either lead author or co-author. We remember, therefore, with some sadness but much gratitude, our friend and quiet colleague who has left us a lasting legacy of a life’s work of over eighty papers in fields of ichnology, sedimentology, taphonomy and fossil–sediment relationships.

SELECTED PUBLICATIONS CITED ABOVE Amos, A.J., Camphell, J.S.W. and Goldring, R. (1960). Australosutura gen. nov. (Trilobita) from the Carboniferous of Australia and Argentina. Palaeontology, 3, 227–236.

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Bin, Hu, Wang, G. and Goldring, R. (1998). Nereites (or Neonereites) from Lower Jurassic lacustrine turbidites of Henan, central China. Ichnos, 6, 203–209. Crimes, T.P. and Haper, J.C. (Eds.) (1970). Trace Fossils, Seel House Press, Liverpool, 547 pp. Crimes, T.P., Goldring, R., Homewood, P., van Stuijvenberg, J. and Winkler, W. (1981). Trace fossil assemblages of deep-sea fan deposits, Gurnigel and Schlieren flysch (Cretaceous–Eocene), Switzerland. Eclogae Geologica Helvetica, 74, 953–995. Frey, R.W. and Goldring, R. (1992). Marine event beds and recolonization surfaces as revealed by trace fossil analysis. Geological Magazine, 129, 325–335. Goldring, R. (1955). The Upper Devonian and Lower Carboniferous Trilobites of the Pilton Beds in North Devon, with an appendix on Goniatites of the Pilton Beds. Senckenbergiana Lethaea, 36, 27–48. Goldring, R. (1957a). The last toothed Productellinae in Europe. Palaöntologisches Zeitschrift, 31, 207–228. Goldring, R. (1957b). Pseudophillipsia (Tril.) from the Permian (or Uralian) of Oman, Arabia. Senckenbergiana Lethaea, 38, 195–210. Goldring, R. (1958). Lower Tournaisian trilobites in the Carboniferous Limestone facies of the south-west province of Great Britain and of Belgium. Palaeontology, 1, 231–244. Goldring, R. (1962). The trace fossils of the Baggy Beds (Upper Devonian) of North Devon, England. Palaöntologisches Zeitschrift, 36, 232–251. Goldring, R. (1964). Trace-fossils and the sedimentary surface in shallow-water marine sediments. In: van Straaten, L.M.J.U. (Ed.), Deltaic and Shallow Marine Deposits: Developments in Sedimentology 1, Elsevier, Amsterdam, pp. 136–143. Goldring, R. (1971). Shallow-water sedimentation as illustrated in the Upper Devonian Baggy Beds. Memoir of the Geological Society of London, 5, 1–88, 12 plates. Goldring, R. (1991). Fossils in the Field: Information Potential and Analysis, Longman, Harlow, 218 pp. Goldring, R. (1995). Organisms and the substrate: response and effect. In: Bosence, D.W.J. and Allison, P.A. (Eds.), Marine Palaeoenvironmental Analysis from Fossils, Geological Society, Special Publication, 83, pp. 151–180. Goldring, R. (1996). The sedimentological significance of concentrically laminated burrows from Lower Cretaceous Ca-bentonites, Oxfordshire. Journal of the Geological Society, London, 153, 255–263. Goldring, R. (1999a). Field Palaeontology, 2nd edition. Longman, Harlow and John wiley, New York, 191 pp. Goldring, R. (1999b). Sedimentological aspects and preservation of Lower Cretaceous (Aptian) bentonites (fuller’s earth) in southern England. Neues Jahrbuch fu¨r Geologie und Palaöntologie Abhandlungen, 214, 3–24. Goldring, R. and Aigner, T. (1982). Scour and fill: the significance of event separation. In: Einsele, G. and Seilacher, A. (Eds.), Cyclic and Event Stratification, Springer, pp. 354–382. Goldring, R. and Alghamadi, J.A. (1999). The stratigraphy and sedimentology of the Reading Formation (Palaeocene to Eocene) at Knowl Hill, near Reading (southern England). Tertiary Research, 19, 107–116.

Goldring, R. and Curnow, C.N. (1967). The stratigraphy and facies of the late Precambrian at Ediacara, South Australia. Journal of the Geological Society of Australia, 14, 195–214. Goldring, R. and Jensen, S. (1996). Trace fossils and biofabrics at the Precambrian–Cambrian boundary interval in Western Mongolia. Geological Magazine, 133, 403–415. Goldring, R. and Kazmierczak, J. (1974). Ecological succession in intraformational hardground formation. Palaeontology, 17, 949–962. Goldring, R. and Langenstrassen, F. (1979). Open shelf and nearshore clastic facies in the Devonian. Special Papers in Palaeontology, 23, 81–97. Goldring, R. and Pollard, J.E. (1988). Atlas of Trace Fossils and Ichnofabric Analysis of the Fulmar Formation in the Central North Sea, 2 volumes, 54 plates. (For Shell UK Exploration and Production, London). Goldring, R. and Pollard, J.E. (1995). A re-evaluation of Ophiomorpha burrows in the Wealden Group (Lower Cretaceous) of southern England. Cretaceous Research, 16, 665–680. Goldring, R. and Seilacher, A. (1971). Limulid undertracks and their sedimentological implications. Neues Jahrbuch fu¨r Geologie und Palaöntologie, Abhandlungen, 37, 422–442. Goldring, R. and Stevenson, D.G. (1970). Did Micraster burrow? In: Crimes, T.P. and Harper, J.C. (Eds.), Trace Fossils, Seel House Press, Liverpool, pp. 179–184. Goldring, R., Bosence, D.W.J. and Blake, T. (1978). Estuarine sedimentation in the Eocene of southern England. Sedimentology, 25, 861–876. Goldring, R., Pollard, J.E. and Taylor, A.M. (1991). Anconichnus horizontalis: a pervasive ichnofabric-forming trace fossil in postPaleozoic offshore siliciclastic facies. Palaios, 6, 250–263. Goldring, R., Astin, T.R., Marshall, J.A.E., Gabbott, S. and Jenkins, C.D. (1998). Towards an integrated study of the depositional environment in the Bencliff Grit (U. Jurassic) of Dorset. In: Underhill, J.R. (Ed.), Development and Evolution of the Wessex Basin, Geological Society, Special Publication, 133, pp. 355–372. Goldring, R., Gruszczynski, M. and Gatt, P.A. (2003). A bow-form burrow and its sedimentological and paleoecological significance. Palaios, 17, 622–630. Goldring, R., Pollard, J.E. and Radley, J.D. (2005a). Trace fossils and pseudofossils from the Wealden strata (nonmarine Lower Cretaceous) of southern England. Cretaceous Research, 26, 665–685. Goldring, R., Taylor, A.M. and Hughes, G.W. (2005b). The application of ichnofabrics towards bridging the dichotomy between siliciclastic and carbonate shelf facies: examples from the Upper Jurassic Fulmar Formation (U.K.) and Jubaila Formation (Saudi Arabia). Proceedings Geologists’ Associationd, 116, 235–249. Pollard, J.E., Goldring, R. and Buck, S.G. (1993). Ichnofabrics containing Ophiomorpha: significance in shallow-water facies interpretation. Journal of the Geological Society, London, 150, 149–164. Taylor, A.M. and Goldring, R. (1993). Description and analysis of bioturbation and ichnofabric. Journal of the Geological Society, London, 150, 141–148. Taylor, A.M., Goldring, R. and Gowland, S.G. (2003). Analysis and application of ichnofabrics. Earth-Science Reviews, 60, 227–259.

S E C T I O N I

THE HISTORICAL BACKGROUND OF ICHNOLOGY

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1 The Wadden Sea, Cradle of Invertebrate Ichnology Gerhard C. Cadeé and Roland Goldring

(in 1928) of the first marine institute devoted entirely to the study of recent sedimentary environments: Senckenberg am Meer in Wilhelmshaven, Germany.

SUMMARY : Invertebrate ichnology developed separately from vertebrate ichnology; many invertebrate traces were first interpreted as fossil algae. Recent traces have helped to discover their real nature. The study of recent traces of invertebrates in the Wadden Sea played an important role in the development of ichnology. In 1928, Rudolf Richter (1881–1957) founded the first marine institute devoted entirely to Aktuogeologie and Aktuopalaöntologie in Wilhelmshaven, and the school of researchers inspired by him was crucial. Their work became widely known and influential when research articles and reviews of their work in the Wadden Sea began to be published in the English language. Ha¨ntzschel’s contribution on ‘Trace Fossils and Problematica’ to the Treatise on Invertebrate Paleontology and Seilacher’s important contributions to the classification of trace fossils and the use of trace fossil assemblages to estimate the depth of deposition crown the work started by Richter in the Wadden Sea.

THE EARLY BEGINNINGS OF ICHNOLOGY The study of invertebrate ichnology developed separately from that of vertebrate ichnology. Vertebrate (paleo)ichnology is the older of the two: bird-like dinosaur tracks were discovered in 1802 in the Connecticut Valley (USA) and the first published record of fossil tracks of quadrupedal reptiles discovered in Dumfriesshire, Scotland in 1814 dates from 1828 (e.g., Buckland, 1828). The earliest history of ichnology characteristically deals practically only with vertebrate traces (Winkler, 1886). In his excellent history, Osgood (1975) gives the reasons for the slow development of invertebrate ichnology: most trace fossils were originally interpreted as fossil brown algae, fucoids, during what he named the ‘Age of Fucoids’ (1828–1881) and therefore omitted by Winkler (1886). When it became clear that most fossil ‘fucoids’ were caused either by sedimentary processes or by burrowing and crawling organisms, the popularity of their study considerably decreased. The ‘Age of Fucoids’ culminated in voluminous monographs such as of Heer (1877) in which numerous Flysch Lebensspuren were described in great detail as plants. It ended in the 1880s when the paleobotanist Nathorst (1881, 1886) proved

INTRODUCTION Ichnology, the study of fossil and recent traces made by organisms, has a history of about 200 years. In understanding the nature and producers of traces, the study of recent organisms has been very important. Shallow, easily accessible intertidal areas have proved to be the best area to start such studies. In this chapter we will underline the important role, research in the Wadden Sea has played in the past and in particular the role of Rudolf Richter the founder

Copyright ß 2007, Elsevier B.V. Trace Fossils: Concepts, Problems, Prospects

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1. THE WADDEN SEA, CRADLE OF INVERTEBRATE ICHNOLOGY

experimentally that many fucoids of earlier authors were in fact traces of invertebrate organisms. Nathorst (1881), Winkler (1886), Osgood (1975) and Ha¨ntzschel (1962, 2nd edition 1975) cite a few paleontologists who rightly described traces as invertebrate trails. Hitchcock (1858) used the first real ichnogenus name ending in -ichnus (e.g., Cochlichnus) for an invertebrate meander trail; Dawson (1862) studied trails by modern Limulus (the horseshoe crab) comparing it with fossil traces Protichnites, and Dawson (1864) interpreted Rusophycus as resting traces of trilobites (see for Dawson also Pemberton et al., this volume). Nicholson (1873: pp. 288–289) regarded Skolithos as dwelling burrows. Indeed, those working on Paleozoic rocks in North America and Great Britain mostly attributed traces to animal activity. In Great Britain, Salter’s work was influential for the British Geological Survey (a.o. Salter, 1857). However, invertebrate ichnology as a science was in our opinion born in 1880 in Kristineberg (Sweden), where Nathorst (1881) experimented with live invertebrates to understand fossil traces. A few years earlier he had already published how worms were able to form branching traces suggesting a ‘fucoid’ nature (Nathorst, 1873).

THE ROLE OF EXPERIMENTS Buckland was the first experimenter in ichnology (1837: footnote p. 261). He compared the Scottish fossil tracks of Dumfriesshire (Buckland, 1828) ‘with the tracks which I caused to be made on soft mud, and clay, and upon unbaked pie-crust, by a living Emys and Testudo Graeca’ (respectively a marsh and a land tortoise). From his experiments, he concluded that the fossil track was made by a land tortoise. Nathorst (1881) was probably unaware of Buckland’s work, so this indicates that the still existing divide between vertebrate and invertebrate ichnology was already present. Nathorst’s (1881) first idea was to let animals crawl over wet plaster in order to get preservable traces. This worked with some (terrestrial) worms and raindrop impressions. However, a mixture of plaster with salt water did not harden and few of the marine animals he wanted to work with liked to perform in a mixture of plaster of Paris and freshwater. He used Kristineberg’s Zoological Station (founded only a few years earlier in 1877) for his experiments. Here, he collected marine mud from several depths and was surprised to observe that a number of traces were produced within a few hours. Finally he succeeded in

casting the traces in plaster, including those made by crustaceans (Carcinus maenas, Crangon vulgaris, Idotea baltica, Corophium, Gammarus), polychaetes (Glycera, Terebella), and an amphiurid with its symbiotic bivalve Mysella bidentata. His well-illustrated study in Swedish (with an extended summary in French) clearly indicates why fossil traces had hitherto been identified as ‘fucoids’. He shows, for example, traces produced by crustaceans Idotea baltica (Nathorst, 1881, plate III), where two animal traces meet each other, where-after both animals used the same path: such traces resemble a bifurcating fucoid. Nathorst also recognised that one organism may produce more than one type of trace. Osgood (1975) identifies the years between 1881 and 1920 as the ‘Period of Controversy’ and describes the heated debate pro and contra Nathorst’s ideas. Only in 1886 did Nathorst take part in the discussion. ‘Fucoids’ were disproved, but there was no surge in interest. It was in continental Europe, especially through Mesozoic and Cenozoic workers, that the fucoid controversy raged (a.o. Saporta, 1884). In any case there was a steady publication of ichnological literature (generally with discussion as to the producers) in the early part of the twentieth century, mainly in the English-speaking world and a few in French (a.o. Fraipont, 1912). Seilacher (1975) gives two reasons for the decline in interest in Europe: first, ‘fucoids’ could no longer be used as reliable fossil guides or as indicators of shallow-water sediments deposited in the photic zone. Second, ‘fucoids’ fell into a taxonomic no-man’s land. They were either omitted from textbooks, or listed under ‘incertae sedis’ or ‘problematica’. And, the chief biostratigraphically useful groups are not actually trace fossil producers! Nathorst’s studies in Sweden did not result in a new research school for trace fossils that might have started at Kristineberg. Nathorst returned to the study of fossil plants. Only later did Rudolf Richter start the first organised study of ichnology in the Wadden Sea. Removing the cradle of ichnology from Kristineberg to the Wadden Sea proved successful.

RESEARCH IN THE WADDEN SEA Rudolf Richter (1881–1957) changed his law studies for geology in 1904 after a field excursion with the famous geologist Emanuel Kayser to the Devonian strata in the Eifel, Germany (Ziegler, 1981). In 1908, he started working at the Senckenberg Museum in Frankfurt and was soon a world authority on

RESEARCH IN THE WADDEN SEA

FIGURE 1.1

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Map of the Wadden Sea; shaded areas are tidal flats.

trilobites, not only on their taxonomy and the role of trilobites in Devonian biostratigraphy, but also on the paleobiology of trilobites. This work was influenced by Dollo (1910), and by the traces trilobites produced, leading to his still very readable articles on ‘Bau und Leben der Trilobiten’ (Richter, 1919–1920). In Germany, Walther (1893–1894) and later Abel (1927, 1935) had promoted the study of modern environments to gain a better understanding of the mode of formation of fossil sediments. It was Richter who selected the Wadden Sea for this purpose (Fig. 1.1). The mesotidal Wadden Sea extends from the North Sea coast of The Netherlands across northern Germany into Denmark. It is bounded on the seaward side by a line of barrier islands (Frisian Islands), interrupted by the estuaries of the Ems, Weser and Elbe. Richter (1926c) recalled his first visits to the Wadden Sea in The Netherlands in 1911. In 1919, he stayed several weeks on a Wohnbake (a small fixed

observation-post on piles on the tidal flat) in the Wadden Sea near Mellum, with his wife Emma who was also a geologist and collaborator. Here, he said he learned much more than during his visits to the (non-tidal) marine institute of Naples or to the rocky shores near the Helgoland Marine Institute (Richter, 1926c; Scha¨fer, 1962b). Walking over a tidal flat surface is an ideal experience for a geologist who wants to see geology at work. In 1920, he gave a lecture at the Senckenberg Museum in Frankfurt on the importance of the study of the Wadden Sea for geology and paleontology. This was never published, but from his series of publications on ‘Flachseebeobachtungen’ (Observations in a shallow sea, Richter, 1920–1926) it is clear what kind of studies he had in mind: a better understanding of sedimentation processes and (trace) fossils by comparison of old and modern deposits (Fig. 1.2). In 1928, he succeeded in founding the first marine institute devoted entirely to actuogeology

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FIGURE 1.2 (A–E) Figures from Richter (1920) to illustrate his objectives in studying Wadden Sea traces, by comparing the modern (tube worm) Sabellaria ‘reefs’ with the fossil trace Skolithos (pipe rock). (A) ‘Sand coral’ ‘reef’ at low tide, Wadden Sea. (B,C) Fragments viewed from the side and above. (D,E) Skolithos (pipe rock), Lower Devonian, Rhineland, bar = 1 cm. (F) Cluster of tubes with annelids; left, external view of two tubes; right, worms seen in three positions. (After Scha¨fer, 1962, Fig. 130.) (All with permission from Senckenbergische Naturforschende Gesellschaft, Frankfurt/Main, Germany.)

and actuopaleontology ‘Senckenberg am Meer’ in Wilhelmshaven, Germany. In 1929, Richter published the manifesto of this institute and from the beginning ichnology was to be one of its major research fields. In the 1920s with Richter, the period of the ‘Modern approach of Ichnology’ started (Osgood, 1975). The foundation of Senckenberg am Meer was also a milestone in the study of actuogeology, the science that ‘makes stones alive’ (Reineck, 1981). Richter’s Wadden Sea studies did not remain unnoticed: already in 1928 a long English review of his publications in German on Scolithus was prepared by Bucher (1928) and this has certainly influenced early ichnologists such as the Fentons in the USA, as it was published in the American Midland Naturalist of which naturalist/paleontologist Caroll Lane Fenton was associate editor from 1923 to 1960 and where the Fentons published a number of their articles on fossil and recent traces starting with Fenton and Fenton (1931). Pemberton and MacEachern (1994) give a complete list of their later ichnological articles.

When Richter became director of Senckenberg Museum in Frankfurt in 1934, he appointed Walter Ha¨ntzschel as his successor as Director at Wilhelmshaven. While in Frankfurt, Richter played an important role to keep Nazi influence in Senckenberg at bay (Ziegler, 1992). He also retained his interest in traces (e.g., Richter, 1942) and remained an influence on the development of ‘his’ Senckenberg am Meer. Ha¨ntzschel (1904–1972) started his geological research on Cretaceous sediments in Germany, and became increasingly interested in fossil traces (see Ha¨ntzschel, 1924, 1931, 1934). From 1934 to 1938, Ha¨ntzschel spent probably the happiest time of his life exploring the Wadden Sea tidal flats. This resulted in a new series of articles now on modern traces, among which star-like traces drew his interest (Ha¨ntzschel, 1935, 1939a, 1940). His work in the Wadden Sea, although published in German, was nevertheless not unknown in North America. It was again Bucher (1938) who after his visit to Wilhelmshaven and the tidal flats of the Wadden Sea in 1937, reviewed in English the many articles

RESEARCH IN THE WADDEN SEA

published in German by scientists from the institute. Rindsberg (pers. comm., 2005) mentioned the influence Bucher’s review had on a.o. the Fentons. Trask invited Ha¨ntzschel to contribute to his benchmark book Recent Marine Sediments published in 1939. His contribution was translated from the German by Marie Siegrist and Trask himself (Ha¨ntzschel, 1939b). This study mainly deals with the tidal sediments themselves rather than with the traces, although the presence of fecal pellets and the role of filter feeders in depositing mud are mentioned (Ha¨ntzschel, 1939b, reprinted in 1955 and 1968). In 1938, Ha¨ntzschel was appointed as curator at the Dresden Museum, providing the opportunity to resume his study of Cretaceous outcrops. The Second World War destroyed his hopes for a better life for himself and his family. He was drafted in 1942 and returned later after three years in a Russian prison camp to find Dresden and its museum destroyed. Not until 1949 was he able to secure a new position at the Geological Institute of Hamburg University as a librarian, where he remained until his retirement in 1969. In Hamburg, he returned to his beloved trace fossils and in an important article from this period he was able to relate the fossil lebensspur Ophiomorpha to callianassid crustaceans (Ha¨ntzschel, 1952). In Hamburg, he also became the foremost expert on trace fossil literature. This led to his greatest contribution to ichnology, the trace fossil part of the Treatise on Invertebrate Paleontology (1962, 2nd edition 1975). The invitation to take part in the First International Salt Marsh Conference in March 1958 at Sapelo Island, and his visit later to several of the leading marine institutes in the USA marked his growing international fame. It also marked the growing interest in the work done in the Wadden Sea. Among the few European scientists invited were three who worked in this area: in addition to Walter Ha¨ntzschel, Wilhelm Scha¨fer and the Dutch sedimentologist L.M.J.U van Straaten (Ragotzkie et al., 1959). Hertweck (1972), Lehmann (1972) and Seilacher (1975) provide a more detailed picture of this great successor of Richter. In 1938, Wilhelm Scha¨fer (1912–1981) followed Ha¨ntzschel as Director at the age of only 26. This proved to be another excellent choice by Richter. By training, Scha¨fer was a marine biologist but he soon became interested in actuopaleontology as can be judged from his publications in the first years at Senckenberg am Meer (see Flemming and Gutmann, 1992), and his review book (Scha¨fer, 1962a, translated in English in 1972). During the war Scha¨fer was in military service, Senckenberg am Meer was severely damaged and finally closed, the

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library was destroyed by the occupation after the war. Scha¨fer returned to Wilhelmshaven in 1947 and started with the help of K. Lu¨ders to rebuild and re-open the marine institute and research regained impetus. In his article on the influence of some 30 benthic organisms on layered sediments (Scha¨fer, 1956), we can see the influence of Hans-Erich Reineck (inventor of the box-core to take undisturbed sediment samples), who started working as an actuogeologist at Wilhelmshaven in 1954. The illustrations in this article demonstrate the great capacities of Scha¨fer as an artist. In 1961, Scha¨fer moved to Frankfurt and H.-E Reineck took over as Director. At Frankfurt Scha¨fer completed his magnum opus. This monumental encyclopedia ‘Aktuopalaöntologie nach Studien in der Nordsee’ published in 1962 gives an excellent overview of the work done not only in Wilhelmshaven but also by others such as Linke and Wohlenberg in the Wadden Sea and the nearby North Sea. Linke’s (1939) work in part of the Wadden Sea (the Jade Busen) is rarely mentioned in the ichnological literature, but Linke gives inter alia an excellent overview of burrows and traces of the Wadden Sea fauna. The English translation of Scha¨fer’s book is now well known: ‘Ecology and Palaeoecology of Marine Environments’ (1972). H.-E Reineck (1918–1999) joined the institute as a geologist in 1954, and was its Director from 1961 until 1984 (Flemming, 1999). Mainly because of his studies of the Wadden Sea tidal sediments Reineck became a sedimentologist and wrote a textbook (in English, with Singh, 1973, later editions in 1980 and 1986) on modern sediments. He often stressed: ‘Nowhere is the seabottom so easy to study as on a tidal flat’ (e.g., Reineck, 1957). He became well known, due to his inventions of new methods to take undisturbed sediment samples with the box-corer (in German, ‘Kastengreifer’), and artificially hardened soft sediment samples in order to study them in cross sections and thin slides, just like ancient sedimentary rocks (Reineck, 1957, 1963b,c, 1967a, 1970b), thus building on earlier inventions by Senckenberg am Meer scientists such as Schwarz (1929) and Ha¨ntzschel (1936). He was one of the few European scientists invited to take part in the Conference on Estuaries held in 1964 at Jekyll Island, Georgia, USA. The publication of the proceedings of this conference (Lauff, 1967; Reineck, 1967b) became a landmark in estuarine research, which has since made many of its contributors well cited. Also, Reineck published many articles on recent traces (e.g., Reineck, 1958, 1968; Reineck et al., 1967, 1968). With his Kastengreifer he was not

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restricted to the Wadden Sea but could also use it in deeper waters, which gave rise to well-illustrated articles such as Reineck (1963a) and Reineck et al. (1967, 1968). The art of making ‘Reliefgu¨sse’ (relief casts) was further perfected to real artwork by Hertweck, who joined the institute in 1964 (e.g., Hertweck and Reineck, 1966), and ‘Kunstharz’ (polyester resin) was used to fill open burrows. Reineck retired in 1984 (Flemming, 1999) to be followed by Burghard Flemming, but remained active in research, and continued publishing on tracks and traces (e.g., Reineck and Flemming, 1997). Research by the Wilhelmshaven team resulted in numerous articles, at first mainly in German. But once the scientists started publishing in English, and went abroad to conferences such as the salt marsh conference in 1958 at Sapelo Island and the Estuaries Conference in 1964 at Jekyll Island, their work became known outside Germany. Wadden Sea work at Senckenberg am Meer concentrated more on ichnofacies zonation (Hertweck, 1970a,b, 1994; Do¨rjes and Hertweck, 1975). The export of their knowledge was also promoted by co-operative research with, for example, James ‘Jim’ Howard and Robert ‘Bob’ Frey in the Sapelo Island region (Howard et al., 1972); in Italy (e.g., Hertweck, 1973), and Taiwan (Reineck and Cheng, 1978; Do¨rjes, 1978). Such co-operation, particularly that with the group of Howard and Frey, who had developed their own research methods such as the use of X-rays in studying the production of traces (Howard, 1968; Howard and Elders, 1970), was fruitful for both groups. Ichnology left its cradle in the Wadden Sea and moved globally. The aims and history of Senckenberg am Meer are well documented, mostly in German (e.g., Richter, 1929; Ha¨ntzschel, 1956; Scha¨fer, 1967; Reineck, 1981; Flemming, 2004).

ICHNOLOGY ELSEWHERE IN THE WADDEN SEA Not all Wadden Sea ichnology studies were based at Wilhelmshaven. Wohlenberg (1937) worked from Sylt, and contributed a detailed study of traces and burrows made by the supratidal beetles. These beetles formed the main subject of an article by Larsen (1936) who worked in the Danish Wadden Sea from the Skalling Laboratory, where Thamdrup (1935) had worked on the tidal flat fauna, including pioneer studies on the burrows of these animals. Van Straaten (1920–2004), a well-known Dutch sedimentologist, worked from Groningen University

in the Dutch sector of the Wadden Sea (Veenstra, 2004). One of his interests was in tidal flat sediments and their recognition in the geological past (van Straaten, 1950, 1952, 1954a,b, 1956). He also discovered a shell-rich layer present at about 25-cm depth below many Wadden Sea tidal flats that proved to be due to the bioturbating activities of the lugworm Arenicola. This worm continuously ingests sand particles and defecates them at the surface. Shells and shell fragments are too large to be swallowed and so become concentrated at the feeding depth of lugworms. Quantitative research on annual rates and seasonal variation of bioturbation by polychaetes and birds in the Wadden Sea was mainly carried out from the Netherlands Institute for Sea Research at the western part of the Wadden Sea on the island of Texel by Cadeé (1976, 1979, 1990, 2001), though earlier estimates of the sediment reworking rates by lugworms in the Wadden Sea had been made by Linke (1939). Wattenmeer station Sylt at the northern end of the Wadden Sea became an important institute for Wadden Sea research before the second World War (Wohlenberg, 1937), and particularly after Karsten Reise became its director. Reise (1985) is already a ‘classic’ concerning tidal flat ecology.

THE PROMOTION OF ICHNOLOGY In the 1960s, ichnology research started blooming all over the world and became accepted as an important area which was attracting international symposia (e.g., Crimes and Harper, 1970). Probably no one has done more to promote ichnology than Dolf Seilacher. Though never part of the Wilhelmshaven team, being a student of Otto Schindewolf at the University in Tu¨bingen, his first research on traces was carried out on the Island of Mellum (in the Jade-Weser estuary in the Wadden Sea) in 1949 (Seilacher, 1951). There he studied the formation of tubes by the worm Lanice conchilega (Fig. 1.3). He mentions his fruitful contacts with the Wilhelmshaven group particularly with Scha¨fer. Seilacher’s early studies in the Wadden Sea (Seilacher, 1951, 1953a, 1957) formed the base for his later influential ethological classification system of traces, building on earlier classifications by Richter (1927) and Krejci-Graf (1932), but much easier to use and thus more appealing. Two articles (Seilacher, 1953b,c) are landmarks in the behavioural classification approach in ichnology. Seilacher’s publications are also legendary for

THE PROMOTION OF ICHNOLOGY

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FIGURE 1.3 The formation of tubes by the polychaete Lanice conchilega (sand mason). (A,B) The tube is first free at the sediment surface. With the help of respiratory currents (arrows) the worm digs into the sediment. (C) In older worms the respiratory current is reversed, thereby enabling the worm to dig deeper. As the tube cannot be widened, the growing worm has to add a new tube which becomes W-shaped. The fringed, feeding crown is finally added (from Seilacher, 1951, Figs. 2 and 4). (D) Lengthening and branching of the tubes into laminated sands and muds (after Scha¨fer, 1962, Fig. 190). (All with permission from Senckenbergische Naturforschende Gesellschaft, Frankfurt/Main, Germany.)

their excellent illustrations. In this he followed his ‘teacher’ Scha¨fer! Seilacher (1957) observed that not all fossil traces had counterparts in the sediments of the Wadden Sea, and that many of the then known Wadden Sea traces had no fossil counterpart. He realised that this discrepancy was due to the fact that so many of the Wadden Sea traces studied were surface traces, often with little fossilisation potential, whereas many ancient traces could be shown to have been formed by organisms burrowing below the sediment surface. These had to be studied in a different way. He promoted the study of modern traces in vertical sections such as that which could be readily examined along eroding creeks in the Wadden Sea. Such studies were aided by the new methods of collecting

undisturbed sediment samples by methods and apparatus invented by Reineck (1957), and used by Scha¨fer (1956). Although Seilacher’s early articles were in German, they were noticed a.o. by Goldring in the UK (Goldring, 1962) and Lessertisseur in France. Lessertisseur had frequent contacts with Seilacher, and Lessertisseur’s 1955 publication, based on his 1953 thesis, gives an ecological classification of traces reviewing the German work in French also and commenting favourably on the trace assemblages approach by Seilacher (1954). His article is illustrated with a nice set of plates of invertebrate traces on tidal flats along the French Atlantic coast. Goldring visited Seilacher in Tu¨bingen in 1956 and helped to make his work better known in

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the UK (Goldring et al., 2000). In the early 1960s, Seilacher started publishing in English as well. He was invited as a guest speaker at the opening of the new sedimentology laboratories in Reading, UK in 1962 in which he presented his scheme of ichnofacies (Goldring et al., 2000). In 1963, Seilacher was invited to give a speech at a meeting of the Geological Society of America in Cincinnati, followed by an invitation for consultation at Humble Petroleum. Thus, with Seilacher’s post-war UK and North American journeys, enthusiasm and his ten principles (Seilacher, 1994), this led to a major response in activity and the establishment of ichnology in the 1960s. More especially, it was his realisation that ichnology could be a major tool in the interpretation of ancient sediments, and thus highly significant to the petroleum industry. Beginning (Seilacher, 1954) with his distinction between flysch (deep water and turbiditic) and molasse (shallow marine and terrestrial) traces in Alpine sediments (Seilacher, 1955 — figure reproduced in the ‘Treatise’ 2nd edition, 1975) and at the 5th International Sedimentology Congress at Geneva, this led to the principles of ichnology and enunciation of ichnofacies (Seilacher, 1964).

CONCLUSIONS Since the early beginnings of ichnology, paleontologists (Nathorst, Abel, Richter, Ha¨ntzschel and Seilacher) have played a dominant role in the study of modern invertebrate traces, because they wanted to understand the fossil traces they found. Without the vision of Richter in the early 1920s and his founding of the Senckenberg am Meer research institute in Wilhelmshaven, the Wadden Sea would never have played the role it did in ichnology. Ichnologists have exported their knowledge gained in the Wadden Sea, certainly since they started publishing in English. Actuoichnology of invertebrates has come of age and left its cradle in the Wadden Sea long ago and is now studied at all academic levels and from (tropical) tidal areas to the deep sea. It has proved its value for the interpretation and classification of fossil traces and their (paleo)environmental significance.

ACKNOWLEDGEMENTS We very much appreciate the interest and help of our colleagues Sally Walker (University of

Georgia, Athens), Gu¨nther Hertweck and Burghard Flemming (Wilhelmshaven) and Geert-Jan Brummer (NIOZ, Texel), we thank John Pollard particularly for his help in the finishing stage. The libraries of Naturalis (Leiden) and NIOZ (Texel) proved excellent for supplying literature. We thank referees Sally Walker and Andres K. Rindsberg for their very useful comments. Coauthor Roland Goldring has been very co-operative in writing this chapter, he has commented on the last draft before it was sent by the editor to referees. Sadly he died the 30th August 2005.

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Harper, J.C. (Eds.), Trace Fossils, Geological Journal Special Issue 3, 235–242. Hertweck, G. (1972). Walter Ha¨ntzschel 16.11.1904-10.5.1972. Palaöntologische Zeitschrift, 46, 105–112. Hertweck, G. (1973). Der Golf von Gaeta (Tyrrhenisches Meer). VI. Lebensspuren einiger Bodenbewohner und Ichnofaziesbereiche. Senckenbergiana Maritima, 5, 179–197. Hertweck, G. (1994). Zonation of Benthos and Lebensspuren in the tidal flats of the Jade Bay, southern North Sea. Senckenbergiana Maritima, 24, 157–170. Hertweck, G. and Reineck, H.-E. (1966). Untersuchungen von Gangbauten und anderen Wu¨hlgefu¨gen mariner Bodentiere. Natur und Museum, 96, 429–438. Hitchcock, E. (1858). Ichnology of New England, A report of the sandstone of the Connecticut Valley especially its footprints, White, Boston, 220 pp. Howard, J.D. (1968). X-ray radiography for examination of burrowing in sediments by marine invertebrate organisms. Sedimentology, 11, 249–258. Howard, J.D. and Elders, C.A. (1970). Burrowing patterns of haustoriid amphipods from Sapelo Island, Georgia. In: Crimes, T.P. and Harper, J.C. (Eds.), Trace Fossils, Geological Journal Special Issue 3, 244–262. Howard, J.D., Frey, R.W. and Reineck, H.-E. (1972). Georgia coastal region, Sapelo Island U.S.A.: Sedimentology and Biology. I. Introduction. Senckenbergiana Maritima, 4, 3–14. Krejci-Graf, K. (1932). Definition der Begriffe Marken, Spuren, Fa¨hrten, Bauten, Hieroglyphen und Fucoiden. Senckenbergiana, 14, 19–39. Larsen, E.B. (1936). Biologische Studien u¨ber die tunnelgrabenden Ka¨fer auf Skallingen. Videnskabelige Meddelelser fra Dansk Naturhistorisk Forening I Københaven, 100, 1–231. Lauff, G.H. (Ed.) (1967). Estuaries. American Association for the Advancement of Science Publication, 83, 1–757. Lehmann, U. (1972). Ein Nachruf. Mitteilungen aus dem Geologisches-Palaöntologisches Insitut der Universita¨t Hamburg, 41, 7–14, (Walter Ha¨ntzschel, 1904–1972). Lessertisseur, J. (1955). Traces fossiles d’activite´ animale et leur significance paleóbiologique. Me´moires de la Socie´te´ Geólogique de France N.S, 74, 1–150. Linke, O. (1939). Die Biota des Jadebusenwattes. Helgola¨nder Wissenschaftliche Meeresuntersuchungen, 1, 201–348. MacGinitie, G.E. (1934). The natural history of Callianassa californiensis Dana. American Midland Naturalist, 15, 166–177. Nathorst, A.G. (1873). Om na˚gra fo¨rmodade va¨xtfossiler. Kongliga Svenska Vetenskaps-Akademiens Handlingar, 9, 25–52, (1874). Nathorst, A.G. (1881). Om spa˚r af evertebrerade djur m. m. och deras paleontologiska betydelse (with abridged french translation: Me´moire sur quelques traces d’animaux sans verte`bres etc. et de leur porteé paleóntologique p. 61–104). Kongliga Svenska Vetenskaps-Akademiens Handlingar, 18, 1–104. Nathorst, A.G. (1886). Nouvelles observations sur les traces d’animaux et autres pheńome`nes d’origine purement mećanique dećrits comme ‘Algues fossiles’. Kongliga Svenska VetenskapsAkademiens Handlingar, 21, 1–58. Nicholson, H.A. (1873). Contributions to the study of the errant annelids of the older Paleozoic rocks. Proceedings of the Royal Society of London, 21, 288–290. Osgood, R.G. (1975). The history of invertebrate ichnology. In: Frey, R.W. (Ed.), The Study of Trace Fossils, Springer-Verlag, New York, pp. 3–12. Pemberton, S.G. and MacEachern, J.A. (1994). Carroll Lane Fenton and Mildred Adams Fenton: Pioneers of North American Neoichnology. Ichnos, 3, 145–153.

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Pemberton, S.G., Gingras, M.K. and MacEachern, J.A. (2007). The antecedents of invertebrate ichnology in North America: the Canadian and Cincinnati schools. In: Miller, W. (Ed.), Trace Fossils: Concepts, Problems, Prospects. Ragotzkie, R.A., Pomeroy, L.R., Teal, J.M. and Scott, D.C. (Eds.) (1959). Proceedings Salt Marsh Conference, Sapelo Island, Georgia, 1958, Athens, Georgia, 133 pp. Reineck, H.-E. (1957). Stechkasten und Deckweiß, Hilfsmittel des Meeresgeologen. Natur und Volk, 87, 132–134. Reineck, H.-E. (1958). Wu¨hlbau-Gefu¨ge in Abha¨ngigkeit von Sediment-Umlagerung. Senckenbergiana Lethaea, 39, 1–23. Reineck, H.-E. (1963a). Sedimentgefu¨ge im Bereich der su¨dlichen Nordsee. Abhandlungen Senckenbergische Naturforschende Gesellschaft, 505, 1–138. Reineck, H.-E. (1963b). Naßha¨rtung von ungesto¨rten Bodenproben im Format 5 x 5 cm fu¨r projizierbare Dickschliffe. Senckenbergiana Lethaea, 44, 357–362. Reineck, H.-E., (1963c). Der Kastengreifer. Natur und Museum, 83, 102–108. Reineck, H.-E. (1967a). Ein Kolbenlot mit Plastik-Rohren. Senckenbergergiana Lethaea, 48, 285–289. Reineck, H.-E. (1967b). Layered sediments of tidal flats, beaches, and shelf bottoms of the North Sea. In: Lauff, G.H. (Ed.), Estuaries, American Association for the Advancement of Science Publication, pp. 191–206. Reineck, H.-E. (1968). Lebensspuren von Herzigeln. Senckenbergiana Lethaea, 49, 311–319. Reineck, H.-E. (1970a). Das Watt. Ablagerungs- und Lebensraum, Kramer, Frankfurt am Main, 142 pp. Reineck, H.-E. (1970b). Reliefguß und projizierbarer Dickschliff. Senckenbergiana Maritima, 2, 61–66. Reineck, H.-E. (1981). Die Wissenschaft die Steine lebendig macht. Natur und Museum, 111, 343–346, (Rudolf Richter Heft). Reineck, H.-E., Gutmann, W.F. and Hertweck, G. (1967). Das Schlickgebiet su¨dlich Helgoland als Beispiel rezenter Schelfablagerungen. Senckenbergiana Lethaea, 48, 219–275. Reineck, H.-E., Do¨rjes, J., Gadow, S. and Hertweck, G. (1968). Sedimentologie, Faunenzonierung und Faziesabfolge vor der Ostkuste der inneren Deutschen Bucht. Senckenbergiana Lethaea, 49, 261–309. Reineck, H.-E. and Singh, I.B. (1973). Depositional Sedimentary Environments, Springer, Berlin, 439 pp. Reineck, H.-E. and Ying Min, Cheng. (1978). Sedimentologische und faunistische Untersuchungen an Watten in Taiwan. I. Aktuogeologische Untersuchungen. Senckenbergiana Maritima, 10, 85–115. Reineck, H.-E. and Flemming, B.W. (1997). Unusual tracks, traces, and other oddities. Courier Forschungsinstitut Senckenberg, 201, 349–360. Reise, K. (1985). Tidal Flat Ecology, Springer, Berlin, 191 pp. Richter, R. (1919–1920). Vom Bau und leben der Trilobiten. I. Das Schwimmen. II. Die Aufenthalt auf den Boden. Der Schutz. Die Erna¨hrung. Senckenbergiana, 1, 213–238; 2, 22–43. Richter, R. (1920). Flachseebeobachtungen I. Ein devonischer ‘Pfeifenquarzit’ verglichen mit der heutigen ‘Sandkoralle’ (Sabellaria, Ann.). Senckenbergiana, 2, 215–235. Richter, R. (1921). Flachseebeobachtungen II. Scolithus, Sabellarifex und Geflechtquarzite. Senckenbergiana, 3, 49–52. Richter, R. (1924a). Flachseebeobachtungen VII. Arenicola von heute und Arenicoloides, eine Rhizocorallide des Buntsandsteins, als Vertreter verschiedener Lebensweise. Senckenbergiana, 6, 119–140.

Richter, R. (1924b). Flachseebeobachtungen IX. Zur Deutung rezenten und fossiler Maänder-Figuren. Senckenbergiana, 6, 141–157. Richter, R. (1926a). Flachseebeobachtungen XII. Bau, Begriff und palaögeographische Bedeutung von Corophioides luniformis (Blanckenhorn, 1917). Senckenbergiana, 8, 200–219. Richter, R. (1926b). Flachseebeobachtungen XIV. Abdru¨cke lebendiger Tiere (Fische und Wu¨rmer). Senckenbergiana, 8, 221–224. Richter, R. (1926c). Eine geologische Exkursion in das Wattenmeer. Natur und Museum, 56, 289–301. Richter, R. (1927). Die fossilen Fa¨hrten und Bauten der ¨ berblick u¨ber ihre biologischen Grundformen Wu¨rmer, ein U und deren geologische Bedeutung. Palaöntologische Zeitschrift, 9, 193–240. Richter, R. (1929). Gru¨ndung und Aufgaben der Forschungsstelle fu¨r Meeresgeologie Senckenberg in Wilhelmshaven. Natur und Museum, 59, 11–30. Richter, R. (1942). Marken und Spuren im Hunsru¨ckschiefer. 3. Fa¨hrten als Zeugnisse des Lebens auf dem Meeresgrunde. Senckenbergiana, 23, 218–260. Salter, J.W. (1857). On annelide-burrows and surface markings from the Cambrian rocks of the Longmynd. Quaterly Journal of the Geological Society of London, 13, 199–206. Saporta, G. (1884). Les organismes proble´matiques des anciennes mers, Masson, Paris, 100 pp. Scha¨fer, W. (1956). Wirkungen der Benthos-Organismen auf den jungen Schichtverband. Senckenbergiana Lethaea, 37, 183–263. Scha¨fer ,W. (1962a). Aktuo-Palaöntologie nach, Studien in der Nordsee. Waldemar Kramer, Frankfurt am Main, 666 pp., (translated in 1972 as Ecology and Paleoecology of marine environments. University of Chicago Press, Chicago). Scha¨fer, W. (1962b). 60 Jahre Mellum. Natur und Museum, 92, 173–176. Scha¨fer, W. (1967). Forschungsanstalt fu¨r Meeresgeologie und Meeresbiologie Senckenberg in Wilhelmshaven. Senckenbergiana Lethaea, 48, 191–217. Schwarz, A. (1929). Ein Verfahren zum Ha¨rten nichtverfestigter Sedimente. Natur und Museum, 549, 204–208. Seilacher, A. (1951). Der Ro¨hrenbau von Lanice conchilega (Polychaeta). Ein Beitrag zur Deutung fossiler Lebensspuren. Senckenbergiana, 32, 267–280. Seilacher, A. (1953a). Der Brandungssand als Lebensraum in Gegenwart und Vorzeit. Natur und Volk, 83, 263–272. ¨ ber die Seilacher, A. (1953b). Studien zur Palichnologie. I. U Methoden der Palichnologie. Neues Jahrbuch fu¨r Geologie und Palaöntologie, Abhandlungen, 96, 421–452. Seilacher, A. (1953c). Studien zur Palichnologie. II. Die fossilen Ruhespuren (Cubichnia). Neues Jahrbuch fu¨r Geologie und Palaöntologie, Abhandlungen, 98, 87–124. Seilacher, A. (1954). Die geologische Bedeutung fossiler Lebensspuren. Zeitschrift der Deutschen Geologischen Gesellschaft, 105, 214–227. Seilacher, A. (1957). An-aktualistisches Wattenmeer? Palaöntologische Zeitschrift, 31, 198–206. Seilacher, A. (1964). Biogenic sedimentary structures. In: Imbrie, J. and Newell, N.D. (Eds.), Approaches to Paleoecology, John Wiley, New York, pp. 296–316. Seilacher, A. (1975). Walter Ha¨ntzschel (1904-1972) and the foundation of modern invertebrate ichnology.

REFERENCES

In: Frey, R.W. (Ed.), The Study of Trace Fossils, Springer, New York, pp. v–viii. Seilacher, A. (1994). Response by Adolf Seilacher. Journal of Paleontology, 68, 917–918. ¨ kologie Thamdrup, H.M. (1935). Beitra¨ge zur O der Wattenfauna auf experimenteller Grundlage. Meddelelser fra Kommissionen for Danmarks Fiskeri- og Havundersøgelser Serie Fiskeri X, 2, 1–125. Trask, P.D. (Ed.) (1939). Recent Marine Sediments, American Association Petroleum Geologists, Tulsa, Oklahoma, 736 pp., (later and enlarged editions in 1955 and 1968). van Straaten, L.M.J.U. (1950). Environment of formation and facies of the Wadden Sea sediments. Tijdschrift Koninklijk Nederlands Aardrijkskundig Genootschap, 67, 94–108. van Straaten, L.M.J.U. (1952). Biogenic textures and formation of shell beds in the Dutch Wadden Sea. I and II. Proceedings Koninklijke Nederlandse Akademie van Wetenschappen (B)55(5), 500–516. van Straaten, L.M.J.U. (1954a). Composition and structure of recent marine sediments in the Netherlands. Leidse Geologische Mededelingen, 19, 1–108.

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van Straaten, L.M.J.U. (1954b). Sedimentology of recent tidal flat deposits and the Psammites du Condroz (Devonian). Geologie en Mijnbouw, 16, 25–47. van Straaten, L.M.J.U. (1956). Composition of shell beds formed in tidal flat environment in the Netherlands and the Bay of Arcachon. Geologie en Mijnbouw, 18, 209–226. Veenstra, H.J. (2004). In memoriam Lambertus Marius Joannes Ursinus van Straaten 1920–2004. Annual Report 2004 of the Geological Society (London), 1, 44–45. Walther, J. (1893–4). Einleitung in die Geologie als historische Wissenschaft, Fischer, Jena, 1055 pp. Winkler, T.C. (1886). Histoire de l’Ichnologie. E˙tude ichnologique sur les empreintes de pas d’animaux fossiles. Archives du Museé Teyler (Se´rie 2), 2, 241–440. Wohlenberg, E. (1937). Die Wattenmeer-Lebensgemeinschaften im Ko¨nigshafen von Sylt. Helgola¨nder Wissenschaftlige Meeresuntersuchungen, 1, 1–92. Ziegler, W. (1981). In Memoriam Rudolf Richter. Natur und Museum, 111, 341–343. Ziegler, W. (1992). Rudolf Richter 1881–1957. In: Klausewitz, W. (Ed.), 175 Jahre Senckenbergische Naturforschende Gesellschaft, Jubilaümsband, 1, Kramer, Frankfurt am Main, pp. 335–350.

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2 The Antecedents of Invertebrate Ichnology in North America: The Canadian and Cincinnati Schools S. George Pemberton, James A. MacEachern, and Murray K. Gingras

has been in use for approximately 175 years, but it is only within the last 20 or 30 years that the importance of ichnology has been recognized. In the past and to a certain degree even recently, trace fossils were classified as ‘Problematica,’ and Caster (1957) defined these as ‘the residuum of paleontologic materials, or of materials supposedly of organic origin, still awaiting definitive systematic assignment’ (Caster, 1957, p. 1025). For most of the nineteenth century, ichnofossils were interpreted to represent fucoids—i.e., fossilized remnants belonging to an order of algae (Fucales), which includes marginal-marine and marine seaweeds, and rockweeds such as modern Sargassum and Fucus. It is easy to see how this early misinterpretation evolved. Many beddingplane-oriented trace fossils display graceful, curving morphologies and possess repeating components that are superficially similar to modern plants. The singular beauty of such examples has been celebrated in Dolf Seilacher’s (1995) book Fossile Kunst (translated title Fossil Art). Trace fossils have been recognized as burrows and trails since the 1880s. This resulted from insightful interpretations published by Nathorst (1873, 1881) that were aimed at dispelling the notion that ichnofossils represented the remains of fossilized algae. By the early 1900s, most researchers accepted trace fossils to be the inorganic expression of an animal’s interaction with a substrate. Osgood (1970, 1975) divided the development of ichnology into 3 broad sections: (1) the Age of Fucoids from 1823 to 1881, which envelopes the period when

SUMMARY : The development of ichnology in North America radiated from two independent centers: the Canadian School, consisting of professional geologists generally associated with the Geological Survey of Canada, and the Cincinnati School, consisting predominantly of amateur paleontologists. Both schools had considerable impact but worked somewhat in isolation from the active European ichnological centers in Germany, France, and England. North American researchers were quick to realize that many of the markings described as fucoids were not seaweeds, but were, in fact, produced by animals.

INTRODUCTION Trace fossils (or ichnofossils) are biologically produced sedimentary structures that include tracks, trails, burrows, borings, fecal pellets, and other traces made by organisms. Markings that do not reflect a behavioral function are excluded. Owing to their nature, trace fossils can be considered as both paleontological and sedimentological entities, thereby bridging the gap between two of the main subdivisions in sedimentary geology. In the multi-disciplinary field of sedimentary geology, ichnology is playing an important role in the interpretation of sedimentary facies, depositional environments, and sequence stratigraphic discontinuities. The term ‘ichnology’


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THE EARLY CANADIAN SCHOOL

biogenic structures were considered to be fossil marine algae, initiated with the article by Brongniart (1823) and ending with the landmark Nathorst (1881) article; (2) the Period of Reaction extending from 1881 to 1925, describing the period when the vegetable origin of fucoids was seriously questioned; and (3) the Development of the Modern Approach from 1925 to 1953, spanning the establishment of the Senckenberg Laboratory by Rudolf Richter in 1925 and ending with the seminal works of Dolf Seilacher. We can now add another division: The Modern Era, which started with the pioneering work of Seilacher in 1953 and extends to the present day. The roots of ichnology go back to the early pioneer European work of Sternberg, Brongniart, Buckland, Salter, and Nathorst (see Osgood, 1970, 1975; Ha¨ntzschel, 1975; for details). However, in North America, two centers of excellence emerged: the Canadian School inhabited by William Logan, John Dawson, Elkanah Billings, and William Matthew; and the Cincinnati School, dominated by Uriah James, his son Joseph James, and Samuel Miller. These two groups made important ichnological discoveries and, despite being isolated from the mainstream researchers, were instrumental in the development of the modern conceptual framework of ichnology.

present day. The Geological Survey of Canada, established in 1842, provided the impetus for extensive geological examination of strata. The early researchers took an active interest in trace fossils and very early on interpreted them correctly as structures produced by the activities of organisms. William Logan, J. William Dawson, Elkanah Billings, and George Matthew were all, in some regard, linked to the Geological Survey of Canada, and were responsible for fundamental advances in how traces fossils were studied.

William Edmond Logan (1798–1875) Biography Sir William Edmond Logan is, perhaps, Canada’s most famous geologist. In fact, during a survey in 1998 the prominent Canadian magazine Maclean’s (July 1, 1998 issue) determined that Sir William Edmond Logan was the most important scientist in Canadian history. He was a stratigrapher, structural, and economic geologist, and was the first director of the Geological Survey of Canada. Details on Logan’s life have been summarized from Harrington (1883) and Winder (1972, 2004). William Logan (Fig. 2.1A) was born on April 29, 1798 in Montreal, where he received his early education at Skakel’s Private School. He was then sent to Scotland and continued his education, first at the Edinburgh High School (1814–1816), and then Edinburgh University (1816–1817), where he studied

THE EARLY CANADIAN SCHOOL Canada played an important role in the development of ichnology and this tradition continues to the

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FIGURE 2.1 (A) Sir William Edmond Logan 1798–1875 (courtesy of the Public Archives of Canada). (B) Type Specimen (GSC Holotype 6299) of Climactichnites wilsoni. This slab was on the wall in Logan’s office (photograph courtesy of the Geological Survey of Canada).

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2. THE ANTECEDENTS OF INVERTEBRATE ICHNOLOGY IN NORTH AMERICA

chemistry, mathematics, and logic. His early work was in the copper mining industry near Swansea in southern Wales. While in Wales, he produced highly accurate topographic and cross-sectional maps of nearby coal seams, which were later adopted by the Geological Survey of Great Britain. In 1840, Logan proposed his theory on the in situ formation of coal, which enabled geologists to determine the location of workable deposits of coalified strata. He subsequently studied the coalfields of Pennsylvania and Nova Scotia in 1841. Logan was appointed the first director of the Geological Survey of Canada in 1842, a position he held until 1869. In order to get this position, Logan compiled an impressive list of testimonials including letters from four of the most influential British geologists of the time: Henry de la Beche, Roderick Murchison, Adam Sedgwick, and William Buckland. His early work at the Geologic Survey included further studies of the coalfields of Nova Scotia and New Brunswick. He also analyzed the copper-bearing rocks on the north shore of Lake Superior, and undertook geologic work on the Gaspe Peninsula. Logan, with the help of one assistant, Alexander Murray, identified and mapped the major geological structures of the Province of Canada, in particular the Laurentian and Huronian series of the Precambrian Shield (Logan, 1858). In 1863, Logan published the monumental work ‘The Geology of Canada,’ followed in 1865 by an atlas, and in 1869 by a larger geological map. During most of his time at the Survey, Logan maintained a twelve-hour day in the field, usually alone carrying all of his own supplies. In the evenings he wrote up his notes and completed his maps. In 1869, at the age of 71, he recognized that a younger man should take over his post and he resigned as the Director. Upon ‘retirement,’ he divided his time between an estate he purchased in Wales and conducting further exploration in Canada. While preparing to do field work in the eastern townships of Quebec, Logan became ill and following a short illness, died on July 22, 1875. Sir William Logan was then buried in the churchyard at Cilgerran, Wales. Based on the high caliber of his work, Sir William Edmond Logan received many honors during his lifetime. In 1851, based on the excellence of his display of Canadian minerals at the London exposition, Logan became the first Canadian-born citizen to be inducted into the Royal Society of London. Similarly, Logan was awarded the Cross of the Legion of Honor at the Paris Exhibition in 1855. The following year, Queen Victoria knighted Logan and he also received the Wollaston Medal from the Royal Society in 1867. Although never associated with a university, he did donate $19, 000

to McGill University in Montreal to establish the Logan Chair in Geology. The first holder of the chair was his good friend William Dawson. Both McGill University in Montreal (1856) and the University of Bishop’s College in Lennoxville, Quebec (1855) conferred honorary degrees on him. During his career, he was a Fellow of the Geological Society of London (1837), a Fellow of the Royal Society of Edinburgh (1861), and a member of the Academy of Natural Sciences of Philadelphia (1846), the American Academy of Arts and Sciences, Boston (1859), and the American Philosophical Society (1860). Contributions to Ichnology Although ichnology was not a main thrust of Logan’s research, he was cognizant of the importance of the subject and recognized that traces were, indeed, constructed by organisms. His work on paleoichnology in Nova Scotia provided the first demonstration of the existence of land animals in the Upper Paleozoic, when he described the first ever traces observed of land animals from the Carboniferous System. The trace consisted of a series of small, but well-marked footprints, found in the lower coal measures of Horton Bluff, Nova Scotia (Logan, 1842). Later, in 1851, Logan documented the occurrence of tracks and footprints from the Potsdam Sandstone of Lower Canada (Logan, 1851, 1852). The tracks were found in a quarry at the village of Beauharnois, on the south side of the St. Lawrence River, about twenty miles above the city of Montreal. They occur on the bedding planes between sandstone units and argillaceous interbeds. The Potsdam Sandstone was determined to be Lower Silurian in age, through the correlation of the presence of Lingula or Scolithus (= Skolithos) and ‘Fucoid’ horizons, in conjunction with graptolite zones. Plaster casts of the tracks were made by Logan and shown to Prof. Owen, who proposed a classification for them under the ichnogenera Protichnites (P. septem-notatus, P. octo-notatus, P. latus, P. multinotatus, P. lineatus, and P. altnans); the ichnospecies were defined on the basis of variations of the median furrow and appendage impressions (Owen, 1852). In all the occurrences of the tracks, there is no clear evidence of unequivocal marks of toes or nails, and most display a median track or impression. Protichnites is now generally considered to be the locomotion structure of trilobites or other arthropods (Ha¨ntzschel, 1975). In 1860, Logan described another occurrence of fossil tracks or trails from the Potsdam Sandstone in the vicinity of Perth, Ontario (Fig. 2.1B). These tracks consisted of a number of parallel ridges and furrows similar to ripple marks, which were arranged between


two narrow, contiguous parallel ridges. The track is gently sinuous, somewhat resembling a ladder of rope. The transverse ridges are either straight or curved, and there is locally a median ridge, which can be sinuous or straight, running between the two parallel side ridges. Logan proposed the name Climactichnites wilsoni (Logan, 1860)

Sir John William Dawson (1820–1899) Biography Sir John William Dawson stands as one of Canada’s most outstanding scientists. During his long and illustrious career, he distinguished himself as a geologist, a paleontologist, an educator, an administrator, and a churchman. Details on Dawson’s life and the significance of his work may be found in publications by Adams (1899), Ami (1900), O’Brien (1971), Clark (1972), and Hofmann (1982). Dawson (Fig. 2.2A) was born on October 19, 1820 at Pictou, Nova Scotia, where his father John was a prominent businessman. At an early age, he developed a love for the natural sciences and made large collections of fossil plants from the Nova Scotia Coal Measures. Dawson was educated at the Pictou Academy. On two separate occasions he spent time at Edinburgh University, where Robert Jamieson and Edward Forbes influenced him. In 1841, he graduated with a Master of Arts degree from Edinburgh University and returned to Nova Scotia to pursue his geological research. During this period, Dawson

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met two individuals who would play prominent roles in his subsequent geological career—Sir Charles Lyell, who was touring North America, and Sir William Logan, who would be the first director of the Geological Survey of Canada. In 1850, at the age of 30, Dawson was appointed Superintendent of Education for Nova Scotia. This position afforded him the opportunity to tour the countryside, and he accumulated an immense body of information dealing with the geology, paleontology, and mineral resources of Nova Scotia. This material was assimilated and his first and, arguably, most important book, ‘Acadian Geology,’ was published in 1855 and appeared in three editions (Dawson, 1868). In 1854, Edward Forbes, a professor of geology and zoology at the University of Edinburgh, died, and Lyell, who was greatly impressed with Dawson’s work, urged him to apply for the vacant chair. Soon after, however, he received word that the position has been filled by a zoologist who had been supported strongly by the medical school. By strange coincidence, he received, almost on the same day, a letter offering him the principalship of McGill University in Quebec. He accepted this position with the proviso that he also assumed the chair of natural history. Under his guidance, McGill progressed from an obscure college with three faculties and 16 professors in 1855, to a world-class educational institution with more than 120 professors by 1900. In addition to his teaching duties, Dawson administered the university, initiated and acted as first librarian for the university, and was a prominent

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FIGURE 2.2 (A) Sir John Dawson Logan (1820–1899) (courtesy of the Redpath Museum, McGill University). (B) Original drawing of Dawson’s Rusichnites acadicus(after Dawson, 1864). (C) Photograph of the specimen depicted in B, Rusophycus acadicus, Redpath Museum No. 3177.

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figure in almost all phases of the educational system in Quebec. During all this, he still managed to find time to carry out original research in numerous areas. As pointed out by Hofmann (1982), Dawson’s scientific productivity was enormous and included articles not only in geology and paleontology, but also in agriculture, anthropology, and theology. Ami (1900) listed 364 contributions in the most comprehensive bibliography ever assembled on Dawson’s work. Of these, Clark (1972) indicated that 198 dealt with some aspect of paleontology. Throughout his career, Dawson received many honors and held numerous important positions. He received an honorary LLD from McGill University (1857) and Edinburgh University (1884); he was elected an honorary or corresponding member of many learned societies. He was a fellow of the Royal Society of London (1862), was awarded the Lyell Gold Medal by the Geological Society of London (1881), was the first president of the Royal Society of Canada (1882), was elected president of the American Association for the Advancement of Science (1882), was created a Knight Bachelor by Queen Victoria (1884), was elected president of the British Association for the Advancement of Science (1886), and was elected president of the Geological Society of American (1893). In 1893, Dawson was seized with a severe attack of pneumonia, and his health became so seriously impaired that he was forced to retire. He passed away on November 19, 1899 at the age of 79. Contributions to Ichnology The synthesis of natural science and religion was influential in Dawson’s works. In effect, his career shows the durability of the two theologies’ tradition (O’Brien, 1971). It was this deep involvement in the two theologies’ tradition which thrusted Dawson into numerous controversies. The reassuring synthesis of science and religion that was so convincing in his youth, seemed to crumble on all sides as he grew older (O’Brien, 1971). During the span of Dawson’s career, geology was in a state of continual controversy, where both new and old ideas were questioned and debated. John William Dawson was well known to be a man always involved with a controversial issue. At the forefront of such controversies stood the question of the origin of Eozoon canadense, ‘the dawn animal of Canada.’ The discovery was made in 1858 in the rocks of Precambrian age, located in the Ottawa valley (Logan, 1858). The coral-like surface of the specimen immediately suggested to Sir William Logan that it might be a fossil; potentially a very important discovery. In 1865, Dawson named the specimen

Eozoon canadense. His involvement was inevitable, since in the 1860’s he was the only accomplished microscopist in Canada and specimens of Eozoon were, as a matter of course, brought to him for investigation (O’Brien, 1971). After examination of the specimen, Dawson declared that it was a foraminifer. Dawson’s advocacy of Eozoon as a foraminifer received much opposition. In 1866, he also proposed that curious holes in rocks containing Eozoon were worm burrows similar to Scolithus (= Skolithos) (Dawson, 1866). However, Dawson knew that, if his opinion were correct, evolutionists would have had to contend not only with an immense gap in time and in the paleontological record, but also with the presence of a very advanced and complex form preceding in time much simpler Foraminifera (O’Brien, 1971; Hofmann, 1971). Once aware of the consequences Eozoon was offered to the theory of evolution, Dawson was determined to exploit them to the fullest. It is important to understand Dawson’s deep involvement in synthesizing science and religion. Such motivation was responsible for most of Dawson’s involvements in other controversies. While the origin of Eozoon has been established as undoubtedly inorganic, the significance or relevance of the controversy on science is important to remember. ‘. . . It provides an example of the manner in which every aspect of 19th Century paleontology was scrutinized for its bearing on evolution. It is also a classic case of the confrontation of younger specialists with each other and with the older generation of broadly trained naturalists’ (O’Brien, 1971, p. 28). Despite Dawson’s keen opposition to evolution and its proponents (particularly Charles Darwin); he remained a forerunner in the most controversial issues apparent in geology during the nineteenth century. Even if all his beliefs and interpretations were to be proven wrong at some point in time, it is his contribution to the progress of geological thought during this time that is important. It was Dawson’s keen eye for observation and his determination, which resulted in numerous other contributions both to geology, and more specifically, ichnology. He went on to propose seven new ichnogenera to the taxonomic classification of ichnofossils, of which two are still considered trace fossils (Diplichnites Dawson, 1873; and Sabellarites Dawson, 1890), three are pseudofossils (Archaeospherina Dawson, 1875; Eozoon Dawson, 1865; and Rhabdichnites Dawson, 1873), and two are invalid (Rusichnites Dawson, 1864, Fig. 2.2B; and Astropolithon Dawson, 1878). Demonstrating that Cruziana and Rusophycus represent the works of animals rather than the remains of algae marks one


of the most significant turning points in the history of invertebrate ichnology. The distinction for achieving this breakthrough is generally attributed to Nathorst (1873, 1881) who, in a series of well-documented articles, was able to defend and disseminate this viewpoint. However, nearly a decade before Nathorst’s work appeared in press, Dawson, had already demonstrated that Rusophycus could not be a plant but, instead, must have been produced by the burrowing activities of trilobites (Fig. 2.2C). He also understood the toponomic relationship of the trace, and its ethologic significance (Pemberton and Frey, 1991). Likewise, Dawson (1890) indicated that Asterophycus Lesquereux was not fossilized seaweed, but represented the burrow of an annelid. Dawson summarized his criteria for distinguishing between algae and the traces of animals as follows: ‘The author of this work has given much attention to these remains, and has not been disposed to claim for the vegetable kingdom so many of them as some of his contemporaries. The considerations, which seem most important in making such distinctions are the following: 1. The presence or absence of carbonaceous matter. True Algae not infrequently present at least a thin film of carbon representing their organic matter, and this is more likely to occur in their case, as organic matters buried in marine deposits and not exposed to atmospheric oxidation are very likely to be preserved. 2. In the absence of organic matter, the staining of the containing rock, the disappearance or deoxidation of its ferruginous coloring matter, or the presence of iron pyrite may indicate the removal of organic matter by decay. 3. When organic matter and indications of it are altogether absent, and form along remains, we have to distinguish from Algae, trails and burrows similar to those of aquatic animals, casts of shrinkage cracks, water marks, and rill marks widely diffused over the surfaces of beds. 4. Markings depressed on the upper surfaces of beds, and filled with the material of the succeeding layer, are usually mere impressions. The cases of possible exceptions to this are very rare. On the contrary, there are not infrequently forms in relief on the surfaces of rocks which are not Algae, but may be shallow burrows arched upwards on top, or castings of worms thrown up upon the surface. Sometimes, however, they may have been left by denudation of the surrounding material, just as footprints on dry snow remain in relief after the surrounding loose material has been drifted away by the wind; the portion consolidated by pressure being better able to resist the denuding agency.’ (Dawson, 1888, pp. 26–27). Dawson also made observations in modern settings of Limulus (Dawson, 1862a,b, 1878) and

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compared its activities to the ichnogenus Protichnites. He experimented with the animals under different substrate consistencies and noted that different markings were produced depending on the nature of the substrate. This represents one of the first experimental neoichnological studies, and predates the landmark work of Nathorst (1873, 1881) and Darwin (1881). Unfortunately, geologists, largely overlooked Dawson’s work on Rusophycus, much like the original article by Nathorst in 1873, because it appeared in an obscure regional journal. Perhaps more importantly, all these works show that the ‘age of fucoids’ was not merely the ‘dark age’ of ichnology, as commonly subsequent authors have depicted it. Nor did North America lag behind Europe in the early development of the discipline, as has commonly been assumed.

Elkanah Billings (1820–1876) Biography Elkanah Billings is generally regarded as Canada’s first paleontologist. Details of Billings’s life are summarized from Whiteaves (1877), Ami (1901), and Clark (1971). Elkanah Billings (Fig. 2.3A) was born on May 5, 1820 by the Rideau River, on a farm located three miles from the town of Bytown (now Ottawa) in the Township of Gloucester, Upper Canada (now Ontario). He received extensive formal education from an early age, initiated by a governess and extended through a family tutor. Later he attended several local private schools up to the age of seventeen. From 1837 to 1839, he spent two years at St. Lawrence Academy at Potsdam, New York, in preparation for a law career. In 1939, Elkanah entered the Law Society of Upper Canada and was articled to several lawyers from both Bytown and Toronto, and at the end of his studies was called to the bar in 1845. While articled to the legal firm Baldwin and Wilson of Toronto, he met and later in, married Eleanor, a sister of the junior partner Adam Wilson (later Chief Justice of Ontario). For eight years he practiced law in Bytown and surrounding area. Following his return to Bytown in 1852, he opened a law office but almost immediately became editor of the Bytown Citizen and retained the position until shortly before joining the Geological Survey of Canada in 1856 (Whiteaves, 1877). As editor of the Bytown Citizen, he began to define his interests in the natural sciences through the writing of popular articles on geological topics and natural history subjects. His love for natural history may have been fostered by his eldest brother,

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FIGURE 2.3 (A) Elkanah Billings 1820–1876 (courtesy of the Geological Survey of Canada). (B) Original figure of Licrophycus ottawaensis from Billings (1862). Specimen is now considered to be Phycodes (courtesy of the Geological Survey of Canada).

Bradish who became an accomplished botanist and entomologist (Clark, 1971). Between 1852 and 1856, he began to learn the principles of geology and zoology. Beginning in 1852, he began to accumulate a large collection of fossils from local Ordovician outcrops and quarries. His collection of asteroids, crinoids, and cystids was particularly good. In 1854, his first two scientific articles concerned with the latter group were published in the Journal of the Canadian Institute of Toronto. These articles stamped him as a capable paleontologist and show that, by this time, he had achieved a mastery of zoological taxonomy and the rules of nomenclature. Billings initiated the publication of ‘Canadian Naturalist and Geologists’ in 1856 for two reasons. Through the articles he could qualify himself as a field geologist and at the same time, they provided the youth of Canada with a convenient means of learning the natural history of their country. Following the publication of the journal, William E. Logan appointed Billings, Paleontologist to the Geological Survey of Canada. While at the Geological Survey of Canada from 1856 until his death in 1876, Billings’ time was devoted to the description and naming of Silurian, Ordovician, and Devonian fossils of Upper Canada (Ontario), Lower Canada (Quebec) and Newfoundland. His recognition of fossil assemblages was instrumental in the determination of the precise limits and distribution

of geologic formations. As a result of Billing’s determination of the age of the rocks of the ‘Quebec Group’ as Germantown and Chazy, Logan was able to demonstrate his ‘great overlap,’ now referred to as Logan’s Line. Among his most important scientific publications are two articles entitled ‘On some new genera and species of Cystoidea from the Trenton Limestone’ which appeared in 1854. It was these two articles that established his ability as a scientist. In his first report to the Survey in 1857, he described one hundred and six new species belonging to thirty-five genera (of which thirteen were new). He continued the work on the ‘Canadian Organic Remains’ series, of which Decades Ill and IV were published in 1858 and 1859, concerned largely with fossil echinoderms. He initiated a second series entitled ‘Palaeozoic Fossils,’ the first volume appearing in 1865, and the first part of the second in 1874. During his time at the Survey, he erected sixty-one new genera and one thousand and sixty-five new species. In a bibliography of more than two hundred titles (Walker, 1901), ninety were concerned directly or indirectly with paleontological subjects (Clark, 1971). This work received recognition in 1867 when the Natural History Society voted him a silver medal ‘for his life-long efforts in the promotion of science in Canada’ and the jurors of the International Exhibition of London in 1862 and


the Paris Exhibition in 1867 also awarded him a bronze medal. Billings continued to work even in the final three years of his life, but was slowed by Brights disease to which he succumbed on June 14, 1876. Billings was buried in the Wilson family plot in Toronto, Ontario. Contributions to Ichnology Although echinoderms were his specialty, he studied and wrote on all invertebrate groups. Over the course of his professional life, he erected sixty-one new genera and 1065 new species. His bibliography comprises over 200 titles, a remarkable feat for essentially a self-taught paleontologist. Billings was an early contributor to the field of ichnology in North America. He erected three ichnogenera, Saerichnites Billings, 1866; (Arthraria Billings, 1872; and Licrophycus Billings, 1862, and at least seventeen ichnospecies including species of Skolithos (S. canadensis Billings, 1862), Cruziana (C. similis Billings, 1874), Palaeophycus (P. incipiens Billings, 1861a; P. congregatus Billings, 1861a; P. beverleyensis Billings, 1862; P. funiculus Billings, 1862; P. obscurus Billings, 1862; and P. beauharnoisensis Billings, 1862), Rusophycus (R. grenvillensis Billings, 1862), and Eophyton (E. jukesi Billings, 1874)). Of these, Saerichnites and Artharia are still considered valid, while Licrophycus (Fig. 2.3B) is now grouped with Phycodes. Many of the species can be incorporated into existing taxa or, as in the case of Eophyton, may represent inorganic structures. Billings’ fossil descriptions indicate that he considered that the fossil remains were those of plants, and not the traces left behind by the activities of an organism. He followed the convention of the day that many of these markings were, in fact, seaweeds.

George Frederic Matthew (1837–1923) Biography The contributions of amateurs have long been a part of the historical development of paleontology and continue to this day. George Frederic Matthew was such an amateur, and growing up in New Brunswick was of significant importance to Matthew’s career because a large percentage of his work as a geologist was focused within a few hundred miles of his hometown. Matthew did not restrict his work to the Maritime Provinces, however, and in working with several individuals was able to study and report on areas such as Sweden and Wales. His unique situation as an amateur geologist created many opportunities for Matthew in some aspects of

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his career while restricting him in others. Details on the life of George Matthew are summarized from Bailey (1923), Matthew (1924), and Miller (1988). George Frederic Matthew (Fig. 2.4A) was born on August 12, 1837 in St. John, New Brunswick to United Empire Loyalist parents. Matthew attended St. John Grammar School, a one storey Anglican school in South St. John near his home for several years, finishing his formal grammar school education at the age of sixteen. He then entered the work force as a staff member of the St. John Customs Service and after several years of excellent service was appointed chief clerk and surveyor of the St. John port. He remained at this post for the remainder of his working life. Matthew’s early life in St. John had cultivated an interest in geology and botany, which by the age of twenty had intensified sufficiently to encourage him to form the Steinhammer Club (Miller and Buhay, 1988). This small club, which studied the geological formations in and near St. John, lead to the formation of The Natural History Society of New Brunswick in 1862. Matthew immediately became a charter member and the society’s first curator. After the Canadian Confederation in 1867, Matthew’s work in New Brunswick received a huge boost as the Geological Survey of Canada undertook the mapping of the provinces. With the sudden availability of money for geological work, Matthew became a temporary, parttime employee of the Survey, while maintaining his position as chief customs clerk. Several field seasons of work in southern New Brunswick followed, during that time Matthew published a number of regional geology maps and amassed a large collection of paleontological data and specimens. From the early 1880s to the turn of the nineteenth century, Matthew’s work became recognized for its excellence, which led to the bestowment of several awards, memberships, and honorary degrees. These included honorary doctorates from Lava1 University and the University of New Brunswick, as well as, charter memberships in the Royal Society of Canada, the Academy of Sciences, and the Paleontological Society. Awards received included the Murchison Medal from the Royal Geographic Society and the Wollaston Medal from the Geological Society of London. Societies such as The Natural History Society of New Brunswick and the Royal Society of Canada had G.F. Matthew as a chartered member and president for several years in the late 1880s and 1890s. Matthew was quick to utilize his positions as president of these societies and began publishing with regularity in both journals. Several years of publishing in these journals allowed Matthew to amass a total of over 200 articles, as well as

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FIGURE 2.4 (A) George Frederic Matthew 1837–1923 (courtesy Randall Miller, New Brunswick Museum). (B) Specimen of Acripes minor (New Brunswick Museum No. 3030).

to cultivate contacts around the globe (Landing and Miller, 1988). Later in his career, while studying Cambro-Ordivician rocks and their contained insects and trackways, Matthew’s focus became ichnological. The resulting collections formed the basis for several later studies and ultimately the classification of several ichnogenera and ichnospecies by Matthew himself, as well as other scientists using his collected data (Miller, 1996). Despite being a fulltime customs officer and parttime geologist, Matthew was also able to have a full family life. His marriage to Katherine M. Diller in 1868 was the beginning of a family that eventually included six sons and two daughters. The eldest of his sons, William Diller Matthew followed his father’s path in becoming a paleontologist, eventually rising to the post of curator of vertebrate paleontology at the American Museum of Natural History. On April 17, 1923, while preparing a paper to defend one of his proposals, George Frederick Matthew died in Hastings-Hudson, New York at the age of 86. Contributions to Ichnology Ichnology became the focus of Matthew’s interests as a result of the study of insects and trackways in Cambro-Ordivician rocks near St. John, New Brunswick. These studies led to the publication of several articles, which discussed new genera and

species of ichnofossils. George Frederic Matthew’s contributions to the emerging field of ichnology had more impact in vertebrate ichnology, where he erected 9 ichnogenera and 18 ichnospecies including some that are still valid today. This work was more successful than his contributions to invertebrate ichnology, which were often marked by equivocal descriptions and poor illustrations. Much of the original material he described has been reclassified or is now viewed as inorganic. Archaeoscolex Matthew, 1899; Eurypterella Matthew, 1889; Halichondrites Matthew, 1890; Phycoidella Matthew, 1890; and Medusichnites Matthew, 1891 are unrecognizable genera and Bipezia Matthew, 1910 is now considered a junior synonym of Cruziana. Two of the forms that he described are listed in Ha¨ntzschel (1975) as valid ichnogenera: Myriapodites Matthew, 1903 and Acripes Matthew, 1910 (Fig. 2.4B). Debate over the synonymy of Acripes Matthew, 1910 and Diplichnites Dawson, 1873 is ongoing. Detailed review using the principles of significant and accessory features indicates that Acripes Matthew is indeed a junior synonym of Diplichnites Dawson (Miller, 1988, 1996). In describing trace fossils, Matthew meticulously discussed their morphology and attempted to remove animal behavior as a premise for his descriptions. Very early work done by ichnologists was focused on

THE CINCINNATI SCHOOL

the organisms making the trace rather than on the trace itself. Matthew, therefore, was one of the first to use a purely descriptive approach to ichnological taxonomy. This trend is presently employed by ichnologists. He also used the traces in stratigraphic correlation, especially in the Cambrian strata in and around the Maritimes (see Matthew, 1888, 1890, 1891, 1899, 1901). George Frederick Matthew established himself as a quality geologist at a time when science was in fierce competition with the church. Despite working as an amateur throughout his career, he was recognized by professional scientists as a valued contributor to the fields of paleontology and stratigraphy. His significance as an ichnologist can be measured in terms of concrete contributions to the science as well as his recognition of the significance of this emerging field of study.

THE CINCINNATI SCHOOL Cincinnati has long been known to be one of the centers of paleontological excellence in the early nineteenth century (Caster, 1982; Davis, 2001). Many of the early paleontologists became interested in the

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fossils of the area as young people, and a booming amateur fossil collecting community fostered their interests. Many of these young people, such as Charles Schuchert, Ray Bassler, Edward Ulrich, and John Nickles went on to become accomplished professionals and some of the most influential paleontologists in the United States. Still others remained essentially amateurs and did their palaeontological work as a hobby. This group included: David T.D. Dyche, Charles B. Dyer, C. Faber, G.W. Harper, J.F. James, U.P. James, J. Mickleborough, S.A. Miller, and A.G. Wetherby. Of these, Uriah James, Joseph James, and Samuel Miller were pioneers in the fledging science of ichnology and their contributions can be considered as the roots of the science in the United States.

Uriah Pierson James (1811–1889) Biography Uriah Pierson James (Fig. 2.5A) was born on December 30, 1811 in the town of Goshen, Orange County, New York. He died 78 years later, at his home near Loveland, Ohio on February 25, 1889. Details on the life and times of Uriah James are taken from the biography by his son Joseph (James, 1889).

B

FIGURE 2.5 (A) Uriah Pierson James (1811–1889) (after James, 1889). (B) Joseph Francis James 1857–1897 (after Gilbert, 1898).

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Uriah was one of the 6 children (3 boys, 3 girls) born to Thomas and Rhoda James. His father, a carpenter, died accidentally in 1824. His mother, Rhoda Pierson, was the daughter of Thomas Pierson and niece of Reverend Abraham Pierson, the first president of Yale College. At the age of 20, Uriah and his brother Joseph left Goshen and traveled west to Cincinnati, Ohio, arriving there in August of 1831. Soon after their arrival Uriah, a printer and stereotyper by trade, set up the U.P. James firm, and began publishing books. In 1847, Uriah and his brother Joseph entered into partnership as publishers, printers, stereotypers, and typefounders. The new firm, J.A. and U.P. James, flourished over the next years. Also in 1847, he married the daughter of an English lady, Olivia Harriet Wood. Together they parented 6 children (3 boys and 3 girls). Unfortunately, one son died in infancy, but Uriah’s other sons survived and continued on their father’s interests. The elder son took over his father’s publishing firm and Joseph, his younger son, continued on with his father’s geological work. Uriah James devoted his leisure time to scientific work. It was not long after his arrival in Cincinnati that he was drawn to the profusion of fossils in the hills surrounding the city. Later in life, Uriah took his son Joseph on these fossil-collecting adventures, and he instilled an early love for geology in his young son. Uriah’s interest in geology never left him and he was collecting fossils up until a few months before his death. After 30 years of fossil collection, James published the first catalog of fossils from the Cincinnati area. Over those years of collection, Uriah amassed an unrivaled collection of fossils from the neighborhood of Cincinnati. During a visit to Cincinnati in 1845 by Charles Lyell, Uriah James was among the distinguished few that guided Lyell through the familiar hills surrounding Cincinnati. Uriah James published 23 articles between 1871 and 1888, and although his writings were merely descriptive, they were complete and accurate. Being the owner of a publishing firm had its advantages. Uriah was able to publish many catalogs of his work, some of which were compiled by committees from the Western Academy of Natural Sciences. He was also able to create a small periodical in 1878 that he called ‘The Paleontologist.’ This periodical contained 7 issues and was distributed to libraries, societies, and correspondents, or could be bought for a hefty 25¢ each. Uriah James was a life member, long-time treasurer, and one-time president, of the Western Academy of Natural Sciences, predecessor to the Cincinnati Society of Natural History. James was also a member

of the American Association for the Advancement of Science, in the early days of the association. Contributions to Ichnology Probably the greatest contribution Uriah James made to the study of ichnology was being the father of and early influence on his son Joseph James. Joseph carried on his father’s geological work with his primary contributions to ichnology involving the re-identification of many fossils to their correct origin and thereby, was able to help clean up the taxonomic nomenclature. Uriah himself described about 130 species of fossils during his 17 years of publications. Many of these species were shells or corals, while others belonged to the genus Fucoides. It was described as being a genus to unite all of the fossils that appeared to have belonged to the family of non-articulate Algae. As a consequence, the ‘genus’ was used as a dumping ground for more than 200 species and sub-genera of obscure or indeterminable origin. Authors were delighted that a new genus had been formed in which they could place innumerable specimens they felt were not of animal but, perhaps vegetable origin. Uriah James was one of these many early paleontologists who misinterpreted the origins of certain Fucoides. Although Uriah James mis-identified a few trace fossils as plants, their original recognition is rightly attributed to him. Thus, Uriah James was able to contribute to ichnology through the recognition of at least 2 ichnogenera: Lockeia James, 1879 and possibly Saccophycus James, 1879, and 3 ichnospecies (Buthotrephis filoiformis James, 1878; Palaeophycus flexuous James, 1879; and Scolithus delicatulus James, 1881). In these publications, Uriah James followed the convention of the day and described these traces as fucoids or plant fossils. Later, James (1883) described tracks that he interpreted to be constructed by crustaceans. His greatest contribution to ichnology would not, however, be in the identification of fossils. Rather it would be his son, Joseph Francis James, who helped to re-identify the origins of many Fucoides, some of which were ichnofossils. Uriah’s love for geology influenced Joseph at a young age and guided him to a life’s work in botany, paleontology, geology, and ichnology.

Joseph Francis James (1857–1897) Biography Joseph Francis James (Fig. 2.5B), the youngest son of Uriah James, was born in Cincinnati, Ohio on


February 9, 1857. Details on his life are based on the biographical accounts of Gilbert (1898) and Stanton (1898). Joseph’s interest in the natural sciences stemmed from his father, and from an early age he collected living plant specimens and fossils from the region. By the time he was 16, Joseph had already assembled a manual of the flora in and around his hometown of Cincinnati. In 1879, at the age of 22, Joseph moved to Los Angeles, California to establish a business and settle down. The business venture failed, however, due to a tragic fire. He then went to work with a railroad construction crew, traveling through southern California, Arizona, and New Mexico. Two years after having moved to California, he returned to Cincinnati. There, he was appointed custodian of the Cincinnati Society of Natural History while serving concurrently as Professor of Medical Botany at the Cincinnati College of Pharmacy. His works during this period were predominantly botanical, but soon his scientific endeavors began to sway toward paleontology. By the time he was 27, he began publishing on the paleontology and geology of the Ordovician- and Silurian-aged rocks of the Cincinnati Group in Ohio. During this period, he married Miss Sarah C. Stubbs, a high school physiology and botany teacher with whom he raised 2 sons. In 1886, Joseph became the chairman of Botany and Geology at Miami University in Oxford, Ohio. After only 2 years, his position was terminated due to his religious inclinations conflicting with other faculty members’ beliefs. He was unfairly accused by his colleagues of being an agnostic, and in his defense, claimed to be a Unitarian. After this, he received a professorship and taught Natural Science at the Agriculture College of Maryland. He moved from there to work as an assistant paleontologist at the United States Geological Survey division for Paleozoic paleontology. Both of these jobs were disappointments to him because of the routine nature of the work, and the opportunities for publication that he had anticipated did not materialize. In 1889, James received an appointment as an assistant vegetable pathologist for the United States Department of Agriculture. He received little gratification from this job as well, and while working there, he devoted his leisure time to the study of medicine. In 1895, he graduated from the Medical School of Columbia University, subsequently accepting work in hospitals in New York and London in the field of bacteriology. In 1896, he opened a practice in Hingham, Massachusetts. Only a few months after having moved there, he died from a severe case of

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pneumonia, contracted during the course of his work on March 29, 1897. Contributions to Ichnology Joseph James’ earliest studies were in the field of botany, and he first assembled a catalog of the flora of the Cincinnati area when he was 16. This was subsequently published in the Journal of the Cincinnati Society of Natural History in 1879. In 1882, James wrote a memorandum to Charles Darwin a few weeks after his death. Darwin’s Origin of Species was published on November 24, 1859, 2 years after Joseph was born. Darwin was an idol of James,’ which can be attested to in his own words: ‘In the hands of Mr. Darwin, order is brought out of chaos, and what would under other circumstances be a mere jumble, is through the medium of his pen a work of lasting value’ (James, 1882, p. 74). James wrote on a diversity of topics in botany, geology, paleontology, ichnology, and stratigraphy. In paleontology, he dealt with mainly fucoids and other problematic organisms, but also sponges, algae, protozoa, cephalopods, corals, Polyzoa (Bryozoa), and fish. In his lifetime, he published over 200 scientific and popular scientific articles (Gilbert, 1898; Stanton, 1898). James was one of the first scientists to make an attempt to bring some order to the undeveloped field of ichnology. In his research, he was patient and competent and dealt mainly with details of description and classification. He tended to re-evaluate and bring some order to problematic species that were poorly understood at the time. His main contribution to the field of ichnology was on the interpretation of fucoids, and he was one of the primary opponents to their plant origins. James concluded that the three main sources for fucoids were: inorganic structures and residues; trails and burrows of organisms; and hydozoa (James, 1885a). Much of his work involved discarding many problematic species names, especially those of Fucoides. He chose to discard many of the old species and lump them together under pre-existing taxa. In many cases, his critical work did not bring favor to his reputation, as he attacked many of the top scientists of the time in the literature. He was skeptical of the organic nature of many problematical specimens attributed to Fucoides (Fig. 2.6B). As a result of his botanical background and critical nature, he was able to assign many of these species to processes other than plants (James, 1884, 1885a,b,c,d, 1890, 1891, 1892a,b, 1893a,b, 1894, 1895a,b).

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FIGURE 2.6 (A) Title page of the James (1892a) paper that revised the systematics of Scolithus (= Skolithos). (B) Title page of the James (1893a) paper that revised the systematics of Fucoides.

James contributed to the sorting out of the ichnogenus Skolithos (which he referred to as Scolithus). Although first recognized as having an annelid burrow character by Logan (1852), most authors considered it a fossil plant. James reviewed all of the known species of Skolithos, and attributed their formation to worm burrows (Fig. 2.6A). For a breakdown of his work, refer to the section on his contributions to ichnological taxonomy below. He noted that it was next to impossible to separate many species of differing ages of Skolithos from one another. Even still, he proposed, ‘that the geological position shall decide the name to be used’ (James, 1892a, p. 43). J.F. James’ contributions to ichnology were mainly in his meticulous and thorough classification, description, and organization of problematic genera and species. He could be considered the first ichnological taxonomist. He was not the most creative of scientists, and did not contribute much to the naming of ichnotaxa, but rather chose to discard taxa and classify them properly. James viewpoint is typified by what he wrote in 1885, where he stated: ‘It is indeed time that this habit of referring to some sort of life for every mark found in the

rocks of the earth, and calling all uncertain marks marine plants, should be protested against. If it is not done the nomenclature of the science will be so encumbered with useless names that chaos will result. The multiplication of species has gone entirely too far already; and when every mark made by a dash of water, every turn made by a worm or shell, and every print left by the claw of a crustacean is described as a new addition to science, it is time to call a halt and eliminate some of the old before making any more new species’ (James, 1885b, p. 167).

Samuel Almond Miller (1837–1897) Biography Samuel Almond Miller (Fig. 2.7A) was born on August 28, 1837, in the community of Coolville, Ohio. Unfortunately, the only biographies of this notable amateur palaeontologist are two very brief obituaries written at his death in 1897 (Bather, 1898; Billings, 1898), and little is known about his youth or how he acquired his deep interest in geology and paleontology. We do know, however, that he


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B

FIGURE 2.7 (A) Samuel Almond Miller (1837–1897) (Front piece from Volume 1 of the Cincinnati Quarterly Journal of Science). (B) Plate 1 from Miller and Dyer (1878a), trace fossils include Blastophycus diadematus (Figs. 1 and 2); Trichophycus lanosus (Figs. 3 and 4); and Rusophycus asper (Figs. 5 and 5a).

went to the Ohio University where he graduated with a degree in Arts, Law and Philosophy, and that this institution later conferred an honorary Ph.D. on Miller, in 1893. Samuel A. Miller was not only the owner of a respected and busy law firm, but was also actively involved in local politics and, for a time, edited a weekly newspaper. However, Miller became interested in the field of paleontology and ultimately in ichnology, and it is remarkable that despite all his other interests, he published more work than many professional palaeontologists of the time (Billings, 1898). In addition to his own voluminous work, Miller also managed to find the time to edit the Journal of the Cincinnati Society of Natural History (of which he was a founding member) and to edit and publish the brieflived (1874–1875) Cincinnati Quarterly Journal of Science. Much of his work was published in these two periodicals. Perhaps Miller’s greatest overall contributions are his two books, American Paleozoic Fossils (Miller, 1877) and the more comprehensive North American Geology and Paleontology (Miller, 1889). Both of these were regarded as indispensable volumes with regard to the study of Paleozoic strata in North America. According to Billings (1898), the latter work

(including the two appendices) constituted 793 pages, with 1457 illustrations, totaling about 3000 figures. Caster (1982) indicated that this volume ‘was probably the most used volume on American paleontology ever compiled, and it certainly was the most ambitious private publication in the discipline.’ (Caster, 1982, p. 25). That such a monumental work was accomplished while maintaining a business and a political career, and while doing other geological work on behalf of five states (Ohio, Illinois, Missouri, Indiana, and Wisconsin) is a credit to Miller’s energy and dedication. It is interesting to speculate upon what more he may have accomplished in his life had cancer of the liver not taken him on December 18, 1897. Contributions to Ichnology Most of Miller’s ichnological contributions are concentrated in three articles, one entirely on trace fossils (Miller, 1880) and two others describing ‘fucoids,’ as well as body fossils, in collaboration with a local collector and fellow amateur, C.B. Dyer (Miller and Dyer, 1878a,b). Miller and Dyer (1878a,b) described 8 new genera and 13 new species of ‘fucoids’; they considered the majority of these to be plant fossils in the classical

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fucoid manner (Fig. 2.7B). They did, however, describe Scolithus [sic] tuberosus and interpreted it as a burrow by analogy with burrows of crayfish seen in local streams, and not a plant. Miller (1880) perhaps stands out as his most significant contribution to the science of ichnology, as it was the first truly ichnological article published by what became the influential ‘Cincinnati School’ of ichnologists. He erected 6 ichnogenera and 8 ichnospecies, which included speculations on possible tracemakers. All six ichnogenera are still considered valid (Petalichnus, Ormathichnus, Teratichnus, Asaphoidichnus, Trachomatichnus, and Plangtichnus). They are all, however, probable arthropod trackways and likely subjects for reassessment, as part of the major overhaul of trackway nomenclature called for by many researchers. It is important to emphasize, however, that Miller was not truly breaking away from the fucoid tradition with this article; all the traces described are trackways (or inorganic structures misidentified as trackways (Osgood, 1970)), and were obviously nothing like ‘fucoids.’ Indeed, Miller (1889) listed all his and other Cincinnati workers’ ‘fucoids’ as such, despite the work of James (1884, 1885a), which exposed almost all Cincinnatian ‘fucoids’ as trace fossils or inorganic structures. However, Miller (1889) did mention that there was controversy regarding the nature of ‘fucoids.’ The quality of Miller’s work is also worthy of mention. Although an amateur, Miller’s articles were very well written, with excellent descriptions and detailed illustrations. Osgood (1970) remarked on this characteristic of Miller’s work, indicating that despite Miller’s ‘fucoid’ interpretations, his morphological descriptions were very accurate and made restudy of Miller’s contributions much easier. As one of the earlier researchers identified with the Cincinnati School, it seems fair to assume that the high quality of Miller’s work, to some extent, inspired the high quality of the work accomplished by later adherents of that notable body.

CONCLUSIONS The development of ichnology in North America radiated from two independent centers: the Canadian School of professional geologists, generally associated with the Geological Survey of Canada, and the Cincinnati School consisting generally of amateur paleontologists. Both schools had considerable impact and worked somewhat in isolation from active European centers in Germany,

France, and England. This isolation could be viewed in a negative light, but it also freed the investigators from the preconceived ideas that were prevalent in Europe. It left them free to explain these obscure structures they saw fit. Although the fucoid interpretation was prevalent in the works of Elkanah Billings, Samuel Miller, and Uriah James, others like William Logan, J. William Dawson, and Joseph James were quick to dismiss that interpretation and considered alternative options. This resulted in some very insightful interpretations, such as Dawson (1864) correctly exposing Rusophycus, one of Europe’s most sacred of all fucoids, as a product of the burrowing activities of trilobites. This interpretation predates the European view by almost 15 years. Convinced of the animal origin of Rusophycus, Dawson ventured on to reinterpret other forms. In an 1873 article on trace fossils in Carboniferous strata of Nova Scotia, he concluded: ‘I have long been of opinion that many of the cylindrical markings which have been described as plants under the names Palaeochorda, Buthotrephis, Palaeophycus, Arthrophycus, etc., are burrows of this kind, but the main difficulty seemed to be to account for their branching in a radiate or palmate manner. I have recently met with specimens from the Primordial and Carboniferous which seem to explain this. They show a central hole or burrow from which the animal seems to have stretched and withdrawn its body in different directions, so as to give an appearance of branching and radiation, possibly due merely to the excursions of the same worm from the mouth of its burrow’ (Dawson, 1873, p. 19). Dawson (1862b) also conducted neoichnological studies on modern Limulus and compared its activities to the ichnogenus Protichnites, a trace discovered by Logan (1852) and named by Owen (1852). Likewise, Logan (1860) correctly interpreted Climactichnites as the locomotion trail of an invertebrate and not a fucoid. Additional work on interpreted arthropod trackways by Dawson (1873), Miller (1880), and Matthew (1903, 1910) all recognized that the trackways were the product of animals, and they speculated on possible track makers as well. Osgood (1970) pointed out that James (1884, 1885a), working independently and in ignorance of Nathorst, arrived at and utilized many of the same criteria that Nathorst used to criticize the fucoid origins of many trace fossils. With his restudy of the systematics of Fucoides, Skolithos, and Arthrophycus, Joseph James (1892a, 1893a,b) brought to light many of the taxonomical nightmares that faced the fledging science (and some are still facing it today) and can rightfully be considered the first ichnotaxonomist.

ACKNOWLEDGEMENTS

ACKNOWLEDGEMENTS We would like to thank Dr. Randall Miller of the New Brunswick Museum for supplying photographs of Matthew. We are also indebted to the Geological Survey of Canada and the Public Archives of Canada for supplying copies of photographs in their collection. The senior author would like to thank the Canada Research Chair Program for support of his research. The Natural Science and Engineering Research Council of Canada provided funding for this research. Finally, we would like to thank Dr. Gerhard Cadeé and Dr. Tony Martin for their excellent and through reviews of this manuscript.

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Caster, K.E. (1982). The Cincinnati School of Paleontology. Earth Science History, 1, 23–28. Clark, T.H. (1971). Elkanah Billings (1820–1876) – Canada’s first paleontologist. Proceeding of the Geological Association of Canada, 23, 11–14. Clark, T.H. (1972). Sir John William Dawson (1829–1899) – Palaeontologist. Proceedings of the Geological Association of Canada, 24, 1–4. Darwin, C. (1881). The Formation of Vegetable Mould, Through the Action of Worms, John Murray, London. Davis, R.A. (2001). Science In The Hinterland: ‘The Cincinnati School of Paleontology.’ Geological Society of American Abstracts With Program, 33, 59. Dawson, J.W. (1862a). Notice on the discovery of additional remains of land animals in the coal-measures of the SouthJoggins, Nova Scotia. Geological Society of London, Quarterly Journal, 18, 5–7. Dawson, J.W. (1862b). On the footprints of Limulus as compared with the Protichnites of the Potsdam sandstone. Canadian Naturalist and Geologist, 7, 271–277. Dawson, J.W. (1864). On the fossils of the genus Rusophycus: Canadian Naturalist and Geologist, New series, 1, 363–367. Dawson, J.W. (1865). On the structure of certain organic remains in the Laurentian limestones of Canada. Geological Society of London, Quarterly Journal, 21, 51–59. Dawson, J.W. (1866). Note on supposed burrows of worms in the Laurentian rocks of Canada. Quarterly Journal of the Geological Society of London, 22, 608–609. Dawson, J.W. (1868). Acadian Geology, 2nd edition. Macmillan & Co., London. Dawson, J.W. (1873). Impressions and footprints of aquatic animals and imitative marking of Carboniferous rocks. American Journal of Science, Third series, 5, 16–24. Dawson, J.W. (1875). The Dawn of Life, Dawson Brothers. Publishers, Montreal. Dawson, J.W. (1878). Supplement to the 2nd Edition of Acadian Geology. In: Acadian Geology, 3rd edition. Macmillan & Co., London. Dawson, J.W. (1888). The Geological History of Plants, D. Appleton & Co. New York. Dawson, J.W. (1890). On burrows and tracks of invertebrate animals in Paleozoic rocks, and other markings. Geological Society of London, Quarterly Journal, 46, 595–617. Gilbert, G.K. (1898). Joseph Francis James 1857–1897. American Geologist, 21, 1–11. Ha¨ntzschel, W. (1975). Trace fossils and problematica, In :Teichert, C. (Ed.), Treatise on Invertebrate Paleontology, 2nd edition. Pt. W, Miscellanea, Supplement 1, Geological Society of America and University of Kansas, Lawrence. Harrington, B.J. (1883).The Life of Sir William E. Logan, Dawson Brothers Publishers, Montreal. Hofmann, H.J. (1971). Precambrian fossils, pseudofossils, and problematica in canada. Geological Survey of Canada Bulletin, 189, 18–22. Hofmann, H.J. (1982). J.W. Dawson and nineteenth century Precambrian paleontology. Proceedings of the Third North American Palaeontological Convention, 1, 243–249. James, J.F. (1882). Charles Robert Darwin. Journal of the Cincinnati Society of Natural History, 5, 71–77. James, J.F. (1884). The Fucoids of the Cincinnati Group, Part 1. Journal Cincinnati Society of Natural History, 7, 124–132.

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James, J.F. (1885a). The Fucoids of the Cincinnati Group, Part 2. Journal Cincinnati Society of Natural History, 7, 151–166. James, J.F. (1885b). Are there any fossil algae? American Naturalist, 19, 165–167. James, J.F. (1885c). On the tracks of insects resembling the impressions of plants. [Translated from the French of M.R. Zeiller.] Journal Cincinnati Society of Natural History, 8, 49–52. James, J.F. (1885d). Remarks on some markings on the rocks of the Cincinnati Group described under the names of Ormathichnus and Walcottia. Journal Cincinnati Society of Natural History, 8, 160–163. James, J.F. (1889). Uriah Pierson James. American Geologist, 1889, 1–7. James, J.F. (1890). Fucoids and other problematic organisms. American Naturalist, 24, 1222. James, J.F. (1891). The manual of paleontology of the Cincinnatin Group. Part 1. Journal Cincinnati Society of Natural History, 14, 45–72, 149–163; 15, 1892–1893, pp. 88–100, 144–159; 16, 1894, pp. 178–208; 18, 1895–1896, pp. 67–88, 115–140; 19, 1897, pp. 99–118. James, J.F. (1892a). Studies in problematic organisms. The genus Skolithus. Bulletin Geological Society of America, 3, 32–44. James, J.F. (1892b). The preservation of plants as fossils. Journal Cincinnati Society of Natural History, 15, 75–78. James, J.F. (1893a). Studies in problematic organisms. Number 2. The genus Fucoides. Journal Cincinnati Society of Natural History, 16, 62–81. James, J.F. (1893b). Remarks on the genus Arthrophycus Hall. Journal Cincinnati Society of Natural History, 16, 82–86. James, J.F. (1894). On the value of supposed algae as geological guides. American Geologist, 13, 95–101. James, J.F. (1895a). Daimonelix, and allied fossil (Abstract of paper read before Biological Society of Washington). Science, New series, 1, 420. James, J.F. (1895b). Remarks on Daimonelix, or ‘Devil’s Corkscrew’ and allied fossils. American Geologist, 15, 337–342. James, U.P. (1878). Descriptions of newly discovered species of fossils and remarks on others, from the Lower and Upper Silurian rocks of Ohio. The Paleontologist, 2, 9–16. James, U.P. (1879). Description of new species of fossils and remarks on some others, from the Lower and Upper Silurian rocks of Ohio. The Paleontologist, 3, 17–24. James, U.P. (1881). Contributions to paleontology: fossils of the Lower Silurian Formation: Ohio, Indiana and Kentucky. The Paleontologist, 5, 33–44. James, U.P. (1883). Descriptions of new species of fossils from the Cincinnati Group, Ohio and Kentucky. The Paleontologist, 7, 57–60. Landing, E. and Miller, R.F. (1988). Bibliography of George Frederick Matthew. In: Landing, E., Narbonne, G.M. and Myrow, P. (Eds.), Trace Fossils, Small Shelly Fossils and the Precambrian–Cambrian Boundary Proceedings, New York State Museum Bulletin, 463, pp. 4–7. Logan, W.E. (1842). Canadian Carboniferous footprints. Proceedings of the Geological Society of London, 3, 707. Logan, W.E. (1851). On the occurrence of a track and foot-prints of an animal in the Potsdam Sandstone of Lower Canada. Quarterly Journal of the Geological Society, 7, 247–252. Logan, W.E. (1852). On the foot-prints occurring in the Potsdam Sandstone of Canada. Quarterly Journal of the Geological Society, 8, 199–213.

Logan, W.E. (1858). On the Laurentian limestones. Canadian Naturalist and Geologist, 4, 300–301. Logan, W.E. (1860). On the track of an animal lately found in the Potsdam formation. American Journal of Science, Second series, 31, 17–23. Matthew, G.F. (1888). On Psammichnites and the early trilobites of the Cambrian rocks in eastern Canada. American Geologist, 2, 1–9. Matthew, G.F. (1889). On some remarkable organisms of the Silurian and Devonian rocks of New Brunswick. Royal Society of Canada, Proceedings and Transactions, 6, 49–62. Matthew, G.F. (1890). On Cambrian organisms in Acadia. Royal Society of Canada, Proceedings and Transactions, 7, 135–162. Matthew, G.F. (1891). Illustrations of the fauna of the St. John Group, no. V. Royal Society of Canada, Proceedings and Transactions, 8, 123–166. Matthew, G.F. (1899). Studies on Cambrian faunas, no. 4. Fragments of the Cambrian faunas of Newfoundland. Royal Society of Canada, Proceedings and Transactions, 5, 97–119. Matthew, G.F. (1901). Monocraterion and Oldhamia. The Irish Naturalist, 10, 135–136. Matthew, G.F. (1903). On batrachian footprints and other footprints from the coal measures of Joggins, Nova Scotia. Bulletin Natural History Society of New Brunswick, 5, 103–108. Matthew, G.F. (1910). Remarkable forms of the Little River Group. Royal Society of Canada, Proceedings and Transactions, Third series, 3, 115–125. Matthew, W.D. (1924). Memorial to George F. Matthew. Bulletin of the Geological Society of America, 35, 181–182. Miller, R.F. (1988). George Frederick Matthew (1837–1923). In: Landing, E., Narbonne, G.M. and Myrow, P. (Eds.), Trace Fossils, Small Shelly Fossils and the Precambrian–Cambrian Boundary Proceedings, New York State Museum Bulletin, 463, pp. 4–7. Miller, R.F. (1996). Location of trace fossils and problematica of George Frederick Matthew from Part W, treatise on invertebrate paleontology. Journal of Paleontology, 70, 169–171. Miller, R.F. and Buhay, D.N. (1988). The Steinhammer Club: geology and a foundation for a natural history society in New Brunswick. Geoscience Canada, 15, 221–226. Miller, S.A. (1877).The American Paleozoic Fossils, A Catalog of the Genera and Species, Published by the author, Cincinnati, 253 pp. Miller, S.A. (1880). Silurian ichnolites, with definitions of new genera and species. Journal of the Cincinnati Society of Natural History, 2, 217–229. Miller, S.A. (1889). North American Geology and Paleontology for the Use of Amateurs, Students and Scientists, Western Methodist Book Concern, Cincinnati, Ohio. Miller, S.A. and Dyer, C.B. (1878a). Contributions to Paleontology, no. 1. Journal of the Cincinnati Society of Natural History, 1, 24–39. Miller, S.A. and Dyer, C.B. (1878b). no. 2. Contributions to Paleontology, Published by the authors, Cincinnati, pp. 1–11. ¨ versigt af Nathorst, A.G. (1873). Om na˚gra fo¨rmodade va¨xtfossilier. O Vetenskapsakademien–Akademie Fo¨rhandlingar, Stockholm, 1873, 25–32. Nathorst, A.G. (1881). Om spa˚r af nagra evertebrerade djur m. och deras palaeontologiska betydelse. K. Svenska Vetenskapsakademien Handlingar, 18, 1–104. O’Brien, C.F. (1971). Sir William Dawson-A life in Science and Religion, American Philosophical Society, Philadelphia, Memoir, 84. Osgood, R.G. (1970). Trace fossils of the Cincinnati area. Paleontographica Americana, 6, 281–444.

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Osgood, R.G. (1975). The history of invertebrate ichnology. In: Frey, R.W. (Ed.), The Study of Trace Fossils, Springer-Verlag, New York, pp. 3–12. Owen, R. (1852). Description of the impressions and foot-prints of the Protichnites from the Potsdam Sandstone of Canada. Quarterly Journal of the Geological Society, 8, 214–225. Pemberton, S.G. and Frey, R.W. (1991). J.W. Dawson and the interpretation of Rusophycus. Ichnos, 1, 237–242. Seilacher, A. (1995). Fossile Kunst: Albumbatter der Erdgeschichte, Goldschneck-Verlag, Korb, Germany. Stanton, T.W. (1898). Memoir of Joseph Francis James. Geological Society of America Bulletin, 9, 408–412.

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Walker, B.E. (1901). List of the published writings of Elkanah Billings, F.R.S., Paleontologist to the Geological Survey of Canada, 1856–1876. Canadian Record of Science, 8, 366–388. Whiteaves, J.F. (1877). Obituary notice of Elkanah Billings, F.G.S. Canadian Naturalist, 8, 251–261. Winder, C.G. (1972). Sir William Edmond Logan (1798–1875) – founder of Canadian geology. Proceedings of the Geological Association of Canada, 24, 39–41. Winder, C.G. (2004). William Edmond Logan (1798–1875) Knighted Canadian Geologist, Trafford Publishing, Victoria, British Columbia.

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3 Edward Hitchcock and Roland Bird: Two Early Titans of Vertebrate Ichnology in North America S. George Pemberton, Murray K. Gingras, and James A. MacEachern

INTRODUCTION

SUMMARY : Vertebrate ichnology in North America has a long and distinguished history, starting with the remarkable discoveries by Edward Hitchcock of dinosaur footprints and trackways from the Connecticut River Valley. Hitchcock assembled a unique collection that is currently housed in the Pratt Museum, Amherst College, and his work essentially constituted the beginnings of ichnology as a viable sub-discipline of paleontology. Although his original interpretation that these Late Triassic repichnia were bird tracks was incorrect, he indirectly linked birds and dinosaurs. In the southwest, the gifted American Museum of Natural History collector Roland T. Bird discovered the first sauropod tracks from Cretaceous strata near Glen Rose, Texas. These tracks gave paleontologists a means of assessing the behavior of sauropods, compared to the inaccuracies of preconceived popular conception, and fledgling skeletal reconstructions. The observations of trackways, recording the activity of the organisms while they were alive, ultimately led to the recognition that sauropods actually walked on land and could support their weight rather than requiring water to buoy them, possessed an upright posture with limbs directly beneath them, held their tails above the ground rather than dragging them, and that some forms had adopted herd behavior.

Vertebrate ichnology has a long and distinguished history, going back to the 1828 discovery of footprints in the Permian of Scotland by Henry Duncan (see Pemberton et al., 1996; Pemberton and Gingras, 2003). In North America, vertebrate ichnology was embraced as a viable sub-discipline of paleontology, because of a number of spectacular finds. Included in this group are: (a) the abundant track sites associated with the Upper Triassic Newark Group in the Connecticut Valley, first described by Hitchcock (1836a); (b) the first traces ever observed of land animals in the Carboniferous of Nova Scotia, first described by Logan (1842); (c) the large spiral burrow Daimonhelix (Devil’s Corkscrew) from the Miocene of Nebraska, first described by Barbour (1892); (d) the abundant dinosaur trackway sites associated with the Upper Jurassic Morrison Formation in the Western United States, first described by Marsh (1899); (e) the tracks, including probable ankylosaur trackways in the Peace River Valley of Alberta


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THE ICHNOLOGY OF THE CONNECTICUT VALLEY

and British Columbia, first reported by Sternberg (1932); (f) the impressive sauropod tracks and trackways in Cretaceous strata near Glen Rose, Texas first described in detail by Bird (1939b); and (g) the well-preserved Chirotherium from the Lower to Middle Triassic Moenkopi Formation of northeastern Arizona first described by Peabody (1948). Of these, the work associated with the Connecticut Valley and the Glen Rose Texas site are particularly noteworthy, and illustrate the central role that North American investigators have played in the development of vertebrate ichnology. This tradition of excellence continues today, as illustrated by the landmark research of investigators in both the United States (Martin Lockley, James Farlow, and Paul Olsen; to name just a few), and Canada (the late Bill Sarjeant, Phil Currie, and Richard McCrea). For a more formal history of vertebrate ichnology see Sarjeant (1975).

THE ICHNOLOGY OF THE CONNECTICUT VALLEY The Newark Supergroup consists of a series of 13 large basins that extends from Nova Scotia to South Carolina. Two of these basins comprise the present day Connecticut Valley: the Deerfield basin in the northern Valley, and the Hartford basin constituting the remainder (Olsen et al., 1996). In the Early Mesozoic, these basins were filled with sediments and formed temporary playa lakes. These lakes, in turn, provided a rich environment for the recording of tracks and traces along their shores. In fact, the richest assemblage of trace fossils in the world can be found at sites in the Connecticut Valley of Massachusetts. Hundreds of fish fossils have been recovered from the gray shales in Sunderland and Turner’s Falls, Massachusetts (Olsen and Rainforth, 2002). Ironically, only a few body fossils of the land-dwelling trackmakers have been found to date (e.g., several prosauropods in Connecticut and southern Massachusetts). The tracks were the subject of considerable study, primarily by Edward Hitchcock, Professor at Amherst College. Collecting, studying, and interpreting the fossil tracks became his primary scientific passion for the last 30 years of his life. The early history of research on the Connecticut Valley footprints has been covered in an excellent article by Steinbock (1989). The dedicated

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amateurs James Deane and John Warren conducted additional work on the tracks. Deane, in particular, was involved in one of the more interesting aspects of this period of study. Vertebrate paleontology in North America has generated some of the most intense rivalries in science, including the Cope–Marsh ‘Bone War’ and the Brown–Sternberg rivalry. Vertebrate ichnology is no exception, and Edward Hitchcock and James Deane ultimately engaged in a bitter dispute over who was the first discoverer of the Connecticut Valley tracks.

Dramatis Personae Edward Hitchcock (1793–1864): Edward Hitchcock (Fig. 3.1A) was a man for all seasons: clergyman (pastor in Conway), teacher (Deerfield Academy and Amherst College), scientist (who executed the first comprehensive state survey in the United States; that of Massachusetts from 1830 to 1833), and administrator (principal of Deerfield Academy, president of Amherst College). He was a prolific author, publishing 26 books, 94 scientific papers, 35 pamphlets, and 80 newspaper articles, comprising a total of 8453 pages, with 256 plates and 1134 woodcuts and included in his published works are a tragedy (Merrill, 1906, p. 152) and a poem (Marche´, 1991). His textbook on geology (Hitchcock, 1840) was widely read and passed through some 30 editions. Details on the life of Edward Hitchcock have been gathered from Lesley (1877), Hitchcock (1895), Foose and Lancaster (1981), and Belt (1989). Hitchcock was born in Deerfield, Massachusetts on May 24, 1793, the youngest of five children born to Justin and Mercy Hitchcock. His father, a hatter by trade, was of modest means and Edward worked his way through Deerfield Academy. In 1811, his observations on a comet marked the beginning of his fascination with science, but his poor eyesight ended any hopes that he had for being an astronomer (Marche´, 1993). Hitchcock then became a teacher at Deerfield Academy from 1815 till 1819. During this time, he met Amos Eaton, the New York geologist, and Benjamin Silliman from Yale, both of them were instrumental in turning his attention towards natural history. Yale offered him an honorary Master of Arts degree in 1818, and he studied theology there in 1820. Following graduation, he served as a pastor in Conway, Massachusetts from June 1821 to October 1825. His interest in science, however, did not wane and he found himself in a position to accept a position at Amherst College. From 1825 until 1845 he was Professor

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3. EDWARD HITCHCOCK AND ROLAND BIRD: TWO EARLY TITANS OF VERTEBRATE ICHNOLOGY IN NORTH AMERICA

A

B FIGURE 3.1 (A) Edward Hitchcock (1793–1864), geologist, clergyman, poet, teacher, administrator, poet, and ichnologist (courtesy of Amherst College Archives). (B) Hind foot prints of Anomoepus major, Specimen 1/7, Amherst Collection (courtesy of Amherst College).

of Chemistry and Natural History. In 1844, Hitchcock was made president of Amherst College and was ultimately considered one of Amherst’s greatest presidents. During his tenure from 1844 to 1854, he raised intellectual standards, doubled the number of students, and saved the college from impending bankruptcy. He also taught natural theology and geology from 1845 until his death in 1864. Hitchcock was one of the foremost proponents of Natural Theology and, like William Dawson in Canada; he saw no conflict between Christianity and a long Earth history. He held an endowed chair (endowed by a local merchant, also named Hitchcock) that he named the Professorship in Natural Theology and Geology, to instruct in both geology and theology in their connected form. Unfortunately, a successor could not be found and within a decade, the chair reverted only to geology (Foose and Lancaster, 1981). Although he was a catastrophist and believed in the Noachian Flood, he admired the more scientific uniformitarian approach expounded by Lyell (Foose and Lancaster, 1981). At the beginning of his career, Hitchcock felt that all scientific truth was revealed in the Bible. By the close of his career, however, he conceded that the Bible was a popular account, not a scientific one, and no correlation existed between the

Scripture and science (Guralnick, 1972; Foose and Lancaster, 1981). Hitchcock was also anti-Darwinian and remained so for the rest of his life (Lawrence, 1972). On June 13, 1821, Edward Hitchcock married Orra White, the daughter of a prosperous Amherst farmer. They had eight children, six of whom lived past infancy. Two sons, Edward Jr. and Charles, became geologists, with Charles rising to the positions of state geologist for Vermont, Maine, and New Hampshire. Orra White was an accomplished artist and illustrated some of Edward Hitchcock’s earliest geological papers and reports. She also created oversize paintings for use in her husband’s classes (Aldrich and Leviton, 2001). At a time when women generally did not study science, the Hitchcocks encouraged the inclusion of science in the curriculum of the all-female school founded by Mary Lyon, which eventually became Mount Holyoke College. Hitchcock was instrumental in trying to organize geologists and other scientists and bring them together to confer and compare results. In 1840, he co-founded the American Association of Geologists, which met for the first time in Philadelphia with Hitchcock serving as its first president. This organization eventually evolved into the American Association


for the Advancement of Science, in 1848. In 1863, Hitchcock became a charter member of the National Academy of Sciences. In 1836, Hitchcock undertook a study of the curious tracks found in the vicinity of Deerfield Massachusetts (Fig. 3.1B). He was convinced that these markings resulted from the activity of birds, and the study of these tracks dominated his latter years. During his career, Hitchcock published 26 articles (Hitchcock, 1836a,b,c,d, 1837, 1841, 1843, 1844a,b, 1845a,b,c, 1847, 1848, 1854, 1855, 1856a,b,c,d, 1857, 1861, 1862, 1863a,b, 1866) and two books (Hitchcock, 1858, 1865) on these tracks and trackways. Edward Hitchcock passed away on February 27, 1864 and was buried in the Amherst Cemetery. James Deane (1801–1858): The person who brought the Connecticut Valley tracks to the attention of Edward Hitchcock was James Deane of Greenfield. Details on the life of James Deane are provided by Bowditch (1858) and Bouve (1859). James Deane was born in Coleraine, Franklin County, Massachusetts, the eighth child of Christopher and Prudence Deane, on February 24, 1801. The Deanes were a farming family and the father wanted his sons to workin the farm. James Deane was educated in the local school but did spend one term at the Deerfield Academy, where he was taught Latin and developed an interest in medicine. He worked the family farm until he was 19, and then went to Boston to find a trade. Unable to find work, Deane returned to Deerfield where he worked copying legal documents in the law office of Elijah Alvard. He remained in Deerfield for 4 years, and saved his money with the intent of going to medical school. Deane entered Medical School at the University of the State of New York in 1829 and graduated with his MD in 1831, just prior to his 30th birthday. Deane moved back to Deerfield and established his medical practice, remaining there for the rest of his life. He was a passionate doctor and was especially adept at operative surgery. During his medical career, he was a frequent contributor to the Boston Medical and Surgery Journal; publishing 20 articles over the period 1837–1855. He also served as Vice President of the Massachusetts Medical Society in 1854, and took an active role in that society. Early on in his life, he developed a love of nature and was a naturalist at heart. He was a member of the Boston Society of Natural History and published a number of his footprint articles in their journal. James Deane was a tall, powerful man who had a commanding presence. He was an able and selftaught artist and a highly talented musician. He constructed his own musical instruments and even

35

crafted an organ. Deane was a devoted family man and in 1836 he married Mary Clapp Russell of Deerfield with whom he had 3 daughters. He was a gifted mimic and would often entertain his friends with his many different voices. He contracted typhoid fever in the spring of 1858, and passed away on June 8 of that year. He was buried in Deerfield. In 1835, Deane was made aware of curious marks in strata at Turner’s Falls near Greenfield and thought that they represented bird tracks. Although a number of prominent citizens had seen the markings, Deane was the only one who actually studied them. On March 7, 1835, he wrote letters to the prominent geologists Edward Hitchcock in Amherst, Massachusetts, and Benjamin Silliman in New Haven, Connecticut. On March 15, 1835, Hitchcock replied but was not very encouraging about the possibilities that the markings could be bird tracks. Deane persisted, and in April 1835 sent another letter to Hitchcock and Silliman, along with plaster casts of the markings. This elicited a visit from Hitchcock who now was determined to study these markings. In Deane’s letter to Silliman, he sent a paper that he wished to be published, but Silliman decided to wait until Hitchcock had completed his study. Deane was also in contact with geologists in Great Britain, and in September, 1842, he wrote to Dr. Gideon Mantell, who transmitted the communication and the casts to the membership of the Geological Society of London. As a result Professor Richard Owen and Sir Roderick Murchison were convinced by the bird track interpretation that Deane suggested. Despite the studies of Hitchcock, Deane persisted in working on the markings and produced a number of scientific papers on them (Deane, 1843, 1844a, 1845a,b,c, 1847a,b, 1848, 1849, 1850, 1856). A posthumously published volume (Deane, 1861) with photographs and etchings completed his work on the tracks (Fig. 3.2). Deane always maintained that he was the first person to fully appreciate the significance of the markings, and was the true scientific discoverer of them. As will be discussed later he, and Hitchcock engaged in a war of words over the traces. Deane felt that Hitchcock had misrepresented what had happened, and had attempted to claim all the scientific credit for the tracks (Deane, 1844b,c; Hitchcock, 1844b). John Collins Warren (1778–1856): Dr. John Collins Warren (Fig. 3.3A) was one of the most renowned American surgeons of the nineteenth century. Details of his life have been gathered from Warren (1860) and Steinbock (1989). Warren was born on August 1, 1778 in Boston, the son of Dr. John Warren, the founder of the Harvard Medical College. Warren started his education at the age of five at Master Vinals reading

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B

A

FIGURE 3.2 (A) Cover page of James Deane’s (1861) ichnological volume. (B) Lithograph from the Deane volume.

and writing school in Boston, and later attended the Public Latin School. In 1793, he enrolled at Harvard College and graduated in 1797. In 1798, he began the study of medicine under the tutelage of his father. In 1799, he went abroad, continuing his medical studies in London and Paris. As an intern, Warren attended and studied at Guy’s Hospital in London with Sir Astley Cooper and later he studied, in Paris under the direction of the naturalist and anatomist Georges Cuvier. He received an honorary medical degree from Harvard in 1819. On his return to America in 1802, Warren entered into partnership with his father, and also began to assist him with anatomical lectures, dissections, and demonstrations at Harvard Medical School. He was named Adjunct Professor of Anatomy and Surgery in 1809. Upon his father’s death, he assumed the Hersey Professorship of Anatomy and Surgery, and he held that post until he retired in 1847. Dr. Warren was also the first dean of the Medical School and promoted its removal from Cambridge to Boston, in order to obtain better access to clinical facilities. He was also closely associated with the foundation of Massachusetts

General Hospital and was that facility’s first surgeon. Warren held an appointment on the hospital staff until 1853, and then served on its Board of Consultation until his death. On October 16, 1846, at Massachusetts General Hospital, Warren performed the first operation on a patient, Gilbert Abbott, under ether anesthesia administered by dentist William T.G. Morton. Over the course of his long career, he assembled an extraordinary teaching collection of 1116 anatomical and pathological specimens. He presented it to the Harvard Medical School in 1847 along with a $5000 endowment consisting of railroad stock. This was the beginning of the Warren Anatomical Museum, which now contains approximately 13 000 items, including anatomical and pathological specimens, various anatomical models, photographs, paintings, drawings, medical instruments and machines, and other medical memorabilia. Warren passed away on May 4, 1856. Aside from his medical pursuits, Warren was also an accomplished naturalist and contributed a number of interesting publications. In 1846, he obtained


A

37

B

FIGURE 3.3 (A) John Collins Warren, 1778–1856 (after Warren, 1860, Volume 1). (B) Counterpart slab (of specimen used in the first photographic image in a scientific publication in North America, specimen is in the Collections of the American Museum of Natural History), specimen 26/10 in the Amherst College collection and was figured in Hitchcock, 1858 as Plate 40, Number 1 (reproduced here).

perhaps the best-preserved Mastodon skeleton ever recovered from the Hudson Valley, and produced a lavishly illustrated monograph about it (Warren, 1852). He also produced a modest tome on the Connecticut Valley footprints (Warren, 1854a) as well as a number of articles on the subject, published in the Proceedings of the Boston Society of Natural History (Rogers et al., 1855; Warren, 1854b, 1855, 1856). Warren obtained his original track specimen from James Deane in 1845. In 1852, the Boston Society of Natural History purchased slabs from the collection of one Mr. Marsh, a mechanic from Greenfield who had died of consumption, and who had collected for James Deane. Additional specimens were obtained from Edward Hitchcock. Like Hitchcock and Deane, Warren ascribed the tracks to ostrich-like birds. Warren’s publication is not particularly noteworthy except for the fact that it contains the first use of a photographic image in an American scientific publication (Steinbock, 1989). The specimen figured in that photograph is now at the American Museum of Natural History. The counterpart slab is specimen 26/10 in the Amherst College collection and was figured in Hitchcock (1858) as his Plate 40, Number 1 (Fig. 3.3B).

The Tracks In 1836, Hitchcock’s first description of Connecticut Valley fossil tracks was published in the American Journal of Science, describing 7 species of what he termed giant bird tracks (Fig. 3.4). The largest of these earliest footprint finds was a natural cast of a threetoed track that he named Orinithichnites giganteus. The specimen was collected from what is now the northern side of Holyoke, Massachusetts, on the east bank of the Connecticut River (Specimen number 15/3 in the Amherst Collection). Later, this track was renamed Eubrontes giganteus; it was the first dinosaur track to be described formally. It was a sensational discovery and a lithograph of the track was at once incorporated into Buckland’s famous ‘Bridgewater Treatise’ (2nd edition , 1837). That same year, Hitchcock published a poem ‘The Sandstone Bird’ in The Knickerbocker magazine under the pseudonym Poetaster (meaning a mediocre writer of verse) just after his original article on the tracks appeared (Hitchcock , 1836a). The poem is about a sorceress bringing the great sandstone bird back to life (Marche´ , 1991) and probably represents the first ichnological poem. Details on the genesis of the poem have been well documented by Marche´ (1991). The Connecticut River Valley tracks also

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A

B FIGURE 3.4 Figures and plate from the initial Hitchcock, 1836 publication on the Connecticut tracks. (A) Figures 1–20, 23, and 24. (B) Plate 1.

inspired the poet Henry Wadsworth Longfellow in the poems ‘Footprints on the Sands of Time’ and ‘To the Driving Cloud’ (Dean, 1969). By 1889, the Amherst College collection included the biogenic structures of 17 pachydactylous birds, 17 leptodactylous birds, 21 ornithoid reptiles, 25 assorted reptiles and amphibians, 17 frogs or salamanders, 6 turtles, 2 fish, 1 marsupial, and 45 insects,

crustaceans, or larvae. All of these 151 species were collected from about 38 localities (Hitchcock, 1889). His ichnological collection was placed on exhibition in the specially designed Appelton Cabinet (Fig. 3.5A) erected in 1855. Samuel Appelton of Boston bequeathed $10 000 to erect the building in order to house the collection (Hitchcock, 1858). Hitchcock insisted upon natural southern light to


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B FIGURE 3.5 (A) The Appelton Cabinet, built in 1855 (after Hitchcock, 1858, Plate 4, bottom). (B) Sketch of the interior of the Ichnological Cabinet (after Hitchcock, 1858, Plate 4, top).

best illuminate the slabs with the tracks. By his own count, over 8000 tracks were on display (Fig. 3.5B). The Appelton Cabinet has since been converted to a dormitory and Hitchcock’s collection currently resides across the Amherst College yard in the basement of the Pratt Museum. Simpson (1942, p. 167) stated that Amherst was perhaps ‘the first college to possess any considerable collection of vertebrate fossils under the study and care of a qualified faculty member.’ Amherst College is currently building a $10 million museum to showcase the footprint collection and to pay homage to Hitchcock’s remarkable discoveries. Hitchcock’s specimens will be displayed on the lower level of the three-story museum. In addition to the dinosaur-track slabs, the collection contains some 11 000 tracks and traces left by other Early Triassic and Jurassic life-forms, including lizards, crocodilians, worms, insects, and other invertebrates.

The Hitchcock–Deane Controversy In his first paper on the tracks, Hitchcock (1836a) credited James Deane as being the first to bring the tracks to his attention. Subsequently, the two men engaged in a public dispute about who really found the first tracks and realized their significance. Hitchcock (1844a) tried to defuse the situation by recounting a story about the young Pliny Moody, whom he suggested was the ‘first’ discoverer of the tracks. The implication of the story is that one can ‘find’ something that is important without comprehending its relevance and therefore, the question is asked, is the ‘discoverer’ the one who collects the specimen, or the one who understands and scientifically expounds their significance? Moody was a farmer in South Hadley, Massachusetts around the

turn of the eighteenth century who, in 1802, plowed up some slabs of dinosaur tracks in one of his fields (Fig. 3.6A). One particular slab stood for many years as a doorstop in the Moody home (Fig. 3.6B). Dr. Elihu Dwight of South Hadley subsequently purchased this slab when Moody left for school and referred to the specimen as ‘Noah’s Raven.’ The tracks are now recognized as Anomoepus scambus, the footprints of a small ornithischian dinosaur. Dwight was in possession of the specimen for nearly 30 years; upon his death, in 1839 Edward Hitchcock purchased the specimen for Amherst College (cataloged as specimen 16/2). Specimens from South Hadley near the site of the original Pliny Moody find are still being excavated (Fig. 3.6C) at the Nash Footprint Quarry. Hitchcock (1844a) then went on to outline that, in 1834, a number of gentlemen in Greenfield made arrangements with one Mr. William Wilson to obtain flagging stones to repair a street. Mr. Wilson brought the stones from a quarry near Montague in the spring of 1835 and noticed marks that he referred to as ‘turkey tracks.’ He pointed out these marks to the Greenfield gentlemen and one of them, James Deane, took considerable interest in them and called them to the attention of Edward Hitchcock. These specimens were subsequently purchased by Edward Hitchcock on behalf of Amherst College from James Deane, and are cataloged as Specimens 18/1 and 18/2. Deane objected to Hitchcock’s (1844a) article and published his own version of events (Deane, 1844a). Deane felt that Hitchcock had belittled his contribution and was upset on several grounds: (1) Deane felt that he, unlike the other early observers mentioned by Hitchcock (e.g., Moody, Wilson, Dwight), had looked at the tracks scientifically and conducted serious study of them.

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A

B

C

FIGURE 3.6 (A) Sketch of the Pliny Moody Quarry where the first specimen was found (after Hitchcock, 1858, Plate 1). (B) Original specimen found by Pliny Moody and dubbed as ‘Noah’s Raven’ by Dr. Elihu Dwight of South Hadley. It was subsequently purchased by Edward Hitchcock for Amherst College in 1839 and cataloged as specimen 16/2 (courtesy of Amherst College). (C) Specimen from the Nash Footprint Quarry, South Hadley, Massachusetts.

This is corroborated by the fact that he published a number of articles (Deane, 1843, 1844a, 1845a,b,c, 1847a,b, 1848, 1849, 1850, 1856) on them and a posthumously published volume (Deane, 1861). It should be pointed out, though, that he waited some 8 years to publish his first article. (2) In 1835, Deane had sent casts and a communication to Benjamin Silliman at the same time he sent them to Hitchcock. The communication was a description, and in it Deane attributed them to the activities of birds. Silliman contacted Hitchcock on July 22, 1835 for his opinion and Hitchcock asked him to withhold publication of

Deane’s manuscript until his study was completed (Hitchcock, 1844b). (3) Deane felt that Hitchcock had intimated that had Hitchcock not published on the tracks, no serious scientific work would have been done on them. The Deane (1844a) article led to one of the first discussion-and-reply scenarios in geology. Hitchcock (1844b) published a rejoinder or discussion of the Deane article, and re-iterated many of the points he made in his earlier article (Hitchcock, 1844a). To his credit, he did append a postscript that related the events of the Silliman intervention on the publication of the Deane description. He stressed the fact that he

ROLAND BIRD AND THE DISCOVERY OF SAUROPOD TRACKS

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B FIGURE 3.7 Plates from Hitchcock, 1858. (A) Plate 57 depicting a variety of tracks. (B) Plate 6 depicting the concept of undertracks (Figs. 1 and 2) and comparative tracks of modern organisms (Figs. 3–13).

had assembled an impressive array of specimens and reiterated that he was the true scientific discoverer of the tracks. He did state, ‘I admit him to have been in a popular sense, the original discoverer of the footmarks; and had it not been for his scientific discernment, probably they would still have remained undiscovered’ (Hitchcock, 1844b, p. 398). Deane (1844b) then followed with his reply to the discussion of Hitchcock (Hitchcock, 1844b) and reiterated his position. Subsequently both men worked on the tracks and the matter was not broached again until Deane’s death, when both Bowditch (1858) and Bouve (1859) brought it up in their memorials to Deane. Hitchcock then felt obliged once again to present his case in his Ichnology of New England volume (Hitchcock, 1858, pp. 191–198). His arguments had not changed at all. Summary Although footprints and other markings made by animals were known to exist before Hitchcock’s work (cf. Pemberton et al., 1996; Pemberton and Gingras, 2003), he was the person most responsible for developing the emerging field of ichnology. His 1858

volume is by far the largest compilation and most comprehensive treatise on vertebrate ichnology published to date. The volume is lavishly illustrated (Fig. 3.7A) and Hitchcock was aware of the concept of undertracks and the need to compare the fossil tracks with modern counterparts (Fig. 3.7B). The volume stands with the William Jardine (1853) book ‘The Ichnology of Annandale’ as an early landmark in the development of ichnological research.

ROLAND BIRD AND THE DISCOVERY OF SAUROPOD TRACKS Perhaps no other moment in the history of vertebrate ichnology in North America compares to the discovery and eventual excavation of the sauropod tracks and trackways from the banks of the Paluxy River near Glen Rose, Texas. It is still regarded as the single largest excavation of a track site, and it is a testament to the work of a tracker extraordinaire, Roland Thaxter Bird.

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Roland Thaxter Bird (1899–1978) The American Museum of Natural History has had its share of intrepid adventurers, including Roy Chapman Andrews, Barnum Brown, Walter Granger, and Bashford Dean; but probably none was as unique as Roland Thaxter Bird. Bird was a self-made man and one of the last of the specialized fossil collectors. Details on the life of Roland Bird were gathered from Colbert (1978), Bird (1985), Farlow (1985), and Farlow and Lockley (1989). Roland Thaxter Bird (Fig. 3.8A) was born on December 29, 1899, the first of four children to Henry and Harriet Bird of Rye, New York. His father, a successful businessman, was also an amateur entomologist who conducted important studies on noctuid moths. He instilled in Roland a love of nature and a respect for learning. As a young boy, Roland was frequently ill and suffered from rheumatic fever, which plagued him for the rest of his life. Due to his illness, it was determined that he should spend time away from the coastal town. He was sent to live with his uncle on a farm near Grahamsville, New York, in the Catskill Mountains. It was here that Bird developed a love for farming, cattle breeding, and the outdoor life. At age 15, Bird’s mother died of tuberculosis and shortly thereafter, he dropped out of Junior High School. At his father’s insistence Bird apprenticed as a plumber but, at the age of 19, Bird went to farm and raised cattle in Florida, where he also invested in land. During the Depression he lost everything so he decided to see the country and constructed a motorcycle with a homemade camper (Fig. 3.8B). He traveled around doing odd jobs until

A

November, 1932, when he discovered a fossilized skull (Stanocephalosaurus birdi) south of Holbrook, Arizona. The skull brought him to the attention of Barnum T. Brown, the curator at the American Museum of Natural History. Brown enlisted Bird to be one of his fossil hunters. Bird joined the staff of the American Museum of Natural History in 1934 and remained Barnum Brown’s right-hand man in the field and the laboratory for many years. Bird had the utmost respect for Brown and even titled his memoirs ‘Bones for Barnum Brown.’ Bird worked tirelessly for Brown and was responsible for many of the finds Brown reported in his latter years. Bird was the perfect assistant for Brown. He was a quiet, modest man and his quest for finding fossils was of great importance to him. He spent his summers happily in the field doing what he loved; he would work with Brown either by himself or with assistants. This passion for fieldwork dominates his memoir (Bird, 1985), and makes it one of the best paleontological reads ever. In it Bird shows his humility, his dedication, and his sense of honor in finding himself associated with such major scientific discoveries. In one of the most touching passages, Farlow (1985) discusses an event when Bird was sick in bed and his wife and sister were reading to him from a book on dinosaurs by Adrian Desmond. Upon hearing a passage that mentioned his work, Bird remarked ‘I am listed among the titans!’ (Farlow, 1985, p. 219). During the summer of 1934, Bird was one of the key figures in collecting the massive sauropods from the Late Jurassic boneyard of the Morrison Formation in

B FIGURE 3.8 (A) Roland Thaxter Bird (1899–1978). (B) Roland Bird on the road with the Harley homemade camper (after Bird, 1985).


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FIGURE 3.9 The map that Bird created of the bones in the Howe Quarry site (after Bird, 1985).

the famous Howe Quarry near Shell, Wyoming. In his obituary for Bird, Colbert (1978) stated that his quarry map (Fig. 3.9) is perhaps the most complex ever produced. Bird suffered from ill health for most of his life and was something of a hypochondriac. This may have been exacerbated by his eccentric diet, which often consisted of a single food item (such as potatoes, chicken, or fish patties) that he would eat meal after meal for weeks at a time (Farlow, 1985). Despite his somewhat frail appearance and health issues, Bird was an energetic field worker. His good friend, V. Theodore Schreiber, described him as ‘one of the toughest little guys I ever met . . . he used to embarrass me no end, the way he could gallop up a mountain goat trail without breathing hard at the top’ (Schreiber, quoted in Farlow and Lockley, 1989, p. 35). Bird’s career as a fossil hunter was relatively short. When Brown retired from the American Museum of Natural History in 1942, Bird continued to do field work for him but eventually the events of World War II brought changes. The Federal Government, in concert with several mining companies, was in the hunt for uranium and vanadium and was in need of

experienced field geologists. Bird resigned from the Museum and accepted a healthy pay raise to search for uranium in the same beds he once scoured for fossils. After the war, due to health issues, Bird was no longer able to do field work and he returned to New York where in 1946 he married Hazel Russell. Shortly afterward the family (Hazel had 2 daughters from a previous marriage) moved to Homestead, Florida, where Bird once again went into the cattle business. In 1952, the American Museum of Natural History was remodeling the Brontosaur Hall, and Edwin H. Colbert, Barnum Brown’s successor, contacted Bird to supervise the reassembly and installation of the Paluxy River trackway slab beneath Brown’s Apatosaurus mount. The slabs that Bird had collected long before were deteriorating in the Museum’s courtyard, and Colbert had the inspiration to place the specimens into context. Despite being weak, Bird took to the task with renewed vigor (Fig. 3.10A) and the resulting display (Fig. 3.10B) was a tribute to both Bird and Barnum Brown. Roland Thaxter Bird died at his home in Homestead, Florida, on January 24, 1978, and was buried in Grahamsville, New York, with a gastrolith in

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A

B FIGURE 3.10 (A) Workers busy assembling the Glen Rose trackway (photograph courtesy of the American Museum of Natural History. (B) The finished product of the reassembly of the Glen Rose tracks behind the dinosaur at the American Museum of Natural History (after Bird, 1954).

Barnum Brown (1873–1963)

FIGURE 3.11 The headstone of Roland T. Bird in the Grahamsville, New York Cemetery.

his pocket. His gravesite overlooks the Catskill Mountains that he had loved in his youth. At the top of his headstone (Fig. 3.11) a picture of a brontosaur is carved and his epitaph reads ‘Discoverer of Sauropod Dinosaur Footprints.’

Barnum Brown (Fig. 3.12A) was an intriguing figure in his own right, and it would be impossible to discuss Roland Bird without commenting on Barnum Brown. Biographical details concerning Barnum Brown are taken from Barton (1941), Lewis (1964), and Preston (1988). Brown was born on February 12, 1873, the youngest child of William and Clara Brown. The Brown’s had left Virginia and moved west by wagon train, settling in what is now Carbondale, Kansas. They named their youngest son after P.T. Barnum, in order to jazz up a somewhat common last name. Brown was the last and most successful of the great fossil hunters, and led expeditions not only throughout the United States, but also Canada, South America, India, and Ethiopia (Fig. 3.12B). He was associated with the American Museum of Natural History for 66 years from 1897 until his death in 1963. To fund expensive digs,


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B FIGURE 3.12 (A) Barnum Brown, Curator of Vertebrate Paleontology at the American Museum of Natural History (after Bird, 1989). (B) Barnum Brown (far right), Roland Bird (left), and Erich Schlaikjer (middle) with the reconstructed skull of Deinosuchus (photography courtesy of the American Museum of Natural History).

he eventually made a deal with the Sinclair Oil Company. He wrote dinosaur booklets for the company and it paid for his expeditions. In the 1930s and 1940s Sinclair gas stations, with their Diplodocus logo, attracted customers, by giving away the booklets. Brown’s collaboration with the Sinclair Oil also resulted in impressive dinosaur exhibits at the Chicago World’s Fair in the 1930s and the New York World’s Fair in the 1960s (Preston, 1988). To dinosaur enthusiasts, Brown’s greatest achievement was likely to be his discovery of Tyrannosaurus rex in Hell Creek, Montana. He discovered the first skeleton in 1902 and a better-preserved skeleton in 1908. Both skeletons were put on display in the American Museum; the 1902 skeleton was subsequently shipped to the Carnegie Museum in Pittsburgh. After he retired from the American Museum of Natural History in 1942, he continued to work as a consulting field geologist for oil companies in both Alberta and Guatemala. Brown also continued his work in Montana, collecting fossils for the Museum, including a skeleton of Plesiosaurus that he excavated at the age of 82. Brown passed away on February 5, 1963, a week shy of his 90th birthday.

Bird’s Ichnological Contributions Bird’s ichnological work is admirably covered in a tribute article by Farlow and Lockley (1989) and an article by Farlow et al. (1989) dealing with specimens of Brontopodus birdi. Highlights of his career in ichnology included a number of fundamental observations that helped interpret dinosaur behavior. His first foray into vertebrate ichnology occurred in the fall of 1935, when he decided to look at and possibly collect some of the abundant footprints in the Triassic of New England. During this trip, he visited the ichnological collections at Amherst College where he described a unique specimen (Bird, 1985, pp. 79–80, see also Fig. 3.1A), which he interpreted as the trace of a squatting dinosaur waiting out a rain shower. The tracks show raindrop impressions up to the point where the dinosaur squatted to wait out the storm, but the body impression and tracks leading away from it show no raindrop marks. In 1937, in a coalmine near Cedaredge, Colorado, Bird excavated (Fig. 3.13A) a large slab weighing 18 000 pounds that contained a set of large hadrosaur tracks (Brown, 1938). Although he did not formally publish on this material, he was instrumental in the excavation of the specimens. Barnum Brown used these specimens (Fig. 3.13B) to determine a step length

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B

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FIGURE 3.13 (A) Roland T. Bird extracting a track from a mine near Cedaredge, Colorado. (B) The extracted tracks from the mine that Barnum Brown calculated a step length of 15 feet (after Brown, 1938).

of 15 feet and postulated that the tracks represented the activities of a giant mystery dinosaur. Using the formula for calculating dinosaur speed, Russell and Be´land (1976) calculated a speed of 27 km/h (some 17 mph). However, Thulborn (1981) showed that the 15-foot step recorded by Brown was really a stride (two steps), and recalculated the speed to be a more realistic 8.5 km/h (or 5 mph). Near Pueblo, Colorado, Bird examined large tracks in the valley of the Pugatoire River in the hope that they might represent sauropod tracks. This site was reported (MacClary, 1938; Bird, 1939a) but the tracks were not considered to be of sauropod origin. The site was abandoned as being too remote and because Museum quality tracks were not exposed. However,

this site is now considered to be one of the most prolific mega-tracksites in the world, with undisputable sauropod tracks (Lockley et al., 1986; Lockley and Hunt, 1995). By far, Bird’s most spectacular find was the footprints at the tracksite on the Paluxy River near Glen Rose, Texas, at the close of the 1938 field season. Although the site had been known before (Shuler, 1917) it was here that Bird discovered both carnosaur tracks and the elusive sauropod tracks that he had been hunting for (Bird, 1939b, 1941, 1944, 1953, 1954). The specimens were suitable for display at the Museum, and Bird returned to the site in the spring of 1940, supported by funds from the Sinclair Oil Company, the State of Texas, and


the federal government. The site excavated by Bird and his crew revealed trails of a dozen sauropods and four carnivores (Lockley, 1991); they quarried a section of rock 29 feet long by 8 feet wide for the American Museum of Natural History, and several adjacent sections for other institutions that were willing to pay the freight costs. In total, the excavated slabs weighed more than 80 000 pounds and constitute the largest track excavation ever undertaken. The slabs for the American Museum of Natural History were shipped more than 2000 miles, and in his memoir Bird stated that he was worried that the tracks might be the target of German submarines that were operating in the vicinity of the Gulf Stream (Bird, 1985). In 1938, at the Paluxy River near Glen Rose in central Texas, Bird uncovered a unique slab that contained two sets of trackways. He believed one set of tracks belonged to a four-legged herbivore (a sauropod), and the other to a two-legged carnivore (a theropod). According to Bird’s track charts (Fig. 3.14), the meat-eater’s tracks run parallel to the tracks of the plant eater. But the tracks also show that

47

at one point, the meat-eater’s tracks take a strange skipping stride or hop, leaving two consecutive right footprints in the mud. Bird believed these two sets of prints with a peculiar hop in the middle represented the moment the smaller carnivore attacked the herbivore. The sequence has since been identified as the ‘attack scenario’ in the excavated slabs. Lockley (1991) has suggested that the footprint evidence does not support such a scenario. There is no change in speed indicated by the tracks, there is no disruption caused by the landing of the supposed ‘hop’ and the missing track may simply be an artifact of preservation. Lockley (1991) thinks that a more likely scenario involves a herd of 12 sauropods followed by 3 theropods. Preliminary work was also done on the Mayan Ranch and Davenport Ranch tracksites. These sites exposed the same bed that was present at Glen Rose and both that contained sauropod tracks, but they were deemed to be inferior to the Glen Rose site and were abandoned. The Mayan Ranch site contains the famous swimming sauropod track (Fig. 3.15A) that was used to reaffirm the popular belief of the time that

A

B

FIGURE 3.14 The attack scenario trackway, Paluxy River bank near Glen Rose, Texas (after Bird, 1939).

FIGURE 3.15 (A) Trackway at the Mayan Ranch that Bird interpreted as resulting from a swimming sauropod. (B) Bird’s sketched interpretation of swimming sauropods (after Bird, 1944).

48


A

B FIGURE 3.16 (A) Roland T. Bird at the Davenport Ranch site examining one of the trackways. (B) He described twenty-three sauropod trackways heading in the same direction and correctly concluded that such evidence pointed to gregarious behavior (after Bird, 1944).

sauropods did not live on land but instead used water to help buoy them (Fig. 3.15B). In 1944, Bird described a trackway consisting almost entirely of sauropod front-foot impressions and he inferred that this might represent a swimming dinosaur (Bird, 1944). This contention is still debated today. Other possible swimming sauropod trackways have been described (e.g., Ishigaki, 1989), though other researchers (e.g., Lockley, 1991) favor the interpretation that these shallow tracks are simply undertracks. At the Davenport Ranch site, Bird uncovered twenty-three sauropod trackways heading in the same direction (Fig. 3.16), and correctly concluded that such evidence supported gregarious behavior (Bird, 1944). Such a concept was revolutionary in the 1930s and Bird is correctly recognized as one of the originators of the herding hypothesis (Farlow and Lockley, 1989). One event associated with the Paluxy River site clearly upset Bird, and that was his role in the ‘ManTrack Controversy.’ Although Bird never reported any real human tracks in the Paluxy Riverbed, his writings

FIGURE 3.17 The supposed Man Tracks that Bird saw in a store in New Mexico that brought the Gen Rose site to his attention (after Bird, 1939b).

49

ACKNOWLEDGEMENTS

would inadvertently lead to the spread of the ‘man track’ claims. Bird (1939b) mentioned and figured (Fig. 3.17) the carved ‘man tracks’ that he saw in the window of a shop in New Mexico that led him to Glen Rose, as well as rumors from locals that ‘giant man tracks’ could be found in the Paluxy riverbed itself. A local farmer directed Bird to one such track, and Bird referred to as a ‘mystery track’ and described it as, ‘something about 15 inches long, with a curious elongated heel’ (Bird, 1939b, p. 257). Noting that the print was too indistinct to diagnose precisely, Bird suggested that it was made by some ‘hitherto unknown dinosaur or reptile’ (Bird, 1939b, p. 257). In his 1985 memoir, Bird relates his frustration at being used as a pawn in trying to suggest that man and dinosaurs coexisted. The curious mystery fossils that Bird described have subsequently been reinterpreted, in a superb article by Kuban (1989), as dinosaur tracks that are indistinct due to mud collapse and erosion.

CONCLUSIONS The discovery and analysis of the Connecticut River Valley tracks and the Glen Rose sauropod tracks are significant episodes in the development of vertebrate ichnology. They quickly established North America as the center of vertebrate ichnological research, and demonstrated the intrinsic value of tracks and trackways in the interpretation of dinosaur behavior. Interestingly, the principal workers on these trackways were essentially amateur scientists. In a very real sense, the work of Edward Hitchcock constituted the first systematic study of ichnology. His collection of tracks was by far the most comprehensive ever assembled, and established Amherst College as the center of ichnological research. Although at first his work was viewed with skepticism, it was soon accepted and his views quickly ignited both the scientific and artistic world. Dean (1969) indicated that Hitchcock’s research had a profound effect on the work of writers like Emily Dickenson (who he knew personally), Henry Wadsworth Longfellow (Nathan Appelton, the benefactor of the building that housed the ichnological collection was Longfellow’s father-in-law), Herman Melville, Oliver Wendell Holmes, and Henry David Thoreau. In his recent homage to Edward Hitchcock, Robert T. Bakker concluded that Hitchcock deserved to be recognized as the first paleontologist to suggest the relationship of dinosaurs to birds and concluded that, ‘In fact, Hitchcock didn’t need help from bones.

He reconstructed the fore and hind paws of Jurassic dinosaurs directly from the footprints with extraordinary sagacity. I find Hitchcock’s inaugural 1836 monograph awe-inspiring. His observations are detailed, his reasoning tight. This one publication made paleoichnology a robust discipline, a window into the grand succession of dominant life forms in the terrestrial sphere’ (Bakker, 2004, p. 3). In their tribute to Roland T. Bird, Farlow and Lockley (1989) summed up his place in history very well when they stated ‘He was the most conscientious American vertebrate ichnologist since Edward Hitchcock, and with the exception of Charles Sternberg and Richard Swan Lull, the only one to produce enduring work in the first half of the twentieth century’ (Farlow and Lockley, 1989, p. 35).

ACKNOWLEDGEMENTS We would like to thank Dr. Whitey Hagadorn and Dr. Edward Belt for supplying photographs from the Amherst College Collection and the archivist at the Amherst College Archives for access to the Hitchcock papers. We are also indebted to the American Museum of Natural History for supplying copies of photographs in their collection. The senior author would like to thank the Canada Research Chair Program for support of his research and funding was provided by the Natural Science and Engineering Research Council of Canada. Finally, we would like to thank Dr. Robert MacNaughton and Dr. Steve Hasiotis for their excellent and through reviews of this manuscript.

References Aldrich, M.L. and Leviton, A.E. (2001). Orra White Hitchcock (1796–1863) geological illustrator; another belle of Amherst. Geological Society of America, Abstracts with Programs, 33, 246. Bakker, R.T. (2004). Introduction: dinosaurs acting like birds and vice versa an homage to the Reverend Edward Hitchcock, first director of the Massachusetts geological Survey. In: Currie, P.J., Koppelhus, E.B., Shugar, M.A. and Wright, J.L. (Eds.), Feathered Dragons, Indiana University Press, Bloomington, Indiana, pp. 1–11. Barbour, I.H. (1892). Notice of new gigantic fossils. Science, 19, 99–100. Barton, D.R. (1941). Father of the dinosaurs [biographical sketch of Barnum Brown]. Natural History, 48, 308–312. Belt, E.S. (1989). A brief sketch of Edward Hitchcock (1793–1864). In: Jordan, W. M. (Ed.), Boston to Buffalo, in the Footsteps of Amos Eaton and Edward Hitchcock, Field Trip Guidebook T169, 28th International Geological Congress, Washington, DC, pp. 14–20. Bird, R.T. (1939a). Letter. Natural History, 43, 425.

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Bird, R.T. (1939b). Thunder in his footsteps. Natural History, 43, 254–261, 302. Bird, R.T. (1941). A Dinosaur walks into the museum. Natural History, 47, 74–81. Bird, R.T. (1944). Did Brontosaurus ever walk on land? Natural History, 53, 60–67. Bird, R.T. (1953). To capture a dinosaur isn’t easy. Natural History, 62, 104–110. Bird, R.T. (1954). We Captured a Live Brontosaur. National Geographic, 105, 707–722. Bird, R.T. (1985). Bones for Barnum Brown: Adventures of a Dinosaur Hunter, Texas Christian University Press, Fort Worth, 225 pp. Bouve, T.T. (1859). Sketch of the life and labors of James Deane. Proceedings of the Boston Society of Natural History, 6, 391–394. Bowditch, H.I. (1858). An Address on the Life and Character of James Deane, M.D, H.D. Mirick and Co., Greenfield, 45 pp. Brown, B. (1938). The mystery dinosaur. Natural History, 41, 190–202, 235. Buckland, W. (1837). Geology and Mineralogy Considered with Reference to Natural Theology, Volume 2, William Pickering, London. Colbert, E.H. (1978). Roland T. Bird (1899–1978). News Bulletin, Society of Vertebrate Paleontology, 114, 43–44. Dean, D.R. (1969). Hitchcock’s dinosaur tracks. American Quarterly, 21, 639–644. Deane, J. (1843). Ornithichnites of the Connecticut River sandstones. American Journal of Science, 45, 177–183. Deane, J. (1844a). On the fossil footmarks of Turner’s Falls, Massachusetts. American Journal of Science, 47, 73–77. Deane, J. (1844b). On the discovery of fossil footmarks. American Journal of Science, 47, 381–390. Deane, J. (1844c). Answer to the rejoinder of Professor Hitchcock. American Journal of Science, 47, 399–401. Deane, J. (1845a). Illustrations of fossil footmarks. Boston Journal of Natural History, 5, 277–284. Deane, J. (1845b). Description of fossil footprints in the New Red sandstone of the Connecticut Valley. American Journal of Science, 48, 158–167. Deane, J. (1845c). Fossil footmarks and raindrops. American Journal of Science, 49, 213–215. Deane, J. (1847a). Notice of new fossil footprints. American Journal of Science, 3, 74–79. Deane, J. (1847b). Fossil footprints. American Journal of Science, 4, 448–449. Deane, J. (1848). Fossil footprints of a new species of quadruped. American Journal of Science, 5, 40–41. Deane, J. (1849). Illustrations of fossil footprints of the valley of the Connecticut. Proceedings of the American Academy of Arts and Sciences, 1849, 209–220. Deane, J. (1850). Fossil footprints of Connecticut River. Journal of the Academy of Natural Sciences of Philadelphia, 2, 71–74. Deane, J. (1856). On the sandstone fossils of Connecticut River. Journal of the Academy of Natural Sciences of Philadelphia, 3, 173–178. Deane, J. (1861). Ichnographs from the Sandstone of Connecticut River, Little, Brown and Co., Boston, Massachusetts, 61 pp. Farlow, J.O. (1985). Introduction and volume notes. In: Schreiber, V.T. (Ed.), Bones for Barnum Brown, Texas Christian University Press, Fort Worth, Texas, pp. 1–15, 208–219. Farlow, J.O. and Lockley, M.G. (1989). Roland T. Bird, dinosaur tracker: an appreciation. In: Gillette, D.D. and Lockley, M.G. (Eds.), Dinosaur Tracks and Traces, Cambridge University Press, New York, pp. 33–36.

Farlow, J.O., Pittman, J.G. and Hawthorne, J.M. (1989). Brontopodus birdi, Lower Cretaceous Sauropod Footprints from the U.S. Gulf Coastal Plain. In: Gillette, D.D. and Lockley, M.G. (Eds.), Dinosaur Tracks and Traces, Cambridge University Press, New York, pp. 371–394. Foose, R.M. and Lancaster, J. (1981). Edward Hitchcock; New England geologist, minister and educator. Northeastern Geology, 3, 13–17. Guralnick, S.M. (1972). Geology and religion before Darwin: the case of Edward Hitchcock, theologian and geologist (1793–1864). Isis, 63, 529–543. Hitchcock, C.H. (1889). Recent progress in ichnology. Proceedings of the Boston Society of Natural History, 24, 117–127. Hitchcock, C.H. (1895). Edward Hitchcock. American Geologist, 133–149. Hitchcock, E. (1836a). Ornithichnology: description of the footmarks of birds (Ornithoidichnites) on New Red Sandstone in Massachusetts. American Journal of Science, 29, 307–340. Hitchcock, E. (1836b). Ornithichnites in Connecticut. American Journal of Science, 31, 174–175. Hitchcock, E. (1836c). Ornithichnology defended. Knickerbocker, 8, 289–295. Hitchcock, E. (1836d). Poetical remarks on reptile tracks from the Connecticut Valley. Knickerbocker, 8, 750–752. Hitchcock, E. (1837). Fossil footsteps in sandstone and graywacke. American Journal of Science, 32, 174–176. Hitchcock, E. (1840). Elementary Geology, J.S. and C. Adams, Amherst, Massachusetts. Hitchcock, E. (1841). Final Report on the Geology of Massachusetts, Commonwealth of Massachusetts, Boston, 831 pp. Hitchcock, E. (1843). Description of five new species of fossil footmarks, from the red sandstone of the valley of Connecticut River. Association of American Geologists Report, 1, 254–264. Hitchcock, E. (1844a). Report on ichnolithology or fossil footmarks, with description of several new species and the coprolites of birds, and of a supposed footmark from the valley of Hudson River. American Journal of Science, 47, 292–322. Hitchcock, E. (1844b). Rejoinder to the preceding article of Dr. Deane. American Journal of Science, 47, 390–399. Hitchcock, E. (1845a). Extract of a letter from Prof. E. Hitchcock, embracing miscellaneous remarks upon fossil footmarks, the Lincolnite, etc, and a letter from Professor Richard Owen, on the great birds’ nests of New Holland. American Journal of Science, 48, 61–65. Hitchcock, E. (1845b). An attempt to name, classify, and describe the animals that made the fossil footmarks of New England. Annals of the Association of American Geographers, 6, 23–25. Hitchcock, E. (1845c). Remarks on fossil footprints. American Journal of Science, 48, 159. Hitchcock, E. (1847). Description of two new species of fossil footmarks found in Massachusetts and Connecticut. American Journal of Science, Series 2, 4, 46–57. Hitchcock, E. (1848). An attempt to discriminate and describe the animals that made the fossil footmarks of the United States and especially of New England. Proceedings of the American Academy of Arts and Sciences, 1848, pp. 129–256. Hitchcock, E. (1854). On fossil footmarks of the Connecticut Valley. Proceedings of the Boston Society of Natural History, 1854, pp. 378–379. Hitchcock, E. (1855). Shark remains from the Coal Formation of Illinois, and bones and tracks from the Connecticut River Sandstone. American Journal of Science, Series 2, 20, 416–417.

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Hitchcock, E. (1856a). On a new fossil fish and new fossil footmarks. American Journal of Science, Series 2, 21, 96–100. Hitchcock, E. (1856b). Additional facts respecting the tracks of the Otozoum moodii on the Liassic sandstone of the Connecticut Valley. American Association for the Advancement of Science, Proceedings, 9, 228. Hitchcock, E. (1856c) On a new fossil fish, and new fossil footmarks. American Journal of Science, Series 2, 21, 96–100. Hitchcock, E. (1856d) Description of a new and remarkable species of fossil footmark, from the sandstone of Turners Falls, in the Connecticut Valley. American Journal of Science, Series 2, 21, 97–100. Hitchcock, E. (1857). On impressions in the sandstone from Turner’s Falls on Connecticut River, Massachusetts. Proceedings of the Boston Society of Natural History, 6, 111. Hitchcock, E. (1858). Ichnology of New England: A Report on the Sandstone of the Connecticut Valley, Especially its Fossil Footmarks, W. White, Boston, 220 pp. Hitchcock, E. (1861). Remarks upon certain points in ichnology. American Association for the Advancement of Science, Proceedings, 144–156. Hitchcock, E. (1862). Supplement to the ichnology of New England. Proceedings of the American Academy of Arts and Sciences, 6, 85–92. Hitchcock, E. (1863a). New facts and conclusions respecting the fossil footmarks of the Connecticut Valley. American Journal of Science, 36, 46–57. Hitchcock, E. (1863b). Reminiscences of Amherst College, Bridgman & Childs, Northampton, Massachusetts, 412 pp. Hitchcock, E. (1865). Supplement to the Ichnology of New England, Commonwealth of Massachusetts, Boston, 96 pp. Hitchcock, E. (1866). Supplement to the ichnology of New England. Proceedings of the American Academy of Arts and Sciences, 85–92. Ishigaki, S. (1989). Footprints of swimming sauropods from Morocco. In: Gillette, D.D. and Lockley, M.G. (Eds.), Dinosaur Tracks and Traces, Cambridge University Press, New York, pp. 83–86. Jardine, W. (1853). The Ichnology of Annandale, W.H. Lizars, Edinburgh, 17 pp. Kuban, G. (1989). Elongate dinosaur tracks. In: Gillette, D.D. and Lockley, M.G. (Eds.), Dinosaur Tracks and Traces, Cambridge University Press, New York, pp. 57–72. Lawrence, P.J. (1972). Edward Hitchcock; the Christian geologist. Proceedings of the American Philosophical Society, 116, 21–34. Lesley, J.P. (1877). Memoir of Edward Hitchcock, (1793–1864). National Academy of Sciences Biographical Memoirs, 113–134. Lewis, G.E. (1964). Memorial to Barnum Brown (1873–1963) Geological Society of America Bulletin , 75, pp. 19–20. Lockley, M.G. (1991). Tracking Dinosaurs, Cambridge University Press, New York, 238 pp. Lockley, M. and Hunt, A. (1995). Dinosaur Footprints and other Fossil Tracks of the Western United States, University of Chicago Press, Chicago, 285 pp. Lockley, M.G., Houck, K. and Prince, N.K. (1986). North America’s largest dinosaur tracksite: implications for Morrison formation paleoecology. Geological Society of America Bulletin, 97, 1163–1176. Logan, W.E. (1842). Canadian Carboniferous footprints. Proceedings of the Geological Society of London, 3, 707. MacClary, J.S. (1938). Dinosaur trails of Purgatory. Scientific American, 158, 72. Marche´, J.D. (1991). Edward Hitchcock’s poem, The Sandstone Bird (1836). Earth Sciences History, 10, 5–8. Marche´, J.D. (1993). Edward Hitchcock’s promising astronomical career. Earth Sciences History, 12, 180–186.

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Marsh, O.C., (1899). Footprints of Jurassic dinosaurs. American Journal of Science, Series 4, 7, pp. 227–232. Merrill, G.P. (1906). Contributions to the history of American geology. United States National Museum Report 1904, pp. 189–734. Olsen, P.E. and Rainforth, E.C. (2002). The ‘Age of Dinosaurs’ in the Newark Basin. American Paleontologist, 10, 2–5. Olsen, P.E., Kent, D.V., Cornet, B., Witte, W.K. and Schlische, R.W. (1996). High-resolution stratigraphy of the Newark rift basin (early Mesozoic, eastern North America), Geological Society of America, Bulletin, 106, pp. 40–77. Peabody, F.E. (1948). Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah. Bulletin Geological Sciences, University of California, 27, 295–468. Pemberton, S.G. and Gingras, M.K. (2003). The Reverend Henry Duncan (1774–1846) and the discovery of the first fossil footprints. Ichnos, 10, 69–75. Pemberton, S.G., Sarjeant, W.A.S. and Torrens, H.S. (1996). Footsteps before the flood: the first scientific report of vertebrate footprints. Ichnos, 4, 321–323. Preston, D.J. (1988). Dinosaurs in the Attic, Ballantine Press, New York, 308 pp. Rogers, H.D., Rogers, W.B., Jackson, C.T. and Warren, J.C. (1855). Footprints and other impressions on Carboniferous red shale of Pennsylvania. Proceedings of the Boston Society of Natural History, 5, 182–186. Russell, D.A. and Be´land, P. (1976). Running dinosaurs. Nature, 264, 486. Sarjeant, W.A.S. (1975). Fossil tracks and impressions of vertebrates. In: Frey, R.W. (Ed.), The Study of Trace Fossils, Springer-Verlag, New York, pp. 283–324. Shuler, E.W. (1917). Dinosaur tracks in the Glen Rose Limestone near Glen Rose, Texas. American Journal of Science, 44, 33–37. Simpson, G.G. (1942). The beginnings of vertebrate paleontology in North America. Proceedings of the American Philosophical Society, 86, 130–188. Steinbock, R.T. (1989). Ichnology of the Connecticut Valley: a vignette of American science in the early 19th century. In: Gillette, D.D. and Lockley, M.G. (Eds.), Dinosaur Tracks and Traces, Cambridge University Press, New York, pp. 27–32. Sternberg, C.M. (1932). Dinosaur tracks from Peace River, British Columbia. Annual Report National Museum of Canada, pp. 59–85. Thulborn, R.A. (1981). Estimated speed of a giant bipedal dinosaur. Nature, 292, 273–274. Warren, E. (1860). The Life of John Collins Warren, M.D. Ticknor and Fields, Boston, Volume 2, pp. 382–420. Warren, J.C. (1852). The Mastodon giganteus of North America, John Wilson, Publisher, Boston, 219 pp. Warren, J.C. (1854a). Remarks on Some Fossil Impressions in the Sandstone Rocks of Connecticut River, Ticknor and Fields, Boston, 54 pp. Warren, J.C. (1854b). Remarks on fossil footprints form the Connecticut Valley. Proceedings of the Boston Society of Natural History, 5, 19–21. Warren, J.C. (1855). On raindrop impressions and footprints from the Connecticut River Sandstone. Proceedings of the Boston Society of Natural History, 5, 258. Warren, J.C. (1856). On new remarkable gigantic fossils and footmarks. Proceedings of the Boston Society of Natural History, 5, 298–300.

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4 The Ichnofacies Paradigm: A Fifty-Year Retrospective James A. MacEachern, S. George Pemberton, Murray K. Gingras, and Kerrie L. Bann

SUMMARY : The ichnofacies paradigm endures as the elegant, unifying framework within which accurate ichnological observations and reliable environmental interpretations can be derived from the rock record. These temporally and geographically recurring, strongly facies-controlled groupings of trace fossils reflect specific combinations of organism behavior (ethology), and constitute the benchmark animal-sediment responses to optimum environmental conditions. Seilacherian ichnofacies are distinctive, archetypal associations of traces. Ichnofacies are part of the total aspect of the rock, and consist of primary biogenic structures imparted by organisms responding in predictable ways to variations in energy conditions, deposition rates, food resource types, substrate consistency, water salinity, oxygenation, subaerial exposure, substrate moisture, and temperature, among others. Like lithofacies, ichnofacies are subject to Walther’s Law, have lateral continuity, display predictable vertical successions, and lead to mappable constructs. Like all facies analyses, interpretations of ichnofaunas are improved substantially when evaluated in the context of the host rocks and their sedimentologic and stratigraphic implications.

wave energy, tidal flux, storm influence, fluvial-sediment input, subaqueous vs. subaerial exposure, salinity, temperature, substrate consistency, water turbidity, oxygenation, and other physicochemical factors. These factors can be very difficult to discern and apply to paleoenvironmental interpretations of the rock record. Ichnology constitutes a valuable tool in diagnosing many of these physico-chemical parameters in ancient systems, particularly when integrated with sedimentological and stratigraphic analysis. Trace fossils are unique, in that they are not merely paleontologic entities but also biogenic sedimentary structures, and must be evaluated in this sense. They are strongly facies controlled, and generally temporally long ranging, making them ideal for facies analysis. Ichnofossils are also readily observable at both outcrop and subsurface core scales, making their identification and interpretation as routine as that of physical sedimentary structures. The integration of both sedimentological and ichnological data, therefore, constitutes a powerful tool in the interpretation of ancient depositional systems. Ichnofacies consist of distinctive, recurring (both in space and time) ethological groupings of trace fossils, reflecting specific combinations of organism responses to environmental conditions. Interpretations of ichnofacies are enhanced when placed into the context of the original ichnocoenoses (temporally and genetically related trace fossils). It must be stressed that ichnofacies are not trace fossil

INTRODUCTION Modern depositional systems are characterized by a complex interaction of numerous physical, biological, and chemical processes, including


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THE RISE OF THE ICHNOFACIES CONCEPT

suites; rather, they are conceptual constructs based on numerous empirical observations, to which particular ichnocoenoses are attributable. The ichnofacies paradigm offers critical information about the conditions operating during deposition (e.g., softground ichnofacies) or during colonization of stratigraphic discontinuities (e.g., substrate-controlled ichnofacies and palimpsest softground ichnofacies). One of the strengths of the ichnofacies concept lies in its ease of integration with classical physical sedimentologic facies analysis, and its adherence to Walther’s Law (the basic tenet of sedimentary geology). The close ties of ichnofacies with lithofacies are further highlighted by the advent of genetic stratigraphic frameworks. Marine and marginal marine discontinuities are commonly demarcated by substrate-controlled trace fossil suites, and there is hardly an article published since 1995 dealing with such stratigraphic discontinuities that has not acknowledged the presence of omission suites attributable to the Glossifungites, Teredolites, and/or Trypanites ichnofacies. Past misuse or misconception of ‘ichnofacies’ has led to considerable scrutiny and discussion of the concept (e.g., Ekdale, 1988; Frey et al., 1990; Bromley and Asgaard, 1991; Pickerill, 1992; Goldring, 1993; Savrda, 1995; Bromley, 1996). Some researchers have argued that if employed independently of lithofacies, the utility of ichnofacies may lead to limited resolution, and may yield grossly over-generalized results (Goldring, 1993; Savrda, 1995). Certainly, any interpretation that ignores the complete dataset is prone to inaccuracy or imprecision. Properly done, however, ichnofacies analysis is fully integrated with the sedimentology, paleontology, and stratigraphy of the succession, and emerges as a powerful tool for highresolution reconstructions of depositional environments (e.g., Kern and Warme, 1974; Crimes et al., 1981; Wightman et al., 1987; Frey et al., 1990; MacEachern and Pemberton, 1992, 1994; MacEachern et al., 1992, 1999; Pemberton and MacEachern, 1995, 1997; Bromley, 1996; Gingras et al., 1998; Pemberton et al., 2001; Bann and Fielding, 2004; Bann et al., 2004; Fielding et al., 2006; MacEachern and Gingras, in press). Without the coherent underpinning of the ichnofacies concept, trace fossil identifications, ichnologic assemblages, and ichnofabric designations have no conceptual basis for interpretation. The ability to understand and therefore utilize ichnology in sedimentology and stratigraphy is contingent upon the unifying paradigm of ichnofacies.

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THE RISE OF THE ICHNOFACIES CONCEPT From the perspective of paleoenvironmental reconstruction of facies, nothing compares to the quantum leap in our comprehension of biogenically modified strata than that imparted by the development of the ichnofacies concept. This contribution cannot be overstated: the ichnofacies model elevated ichnology from the obscure concern with animal and plant ‘scribbles’ on rocks and disruptions in modern sediments, to a valuable facies analysis tool, superbly suited to outcrop and subsurface studies. As a conceptual framework, it forms the template within which ichnological data can be interpreted environmentally. The concept of ichnofacies was developed by Adolf Seilacher in the 1950s and 1960s (Seilacher, 1953a,b, 1967), originally based on the empirical observation that many of the parameters controlling the distribution of tracemakers tended to change progressively with increasing water depth (Fig. 4.1). In response to the potential geological value of this bathymetric relationship, the ‘Seilacherian’ ichnofacies framework soon came to be regarded almost exclusively (albeit erroneously) as a relative paleobathymeter (e.g., Weimer and Hoyt, 1964; Farrow, 1966). Though ichnofacies remain essential to environmental reconstructions, paleobathymetry is only one aspect of the modern concept. The principal controls on ichnofacies distributions tend to change progressively with bathymetry, and so ichnofacies are properly regarded to display a passive relationship to water depth (e.g., Ekdale et al., 1984; Ekdale, 1988; Frey et al., 1990). Organism behaviors, and their resulting biogenic structures are principally controlled by factors such as substrate consistency, energy near the bed, food resource types, water turbidity, water salinity, depositional rates, oxygenation, and temperature, among others (Fig. 4.1). Seilacher (1967) defined six original ichnofacies, named for a characteristic ichnotaxon. These fall into four softground marine types (Skolithos, Cruziana, Zoophycos, and Nereites), one substrate-controlled type (Glossifungites), and a single softground continental type (Scoyenia). Frey and Seilacher (1980) added the Trypanites Ichnofacies to characterize borings associated with hardground substrates. Bromley et al. (1984) introduced the Teredolites Ichnofacies to encompass borings into xylic (woody) substrates. Frey and Pemberton (1987) proposed the Psilonichnus Ichnofacies for permanent vertical to inclined

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4. THE ICHNOFACIES PARADIGM: A FIFTY-YEAR RETROSPECTIVE

Seilacher's Concept of Recurring Ichnofacies TRACE FOSSILS

BEHAVIOR

ENVIRONMENT

Trace fossils are a manifestation of behavior which can be modified by the environment.

Agrichnia

Cubichnia

Feeding

Fodinichnia

Resting

Fugichnia

Dwelling

Locomotion

Pascichnia Domichina

A

B ECOLOGICAL CONTROLS

C

Distributions and behaviors of benthic organisms are limited by interrelated ecological controls, including:

D

Soupground

Softground

Looseground

Stiffground

Nereites Zoophycos

1. Sedimentation Rate

5. Turbidity

2. Substrate Coherence

6. Light

3. Salinity

7. Temperature

4. Oxygen Level

8. Depositional Energy

Firmground

Hardground

Woodground

Zoophycos

Cruziana Mermia Skolithos Psilonichnus Scoyenia Glossifungites Trypanites Coprinisphaera Entobia Gnathichnus Teredolites

FIGURE 4.1 Seilacher’s concept of recurring ichnofacies. (A) Ethological classification of trace fossils and their relationships with body fossils (Modified from Pemberton et al., 2001). (B) Behavioral classification of biogenic structures. With environmental fluctuations, virtually all traces are intergradational with the fugichnia (Modified from Pemberton et al., 2001). (C) Ecological controls that affect the distribution of trace-making organisms, many of which change predictably with relative water depth. (D) Relationship of substrate type and the distribution of the named ichnofacies.

CONTINENTAL ICHNOFACIES

dwellings in sand-prone substrates typical of high intertidal and supratidal coastal settings. These constitute the nine ichnofacies that have demonstrated recurrence both spatially and temporally. More recently, the hardground setting has been proposed to include two additional ichnofacies (Gnathichnus and Entobia) (Bromley and Asgaard, 1993). The continental setting has likewise seen some expansion, with the initial proposal of the Termitichnus Ichnofacies to address assemblages associated with paleosols (Smith et al., 1993) and Mermia Ichnofacies to reflect suites occupying lacustrine settings (Buatois and Mańgano, 1995). Since then, the Termitichnus Ichnofacies has been discarded, in favor of the Coprinisphaera Ichnofacies (Genise et al., 2000).

CONTINENTAL ICHNOFACIES There are currently three continental ichnofacies: Scoyenia, Mermia, and Coprinisphaera (Table 4.1). The systematic ichnological analysis of the continental realm has been a relatively recent development, with an ever increasing number of case studies being added to the developing models. Researchers have demonstrated that the continental regime is far more diverse and complex ichnologically than previously considered. Buatois and Mańgano (2004) have recently summarized the Mermia and Scoyenia ichnofacies, typical of permanently to intermittently aquatic continental environments. Genise et al. (2000, 2004) have summarized many of the principal elements of the Coprinisphaera Ichnofacies, characteristic of more or less permanently terrestrial conditions, ranging from dry and cold to humid and warm climates. Donovan (1994) and Hasiotis (2002) have approached the study of continental ichnology from slightly different perspectives, yielding innovative insights into these regimes as well.

Scoyenia Ichnofacies Frey et al. (1984) summarized and refined the original designation of Seilacher’s (1967) Scoyenia Ichnofacies, and concluded that it remained a valid recurring grouping. Buatois and Mańgano (1995) further refined the Scoyenia Ichnofacies, and placed it within a broader continental spectrum. The Scoyenia Ichnofacies (Fig. 4.2A, Table 4.1) is characteristic of low-energy continental settings characterized by periodically subaerial conditions. Most settings are inundated intermittently with freshwater. Common depositional environments include lake margins,

55

fluvial channel margins and overbanks, progressively desiccated crevasse splays, and wet interdune areas (e.g., Seilacher, 1967; Ekdale et al., 1984; Frey et al., 1984; Frey and Pemberton, 1987; Bromley and Asgaard, 1991; Buatois and Mańgano, 1995, 2004). The Scoyenia Ichnofacies encompasses trace fossil suites that consist of: (1) horizontal, meniscate (backfilled) structures made by mobile deposit-feeding organisms (e.g., Scoyenia (Fig. 4.2D), Beaconites, Taenidium, and adhesive meniscate burrows; Fig. 4.2E); (2) horizontal, mobile deposit-feeding structures (e.g., Planolites); locomotion traces, including tracks and trails (e.g., Umfolozia, Hexapodichnus, Acripes, and Cochlichnus); (3) fish fin markings (e.g., Undichna; Fig. 4.2F); (4) vertical dwelling structures (e.g., Camborygma, Macanopsis, Skolithos, and Cylindricum); (5) horizontal dwelling structures (e.g., Palaeophycus); (6) a mixture of invertebrate (predominantly arthropod) and vertebrate structures (dwelling structures and footprints); and (7) plant root traces. Suites tend to display low to moderate diversities, with localized high abundances. Ornamented structures and scratch marks (e.g., Scoyenia) are more typical of endobenthic activity during subaerial exposure and substrate desiccation. The Scoyenia Ichnofacies may comprise two distinct expressions: one characterized by meniscate, backfilled structures without ornamentation developed in a soft substrate, and the second characterized by striated traces developed in a firm substrate, which commonly cross-cut the former (Buatois and Mańgano, 2004).

Mermia Ichnofacies The Mermia Ichnofacies (Fig. 4.2B, Table 4.1) was proposed by Buatois and Mańgano (1995) for freshwater assemblages associated with low energy, permanently subaqueous conditions, largely characterized by high degrees of environmental stability. Such suites probably record the highest preservation potential of all continental regimes (Buatois and Mańgano, 2004). In recent years, a number of case studies identifying the Mermia Ichnofacies have been recorded. Buatois and Mańgano (1995) included a table summarizing occurrences of the Mermia Ichnofacies from the Carboniferous to the Pleistocene. Suites attributable to the Mermia Ichnofacies are characterized by a dominance of horizontal to subhorizontal grazing (e.g., Mermia, Gordia; Fig. 4.2G, Cochlichnus, and Helminthoidichnites) and feeding traces produced by mobile detritus and deposit feeders (e.g., Planolites, Treptichnus, and Circulichnus),

56


TABLE 4.1 Summary of Basic Features and Environmental Implications of Continental Ichnofacies. (Modified from Buatois and Mańgano, 1995 and Pemberton et al., 2001) Characteristic Trace Fossils

Typical Benthic Environment Scoyenia Ichnofacies

Small, horizontal, lined, back-filled feeding burrows; curved to

Moist to wet, pliable, argillaceous to sandy sediment at low energy

tortuous, unlined feeding burrows; crawling traces, vertical cylindrical to irregular shafts; tracks and trails. Invertebrates

sites; either very slightly submerged lacustrine or fluviatile deposits periodically becoming emergent, or water side subaerial deposits

mostly deposit feeders and predators; vertebrates are grovellers,

periodically or becoming submergent; semi-aquatic vegetation may

predators or herbivores. Invertebrate diversity typically low, yet

be present. Intermediate between fully aquatic and non-aquatic,

some traces may be abundant. Vertebrate tracks may be diverse and

continental settings. Physical sedimentary structures may include

abundant around water bodies; dung or coprolites occur locally.

desiccation cracks and allied features. Typical sedimentary envir-

Trackways moderately diverse and dominant in Paleozoic exam-

onments: transitional alluvial lake zones, floodplains, ephemeral

ples. Arthropods comprise the most important invertebrate trace-

lakes, ponds, and wet interdunes.

maker. Typical components include Scoyenia, Beaconites, Planolites, Skolithos, Cruziana, Rusophycus, Camborygma, Palaeophycus, Umfolozia, Acripes, and vertebrate tracks. Mermia Ichnofacies Small, horizontal to subhorizontal, simple, non-specialized grazing

Non-cohesive, fine-grained sediment in well-oxygenated, low

trails dominant; common feeding traces; rare locomotion traces.

energy, permanently subaqueous zones; sedimentation rates are

Tracemakers mostly mobile deposit feeders. Diversity moderate to

normally low, but punctuated episodic deposition (e.g., turbidity

high. Colonization suites are typically of low diversity. Producers

currents, density underflows) may occur. Physical sedimentary

may include annelids, arthropods, nematodes, nematomorphs, oligochaetes, bivalves, gastropods, and fishes. Trails are dominant

structures may include parallel lamination, ripple cross-lamination, normal grading, tool and flute marks, as well as soft-sediment

in Paleozoic examples, whereas an increase in burrows is recorded in

deformation structures. Typical sedimentary environments include

post-Paleozoic occurrences. Typical components include Mermia,

deep and shallow lakes, and fjord lakes.

Gordia, Helminthoidichnites, Cochlichnus, Treptichnus, Undichna, Lockeia, Tuberculichnus, Maculichna, and Planolites. Coprinisphaera Ichnofacies Large and small traces, mostly dwelling burrows (including

Soft to incipient cohesive muddy, silty, sandy and marly sediment,

breeding structures), less common feeding burrows, rhizoliths, tracks, coprolites, and bite traces in leaves. Termite, bee, and beetle

in low-energy terrestrial areas; associated plant growth is highly variable, from humid forest to open country. Associated inorganic

nests are typical. Ichnodiversity is moderate to high. Tracemakers

sedimentary structures include parallel lamination, erosive sur-

comprise a mixture of vertebrates (mainly mammals), invertebrates

faces, and a wide variety of paleosol and diagenetic features (e.g.,

(particularly various types of arthropods, as well as oligochaetes and

concretions). Sedimentary environments include various types of

annelids), and plants. Typical components include Coprinisphaera,

mature and, more rarely, immature paleosols developed within

Termitichnus, Edaphichnium, Scaphichnium, Celliforma, Macanopsis,

alluvial plains, desiccated floodplains, abandoned fluvial bars,

Ichnogyrus, Attaichnus, Pallichnus, Daimonelix, and Uruguay.

zones marginal to dune fields, and coastal plains.

as well as subordinate occurrences of locomotion traces (e.g., Undichna and Maculichna). Assemblages generally lack striated or scratch-marked structures, and vertebrate trackways. Fish, amphibian, reptile, and possibly even mammal feeding structures may, however, be present. Suites display relatively high to moderate diversities and abundances, particularly for lacustrine settings that are hydrologically open. Restriction of the water body commonly leads to heightened salinities and oxygen reduction, and ichnogenera diversities decline markedly. Consequently, ephemeral lakes may be largely devoid of bioturbation.

Coprinisphaera Ichnofacies The Coprinisphaera Ichnofacies (Fig. 4.2C, Table 4.1) was erected by Genise et al. (2000) to accommodate suites associated with more or less permanently subarially exposed continental settings. Their analysis showed the recurrence of 28 suites derived from 58 paleosol intervals, reflecting a variety of geographic locations. Recurrence in time is less clearly extensive, with assemblages spanning the Paleocene to Holocene. Ethologically, the principal grouping is nesting/breeding (calichnia), but suites also include dwellings employed as refugia, aestivation, and ambush

57

CONTINENTAL ICHNOFACIES

amb

amb

amb

Sc

Sc

A D

amb

E

F

U

B

Go

F

G

amb

Tm

C

H

FIGURE 4.2 Schematic block diagrams of continental ichnofacies. (A) Diagram of the Scoyenia Ichnofacies. Traces include Ancorichnus (An), adhesive meniscate burrows (amb), Camborygma (Ca), Cochlichnus (Cl), tetrapod footprints (F), Macanopsis (M), Palaeophycus tubularis (Pt), Planolites (P), rhizoliths (R), Scoyenia (Sc), and Skolithos (S). (B) Diagram of the Mermia Ichnofacies. Traces include bivalve dwellings, Cochlichnus (Cl), Gordia (Go), Helminthoidichnites (He), Mermia (Me), Planolites (P), Treptichnus (Tr), Palaeophycus tubularis (Pt), and Undichna (U). (C) Diagram of the Coprinisphaera Ichnofacies. Traces include Celliforma (Ce), Coprinisphaera (Co), Eatonichnus (Ea), footprints (F), roots (Rt), Skolithos (S), adhesive meniscate burrows (amb), Teisseirei (Ti), and Termitichnus (Tm). (D) Scratch-marked expression of Scoyenia (Sc), with meniscate visible in the right-hand example, Triassic Tarkastad Subgroup, Karoo Basin, South Africa. (E) Adhesive meniscate burrows (amb), Lower Cretaceous Mannville, Group, Alberta, Canada. (F) Modern Undichna (U), formed by the pectoral fins of fish, and tetrapod footprints (F) in mud, Australia. (G) Gordia (Go), Upper Permian Balfour Formation, Karoo Basin, South Africa. (H) Termitichnus (Tm), Pleistocene of the Karoo Basin, South Africa. Photo (D) courtesy of Dr. Fiona J. Evans.

58


predation. Some mobile deposit-feeding structures, larger (vertebrate) domiciles, and rhizoliths may also be included in some suites. Predominant tracemakers include bees, ants, wasps, beetles, termites, and other unassigned insects. The ichnofacies namesake is for one of the most common structures; the nest structure of dung beetles. Trace fossil suites are prone to complex tiering patterns, particularly in mature soils, reflecting the variable depths of emplacement of hymenopterous, termite, and dung beetle nests. Suites show moderate to relatively high diversity, and generally high abundance of traces, particularly in mature paleosols. The suites attributable to the Coprinisphaera Ichnofacies typically contain dung beetle nests (Coprinisphaera), bee traces (e.g., Celliforma, Uruguay, Ellipsoideichnus, Palmiraichnus, and Rosellichnus), wasp nests (e.g., Chubutolithes), ant traces (e.g., Attaichus and Parowanichnus), other beetle traces (e.g., Monesichnus, Fontanai, Pallichnus, Eatonichnus, and Teisseirei), and termite nests (e.g., Termitichnus; Fig. 4.2H, Syntermesichnus, and Tacuruichnus). Various larger mammal ‘caves’ may also be present, and the ichnofacies probably includes dwelling networks of rodents and other burrowing organisms. Settings characteristic of the Coprinisphaera Ichnofacies correspond to paleosols developed in paleoecosystems of herbaceous communities. This may effectively limit the ichnofacies to units ranging from Late Cretaceous to the Holocene as there were no herbaceous communities earlier in Earth history. Climatically, settings range from arid and cold steppes (dominated by hymenopterous nests) to humid and hot subtropical savannas (dominated by termite nests). Paleosol settings occupy alluvial plains, desiccated floodplains, crevassse splays, levees, abandoned point bars, and vegetated eolian environments (Genise et al., 2000). These settings are strongly controlled by microclimates (e.g., temperature, radiation, humidity, and wind speed near the ground) associated with vegetation, topography, and overall climatic conditions (cf. Hasiotis, Chapter 16).

SOFTGROUND MARINE ICHNOFACIES Softground ichnofacies tend to be differentiated from one another by variables that are typically depth related. The Zoophycos and Nereites ichnofacies are more characteristic of deeper-water environments, whereas the Psilonichnus, Skolithos, and Cruziana ichnofacies are represented in nearshore marine or coastal environments (Table 4.2). Summaries of the

ichnology of marine shoreface environments can be found in publications such as MacEachern and Pemberton (1992), Bromley (1996), MacEachern et al. (1999), Pemberton et al. (2001), and Bann et al. (2004). The Zoophycos Ichnofacies and especially the Nereites Ichnofacies tend to characterize outer shelf, slope, and bathyal to abyssal settings. For details on the ichnology of deep-marine deposits, see Uchman (2004).

Psilonichnus Ichnofacies The Psilonichnus Ichnofacies (Fig. 4.3A, Table 4.2) represents a mixture of marine, quasi-marine, and non-marine conditions. Typical environments include the beach backshore, coastal dunes, washover fans, and supratidal flats. Frey and Pemberton (1987) indicated that such environments are subject to extreme variations in energy levels, sediment types, and physical and biogenic sedimentary structures. Marine processes generally dominate during spring tides and storm surges, whereas maritime eolian processes predominate during neap tides and nonstorm periods. Such conditions can result in alternations of wind and water deposition, producing complex, truncated laminae dipping shallowly in diverse directions. Owing to their topographic position, few such substrates are available to benthic marine animals. The only persistent, notable exceptions are amphibious crabs of the Family Ocypodidae (Figs. 4.3B,D), which include both scavengers and surficial deposit feeders; these animals typically excavate J-, Y-, or U-shaped dwelling burrows referable to the trace fossil Psilonichnus (Fig. 4.3C,E and F). The mud shrimp Upogebia can also construct Psilonichnus in subaqueous estuarine mouth deposits, where it constitutes part of the Skolithos Ichnofacies (Nesbitt and Campbell, 2002). Other biogenic structures are generated by essentially terrestrial organisms and include: (1) the vertical shafts of insects and spiders; (2) the horizontal tunnels of other insects and tetrapods; and (3) the ephemeral tracks, trails, and fecal pellets of insects, reptiles, birds, and mammals. The other major type of biogenic structure relates to plant-root penetrations. The types of plants able to exploit these substrates range from intertidal halophytes on the distal margins of some washover fans, to maritime or terrestrial grasses, weeds, vines, shrubs, bushes, and trees on backshore dunes. To the extent that ocypodid crab burrows may occur in the uppermost foreshore or the upper part of

59

SOFTGROUND MARINE ICHNOFACIES

TABLE 4.2 Recurring Archetypal Marine Softground Trace Fossil Associations and their Common (but not exclusive) Environmental Implications (Adapted from Pemberton et al., 2001) Characteristic Trace Fossils

Typical Benthic Environment Psilonichnus Ichnofacies (shifting substrates I)

Predominantly vertical small shafts, some with bulbous basal cells, to

Supralittoral to upper littoral, moderate to low-energy marine and/or

larger, irregularly J-, Y-, or U-shaped dwelling burrows; local invertebrate and vertebrate crawling and foraging traces or surficial

eolian conditions subject to modification by torrential rains or storm surges. Associated with well-sorted, variably laminated to cross-

tunnels; algal mats, vertebrate tracks and coprolites may be present.

stratified sands, to root- and burrow-mottled, poorly sorted sands or

Invertebrates mostly predators or scavengers of low diversity.

muddy sands. A common coastal setting, typically represented by the

Vertebrates mostly predators or herbivores; diversity may be

beach backshore and dunes, but also by washover fans and supratidal

appreciable locally. In pre-Cretaceous occurrences, crab-like dwelling

flats. Intergradational with the maritime terrestrial zone.

structures may be absent. Skolithos Ichnofacies (shifting substrates II) Vertical, cylindrical or U-shaped dwelling burrows; protrusive and retrusive spreiten in some U-burrows, developed mainly in response

Lower littoral to infralittoral, moderate to relatively high-energy conditions most typical. Associated with slightly muddy to clean,

to substrate aggradation or degradation (escape or equilibrium

well-sorted, shifting sediments subject to abrupt erosion or deposi-

structures); forms of Ophiomorpha consisting predominantly of vertical

tion. Higher energy increases physical reworking and obliterates

or steeply inclined shafts. Animals are chiefly suspension feeders or

biogenic sedimentary structures, leaving a preserved record of

passive (tubicolous) carnivores. Diversity is low, though given kinds of

physical stratification. Generally corresponds to the beach foreshore

burrows may be abundant. Vertebrate biogenic structures may occur

and shoreface; but numerous other settings of comparable energy

locally, especially in low-energy intertidal settings.

levels also may be represented, such as some estuarine point bars,

tidal deltas, and deep-sea fans. Cruziana Ichnofacies (shifting to stable substrates) Abundant crawling traces, both epi- and intrastratal; inclined

In shallow marine settings, typically includes infralittoral to shallow

U-shaped burrows with mostly protrusive spreiten (feeding swaths;

circalittoral substrates below minimum but not maximum wave base,

soft-sediment

Rhizocorallium);

forms

of

Ophiomorpha

and

to somewhat quieter conditions offshore; moderate to relatively low

Thalassinoides consisting of irregularly inclined to horizontal compo-

energy; well-sorted silts and sands, to interbedded muddy and clean

nents; scattered vertical cylindrical burrows (suspension feeders or

sands, moderately to intensely bioturbated; negligible to appreciable

passive carnivores). Animals may include mobile carnivores as well

(though not necessarily rapid) sedimentation. A very common type of

as various mixtures of suspension and deposit feeders. Diversity and abundance generally high, although crawling traces of limited

depositional environment, including not only shelves and epeiric embayments but also littoral to sub-littoral parts of certain estuaries,

diversity may predominate in certain Paleozoic nearshore settings.

bays, lagoons, and tidal flats.

Zoophycos Ichnofacies (oxygen-poor settings) Relatively simple to moderately complex, efficiently executed grazing

Circalittoral to bathyal, quiet-water conditions, or protected intra-

traces and shallow feeding structures; spreiten typically planar to

coastal to epeiric sites (silled basins, restricted lagoons) with muds or

gently inclined, distributed in delicate sheets, ribbons, lobes, or

muddy sands rich in organic matter but more or less deficient in

spirals (flattened forms of Zoophycos or, in pelitic sediments,

oxygen. Epeiric or coastal sites reflect somewhat stagnant waters.

Phycosiphon). Virtually all animals are deposit feeders. Diversity is very low, though given structures are typically abundant. The

Offshore sites range from just below maximum wave base to fairly deep water, in areas free of turbidity flows or significant bottom

ichnogenus Zoophycos may also be abundant in the Cruziana and

currents. Where relict or palimpsest substrates are present, particu-

Nereites ichnofacies, under normal oxygen levels; occurrences of the

larly if swept by shelf-edge or deeper water contour currents, this

ichnogenus thus do not necessarily constitute the ichnofacies.

ichnofacies may be omitted in the transition from infralittoral to abyssal environments.

Nereites Ichnofacies (turbidite-type settings) Complex grazing traces and patterned feeding/dwelling structures,

Bathyal to abyssal, mostly quiet but oxygenated waters, in places

reflecting highly organized, efficient behavior; spreiten structures typically nearly planar, although Zoophycos forms are spiraled,

interrupted by down-slope or down-canyon bottom currents or turbidity flows (flysch settings). Resident pelagic muds are typically

multilobed, or otherwise very complex. Numerous crawling/grazing

bounded above and below by turbidites, some exhibiting complete

traces and sinuous fecal castings (Helminthoida, Cosmorhaphe), mostly

Bouma cycles. In more distal regions, the sedimentary record is

intrastratal. Animals, chiefly deposit feeders or scavengers, although

mainly one of continuous deposition and bioturbation; few physical

some may trap or farm microbes within essentially permanent, open

or biogenic structures are preserved, unlike the Nereites Ichnofacies

domiciles (Paleodictyon, Megagrapton). Diversity and abundance are

sensu stricto.

generally significant.

60


Ps

Ps

tb

tb

FIGURE 4.3 The Psilonichnus Ichnofacies. (A) Diagram of the Psilonichnus Ichnofacies developed in a back-barrier coastal dune setting. Traces include Aulichnites (Au), Lockeia (Lo), Macanopsis (M), Planolites (P), Protovirgularia (Pr), Psilonichnus (Ps), and rhizoliths (R). (B) Opening of modern Ocypoda quadrata in the backshore (arrow). (C) Y-shaped Psilonichnus (Ps) of the modern ghost crab in the backshore of Sapelo Island, Georgia, USA. (D) Ocypoda quadrata and the burrows that it makes (arrows) in the backshore, St. Catherines Island, Georgia, USA. (E) Outcrop photo of an inferred Psilonichnus (Ps), Pleistocene outcrop, Willapa Bay, Washington, USA. It is infilled with rhythmic (passive) laminations. (F) Resin cast of the burrows (unlabeled arrows) of Hemigrapsus oregonensis (shore crab) from the middle intertidal zone, Willapa Bay, Washington. Notable are the chelae impressions and (locally) commensal threadworm burrows (tb), likely of the capitellid polychaete Heteromastus.


estuarine point bars, the Psilonichnus Ichnofacies may slightly overlap the Skolithos Ichnofacies; however, the boundary between these two ichnofacies is normally distinct. In contrast, because of its potentially large numbers of terrestrial traces, the Psilonichnus Ichnofacies may be broadly intergradational with the continental Scoyenia and Coprinisphaera ichnofacies.

Skolithos Ichnofacies The Skolithos Ichnofacies (Fig. 4.4A, Table 4.2) is indicative of relatively high levels of wave or current energy, and is typically developed in clean, well-sorted, loose or shifting particulate substrates. Abrupt changes in rates of deposition, erosion, and physical reworking of sediments are characteristic. Such conditions commonly occur on the shoreface and sheltered foreshores, but similar conditions may occur in a wide range of depositional environments (e.g., proximal wave-dominated delta fronts, sandy bars and spits, tidal channels and inlets, flood- and ebb -tidal deltas, sandy bay margins, low intertidal sand flats, estuary mouth complexes, and submarine fans). Associated stratification features typically consist of fine-scale, parallel to subparallel, gently seaward-dipping laminae (swash zone cross-strata) to large- and small-scale, multidirectional trough cross-stratification with current ripple cross-laminae. In strongly storm-dominated settings, low-angle, undulatory parallel lamination may be erosionally amalgamated into thick bedsets of swaley cross-stratification (SCS). In turbidites, beds may display massive, horizontal planar parallel, and current ripple cross-lamination (Bouma A, B, and C divisions). Settings characterized by tidal processes may show trough cross-beds and current ripples with cyclic development of mud drapes on foresets (i.e., tidal bundles), bidirectional orientations, and/or thin lenses of mud in the ripple troughs (i.e., flaser bedding). As dictated by fundamental interrelationships of water agitation, sediment transport, and animal distribution, most tracemakers are suspension feeders. Substrates serve mainly as an anchoring medium. Infaunal organisms typically construct deeply penetrating, more or less permanent domiciles (Figs. 4.4B–I). Depth of burrowing in the intertidal zone is controlled, in part, by tidal range and height of the low-tide interstitial water column in the substrate. During low-tide, moist sediments at depth help to buffer organisms against desiccation and salinity or temperature shock, and also help to provide respiratory water. In both intertidal and high-energy

61

subtidal settings, deep burrowing is one means of escaping the instability of the ever-shifting substrate surface (Fig. 4.4). The Skolithos Ichnofacies is characterized by: (1) predominantly vertical, cylindrical, or U-shaped burrows; (2) protrusive and retrusive spreiten in some U-burrows, which develop in response to substrate aggradation or degradation, respectively; (3) few horizontal structures; (4) few structures produced by mobile organisms; (5) low diversity suites, although individual forms may be abundant; (6) predominance of dwelling burrows constructed by suspension feeders or passive carnivores; and (7) vertebrate traces in some low-energy intertidal settings. Typical ichnogenera include Skolithos (Fig. 4.4I), Diplocraterion (Fig. 4.4H), Ophiomorpha (Fig. 4.4C,G and I), Conichnus (Fig. 4.4E,F,) Bergaueria, Lingulichnus, Piscichnus, Schaubcylindrichnus, Palaeophycus, Arenicolites (Fig. 4.4B), and Gyrolithes saxonicus. Possible depositfeeding structures that can be associated with the Skolithos Ichnofacies include Taenidium, Siphonichnus, Macaronichnus, Cylindrichnus, and Rosselia (Fig. 4.4D). The Skolithos Ichnofacies ordinarily grades landward into supratidal or terrestrial zones and seaward into the Cruziana Ichnofacies. The landward boundary tends to be more abrupt than the latter. Finally, the Skolithos Ichnofacies may appear in slightly to substantially deeper-water deposits, wherever energy levels, food supplies, and/or hydrographic and substrate characteristics are suitable (Crimes et al., 1981). Potential examples include submarine canyons, deep-sea fans, and bathyal slopes swept by strong contour currents. Therefore, as emphasized previously, paleobathymetric interpretations cannot be based solely on checklists of trace fossil names: evaluation of associated physical sedimentary structures, stratigraphic position, and other facies evidence is essential, even in normal beach-to-offshore successions.

Cruziana Ichnofacies The Cruziana Ichnofacies (Fig. 4.5A, Table 4.2) is most characteristic of permanently subtidal, poorly sorted, and unconsolidated cohesive (muddy) substrates in shallow marine settings typified by uniform salinity. Conditions typically range from moderate energy levels lying below fair-weather (minimum) wave base but above storm wave base, to lower energy levels in deeper, quieter waters. The most common settings correspond to the offshore extending to the very distal fringes of the lower shoreface. Variably impoverished

62


B

A

C

D

E

F

O

Sk

O

O

Sk O

Sk

G

H

I

FIGURE 4.4 The Skolithos Ichnofacies. (A) Schematic block diagrams of the Skolithos Ichnofacies (artwork by Tom Saunders). (B) Sandstone with Arenicolites (arrow), Upper Cretaceous Horseshoe Canyon Formation, Alberta. (C) Siderite-cemented Ophiomorpha borneensis (arrow) from the Upper Cretaceous Appaloosa Sandstone, Drumheller, Alberta. (D) Vertically stacked (re-equilibrated), siderite-cemented Rosselia socialis (arrow), Upper Cretaceous Appaloosa Sandstone, Drumheller, Alberta. Rosselia is a common ichnogenus associated with the Skolithos Ichnofacies in storm-dominated successions, though it is a facies-crossing element of the Cruziana Ichnofacies. (E) Conichnus conicus (upper arrow) with associated escape/collapse structure (lower arrow) in upper shoreface deposits of the Upper Cretaceous Blackhawk Formation, Book Cliffs, Utah. (F) Conichnus conicus (arrow) from upper shoreface deposits of the Upper Cretaceous Appaloosa Sandstone, Drumheller, Alberta. (G) Ophiomorpha nodosa (arrow) with siderite-cemented pelleted margins, from the proximal lower shoreface deposits of the Upper Cretaceous Sego Sandstone, Utah. (H) Abundant Diplocraterion habichi (arrows), Middle Jurassic Fensfjord Formation, Northern North Sea, Norway. (I) Thick tempestite of the middle shoreface, with Ophiomorpha nodosa (O) and unlined Skolithos linearis (Sk), Upper Cretaceous Appaloosa Sandstone, Drumheller, Alberta.

63


Helminthopsis Proximal Expression Rosselia Chondrites Distal Expression

Ophiomorpha

Schaubcylindrichnus

B Archetypal Rhizocorallium Asterosoma

A

D

C

E H

Ch P Te

Z

Te As

Ph

Ch Ph

Z

Ch

Pa

Ch Rh

F

G

H

I

As

FIGURE 4.5 The Cruziana Ichnofacies. (A) Diagram of the Cruziana Ichnofacies showing the archetypal as well as distal and proximal expressions (artwork by Tom Saunders). (B) Sideritecemented Rosselia socialis (arrow), Lower Cretaceous Viking Formation, Alberta. (C) Complete Asterosoma (arrow) exposed on bedding plane of outcrop, Upper Cretaceous Cardium Formation, Alberta. (D) Asterosoma lobes (arrows) in outcrop, Upper Cretaceous Blackhawk Formation, Book Cliffs, Utah. (E) Silicified Thalassinoides (arrow) showing Y-shaped branch, Mississippian Mount Head Formation, Mount Greenock, Jasper, Alberta. (F) Storm-bedded upper offshore deposits, with Teichichnus (Te) and Chondrites (Ch), Upper Cretaceous Cardium Formation, Alberta. (G) Heterolithic distal delta front deposits, with dense Chondrites (Ch), small Teichichnus (Te), Planolites (P), and Rhizocorallium (Rh), Lower Cretaceous Bow Island Formation, Alberta. (H) Upper offshore deposits with Asterosoma (As) (reburrowed with Chondrites), Phycosiphon (Ph), and robust Chondrites (Ch), Upper Cretaceous Cardium Formation, Alberta. (I) Upper offshore deposits with Helminthopsis (H), Zoophycos (Z), Phycosiphon (Ph), Palaeophycus (Pa), and Asterosoma (As), Upper Cretaceous Cardium Formation, Alberta.

64


expressions of the ichnofacies may also correspond to prodelta to distal delta-front settings, fully marine lagoons, and open bays. Variants of the ichnofacies occur in subtidal to intertidal mud-prone environments that may experience some salinity reductions, such as marginal marine central bays of estuaries, brackish lagoons, mixed sand and mud tidal flats, and inclined heterolithic stratification (IHS) in lateral accretion beds of tidally modified channels (MacEachern and Pemberton, 1994; MacEachern and Gingras, in press). Sediment textures and bedding styles exhibit considerable diversity, including thinly bedded, well-sorted silts and sands, discrete mud and shell layers, interbedded muddy and clean silts and sands, and extremely poorly sorted beds derived from any of the above, through intense bioturbation. Physical sedimentary structures, where not modified or destroyed by bioturbation, most commonly include low-angle, undulatory, parallel and subparallel lamination (interpreted as hummocky cross-stratification (HCS) and oscillation ripple laminated sand, alternating with silty or sandy mudstones. In restricted bays, estuarine central basins and lagoons, HCS is less common and/or more thinly bedded, but oscillation and combined flow ripples are typically abundant. Mixed sand and mud flats may display classical wavy, lenticular and pinstripe heterolithic bedding with current rippled sand beds, but in less markedly stressed examples such units may be pervasively bioturbated. Small-scale trough cross-bedded and current-rippled sands may also occur in some tidally generated lateral accretion bedding. Sediment deposition rates may be highly variable, and range from negligible to appreciable, though they are not normally rapid. As a result of reduced but not negligible energy levels, food supplies consist of both suspended and deposited components; either fraction may predominate locally, or the two may be intermixed. Characteristic organisms, therefore, include suspension and deposit feeders, as well as mobile carnivores and scavengers. In response to lowered energy and cohesive substrates and an abundance of deposited food, tracemakers tend to construct their burrows horizontally rather than vertically, although scattered vertical or steeply inclined burrows occur locally. Profusions of burrows may be present at stable, low-energy sites. Trails of epibenthic and endobenthic foragers may also be common and reflect the abundance, diversity, and accessibility of food (Fig. 4.5). Surface grazing is also commonly associated but does not dominate the suites.

The Cruziana Ichnofacies is characterized by: (1) a mixed association of horizontal, inclined, and vertical structures, many of them corresponding to permanent to semi-permanent dwellings; (2) structures constructed by mobile organisms; (3) generally high diversity and abundance; (4) predominance of deposit-feeding structures with subordinate grazing structures; and (5) common overprinting of deep-tier over shallow-tier structures during continued burial, locally leading to the preservation of composite structures and complex structures. The dominant Cruziana Ichnofacies elements comprise both deposit-feeding structures and permanent dwellings of inferred deposit feeders (see Table 4.2). These encompass a highly diverse group, and include Taenidium, Siphonichnus, Cylindrichnus, Rosselia (Fig. 4.5B), Teichichnus (Fig. 4.5F), Planolites, Rhizocorallium (Fig. 4.5G), Thalassinoides, Phoebichnus, Phycodes, Asterosoma (Figs. 4.5C,D,I), Chondrites (Fig. 4.5F–H), and Zoophycos (Fig. 4.5I), though this list is by no means exhaustive. Resting structures and surface trails associated with deposit feeding are also common and include such structures as Rusophycus, Cruziana, Lockeia, Gyrochorte, and numerous others. Significant numbers of grazing structures such as Helminthopsis and Phycosiphon (Fig. 4.5H,I) are common and pervasive, with less common Cosmorhaphe present locally. Passive carnivore structures such as Palaeophycus (Fig. 4.5I) and Schaubcylindrichnus may also be present. Permanent dwelling structures of inferred suspension-feeding and omnivorous tracemakers are generally uncommon, though in some successions they comprise significant elements to the suites. The main ichnogenera include Ophiomorpha, Diplocraterion, Arenicolites, and Skolithos. In shallow waters, periodic scour by storm waves and renewed deposition following their cessation may lead to tempestites incorporated within a succession of otherwise low-energy deposits (Pemberton and MacEachern, 1997). Development of hummocky crossstratification may involve the introduction of new sediment as well as the reworking of previously deposited sediment. Any of these conditions may yield burrow truncations and escape structures. Increased energy and allied parameters thus represent a temporary excursion of Skolithos-type conditions into an otherwise Cruziana-type setting. However, this overall bedding style differs from that of the main Skolithos Ichnofacies, in which stratification features, substrate scour, burrow truncations, and escape structures are contained entirely within discrete high-energy event beds, rather than persisting throughout the facies. Eventually, the storm beds are


overprinted with suites attributable to the Cruziana Ichnofacies.

Zoophycos Ichnofacies Of all recurring marine ichnofacies, the Zoophycos Ichnofacies is most debated and least understood. The ichnogenus Zoophycos has an extremely broad paleobathymetric range; hence its designation as name-bearer for a supposedly depth-related ichnofacies has long been controversial (see Kotake, 1991; and Uchman and Demı´rcan, 1999). In popular bathymetric schemes, the Zoophycos Ichnofacies is typically portrayed as an intermediary between the Cruziana and Nereites ichnofacies, at a position corresponding more or less to the continental slope. More specifically, the original designation placed it in flysch-molasse areas below wave base and free of turbidites, within a broad depositional gradient (Seilacher, 1967). As reevaluated (Seilacher, 1978; Frey and Seilacher, 1980), one of the major environmental controls represented by the ichnofacies is lowered oxygen levels, associated with organic debris accumulation in quiet-water settings. To some extent, these conditions do occur across the shelf-slope break, and thus the popularized bathymetric placement of the ichnofacies is commonly suitable. However, such reducing conditions replete with a dominance of Zoophycos are perhaps even better known in shallower water, epeiric deposits. The Zoophycos Ichnofacies (Fig. 4.6A, Table 4.2) is characterized by suites that display: (1) low diversity, although individual traces may be abundant; (2) predominance of grazing structures and feeding structures produced by deposit feeders; (3) both shallow- and deep-tier structures; and (4) horizontal to gently inclined, spreiten-bearing structures. Suites appear impoverished by comparison with distal expressions of the Cruziana Ichnofacies, and are dominated by Zoophycos (Figs. 4.6B–D), Helminthopsis (Fig. 4.6C), Phycosiphon (Figs. 4.6E–G), Cosmorhaphe (Fig. 4.6C), and Planolites (Figs. 4.6B,G), with lesser Chondrites, Thalassinoides (Figs. 4.6F,G), Scolicia (Figs. 4.6F, G), and Spirophyton (Figs. 4.6F). Considering the above characteristics of the ichnofacies, together with the widespread distribution of individual specimens of Zoophycos in both shallowand deep-water deposits (Frey et al., 1990; Olivero and Gaillard, 1996; Uchman and Demı´rcan, 1999), we speculate that Zoophycos-producing animals were simply broadly adapted in most ecologic respects. Some animals tolerated not only a considerable

65

range of water depths but also numerous substrate types, variable food resources, and different energy and oxygen levels. Their traces, therefore, appear in the Cruziana through Nereites ichnofacies (Crimes et al., 1981). Indeed, in final analysis, their tolerance may be their most distinguishing environmental characteristic. The animals were able to complete successfully with diverse tracemakers under Cruziana- and Nereites-type conditions, but few other animals were able to compete with them under the restricted conditions outlined above. Due to its singular prominence in many restricted settings, the association seems to warrant its own ichnofacies designation. Conversely, the less restrictive the environment at a given site, the less distinctive the ichnofacies is as a separate entity. In numerous places, the ichnofacies is hardly discernible in the broad transition from the Skolithos or Cruziana to the Nereites ichnofacies, especially on unstable ancient slopes originally subject to turbidity flows, or swept by shelf-edge or contour currents. Whatever the major environmental implications of the Zoophycos Ichnofacies and its variants, the final word is not yet in. The most important factors in the distribution of the animal, in addition to its own opportunism, evidently include water depth, depth of burrowing, sediment cohesiveness, and interstitial or bottom-water oxygen levels (Kotake, 1991; Olivero and Gaillard, 1996; Uchman and Demı´rcan, 1999; and Olivero, 2003). Stressed quiet-water environments, particularly those exhibiting anoxia, seem to be the primary common denominator, even though the animal itself was cosmopolitan.

Nereites Ichnofacies In most respects, bathymetric implications of the Nereites Ichnofacies (Fig. 4.7A, Table 4.2) are less equivocal than those of any other recurrent ichnofacies. Although numerous trace fossils otherwise typical of shallow-water deposits may range into deep-sea deposits, the reverse is not ordinarily true. In addition to water depth, turbidite deposition strongly influenced original environmental interpretations of the Nereites Ichnofacies. Despite this, depth- and energyrelated variables appear to be of greater importance than turbidite deposition per se (Crimes et al., 1981; Leszczyn´ski and Seilacher, 1991; Miller, 1993). For example, the ichncoenose persists today on distant abyssal plains essentially beyond the reach

66


A

Z

Z

Z

Z

Z P

Z

Z

Z

Z

H Z

B

C

D

Cr

Sc

Sc P

Sc Ch

As

Ph

Th

Sp Sc

Ph Th

E

F

G

FIGURE 4.6 The Zoophycos Ichnofacies. (A) Diagram of the Zoophycos Ichnofacies. Traces include Chondrites (Ch), Cosmorhaphe (Cr), Phycosiphon (Ph), Planolites (P), Scolicia (Sc), Spirophyton (Sp), Thalassinoides (Th), and Zoophycos (Z). (B) Abundant Zoophycos (Z) and Planolites (P), Upper Cretaceous Doe Creek Formation, Alberta. (C) Zoophycos (Z), Helminthopsis (H), and Cosmorhaphe (Cr) in shelf deposits, Upper Cretaceous, Northern North Sea, Norway. (D) Zoophycos (Z) structure from slope deposits of the Upper Cretaceous Cedar District Formation, British Columbia. (E) Abundant Phycosiphon (arrows) in a shelf diatomite, Miocene Monterey Formation, San Joaquin Basin, California. (F) Scolicia (Sc), Spirophyton (Sp), Chondrites (Ch), Phycosiphon (Ph), Thalassinoides (Th), and diminutive Asterosoma (As) in shelf deposits of the Upper Cretaceous Northern North Sea, Norway. (G) Scolicia (Sc), Planolites (P), Phycosiphon (Ph), and Thalassinoides (Th) from shelf deposits of the Upper Cretaceous San Miguel Formation, Texas.

67


B

Z

H

H Cr

Z C

A

D

E

F

G

Cr

FIGURE 4.7 The Nereites Ichnofacies. (A) Diagram of the Nereites Ichnofacies. Traces include Chondrites (Ch), Cosmorhaphe (Cr), Fustiglyphus (Fg), Helminthorhaphe (He), Lorenzinia (Lr), Nereites (Ne), Paleodictyon (Pd), Planolites, Scolicia (Sc), Spirodesmos (Sd), Spirophycus (Sh), Spirophyton (Sp), Spirorhaphe (Sr), Thalassinoides (Th), Urohelminthoida (Ur), and Zoophycos (Z). (B) Bedding plane of Scolicia (arrows), Upper Cretaceous Nanaimo Group, British Columbia. (C) Thin, muddy Zoophycos (Z), with Helminthopsis (H), and Cosmorhaphe (Cr), Upper Cretaceous, North Slope of Alaska. (D) Bedding plane entirely covered with Nereites, Eocene Zumaya Flysch, Spain. (E) Bedding plane with abundant Nereites, Eocene, Austria. (F) Paleodictyon cast on the sole of a thin turbidite bed, Eocene Zumaya Flysch, Spain. (G) Spirorhaphe cast on the sole of a thin turbidite bed, Eocene, Austria.

68


of turbidity currents, but is absent among welldeveloped, shallow-water turbidite successions. Nevertheless, most trace fossil suites attributable to the Nereites Ichnofacies studied to date occur in turbidite-rich successions, probably because the stratigraphic record of deep-water deposits examined in this context mainly represent subsiding basins or subduction zones, rather than the broad abyssal plain. Thus, associated sediments may consist of virtually any lithology, except that the ratio of sediment-gravity derived sand to hemipelagic or pelagic mud tends to diminish toward distal extremities of the deposit, and carbonates become increasingly scarce as the calcite compensation depth is approached. Bouma cycles or modified successions are common locally, and physical sedimentary structures may include flute, groove, and load casts as well as prod marks, flame structures, and linguoid or other current ripples. The Nereites Ichnofacies is characterized by: (1) high diversity but low abundance; (2) complex horizontal grazing traces and patterned feeding/dwelling structures; (3) numerous crawling/grazing traces and sinuous fecal castings; and (4) structures produced by deposit feeders, scavengers, or possibly harvesters (i.e., agrichnia). Animals exploiting lower bathyal to abyssal environments have two principal concerns: (1) scarcity of food, relative to more abundant supplies in shallower settings, and (2) periodic disruption by strong, down-canyon bottom currents or actual turbidity currents. In response to the latter factor, and over long spans of geologic time, the overall community ultimately developed two component parts: pre-turbidite and post-turbidite associations, as documented by their respective traces (Leszczyn´ski and Seilacher, 1991; Miller, 1993). The pre-turbidite resident association is characteristic of quiet, normal conditions and is dominant wherever the substrate is free of the influence of turbidity currents. It tends to be overwhelmed or eliminated by severe erosion or turbulence, however, and is replaced by the postturbidite association after cessation of the turbidity current. As conditions then revert to the normal, prevailing low-energy setting, the pre-turbidite association gradually reestablishes itself. Pre-turbidite animals thus comprise a stable, persistent community, well adapted to quiet conditions, derived mainly from original early-Paleozoic colonizers of the deep-sea floor. In contrast, post-turbidite animals represent a more opportunistic, less stable community better adapted to turbidite colonization, derived mainly from subsequent evolutionary immigrants from shallower waters (Frey and Seilacher, 1980).

In addition to pre- and post-turbidite associations, numerous turbidites display ichnologic gradients along depositional dips, particularly where they are related to submarine fan development (Crimes et al., 1981). Where strong bottom currents issue from submarine canyons or flow along submarine fan channels, components of the Skolithos Ichnofacies may be present (e.g., Ophiomorpha and Diplocraterion). Otherwise, proximal parts of turbidites may be characterized by rosetted or radiating traces (e.g., Lorenzinia, Spirorhaphe (Fig. 4.7G), Spirophycus, and Zoophycos (Fig. 4.7C)), as well as gently meandering forms of Scolicia (Fig. 4.7B). Medial areas of deep-sea fans may be indicated by spiraled or tightly meandering traces (e.g., Helminthorhaphe, Urohelminthoida, and Cosmorhaphe (Fig. 4.7C)), while patterned networks typify distal regions (e.g., Nereites (Figs. 4.7D,E), Paleodictyon (Fig. 4.7F), Paleomeandron, and Fustiglyphus) although other traces are generally present as well. Zoophycos is common locally in various settings, but it tends to be multi-lobed, and in places is more complex than in the Zoophycos Ichnofacies (cf. Savary et al., 2004). Finally, the Nereites Ichnofacies is recognized in Deep Sea Drilling Cores, within unconsolidated, finegrained sediments, including distal turbidites and pelagic rhythmites of modern ocean basins. However, the association per se, if present, tends not to be preserved on great expanses of abyssal plain, where sedimentation and bioturbation are more or less constant, rather than episodic (Scholle et al., 1983).

SUBSTRATE-CONTROLLED ICHNOFACIES The ichnofacies paradigm recognizes three substrate-controlled ichnofacies: Glossifungites, Teredolites and Trypanites (Table 4.3). Each ichnofacies reflects different substrate consistencies at the time of colonization, and so, intuitively reflect palimpsest suites that typically cross-cut the original suites. In many examples, these ichnofacies are associated with erosionally exhumed discontinuities in the rock record, though scenarios favoring autocyclic development are also locally common (see MacEachern et al., Chapter 7). In the case of the Glossifungites Ichnofacies, firmground suites may be intergradational with palimpsest softground suites, particularly where substrates pass from muddy to sandy; burial compaction may lead to firm or stiff mud, but allow sands to retain their non-cohesive character. Likewise, trace suites attributable to the Glossifungites Ichnofacies may

SUBSTRATE-CONTROLLED ICHNOFACIES

69

TABLE 4.3 Recurring Archetypal Substrate-Controlled Trace Fossil Associations and their Common (but not exclusive) Environmental Implications (Adapted from Pemberton et al., 2001) Characteristic Trace Fossils

Typical Benthic Environment Glossifungites Ichnofacies (firm substrates)

Vertical cylindrical, U-, or tear-shaped borings, or sparsely to

Firm but unlithified marine littoral and sublittoral omission

densely ramified dwelling burrows, or various mixtures of burrows and borings. Protrusive spreiten in some U-shaped burrows,

surfaces, especially semiconsolidated carbonate firmgrounds or stable, cohesive, partially dewatered muddy substrates either in

developed mostly through growth of animals (fan-shaped

protected, moderate-energy settings or in areas of somewhat higher

Rhizocorallium and Diplocraterion, formerly Glossifungites). Many

energy where semiconsolidated micritic or siliciclastic substrates

intertidal species (e.g., crabs) leave the burrows to feed; others are

offer resistance to erosion. The final sedimentary record typically

mainly suspension feeders. Diversity is typically low, yet given

consists of a mixture of relict and palimpsest features, including

kinds of structures may be abundant. Unlike ichnogenera of the

cross-cutting ichnofaunas.

Trypanites Ichnofacies, those of Glossifungites tend to avoid obstructions within the substrate. Teredolites Ichnofacies (xylic substrates) Sparse to profuse clavate (shipworm) borings. Dense excavations

Resistant substrates consisting of driftwood pavements, peat

may be deformed but ordinarily do not interpene trate. Boring walls

deposits, or related xylic substances, many of which appear as

may be ornamented with the texture of the host substrate (e.g., tree-

lignite or coal in the rock record. May represent omission surfaces

ring xenoglyphs). Stumpy to elongate, subcylindrical, subparallel

developed on matted wood clasts, log jams, or other xylic materials

excavations predominate in marine or marginal marine settings.

(but not single clasts or trunks), or slow deposition in marshy or

Shallower, sparse to profuse nonclavate etchings (isopod borings)

swampy areas of peat accumulation. Most common in estuarine,

typify freshwater ichnofaunas.

deltaic, or various backbarrier environments. Trypanites Ichnofacies (hard substrates)

Cylindrical to vase-, tear-, or U-shaped to irregular domiciles of

Consolidated marine littoral and sublittoral omission surfaces

endolithos, oriented normal to the respective substrate surface, or

(rocky coasts, beachrock, hardgrounds), reefs, or particulate strata

shallow anastomosing systems of borings (sponges, bryozoans);

formed of organic constituents (bone beds, shell beds, coquinites,

excavated mainly by suspension feeders or passive carnivores.

but not individual bones, shells, or clasts). Bioerosion is as

Raspings and gnawings of algal grazers and equivalent organisms

important as (and serves to accelerate), physical erosion of the

(chitons, limpets, echinoids mainly). Diversity moderately low,

substrate. Intergradational with the Glossifungites Ichnofacies; in

although borings or scrapings of given kinds may be abundant. In particulate lithic substrates, margins of borings cut through grains

sequential hardground development, suites of the Trypanites Ichnofacies may crosscut earlier suites of the Glossifungites or

or shells instead of skirting them.

Cruziana ichnofacies.

be intergradational with hardground suites of the Trypanites Ichnofacies, where differential compaction and/or cementation occur (e.g., Bromley, 1975, 1996). The Teredolites Ichnofacies is somewhat more problematic in this grouping, as the consistency of the substrate may or may not fundamentally change prior to colonization. Some woodground suites correspond to the colonization of the xylic substrate prior to coalification, and this is particularly apparent in modern ichnocoenoses of Willapa Bay (Gingras et al., 2004). Some, however, are associated with erosional discontinuities that have ‘bottomed-out’ on a coal seam (presumably xylic material coalified prior to exhumation) (e.g., Bromley et al., 1984). The anomalous nature of a xylic medium for endobenthic colonization probably justifies its inclusion with these other ‘substrate-controlled’ ichnofacies, though it is somewhat distinct from the progressive change in

original substrate consistency exhibited from softground through firmground and into hardground scenarios.

Glossifungites Ichnofacies The Glossifungites Ichnofacies (Fig. 4.8A, Table 4.3) is characteristic of firm but unlithified substrates, such as dewatered muds, though less commonly incipiently cemented sands may also host the firmground ichnogenera. In most siliciclastic settings, trace suites attributable to the Glossifungites Ichnofacies constitute the most widespread and pervasive expression of the substrate-specific suites. These demarcate a number of discontinuities of both sequence stratigraphic importance (e.g., sequence boundaries, transgressive surfaces of erosion, and amalgamated sequence

70


A

B

C

D

F

E

Sk

Rh Th

Th Th

G

Th

H

FIGURE 4.8 The Glossifungites Ichnofacies. (A) Diagram of the Glossifungites Ichnofacies. Firmground ichnogenera include Skolithos (S), Gastrochaenolites (G), Arenicolites (A), Diplocraterion (D), Psilonichnus (Ps), Conichnus (C), Bergaueria (B), Palaeophycus (P), Taenidium (Ta), Rhizocorallium (Rh), Thalassinoides (Th), Chondrites (Ch), and Zoophycos (Z). (B) Firmground Skolithos crosscutting offshore mudstone and subtending from an amalgamated sequence boundary and flooding surface, Lower Cretaceous Viking Formation, Alberta. (C) Firmground Arenicolites filled with coarse-grained sandstone, associated with a transgressive surface of erosion, Lower Cretaceous Viking Formation, Alberta. (D) Firmground Thalassinoides subtending from an incised valley complex, Upper Cretaceous Dunvegan Formation, Alberta. (E) Firmground Rhizocorallium subtending from the base of an estuarine incised valley complex, Lower Cretaceous Viking Formation, Alberta. (F) Firmground Diplocraterion associated with a transgressive surface of erosion, Jurassic Gravelburg Formation, Saskatchewan. (G) Submarine canyon margin with a firmground suite of Thalassinoides (Th), and Skolithos (Sk), lower Miocene Nihotupu and Tirikohua formations, Northland, New Zealand. (H) Firmground Rhizocorallium (Rh) and Thalassinoides (Th) demarcating the same discontinuity as shown in (G).


boundaries and flooding surfaces) and autocyclic derivation (e.g., cut-bank margins of tidal channels, periodically exposed intertidal flats, etc.). The sequence stratigraphic significance of the Glossifungites Ichnofacies has been addressed by Savrda (1991a), MacEachern et al. (1992), Pemberton and MacEachern (1995, 2005), Pemberton et al. (2004) and MacEachern et al. (this volume). Firmground ichnogenera are dominated by vertical to subvertical dwelling structures of suspension-feeding organisms (Figs. 4.8B–F). The most common structures correspond to the ichnogenera Diplocraterion (Fig. 4.8F), Skolithos (Figs. 4.8B,G), Psilonichnus, Arenicolites (Fig. 4.8C) Conichnus, Bergaueria, and firmground expressions of Gastrochaenolites. Dwelling structures of inferred deposit-feeding organisms are also constituents of the ichnofacies, and include firmground Thalassinoides (Figs. 4.8D,G,H), Spongeliomorpha, Taenidium, Palaeophycus, Chondrites, and Rhizocorallium (Figs. 4.8E,H). More recently, Zoophycos has been recognized to occur within firmground suites (MacEachern and Burton, 2000). The presence of vertical shafts within shaly intervals is anomalous, as these structures are not capable of being maintained in soft muddy substrates. Glossifungites elements are typically robust, commonly penetrating 20–100 cm below the bed junction. Many shafts tend to be of large diameter (e.g., 0.5–1.5 cm), particularly Diplocraterion habichi and Arenicolites. This scale of burrowing contrasts markedly with the predominantly horizontal and diminutive trace fossils typical of shaly intervals. Firmground traces are also generally sharp-walled and unlined, locally with scratch-marked margins, reflecting the stiff, cohesive nature of the substrate at the time of colonization and burrow excavation. Further evidence of substrate stability, atypical of soft muddy beds, is the passive nature of burrow fill. This demonstrates that the structure remained open after the trace-maker vacated the domicile, thus allowing material from subsequent depositional events to be piped into the open burrow. The post-depositional origin of trace fossil suites attributable to the Glossifungites Ichnofacies is clearly demonstrated by the ubiquitous cross-cutting relationships with the previous softground assemblages. The final characteristic of the firmground suites is their tendency to demonstrate colonization in large numbers. In numerous examples, seven to fifteen firmground traces, most commonly Diplocraterion habichi, have been observed on the bedding plane of

71

a 9 cm (3.5 inch) diameter core, corresponding to a density between 1100 and 2300 shafts per m2.

Teredolites Ichnofacies The Teredolites Ichnofacies (Fig. 4.9A, Table 4.3) encompasses suites of borings excavated into xylic (woody or coaly) substrates (Bromley et al., 1984; Savrda, 1991b). It is critical to identify whether the woodground borings were excavated into an in situ xylic horizon (i.e., reflecting a substrate) or allochthonous (e.g., transported logs in coastal or marine environments). Savrda et al. (1993) applied the term ‘log-grounds’ to high concentrations of allochthonous wood strewn across a depositional surface. Only traces excavated into an in situ substrate, or bored into an allochthonous log-ground after log deposition constitute the Teredolites Ichnofacies (cf., Pemberton et al., 2001; MacEachern et al., Chapter 7). Isolated logs containing wood borings do not constitute the Teredolites Ichnofacies. Log-grounds consisting of logs bored prior to emplacement may form useful mappable horizons but do not constitute the ichnofacies, because the borings do not record colonization of a continuous substrate. Determining the timing of wood boring in such log-grounds may prove challenging. The Teredolites Ichnofacies, as described from the rock record, is probably confined to marine and marginal marine settings. The principal namesake, Teredolites, reflects the borings of wood-boring bivalves (Fig. 4.9C), which in the present day only occur in fully marine to slightly salinity-reduced environments. The presence of the ichnogenera Teredolites (Figs. 4.9B–E,G), Thalassinoides (Fig. 4.9F), and Diplocraterion excavated into xylic material is taken, therefore, to indicate largely marine conditions. Non-marine wood borings do occur, but these are predominantly insect generated and lack marine ichnogenera. Hasiotis (2002) provides a good summary of the characteristics of terrestrial wood borings. Most rock-record occurrences of woodgrounds display a low diversity of trace fossils (e.g., Bromley et al., 1984; Savrda, 1991b; Savrda et al., 1993). These low-diversity suites are dominated by penetrative borings attributable to Teredolites longissimus and Teredolites clavatus. Woodground trace suites are commonly monospecific, however, sizeclass variations have been observed in some of the boring assemblages (e.g., Bromley et al., 1984; Savrda et al., 1993). Modern wood-boring occurrences in the marine realm show higher diversities

72


Teredolites

C D

A E

B

Th Th

F

G

FIGURE 4.9 The Teredolites Ichnofacies. (A) Diagram of the Teredolites Ichnofacies (artwork by Tom Saunders). (B) Teredolites clavatus (white arrow) in peat horizon, truncated by mud-filled channel (black arrow), Upper Cretaceous Horseshoe Canyon Formation, Drumheller. (C) The wood-boring bivalve Martesia sp. at the base of the Teredolites clavatus depicted in (B) and (D). (D) Teredolites clovatus from the horizon depicted in (B) and (C). (E) Siderite-cemented Teredolites clavatus, Upper Cretaceous Horseshoe Canyon Formation, Drumheller. (F) Woodground Thalassinoides (Th), at the base of a tidal channel excavated into coal, Upper Cretaceous Ferron Sandstone, Utah. (G) Teredolites (arrows) excavated into lignitic coal, Lower Cretaceous Grand Rapids Formation, Alberta.


73

Entobia

B

Trypanites Gastrochaenolites

A C

D

E FIGURE 4.10 The Trypanites Ichnofacies. (A) Diagram of the Trypanites Ichnofacies (artwork by Tom Saunders). (B) Entobia in carbonate, Oligocene–Miocene Bluff Formation, Grand Cayman Island. (C) Gastrochaneolites with in situ bivalves (Zirfaea pilsbyri), excavated into Triassic sandstones along the margin of the Bay of Fundy, Economy, Nova Scotia. (D),(E) Trypanites excavated into carbonate hardground, marking the Silurian–Devonian disconformity, southern Ontario.

than generally recorded from the rock record (Gingras et al., 2004).

The Trypanites Ichnofacies The Trypanites Ichnofacies (Fig. 4.10A, Table 4.3) is characteristic of fully lithified marine substrates such as reefs, hardgrounds, rocky coasts, beach rock, unconformities, and other omission surfaces. As in the case of the Teredolites Ichnofacies, the concept does not apply to borings in individual shells, bones, and

clasts. Bromley and Asgaard (1993) erected the ‘Entobia Ichnofacies’ and the ‘Gnathichnus Ichnofacies’ to either serve as subsets of the Trypanites Ichnofacies, or as its replacement. In reality, these new additions are closely associated with tiers. The ‘Entobia Ichnofacies’ is broadly similar to the Trypanites Ichnofacies, in that it corresponds to long-term bioerosion of a lithified surface (typically carbonate), with little or no contemporaneous sedimentation, allowing deep-tier dwelling structures to be excavated and maintained, and superficial borings to be obliterated. The ‘Gnathichnus Ichnofacies’

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encompasses ichnocoenoses associated with predominantly surficial bioerosion structures, but predominantly on isolated clasts, or skeletons. Such structures do not form continuous mappable surfaces, and do not correspond to the classical meaning of the word ‘facies.’ We suggest that Trypanites better serves as the ichnofacies while Entobia and Gnathichnus serve as expressions of the ichnocoenoses that characterize the ichnofacies as a whole. Suites attributable to the Trypanites Ichnofacies consist of sharp-walled, unlined, cylindrical, vase- and tear-shaped domiciles (e.g., Trypanites, (Figs. 4.10D,E), Gastrochaenolites (Fig. 4.10C), and Ubiglobites), irregular dwellings (e.g., Entobia, Fig. 4.10B), irregular pits or borings formed by barnacles (e.g., Rogerella), shallow anastomose systems excavated by sponges, bryozoans, suspension feeders, or passive carnivores, and/or raspings and gnawings of algal grazers such as echinoids, chitons, or limpets. Golubic et al. (1984) described a number of microbial endolithic borings that may also be associated. Borings are distinctive, in that they cut through shells or grains, and are commonly oriented normal to the substrate. Suites attributable to the Trypanites Ichnofacies are commonly intergradational with those of the Glossifungites Ichnofacies, and may crosscut former softground and firmground suites (Bromley, 1975, 1996). Suites commonly show moderately low diversities, though trace abundances may be high.

USING THE ICHNOFACIES PARADIGM We have asserted that ichnofacies serve as theoretical constructs, based on numerous case studies that demonstrate global and temporal recurrence. We have maintained that these formally defined ichnofacies record particular environmental conditions. As in formal, physically based facies models (e.g., Walker and James, 1992; Reading, 1996), the ichnofacies serve as models for evaluating discrete trace suites (MacEachern and Pemberton, 1992; Pemberton et al., 1992), a point echoed by Genise et al. (2000) in their analysis of the ichnofacies paradigm for the continental regime. In practice, the trace fossil suites are identified from the rock record and integrated with all aspects of the physical sedimentology, and with as many other lines of evidence as considered reasonable for the scope and limitations of the study. The trace suites are then evaluated in the context of various environmental factors and attributed to the relevant ichnofacies.

The generalized character of the ichnofacies, in contrast to the detailed information of the suite, has led many to erroneously conclude that the ichnofacies are too broad to yield precise paleoenvironmental interpretations. McIlroy (2004) has suggested that ichnofacies may serve as a starting point, but that otherwise, ichnology has outgrown the concept. In contrast, to turn a phrase of Walker (1992), it is the generality embodied by the ichnofacies, as opposed to the summary of one particular case study, that enables the ichnofacies concept to serve its most valuable functions. Like facies models, the ichnofacies paradigm serves three main functions for ichnological analysis: (1) It acts as a norm for the purposes of comparison. The ichnofacies comprises the features shared by all suites attributable to the ichnofacies. Any individual suite need not contain all the ichnogenera characteristic of the ichnofacies, nor even the namesake element. Rather, it must contain traces that are consistent with the ethological grouping that defines the ichnofacies–it is what all suites, regardless of age and locality, have in common. Archetypal ichnofacies, by acting as a norm for comparison, allows new trace suites to be compared–does the new suite meet the criteria for inclusion within a particular ichnofacies? It also allows one to recognize departures from the archetypal expressions of the ichnofacies, permitting the identification of depositional stresses in the setting. Such stresses may indicate deltaic sedimentation (e.g., Gingras et al., 1998; MacEachern et al., 2005), or brackish-water accumulation (e.g., Beynon and Pemberton, 1992; MacEachern and Pemberton, 1994; Gingras et al., 1999; Bann et al., 2004; MacEachern and Gingras, in press). Without this norm for comparison, one cannot determine whether a new ichnocoenose contains any unusual or anomalous characteristics. (2) The ichnofacies concept acts as a framework or guide for future observations. Sand-prone marine successions tend to carry the Skolithos Ichnofacies. When the ichnologist is working in such units, mental search criteria are erected. The ichnologist working in sandy successions therefore knows that most elements of the suite tend to be vertical dwellings, branching dwellings, escape or equilibrium-adjustment structures, and lined horizontal dwellings, many of them exceedingly subtle in well-sorted sandstones. (3) The ichnofacies concept serves as a predictor in new situations. The paradigm erected by

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ACKNOWLEDGEMENTS

Seilacher demonstrates that the various ichnofacies correspond to different but predictable combinations of environmental parameters. In a simple shoreline to basinal shoreline profile, these parameters tend to change progressively, according to a predictable distribution of ichnofacies. The Skolithos Ichnofacies, for example, corresponds to high-energy, shifting particulate substrates, generally in marine water. The Cruziana Ichnofacies records lower energy, generally more cohesive substrates, with mainly suspended sediment accumulation. We may then, reasonably, consider that if we have a locality with suites attributable to the Skolithos Ichnofacies, and the other facies indicators are consistent with an open marine, upper shoreface environment, then by moving in a more distal direction, we would expect to encounter mudprone, open marine facies carrying suites attributable to the Cruziana Ichnofacies. Having done so, we can, with even greater confidence predict the presence of the Zoophycos Ichnofacies and of shelf-like conditions further basinward. Alternatively, should we move in what we believed to be the seaward direction, but encounter sand-prone environments with trace suites corresponding to the Psilonichnus Ichnofacies, then we can predict that we have erred in our reconstruction of the paleogeography. In reality, the role of ichnofacies as a predictor is far more complex than this simple example suggests. A physical facies model displays a fourth use: it may act as an integrated basis for interpretation of the system that it represents. Such a use is achieved once the model is fully mature, and is based on the combined features of many case studies. The turbidite model, for example, has reached this level: it has a hydrodynamic basis for interpretation of the event beds, based on many thousands of occurences. The ichnofacies concept is starting to approach this use, owing to the continued clarification of the environmental parameters that constrain the faunal behaviors and the types and diversities of the resulting ichnogenera. Such process-based ichnofacies analyses are not far off (e.g., MacEachern et al., 2005). The Skolithos and Cruziana ichnofacies, for example, are particularly well poised to move into this arena, because of the great abundance of shallow marine successions that have been studied. Once a suite is identified to be attributable to a particular ichnofacies, a particular grouping of paleoenvironmental characteristics are indicated. A suite attributable to the

Skolithos Ichnofacies reflects persistent, high-energy deposition, shifting substrates, and clean (nonturbid) marine water. No matter what particular depositional environment is ultimately determined for the facies, it must embrace these physico-chemical parameters. The ichnofacies paradigm comprises the unifying framework within which ichnological observations can be accurately interpreted in a depositional context. Rather than outgrowing the ichnofacies paradigm, it continues to operate as the solid underpinning of the entire science, and will continue to facilitate high-resolution paleoenvironmental interpretations of the rock record.

ACKNOWLEDGEMENTS The authors would also like to thank the Natural Science and Engineering Research Council of Canada (NSERC) for research funding; Discovery Grant 184293 to J.A. MacEachern, Operating Grant No. A0816 to S.G. Pemberton; and Discovery Grant (PRG) No. 238530-03 to M.K. Gingras. Pemberton would like to thank the Canada Research Chairs program for their support of his research. The authors wish to thank Davide Olivero for his constructive review of this manuscript.

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Palaeoenvironmental and Stratigraphic Analysis, Geological Society, London, UK, Special Publication, 228, pp. 355–382. Gingras, M.K., MacEachern, J.A. and Pemberton, S.G. (1998). A comparative analysis of the ichnology of wave- and river-dominated allomembers of the Upper Cretaceous Dunvegan Formation. Bulletin of Canadian Petroleum Geology, 46, 51–73. Gingras, M.K., MacEachern, J.A. and Pickerill, R.K. (2004). Modern perspectives on the Teredolites Ichnofacies: observations from Willapa Bay, Washington. Palaios, 19, 79–88. Gingras, M.K., Pemberton, S.G., Saunders, T. and Clifton, H.E. (1999). The ichnology of brackish water Pleistocene deposits at Willapa Bay, Washington: variability in estuarine settings. Palaios, 14, 352–374. Golubic, S., Campbell, S.E., Drobne, K., Cameron, B., Balsam, W.L., Cimerman, F. and DuBois, L. (1984). Microbial endoliths: a benthic overprint in the sedimentary record, and a paleobathymetric cross-reference with foraminifera. In: Miller, M.F., Ekdale, A.A. and Picard, M.D. (Eds.), Trace Fossils and Paleoenvironments: Marine Carbonate, Marginal Marine Terrigenous and Continental Terrigenous Settings, Journal of Paleontology, 58, 351–361. Goldring, R. (1993). Ichnofacies and facies interpretation. Palaios, 8, 403–405. Hasiotis S.T. (2002). Continental Trace Fossils. Society of Economic Paleontologists and Mineralogists, Short Course, Notes No. 51, Tulsa, Oklahoma, 132 pp. Kern, J.P. and Warme, J.E. (1974). Trace fossils and bathymetry of the Upper Cretaceous Point Loma Formation, San Diego, California. Geological Society of America Bulletin, 85, 893–900. Kotake, N. (1991). Non-selective surface deposit feeding by the Zoophycos producers. Lethaia, 24, 379–385. Leszczyn´ski, S. and Seilacher, A. (1991). Ichnocoenoses of a turbidite sole. Ichnos, 1, 293–303. MacEachern, J.A. and Burton, J.A. (2000). Firmground Zoophycos in the Lower Cretaceous Viking Formation, Alberta: a distal expression of the Glossifungites Ichnofacies. Palaios, 15, 387–398. MacEachern, J.A. and Gingras, M.K. (in press). Recognition of brackish-water trace fossil assemblages in the Cretaceous Western Interior Seaway of Alberta. In: Bromley, R., Buatois, L.A., Mańgano, M.G., Genise, J. and Melchor, R. (Eds.), SedimentOrganism Interactions: A Multifacetted Ichnology, Society of Economic Paleontologists and Mineralogists, Tulsa, OK, Special Publication 88. MacEachern, J.A. and Pemberton, S.G. (1992). Ichnological aspects of Cretaceous shoreface successions and shoreface variability in the Western Interior Seaway of North America. In: Pemberton, S.G. (Ed.), Applications of Ichnology to Petroleum Exploration, A Core Workshop, Society of Economic Paleontologists and Mineralogists, Tulsa, OK, Core Workshop, 17, pp. 57–84. MacEachern, J.A. and Pemberton, S.G. (1994). Ichnological character of incised valley fill systems from the Viking Formation of the Western Canada Sedimentary Basin, Alberta, Canada. In: Dalrymple, R., Boyd, R. and Zaitlin, B. (Eds.), Incised-Valley Systems: Origin and Sedimentary Sequences, Society of Economic Paleontologists and Mineralogists, Tulsa, OK, Special Publication, 51, pp. 129–157. MacEachern, J.A., Raychaudhuri, I. and Pemberton, S.G. (1992). Stratigraphic applications of the Glossifungites ichnofacies: delineating discontinuities in the rock record. In: Pemberton, S.G. (Ed.), Applications of Ichnology to Petroleum Exploration, A Core Workshop, Society of Economic Paleontologists and Mineralogists, Tulsa, OK, Core Workshop, 17, pp. 169–198.

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S E C T I O N II

CONCEPTS, METHODS, THEORY, AND CONNECTIONS TO THE EARTH AND BIOLOGIC SCIENCES

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5 What’s in a Name? Nomenclature, Systematics, Ichnotaxonomy Markus Bertling

is best referred to Pickerill (1994), who touched upon some of the attached problems. Against this background it will not be necessary to repeat the contents of these articles; rather, new perspectives on old problems are offered here. The aim of this largely theoretical contribution is twofold: first, to point out the present framework for naming trace fossils, strictly distinguishing between nomenclature and taxonomy, and including an accentuated review of inherited problems. The target group of the related sections are mostly, but not exclusively, readers with limited personal experience in the treatment of trace fossil names. Second, the succeeding chapters suggest future guidelines to avoid the problems which hitherto have just been described at best. In order to overcome existing problems, some of these guidelines have to question generally accepted procedures for naming trace fossils. The suggestions are intended to stimulate discussions among experienced colleagues who feel uncomfortable with their science as it consists of many individual cases, which are not rooted within a theoretical framework.

SUMMARY : Trace fossil diagnoses are subject to the principles of ichnotaxonomy, which seemingly lacks a standardized theoretical basis. The existing problems of this science, such as insufficient diagnoses of ichnotaxa or inadequate ichnotaxobases for newly introduced trace fossil names, are classified and solutions are suggested. A plea is made for a comprehensive two-level approach: similar trace fossils should have identical ichnotaxobases, and a universally acceptable framework of morphologybased ichnotaxobases should be sought. In both cases, a hierarchically organized system containing only geometrical criteria and principal types of substrate should be pursued. Biological affinity of trace makers, spatio-temporal distribution and other extrinsic factors, as well as inferences about the behaviour of the producers of trace fossils are to be avoided as criteria in ichnotaxonomy.

INTRODUCTION Scope of this Chapter Nomenclature, systematics and taxonomy are frequently confounded, adding to a widespread uncertainty about how to treat biological and trace fossil names. This chapter tries to explain the demarcation of the three related fields. The principles of naming trace fossils have been the subject of several major papers (Bromley, 1990; Magwood, 1992; Pickerill, 1994). For a comprehensive review of established taxonomic and nomenclatural procedures, the reader

Names of Trace Fossils and Other Things Any object is best remembered if it bears a name, and communication about objects is very difficult without names—that is why we have language. The names of daily-life objects are learned by small children quickly, because it is easy to discern a limited number of objects belonging to a certain group.


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5. WHAT’S IN A NAME? NOMENCLATURE, SYSTEMATICS, ICHNOTAXONOMY

Furniture or farm animals are good examples, for such groups generally contain hardly more than a dozen names. The situation is more difficult in systems with hundreds or more similar objects. It can be expected that their distinction sometimes is slight, which would call for many words if labelled descriptively. For this reason, a formalized identification system for such groups is almost inevitable. One way to establish such a system is to use numbers and bar codes such as those found on sales goods for computers to identify them. This makes these objects unique in their identification, but it hampers human, language-based communication about them. A different approach is established for biological objects, which are identified by names with a genus and species component in many languages. For universal scientific identification, that system using Latin or latinized words has worked well for more than 250 years. The names for higher biological entities, abstract levels such as family or phylum, are constructed in a similar manner. Altogether, from species to kingdom, they are called biotaxa. In essence, all of them are just more or less euphonic letter codes which need not have any intrinsic meaning. Trace fossils are not biological objects in a strict sense. In many cases, trace fossils directly reflect substrate conditions, putting them close to primary sedimentary structures. These are not very numerous and thus are named in a descriptive way. The dual nature of trace fossils as both fossils and sedimentary structures opens both options of naming: descriptively like sedimentary structures or encoded by Latin names like biotaxa. Historical development has made this decision easy because the first describers of trace fossils in the nineteenth century usually mistook them for plant body fossils, and consequently they applied the naming system of botany. In due course, this has resulted in their inclusion in the juristic set for living objects, so-called biological nomenclature. When subsequently the true nature of those trace fossils became apparent, they were transferred from botanical to zoological nomenclature, because they were recognized as animal-produced structures.

TREATING NAMES OF TRACE FOSSILS: NOMENCLATURE The highly formalized International Code of Zoological Nomenclature (ICZN, 1999 in its fourth edition) recognizes trace fossils made by all kinds of organisms as objects of its ruling. This means that trace fossils not only of animal origin but also of plants,

fungi, and microorganisms as well are to be considered in exactly the same way as animal taxa when it comes to deciding about the availability and validity of their names. They are not true biotaxa, so they are called ichnotaxa in order to properly demarcate them. Ichnologists are satisfied with this situation usually, because it has two major nomenclatural implications: first, all trace fossil names are treated uniformly. Second, no change will occur if knowledge about the suspected producer of a trace improves and changes the interpretation, for example, from fungal to animal. The only serious alternative to the ICZN would be a separate code for trace fossil nomenclature, as proposed by Sarjeant and Kennedy (1973). Such an independent trace fossil code has never gained acceptance. Treating ichnotaxa within the framework of zoological nomenclature has two other important effects. First, organisms and their traces must be kept apart in their names. This is because zoologists do not wish to rename an animal if it is discovered that its burrow or faeces were described before the animal itself was named. Even if some borings especially of small organisms perfectly represent their outer shape, they do not contain organs and hence must be given separate names. As an explanation, consider an individual dinosaur: it belongs to a single biotaxon, but it may produce several different ichnotaxa as it walks, sits, wallows or digs a nest. The second effect is born out of the logical consequence of this approach. The zoological code does not allow inclusion of ichnotaxa in any biological category. For example, consider a track preserved in such detail that it can be ascribed to a certain family of dinosaurs as its producer. The name of this track does not belong to the family of dinosaurs, because the former is an ichnotaxon, the latter is a biotaxon, and both fields must not overlap. Clarity about the formal position of trace fossil names, however, only means clarity how to formally handle established names as such—it does not give hints about how to name specific trace fossils or how to distinguish them. This is because nomenclature is not a science; it is just a jurisdiction to be applied in doubtful cases. Thus, the ICZN is concerned with specific procedures regarding the currently appropriate names, synonymy, homonymy, etc.

CLASSIFYING TRACE FOSSILS: SYSTEMATICS The goal of the ICZN is not to try to find the most scientifically meaningful grouping of traces either;

NAMING TRACE FOSSILS: ICHNOTAXONOMY

this is the role of systematic ichnology, a science with opinions and with interpretations that can be expected to vary through time. This field has received very little attention as yet; systematic grouping of trace fossils has only sporadically been extended above the genus level (e.g., Vyalou, 1972; Rindsberg, 1990). The ICZN (1999) explicitly encompasses ichno-families, but currently this systematic hierarchy only contains isolated taxa. Not all of them have been introduced by their authors with the intention to establish formal ichnotaxa, but nonetheless most are valid and available. The apparent lack of formal systematic hierarchies for trace fossils above the genus level mirrors the logical gaps in the system to name them. Even informal groups as proposed by Simpson (1975) or Ksia˛zˇkiewicz (1977) have not received the elaboration they may have deserved. Ekdale and Lamond (2003) have offered a promising approach to overcome this situation by introducing ideas of cladistic analysis to trace fossil taxonomy, even though their main aim (reconstructing evolutionary pathways) differs from the one pursued here. Extending the ordering scheme of trace fossils to suprageneric levels will help to structure the wealth of forms, even if many ichnotaxa will be hard to classify. It is far beyond the scope of this chapter, however, to suggest a framework of ichnotaxa above the genus level, let alone to discuss the usefulness of suprafamiliar ichnotaxa, which are not covered by the ICZN anyway. Systematics has an intimate contact with taxonomy (Fig. 5.1). This science searches for characters that are meaningful and useful in the distinction of a

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group of objects. This group of objects may be a genus, a family or a higher-ranking level, i.e., order, class, phylum or regnum (all with subdivisions). Systematicists define a group of objects based on the information given by taxonomists, who identify characters common to these objects. At the same time, other criteria will be used to exclude other objects from this group; they may form a different group at the same systematic level. Working this way implies constant feedback from taxonomy and vice versa in order to achieve the most consistent and comprehensive way to classify and to name objects.

NAMING TRACE FOSSILS: ICHNOTAXONOMY Ichnotaxobases: Introduction Taxonomy looks for meaningful taxobases to be applied in the description and identification of objects. In the case of trace fossils, it is called ichnotaxonomy, and it attempts to establish and apply the specific criteria for naming trace fossils, the so-called ichnotaxobases (Bromley, 1990). As a consequence of the nomenclatural position of trace fossil names, taxobases for organisms and trace fossils should be separated as well. This means that biological taxobases should not be used to distinguish trace fossils. They may be evaluated, however, when striving for the most suitable ichnotaxobases. Acknowledging these criteria will help understand

FIGURE 5.1 Relationship of the sciences of taxonomy and systematics; note the absence of names, as they are dealt with exclusively by the legal rules of nomenclature.

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FIGURE 5.2 Problematic issues in ichnotaxonomy and their solutions; question marks for issues that require considerable discussion, exclamation marks for simple actions.

and avoid the common problems in the identification of trace fossils. Problematic issues in ichnotaxonomy are of two types (Fig. 5.2): one type relates to individual ichnotaxa only, whereas the other is of a general kind, requiring a simultaneous discussion of several ichnotaxa. The first type, in the following sections called ‘individual problem,’ is usually identified much easier, so these problems and their mostly simple solutions are discussed first. The second type, called ‘general problem’ here, requires a more comprehensive approach (see relevant sections below) and will have to be discussed before a general consensus is reached.

Individual Problem 1: Monotypic Ichnogenera Many currently recognized ichnogenera contain a single ichnospecies; in other words, they are monotypic ichnogenera. As a result, the novice to ichnology will get the impression that trace fossils mostly represent highly stereotypic behaviour (Pickerill, 1994). This may be true to a limited extent only. The situation has become irritating, because many authors in the past obviously were not thinking beyond their current research object. When introducing a new ichnogenus, authors nowadays have to provide an ichnogeneric diagnosis and a type ichnospecies. Usually this is erected in the same article, and sometimes just by referring to the diagnosis of the ichnogenus. Applying biological reasoning to the ichnologic phenomenon of monotypic ichnogenera indicates inadequate choice of ichnotaxobases. As evolution of characters and behaviour is to be expected, most

(ichno)genera should be represented by more than one (ichno)species through time. Related biological species may well have retained their specific behaviour and attributes during their evolution, thus creating identical trace fossils. It is hard to imagine, however, that so many cases of highly stereotypic producer behaviour should have existed as to support so many monotypic ichnogenera as are currently recognized. When an author declares (and an editor allows) a new ichnospecies to bear the same exact diagnosis as its ichnogenus, certainly there will be problems when it comes to relating the ichnotaxon to others for systematic, ecological or evolutionary purposes. The solution is simple: an ichnospecies should have a sufficiently narrower diagnosis than its ichnogenus.

Individual Problem 2: Questionable Holotypes In the early years of ichnology, trace fossil names were coined on a less elaborate background than nowadays. Unaware of the nature of these structures, early authors often described what they thought to see, and their ichnotaxa are poorly diagnosed now. A type specimen may have been lost, or it may not be indicated within a set of similar but not identical traces, or it may not show the criteria considered relevant nowadays. The rules of nomenclature protect the original names, as ill-defined they may be, and as a result, even some widespread ichnotaxa are being used currently without proper diagnosis. Their use thus depends on the personal concepts of individual workers, leaving ample room for doubtful


assignments of ichnospecies and unclear validity of various ichnotaxa. In these cases, identification of trace fossils is governed more by tradition than by a thorough ichnotaxonomic approach. As a consequence, long-term stability of such names may not be expected. The problems mentioned may be solved in some cases by clarifying the status of the type specimen according to the rules of nomenclature: a lost holotype may be replaced by one carefully selected anew, the neotype, or a lectotype may be selected from a collective of types. If an original type specimen is too badly preserved to show the details that are relevant nowadays, the related species has to be considered a ‘nomen dubium’ (= doubtful name) and should not be used anymore.

Individual Problem 3: Exceptionally Broad Diagnoses

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no easy solution satisfying all specialist workers is to be expected.

General Problem 2: Inconsistent Ichnotaxobases of Related Trace Fossils Different ichnotaxobases are not only used for different types of trace fossils; but also even ethologically related taxa are sometimes diagnosed on diverging characters. One example is found in the group of simple clavate borings (Fig. 5.3) : in wood, the only generally accepted ichnospecies so far is Teredolites clavatus Leymerie, which is defined independent of its longitudinal outline or length:diameter ratio. In rock, corals and similar lithic substrates, four ichnospecies of Gastrochaenolites are distinguished based on these very criteria (Kelly and Bromley, 1984). In addition, Gastrochaenolites ornatus Kelly and

Some original diagnoses of ichnotaxa were extremely broad and hence include various forms that could and should be distinguished in order to convey more detailed information about stratigraphy, sedimentology or ecology. The rather simple solution here is to revise these structures by applying adequate ichnotaxobases in order to narrow the original diagnoses.

General Problem 1: Heterogeneity of Trace Fossils Everyone concerned with trace fossils acknowledges their dual biological and physical nature. It is equally undoubted that trace fossils are always the result of certain behaviour of their producers. The importance of biological affinity, substrate conditions and producer behaviour as ichnotaxobases, however, has been the matter of considerable debate. Currently there is no full agreement among ichnologists on generally appropriate ichnotaxobases, let alone their hierarchy. This is partly a result of specialization in a certain type of trace fossils. For example, vertebrate tracks are diagnosed in grossly different ways than coprolites, or burrows may have different ichnotaxobases than insect nests. As a result, the path of a trackway is irrelevant, as it reflects the speed of the producer (Braddy, 1995), whereas the straightness or sinuosity of a trail or of some burrows may be a significant feature. Much confusion thus arises from the heterogeneity of trace fossils, and taxonomy being a science rather than jurisdiction,

FIGURE 5.3 Naming of borings with round cross sections in xylic and lithic substrates as an example of inconsistent ichnotaxobases. (A–D) Teredolites clavatus Leymerie. (A) Original sketch. (B) Specimen from the Santonian of Haltern/Germany. (C,D) Specimens from the Langhian of Hambach/Germany. (E) Gastrochaenolites turbinatus Kelly and Bromley. (F) Gastrochaenolites lapidicus Kelley and Bromley. (G) Gastrochaenolites torpedo Kelly and Bromley. (H) Gastrochaenolites orbicularis Kelly and Bromley (schematic longitudinal sections for easy comparison, not to scale, (A,E–H) redrawn from Kelly and Bromley, 1984).

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Bromley is reserved for rockground borings with bioglyphs of the producers, whereas identical scratch traces frequently found in wood borings (e.g., Bertling et al., 1995) do not serve as an ichnotaxobase according to current practice. An example from the variety of burrows is the well-known complex of ichnotaxa used for various crustacean or worm burrows. Spongeliomorpha is separated from related ichnogenera on the basis of its horizontality, to a lesser extent of its often scratched walls, whereas Thalassinoides, Ophiomorpha and other three-dimensional trace fossils are identified mainly on the basis of their wall structure (to a lesser extent of the overall geometry of the burrow system; Ha¨ntzschel, 1975). As a result, any author may set up an individual hierarchy of ichnotaxobases here and assign ichnospecies to any of the ichnogenera with fair reasoning—clearly an intolerable situation. Contrary concepts have been proposed by Fu¨rsich (1973) and Schlirf (2000) but their logical thinking has not yet found universal recognition by practicing ichnologists. Considering burrows in general, ichnogenera are frequently distinguished on the basis of their orientation within the substrate. U-shaped burrows with spreiten are called Rhizocorallium if dug horizontally and Diplocraterion if constructed vertically. The ichnospecies Rhizocorallium hohendahli Hosius deviates from this pattern in being mainly vertical, but has not been excluded from the ichnogenus as yet (Mu¨ller, 1989). Similarly, burrows are frequently distinguished based on the presence, absence or type of wall, with Planolites versus Palaeophycus as a wellknown example (Pemberton and Frey, 1982). This approach excludes some burrows, partly following highly interpretative reasoning, for instance Gyrolithes, Balanoglossites, Skolithos or Psilonichnus, which comprise forms with and without wall linings (Bromley and Frey, 1974; Knaust, 2002; Schlirf and Uchman, 2005; Nesbitt and Campbell, 2006). On the level of ichnospecies, more inconsistencies may be encountered: the complex burrow systems Zoophycos and Chondrites are subdivided based on their overall morphology, but only partly so the equally complex Thalassinoides or Asterosoma. These examples show that ichnotaxobases are not applied consistently even in related structures constructed by similar producers. It is hard to comprehend why a certain hierarchy of characters should apply for one trace fossil and not for another taxon of the same ethological group, even if historically these ichnotaxa were defined based on other criteria.

Potential Solutions for General Problems: A Comprehensive Approach Individual historically inherited ichnotaxonomic problems obviously can be overcome by applying standard nomenclatural techniques. The biggest stumbling blocks in ichnotaxonomy in general are differing opinions of various specialists on the validity of diverse ichnotaxobases for their research objects. Unfortunately, the current condition is paralysed by dragging along frequent but ill-defined ichnotaxa in a meaning according to personal preferences of individual authors. As soon as this situation changes, we can expect a comprehensive framework and stability of trace fossil names in due course. It is high time to critically review the principal concepts of ichnotaxobases and of naming various trace fossils before the taxonomy of burrows, borings, tracks, trackways and plant traces diverges even stronger than currently. One aim of this chapter is to lay the foundations for standardizing general ichnotaxonomy to the largest possible extent. It is hoped this will make the existing wealth of ichnotaxa easier to understand and will help avoid addition of ill-defined ichnotaxa in the future. Besides, it is an important expression of the unification of all areas of ichnology. The standardization of general ichnotaxonomy may progress on two different levels independently (Fig. 5.2). The first level is to apply identical ichnotaxobases at identical levels within a more or less coherent group of trace fossils (see General Problem 2). This will demand a homogenized treatment of related ichnotaxa by employing a consistent set of diagnostic criteria for classifying and naming similar types of trace fossils. The second level is to recognize a few universally valid ichnotaxobases for all trace fossils (see General Problem 1). To this end, potential ichnotaxobases for borings, burrows, tracks and trails need to be discussed, and a consensus among active ichnologists needs to be sought. Ichnotaxa are very diverse in their mode of formation, their substrate, their occurrence and their preservational mode, and all of these aspects have a potential for affecting the choice of appropriate ichnotaxobases.

Valid Ichnotaxobases Theoretically possible ichnotaxobases include the intrinsic components in their formation, i.e., behaviour and systematic position of the producer, as well as the extrinsic factors, such as substrate and type of preservation. Some authors additionally


TABLE 5.1 Useful

Useful and Rejected Ichnotaxobases Rejected

Morphological criteria (substrate) Size Geological age Geographic location Mode of preservation Behaviour of producer Sedimentary environment Systematic position of producer

propose geological age, location or sedimentary environment at least for individual instances (e.g., Haubold, 1996; Schallreuter and Hinz-Schallreuter, 2003). Currently no consensus exists about the importance of extrinsic and some intrinsic factors as ichnotaxobases, although Bertling et al. (2006) have reviewed the possibilities of their universal application. For advances on the second level of standardization in ichnotaxonomy, the central parts of their results are summarized here (Table 5.1). The only ichnotaxobase accepted for all trace fossils is their form, i.e., general geometry and detailed morphology, as it reflects producer geometry, shape and behaviour. It is determined by external and internal criteria, some of which are the best candidates for the highest hierarchical levels in a standardized ichnotaxonomy. The external shape is most important, and for tracks and other trace fossils made up of subunits, their pattern of arrangement is relevant as well. For tracks, detailed criteria are internal versus external width, number and angle of foot or claw imprints (Anderson, 1981; Trewin, 1994). For burrows and borings, branching with all its characters, i.e., order, angle, size relations, provides a special condition, as well as the outline in cross section (e.g., Bromley, 1990: pp. 147 ff.). Many trace fossils are also distinguished by their orientation to the substrate. This not only means horizontal, vertical or oblique, but it also refers to the position of biting traces. Burrows may be distinguished by internal characters such as the presence or absence of a wall (plus its structure, if applicable) and the type of fill. An active fill may provide additional ichnotaxobases (meniscate structure or lamination), whereas passive fill results in no additional relevant features. Among all these criteria, the best are those that are best preservable. Structures which are eroded easily or rarely observable, (vertebrate skin impressions, burrow funnels, etc.), should not be considered as ichnotaxobases (Schlirf and Uchman, 2005; Bertling et al., 2006). For similar reasons, surface features such

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as wall ornament in burrows usually are diagnostic for ichnospecies at best. It is tempting to embark on a ‘whodunit’ game and to search for close connections of trace fossils to their producers. This relationship, however, is usually dubious, because a one-on-one correspondence cannot be reconstructed from the ancient record with certainty. This is the main argument for nomenclatural separation of ichnotaxa and biotaxa, and it is a valid principle in ichnotaxonomy as well. As a consequence, the systematic position of an alleged producer must never be an ichnotaxobase. Some trace fossils can be assigned to biotaxa with a relatively high degree of certainty, including many borings (e.g., Bromley, 1994) and vertebrate tracks (e.g., Haubold, 1971; Lockley, 1998). This is because of their rich morphological detail, not because one knew the producer beforehand. Advocates of producer-related ichnotaxobases tend to neglect this epistemological sequence, thus blurring the importance of morphology. Information about producer biology nonetheless may provide important clues for the proper selection of ichnotaxobases (Fu¨rsich, 1974). Size, as expressed by single dimensions as length and width, has occasionally been used to distinguish ichnospecies, mainly because a different producer was suspected. This reasoning should be rejected, provided their overall form is truly identical. Trace fossils that do not differ geometrically and thus show identical proportions of morphometric parameters should be synonymized. Changing proportions, however, that result in a different shape and hence taxonomic individuality, should permit morphometry to play an important role in ichnotaxonomy (also see Pickerill, 1994). Substrate is usually regarded as the most important extrinsic factor in ichnotaxonomy, as it may control tracemaker behaviour. Burrowing in soft sediments requires different techniques than boring in cemented rock; walking on stiffened surfaces implies other movements than trudging through mud. Borers scrape off the substrate with their hard parts (e.g., Rice, 1969; Ro¨der, 1977) or etch it away by biochemical secretions (e.g., Bromley, 1994), whereas burrowers push aside loose sediment grains by extensions and contractions of their body (e.g., Bromley, 1990). These differences in behaviour usually result in discernible differences in the form of trace fossils. There are simple forms that can only be distinguished by microscopic analysis of grain displacements or cuttings in order to tell burrowing from boring action during their production. Examples are the needleshaped Skolithos linearis Haldeman in soft sediments versus Trypanites weisei Ma¨gdefrau in rock, or the

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triplet of the club-shaped Teredolites clavatus Leymerie (borings in wood), Gastrochaenolites lapidicus Kelly and Bromley (borings in rock) and Amphorichnus papillatus Ma¨nnil (burrows in firmground). The grain size does not matter ichnotaxonomically either in hard substrates or in soft and firm sediment, because there is no clear grain size boundary. Substrate thus can be looked upon as an indirect ichnotaxobase for most trace fossils. There are more specific cases in bioerosion: very few species bore in more than one type (lithic, woody or other) of hard substrates, and some wood borers are even restricted to individual host species (e.g., Vite´, 1952; Genise, 1995). The principal types of lithic, woody and soft substrates may thus reflect true ichnotaxobases but usually there are morphologic differences that will contribute to the distinction. Substrate as a sole criterion to name a new ichnotaxon is not acceptable. Differing states of preservation as a consequence of events during fossilization of traces have been discussed by various authors with varying opinions (e.g., Uchman, 1995; Goldring et al., 1997). The preservational variants of trace fossils may convey interesting biological and sedimentological information, but there are too many possible transitions between these variants to accept preservation mode as an ichnotaxobase (Bromley, 1990; Magwood, 1992). Trace fossils altered this way may receive informal descriptive prefixes or suffixes to their formal names, but they do not merit independent nomenclatural status. The last extrinsic ichnotaxobases to be discussed have more rarely been considered to be valid: geological age, geographical occurrence or depositional environment should not be used to distinguish morphologically identical trace fossils. In principle, they all are unrelated to producer behaviour. They may be considered indirectly only, maybe because their specialized producer existed during a limited interval, or because the range of Platypus with its typical burrows does not extend beyond Australia. Behaviour that has remained unchanged through time may well become manifest as similar trace fossils discontinuously—apparent stratigraphical gaps are the result. If these gaps coincide with evolution of the supposed producers, it may be tempting to assign different ichnotaxa to these structures. Stratigraphical considerations, however, should not delimit biotaxa, and the same reasoning must be valid for ichnotaxa. The same is essentially true for geographic occurrence, because temporal and spatial distributions are simply variations on the same theme. Continuing this train

of thought, one must also reject sedimentary environment as an ichnotaxobase: trace fossils are biological objects nomenclaturally, so they should deserve a comparable status taxonomically. This means that they should not be classified and named on the basis of their occurrence but for what they are.

Hierarchy of Ichnotaxobases Fu¨rsich (1974) suggested considering features indicating highly significant behaviour as ichnogeneric ichnotaxobases. The decision of which component of a more complex behaviour is the most significant, however, has hitherto been largely subjective, because it was based on interpretation more than on pure observation. Already Simpson (1975) demanded that objects named on the basis of their form should be judged morphologically only. This statement seems to be trivial, but current ichnological practice does not follow it. As an example, consider the wall linings in burrows. Miller (1998) has pointed out that they may be produced during construction, operation or maintenance of a burrow. Consequently, linings have been considered important when deposited during construction of a burrow but not during its maintenance (explicitly so by Schlirf and Uchman, 2005; implicitly e.g., by Knaust, 2002; Nesbitt and Campbell, 2006). This reasoning is thus inspired by interpreting the supposed producer behaviour, not by mere morphological observation. It is logically inconsistent therefore, if applied within a framework of morphology-based ichnotaxonomy. This statement does not imply that knowledge about producer behaviour should be abandoned when selecting ichnotaxobases for a group of trace fossils. It does imply that, once established, these criteria should be applied generally within this group. For the example above, it means that wall linings should be important for all or for no burrows. With substrate and morphological criteria identified as the only desirable ichnotaxobases (Table 5.1), the question of the hierarchy of their numerous characteristics has remained unanswered. In an approach similar to the behavioural cladistics of Ekdale and Lamond (2003), two weighted lists are suggested here for the most common ethological groups (Figs. 5.4 and 5.5). They follow morphological criteria but take into account producer behaviour as well, so that even opponents of a strict morphological approach to ichnotaxonomy should be able to agree.


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FIGURE 5.4 Ichnotaxonomic importance of various morphological features as results of tracemaker behaviour during the construction of burrows.

In burrows (Fig. 5.4), characters such as active fill, backfill or wall structures result from very basic components of producer behaviour independent of the morphology of its burrow. Therefore, they should be able to serve as consistently high-ranking ichnotaxobases for all burrows, as they are usually present constantly. Scratch traces, lineations and other indications of the way substrate was moved frequently are linked to certain preservational aspects; their ichnotaxonomic importance is low (ichnospecies level) for this reason. Modular elements in burrows, mostly caused by repeated and foreseeable changes in direction distinguish this type of burrow from a simpler construction, but they result from only intermittent behaviour. Accordingly, their ichnotaxonomic importance is high but not top ranking. Even compositionally or structurally complex trace fossils should be named basically by the characters of their modules, less so by the combination of these modules. Singular events in burrow construction, such as the initial path of the larva, are responsible for the inclination within the substrate, usually regarded a less important characteristic. Horizontal versus vertical orientation, however, are considered much more significant. Finally, accidental deviations from the general pattern of a burrow, which may be caused by the need to bypass obstacles or to avoid a disturbance, have no ichnotaxonomic relevance, because they are not recurring features. Occasionally, wall structures, orientation or branching of burrows change over a short distance due to varying substrate. According to the scheme suggested above, these differences should be reflected in ichnogeneric distinction of individual parts of the same burrow (e.g., Bromley and Frey, 1974).

This procedure also warrants the possibility to label individually preserved parts of complex trace fossils. An alternative handling of large burrow systems with variable internal structure would be to treat them as compound trace fossils (Pickerill, 1994). They should not receive formal names normally, except in those unique situations where all structures can be demonstrated to have been produced simultaneously (Bertling et al., 2006). Composite trace fossils may provide interesting insights into producer biology but should never be named formally (Bertling et al., 2006). For borings, the situation is somewhat simpler, because no compound structures are known. Weighing morphological characteristics analogously to the list for burrows nonetheless results in a more complicated picture (Fig. 5.5). This is due to the traditional view that the principal substrate of borings (lithic, xylic, osteic), following specific settlements of the larvae, should be kept apart ichnotaxonomically. This view was retained by Bertling et al. (2006), but comparing Figs. 5.4 and 5.5 makes the logical inconsistency of this generally accepted approach apparent. Future discussions will show whether the current separation of various hard substrates as ichnotaxobases still makes sense against the background of the endeavour to unify ichnotaxonomy. Microscopic characteristics may well become more important to distinguish between burrows and borings and perhaps between borings in certain types of substrate. Very much like for burrows, the results of constant tracemaker action, i.e., the basic component of behaviour, are regarded most important for naming borings: as the producer grows, its overall form is mirrored by its boring. Again, traces of the removal of

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FIGURE 5.5 Ichnotaxonomic importance of various morphological features as results of tracemaker behaviour during the construction of borings.

substrate like scratches or other bioglyphs, have no or little significance. Modular elements in borings are branching or chambered structures, mostly made by colonial producers during extension of the growing colony. This occurs intermittently only, and hence has medium importance for ichnotaxonomy. Again analogous to burrows, the inclination of borings within the substrate is not considered much relevant. The proposals condensed in Figs. 5.4 and 5.5 are intended as a basis for discussion and as a stimulus to test this scheme for the remaining ethological groups of trace fossils, mainly locomotion structures, predation traces and coprolites. Critical but open minds will be important in this process.

CONCLUSIONS Nomenclature, systematics and taxonomy have to be separated strictly: nomenclature treats established names of trace fossils as if within the biological system; thus they are subject to the International Code of Zoological Nomenclature (ICZN). The ICZN can guarantee stability of names once established but has no regulatory power for the selection of proper criteria for naming; this is the subject of ichnotaxonomy. The current state of this science is problematical due to both historical and recent confusions. Insufficient or inappropriate diagnoses of individual ichnotaxa may result from three types of errors of their authors: unreasonably narrow diagnoses, inefficiently broad diagnoses and improper identification of holotypes. A general problem is the selection of irrelevant ichnotaxobases for newly introduced names, partly due to the heterogeneity of trace fossil nature.

A comprehensive approach in ichnotaxonomy should seek two challenging goals: first, identical ichnotaxobases should be applied within a coherent group of trace fossils. A hierarchical system is suggested for burrows and borings on the basis of the visible continuity of potential ichnotaxobases. Moreover, ichnotaxonomy should exclusively deal with the products, not with the processes of tracemaker behaviour. Second, a few universally valid ichnotaxobases should be identified for all trace fossils. For the latter issue, the conceptual consequence of the legal treatment of ichnotaxa as animal biotaxa should be to focus on intrinsic ichnotaxobases, such as trace fossil morphology. At a microscopic level, this will help to distinguish burrows from borings in a different way from looking at the principal type of substrate. In any way, extrinsic factors, such as preservation mode and spatiotemporal occurrence, should be rejected as ichnotaxobases.

ACKNOWLEDGEMENTS This article has much benefited from discussions with several colleagues who attended one or two of the Workshops on Ichnotaxonomy (WIT), including Simon Braddy (Bristol, UK), Richard Bromley (Copenhagen, Denmark), Georges Demathieu (Lyon, France), Radek Mikula´sˇ (Prague, Czech Republic), Andrew K. Rindsberg (Livingston, USA), Michael Schlirf (Wu¨rzburg, Germany) and Alfred Uchman (Krakow, Poland); their input in the joint endeavour for a better foundation of our science is gratefully acknowledged. The constructive

REFERENCES

reviews by Tony Ekdale (Salt Lake City, USA) and Ron Pickerill (New Brunswick, Canada) improved a previous manuscript linguistically and provided additional aspects. Finally, William Miller III (Arcata, USA) was critical but encouraging and patient during the editing process of this chapter.

References Anderson, A.M. (1981). The Umfolozia arthropod trackways in the Permian Dwyka and Ecca series of South Africa. Journal of Paleontology, 55, 84–108. Bertling, M., Hermanns, K. and von der Hocht, F. (1995). Sedimentologie und Palaöo¨kologie autochthoner MuschelBohrungen in Kohleflo¨zen (Neogen der Niederrheinischen Bucht). Neues Jahrbuch fu¨r Geologie und Palaöntologie, Monatshefte, 1995, 711–736. Bertling, M., Braddy, S., Bromley, R.G., Demathieu, G.D., Genise, J., Mikula´sˇ, R., Nielsen, J.K., Nielsen, K.S.S., Rindsberg, A.K., Schlirf, M. and Uchman, A. (2006). Names for trace fossils: a uniform approach. Lethaia, 39, 265–286. Braddy, S.J. (1995). The ichnotaxonomy of the invertebrate trackways of the Coconino Sandstone (Lower Permian), northern Arizona. In: Lucas, S.G. and Heckert, A.B. (Eds.), Early Permian Footprints and Facies. Bulletin of the New Mexico Museum of Natural History and Science, 6, 219–224. Bromley, R.G. (1990). Trace Fossils: Biology and Taphonomy, Unwin Hyman, London, 280 pp. Bromley, R.G. (1994). The palaeoecology of bioerosion. In: Donovan, S.K. (Ed.), The Palaeobiology of Trace Fossils, Johns Hopkins, Baltimore, pp. 134–154. Bromley, R.G. and Frey, R.W. (1974). Redescription of the trace fossil Gyrolithes and taxonomic evaluation of Thalassinoides, Ophiomorpha and Spongeliomorpha. Bulletin of the Geological Society of Denmark, 23, 311–335. Ekdale, A.A. and Lamond, R.E. (2003). Behavioral cladistics of trace fossils: evolution of derived trace-making skills. Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 335–343. Fu¨rsich, F.T. (1973). A revision of the trace fossils Spongeliomorpha, Ophiomorpha and Thalassinoides. Neues Jahrbuch fu¨r Geologie und Palaöntologie, Monatshefte, 1973, 719–735. Fu¨rsich, F.T. (1974). On Diplocraterion Torell 1870 and the significance of morphological features in vertical, spreiten-bearing, U-shaped trace fossils. Journal of Paleontology, 48, 952–962. Genise, J.F. (1995). Upper Cretaceous trace fossils in permineralized plant remains from Patagonia, Argentina. Ichnos, 3, 287–299. Goldring, R., Pollard, J.E. and Taylor, A.M. (1997). Naming trace fossils. Geological Magazine, 134, 265–268. Ha¨ntzschel, W. (1975). Part W, Miscellanea, Supplement 1. Trace Fossils and Problematica. In: Moore, R.C. and Teichert, C. (Eds.), Treatise on Invertebrate Paleontology, 2nd edition. Geological Society of America and University of Kansas Press, Boulder-Lawrence, pp. 1–269. Haubold, H. (1971). Ichnia Amphibiorum et Reptiliorum fossilium. In: Kuhn, O. (Ed.), Handbuch der Palaöherpetologie, Teil 18.G, Fischer, Stuttgart, 124 pp. Haubold, H. (1996). Ichnotaxonomie und Klassifikation von Tetrapodenfa¨hrten aus dem Perm. Hallesches Jahrbuch fu¨r Geowissenschaften, B18, 28–86.

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ICZN (International Commission for Zoological Nomenclature) (1999). International Code of Zoological Nomenclature, adopted by the International Union of Biological Sciences, 4th edition. International Trust for Zoological Nomenclature, London, 232 pp. Kelly, S.R.A. and Bromley, R.G. (1984). Ichnological nomenclature of clavate borings. Palaeontology, 27, 793–807. Knaust, D. (2002). Ichnogenus Pholeus, revisited. Journal of Paleontology, 76, 882–891. Ksia˛zˇkiewicz, M. (1977). Trace fossils in the flysch of the Polish Carpathians. Palaeontologica Polonica, 36, 1–208. Lockley, M. (1998). Philosophical perspectives on theropod track morphology: blending qualities and quantities in the science of ichnology. Gaia, 15, 279–300. Magwood, J.P.A. (1992). Ichnotaxonomy: a burrow by any other name? In: Maples, C.G. and West, R.R. (Eds.), Trace Fossils, Paleontological Society Short Courses in Palaeontology, pp. 15–33. Miller, W., III (1998). Complex marine trace fossils. Lethaia, 31, 29–32. Mu¨ller, A.H. (1989). Lehrbuch der Palaözoologie Band II Invertebraten, Teil 3: Arthropoda 2 – Hemichordata, 3rd edition. Gustav Fischer, Jena, Stuttgart, 775 pp. Nesbitt, E.A. and Campbell, K.A. (2006). The environmental significance of Psilonichnus. Palaois, 21, 187–196. Pemberton, S.G. and Frey, R.W. (1982). Trace fossil nomenclature and the Planolites-Palaeophycus dilemma. Journal of Paleontology, 56, 843–881. Pickerill, R.K. (1994). Nomenclature and taxonomy of invertebrate trace fossils. In: Donovan, S.K. (Ed.), The Palaeobiology of Trace Fossils, Johns Hopkins, Baltimore, pp. 3–42. Rice, M.E. (1969). Possible boring structures of Sipunculida. American Zoologist, 9, 803–812. Rindsberg, A.K. (1990). Ichnological consequences to the 1985 International Code of Zoological Nomenclature. Ichnos, 1, 59–63. Ro¨der, H. (1977). Zur Beziehung zwischen Konstruktion und Substrat bei mechanisch bohrenden Bohrmuscheln (Pholadidae, Teredinidae). Senckenbergiana Maritima, 9, 105–213. Sarjeant, W.A.S. and Kennedy, W.J. (1973). Proposal of a code for the nomenclature of trace fossils. Canadian Journal of Earth Sciences, 10, 460–475. Schallreuter, R. and Hinz-Schallreuter, I. (2003). Lapis musicalis. Geschiebekunde aktuell, 19, 34–46. Schlirf, M. (2000). Upper Jurassic trace fossils from the Boulonnais (northern France). Geologica et Palaeontologica, 34, 145–213. Schlirf, M. and Uchman, A. (2005). Revision of the ichnogenus Sabellarifex Richter, 1921 and its relationship to Skolithos Haldeman, 1840 and Polykladichnus Fu¨rsich, 1981. Journal of Systematic Palaeontology, 3, 115–131. Simpson, S. (1975). Classification of trace fossils. In: Frey, R.W. (Ed.), The Study of Trace Fossils, Springer, Berlin, Heidelberg, New York, pp. 39–54. Trewin, N.H. (1994). A draft system for identification and description of arthropod trackways. Palaeontology, 37, 811–823. Uchman, A. (1995). Taxonomy and palaeoecology of flysch trace fossils: the Marnoso-arenacea Formation and associated facies (Miocene, northern Apennines, Italy). Beringeria, 15, 1–115. Vite´, J.P. (1952). Die holzzersto¨renden Insekten Mitteleuropas, Musterschmidt, Go¨ttingen, 155 pp. Vyalou, O.S. (1972). The classification of the fossil traces of life. 24th International Geological Congress. Section 7, 634–644.

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6 Taphonomy of Trace Fossils Charles E. Savrda

SUMMARY : The taphonomic state of ichnofossil assemblages can be measured using two independent parameters: (1) completeness of the preserved record of biogenic activity that occurred in a substrate (ichnologic fidelity); and (2) degree of manifestation of the trace fossils that are preserved (trace fossil visibility). These parameters are controlled by environmental dynamics, tracemaker behavior and position in substrates, and a range of diagenetic processes (mechanical compaction, selective mineralization, lithification, and weathering). Consequently, trace fossil preservational modes can be exploited in studies of depositional regimes, paleobiology, and post-depositional histories. Trace fossil assemblages characterized by relatively high ichnologic fidelity, trace fossil visibility, or both may be particularly informative and, hence, can be considered as ichnofossil-lagersta¨tten.

microbial decomposition, and dissolution may severely degrade the fidelity of the body fossil record. High-fidelity fossil assemblages, including certain fossil-lagersta¨tten, only form under special conditions where the number and/or effectiveness of taphonomic filters are reduced. Fortunately, comparative taphonomic observations, including the recognition of taphofacies, can be put to constructive use in sedimentologic and paleoenvironmental studies (e.g., Brett and Baird, 1986; Wilson, 1988). Trace fossils too are subject to a range of taphonomic processes, many of which are analogous to those that control body fossil preservation. Because trace fossils are not once-living things, necrolysis does not apply. However, entry and manifestation of biogenic structures in the stratigraphic record are influenced by a variety of ichnostratinomic factors that operate during trace production and before host substrates exit the zone of active biogenic activity (i.e., benthic boundary layer). Trace fossils are also subject to physical and chemical processes that operate during burial and in weathering regimes (ichnofossil diagenesis). Some of these factors represent taphonomic filters (Bromley, 1996) that govern ichnologic fidelity, or the degree to which a preserved ichnofossil assemblage or ichnofabric reflects the complete range of activities of a community, or communities, of trace-making organisms. Others influence the extent to which traces are visible or accessible to the viewer. These two aspects of trace fossil preservation—ichnologic fidelity and trace fossil visibility—may be independent of one another. Ichnofabrics may have high ichnologic fidelity, but some or all trace fossils represented therein may be difficult to discern. Conversely, other ichnofabrics may record only a fraction of the biogenic activity that

INTRODUCTION Taphonomy, the study of fossilization, is an important element of paleontology. Processes that influence the potential for and quality of body fossil preservation are diverse and include those affecting organisms at the time of death (necrolysis), those operating in the interval between death and final burial (biostratinomic processes), and those impacting organism remains after burial (fossil diagenesis). These processes represent taphonomic filters that govern the degree to which fossil assemblages mirror original faunal communities and set limits on the accuracy of paleoecologic reconstructions. Processes such as scavenging, reworking, mechanical fragmentation,


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occurred in a substrate, yet those trace fossils that are present may be very well expressed. Such preferentially preserved structures are referred to as ‘elite trace fossils’ (Bromley, 1996). Although sometimes not recognized or fully appreciated, taphonomy is inherently embedded in ichnology. Detailed paleobiologic and ethologic studies based on trace fossils are dependent on well-preserved specimens (e.g., Miller, 2003) and differential preservation of trace fossils may complicate ichnotaxonomy (Pickerill, 1994; MacNaughton and Pickerill, 2003). Moreover, environmental parameters that govern organism behavior and are reflected in resulting biogenic structures may also have an impact on trace preservation. Hence, extent and modes of preservation are just as important as ichnofossil assemblage composition for deciphering paleoenvironmental conditions. The close links among environmental regimes, trace fossils, and preservation are reflected in some archetypal ichnofacies. They are most dramatically illustrated by the Nereites ichnofacies, the development of which is so dependent on preservational factors that it can be considered justifiably as a taphofacies (Bromley and Asgaard, 1991). Aspects of trace fossil preservation have been summarized in earlier works (e.g., Simpson, 1957; Hallam, 1975; Bromley, 1996). The goal of this chapter is to describe the processes that impact both ichnologic fidelity and trace fossil visibility. Focus is on taphonomy of ichnofossils in the marine realm, although concepts addressed are equally applicable to continental deposits. Taphonomic factors associated with soft substrates (softgrounds) are emphasized, but preservation of traces emplaced in other substrates (firm-, hard-, and woodgrounds) are also considered. The chapter concludes with a brief discussion of exceptional trace fossil preservation and the concept of ichnofossil-lagersta¨tten.

TRACE FOSSIL PRESERVATION IN SOFT MUD Softground substrates, consisting of sediments that are neither very soupy nor consolidated, vary considerably in texture and accumulate in a broad range of environmental regimes. Because taphonomic processes that impact preservation in these substrates are highly variable, it is difficult to define a normal condition for softground trace fossil preservation. Hemipelagic and pelagic muds deposited slowly and continuously in quiet marine settings reflect

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more or less steady-state conditions and provide a useful starting point to address trace fossil taphonomy.

Normal Preservation in Marine Mud Preservation of trace fossils in oxygenated marine mud, including carbonate ooze, is strongly linked to burrow stratigraphy or substrate tiering. The benthic boundary layer in marine hemipelagic/pelagic substrates can be generally divided into two main components—the surface mixed layer and transition layer—based on character and extent of active bioturbation (Berger et al., 1979; Ekdale et al., 1984) (Fig. 6.1). The surface mixed layer, generally 3–15 cm thick, is a zone of rapid and continuous homogenization by epibenthic and shallow endobenthic animals. These organisms may produce surface tracks and trails, as well as endogenic locomotion, dwelling, feeding, and gardening structures. The transition layer, the thickness of which varies as a function of oxygenation and other environmental factors, is a zone of heterogeneous mixing by organisms that live and/or feed at greater depths in the substrate. Variable behaviors of transition-layer organisms result in suites of traces that may include open and actively filled burrows or burrow systems, as well as complex spreite structures. The transition layer itself may also be tiered; that is, trace-producing organisms may preferentially occupy different levels beneath the mixed layer (Fig. 6.1). Under steady-state conditions, ichnofabrics that enter the stratigraphic record normally have relatively low ichnologic fidelity owing to poor preservation potential of mixed layer traces. Because mixed layer sediments are generally more fluid (in some cases, representing perched soupgrounds), burrows produced therein may collapse shortly after formation (e.g., the biodeformational structures of Lobza and Scheiber, 1999), and associated passively and actively filled burrows may be subsequently compacted beyond recognition. Most important, surface traces, shallow endogenic structures, and upper parts of some transition-layer burrows are extensively overprinted, if not destroyed altogether, as mixed and transition layers migrate upward in pace with sedimentation. Hence, historical layer ichnofabrics, those produced as sediments pass below the benthic boundary layer, are normally biased towards transition-layer traces. The only vestiges of the diverse mixed layer biogenic activities are the homogeneous to diffusely burrow-mottled background fabrics upon

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6. TAPHONOMY OF TRACE FOSSILS

Benthic Boundary Layer

E Sediment segregation by tracemaker

Mixed Layer

Transition Layer Phycosiphon

A

Historical Layer

B

F Concretion growth

C G

Thalassinoides

Differential erosion Zoophycos

D Chondrites

FIGURE 6.1 Burrow stratigraphy and factors controlling trace fossil preservation in marine pelagic/hemipelagic mud. Under steady-state conditions, mixed layer structures are not preserved. Historical layer fabrics are dominated by transition-layer structures, the visibility of which may be limited by poor contrast between ichnofossils and host sediments (A,C). Visibility of transition-layer structures may be enhanced by changes in sediment character and active or passive downward transport of contrasting sediments (bed-junction preservation; B,D), textural or compositional segregation by tracemakers (E), and diagenetic mineralization (F) or differential weathering/erosion (G) of burrows or host sediments. Trace fossils in bed-junction preservation are particularly well manifest where they crosscut previously unbioturbated sediments (e.g., dark, laminated shales; D).

which transition-layer burrows are superimposed (Fig. 6.1). Composition and diversity of preserved transitionlayer trace fossil assemblages vary with environmental conditions (e.g., oxygenation levels, food availability); assemblages may be representative of the Cruziana ichnofacies, Zoophycos ichnofacies, or, in the case of carbonate oozes, what Bromley and Ekdale (1984a) refer to generally as ‘chalk ichnofacies.’

Although transition-layer trace fossils in these assemblages have a better chance of entering the stratigraphic record, they are typically subject to other taphonomic processes.

Preservation of Transition-Layer Traces Preservation of transition-layer structures does not guarantee that these traces will be clearly manifested.

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Distinctiveness of traces depends in part on visual contrast with host sediments. In homogeneous, more or less monochromatic mudrocks, including some chalks, transition-layer burrows may be difficult to decipher. In other cases, transition-layer burrows may not fully escape compaction, particularly those in clayey substrates with shallow and thin transition layers. The inability to recognize some or all traces and their morphological detail further limits the information that can be gleaned from ichnofabrics. Several factors govern the degree to which trace fossil contrast is naturally enhanced. These include long-term temporal changes in sediment composition, preferential diagenesis, and tracemaker behavior. In surface exposures, weathering can also impact trace fossil visibility.

Changes in Sedimentation Long-term changes in sediment influx may be recorded in the stratigraphic record as vertical variations in sediment color. Variations in organic content and/or ratios of clastic to biogenic sediment caused by changes in paleoceanographic conditions commonly result in alternation of lighter and darker beds and localized enhancement of transition-layer traces (Fig. 6.1). This is exemplified by ichnofabrics in the Cretaceous Demopolis Chalk (eastern Gulf coastal plain, USA; Locklair and Savrda, 1998). This unit is characterized by decimeter-scale alternation of lighter chalks and darker marls. Distinct transition-layer burrows are well expressed only near bed boundaries (Fig. 6.2). In marl-to-chalk transitions, trace fossil visibility is enhanced because, for finite periods, most transition-layer structures were emplaced into darker marl intervals but were, at least in part, actively or passively filled with the lighter oozes that were accumulating on the seafloor. Conversely, trace fossil expression in chalk-to-marl transitions reflects times when structures emplaced within lighter chalks were wholly or partly filled with darker marls derived from above. Preservation of trace fossils in this manner exemplifies what Simpson (1957) referred to as bed-junction preservation. The extent to which trace fossil visibility is enhanced due to bed-junction preservation depends on the level of contrast. Transition-layer ichnofossils are commonly very well expressed where they have been emplaced downward into dark, laminated mud that was not subject to mixed-layer bioturbation (e.g., due to an earlier phase of oxygen-deficiency; Fig. 6.3).

Zo

Th Te Ch Ph

FIGURE 6.2 Bed-junction preservation of transition-layer ichnofossils at marl–chalk transition (Upper Cretaceous Demopolis Chalk, western Alabama). Zo Zoophycos, Te Teichichnus, Ch Chondrites, and Th Thalassinoides (scale is in centimeter). Inset shows Phycosiphon (Ph) wherein contrast is enhanced by sediment processing and segregation by tracemaker (scale = 1 mm).

FIGURE 6.3 Acute bed-junction preservation of transition-layer burrows emplaced in dark, laminated, organicrich shale (bedding-plane view; Jurassic Posidonienschiefer, Germany). Lens cap is 5.5 cm in diameter.

Diagenetic Controls Diagenetic processes commonly enhance trace fossil visibility. Sediments that fill or comprise biogenic structures may differ from host sediments with regard to texture, packing, and composition. These differences may result from bed-junction preservation or they may be directly related to activities of tracemakers. Even if subtle, these contrasts may render biogenic structures more or less susceptible to diagenetic mineralization (Figs. 6.1, 6.4, and 6.5). Depending on depositional and early

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Collateral Mineralization

Burrow Selective Mineralization

concretion

Overmineralization

Preferential mineralization of burrow fills, linings, etc.

Incidental preservation during sediment mineralization

FIGURE 6.4 Schematic illustrating potential relationships between concretion growth and ichnofossils (diagenetic preservation).

A

B

E

C

D

F

FIGURE 6.5 Examples of diagenetic preservation and differential weathering/erosion of ichnofossils. (A–C) Siliceous (porcelanitic) concretions nucleating on and entombing Gyrolithes (siliceous claystones, Eocene Tallahatta Formation, western Alabama). (D,E) Burrow segments of Thalassinoides (D) and Ophiomorpha (E) collaterally preserved in negative relief on phosphate concretion exteriors (shelf muds, Cretaceous Ripley Formation, central Alabama). (F) Preferentially carbonate-cemented burrow fills (Thalassinoides) weathering in positive relief (shelf deposits, Paleocene Clayton Formation, Alabama). Scale bars in (A–E) are 2 cm long. Pick handle in (F) is 61 cm long.

diagenetic regimes, trace fossils may be replaced by or entombed in pyrite (e.g., Scheiber, 2002), silica (e.g., Bromley and Ekdale, 1984b), phosphate (e.g., Allison, 1988a), and/or various phases of carbonate (e.g., Brown and Farrow, 1978; Morrow, 1978; Archer and Hattin, 1984). Selective mineralization of trace

fossils, which Simpson (1957) referred to as diagenetic preservation, generally enhances the presence of affected structures. The degree to which mineralized masses reflect trace morphology depends on whether mineralization is restricted to the structure or the diagenetic front extends beyond the structure’s


margins (Figs. 6.4 and 6.5A–C) (e.g., oversilicification of trace fossils preserved in flints; Bromley and Ekdale, 1984b). Diagenetic minerals need not nucleate on trace fossils to impact preservation. Mineral growth from other nuclei can pervade bioturbated sediments, and resulting concretions may collaterally preserve elements of ichnofabric (Fig. 6.4). Ichnofabrics may be preserved within concretions. Moreover, because biogenic structures may impact migration of mineralization fronts, individual trace fossils may be manifested in negative or positive relief on concretion exteriors (Figs. 6.4 and 6.5D,E). The role of concretion growth is particularly crucial in clay-rich mudrocks. In some cases, early-formed concretions contain evidence of biogenic activity that otherwise would have been masked by significant compaction (Archer and Hattin, 1984; Buck and Bottjer, 1985; Maples, 1986; Savrda and Bottjer, 1988).

Ethological Controls The potential influences of tracemaker behavior on ichnofossil expression can be exemplified in the context of the bed-junction and diagenetic preservation described above. Enhancement of structures at bed transitions is generally limited to those activities that facilitate downward piping of sediments. Preservation is biased towards (1) open burrows, connected to the seafloor, that are maintained as dwelling or feeding structures but are susceptible to passive filling from above (e.g., Thalassinoides; Fig. 6.1) and (2) structures produced by deep-dwelling reverse conveyors that actively transport surface or near-surface sediment downward into the transition layer (e.g., some Zoophycos; Fig. 6.1). Traces produced by deep-dwelling vagile organisms in the process of simple locomotion or deposit feeding (e.g., Planolites) are commonly filled with adjacent sediment and hence do not lend themselves to bed-junction preservation. Nonetheless, some vagile deposit feeders may generate their own contrast by spatially segregating sediment by composition or texture. This is exemplified by Phycosiphon (Figs. 6.1 and 6.2), with its commonly lighter colored mantle of processed sediment and a darker, organic-rich fecal core (see Wetzel and Bromley, 1994). Tracemaker behavior may predetermine the diagenetic potential of ichnofossils. Sediments that comprise trace fossils are typically more porous and permeable and hence represent preferred sites for diagenetic fluid migration and mineralization. As an

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example, passively filled Thalassinoides commonly have served as fluid conduits and concretion nuclei (e.g., Bromley and Ekdale, 1984b). Preferential mineralization of Thalassinoides (e.g., Fig. 6.5F) and other structures may also be linked to tracemaker activities that determine the distribution of chemically reactive organic matter (e.g., concentration of organic detritus during farming, secretion of mucus linings, etc.). Selective mineralization of trace fossils by pyrite, phosphorite, and/or carbonate is mediated by microbes in organic microenvironments developed within or along the margins of biogenic structures.

Impact of Weathering The type and extent of weathering may have a significant impact on trace fossil visibility in surface exposures. Compositional differences between trace fossils and host sediments, whether caused by bed-junction preservation, diagenetic preservation, and/or tracemaker behavior, often result in differential erosion. Most commonly, trace fossils are relatively resistant and weather out in positive relief, in some cases providing otherwise unobtainable views of their three-dimensional geometry (Fig. 6.5F). In other cases, weathering may obscure original contrasts between ichnofossils and host sediments. In the aforementioned Demopolis Chalk, color contrasts between chalk and marl manifested in relatively fresh, moist exposures are essentially lost after prolonged exposure, leaching, and/or precipitation of secondary carbonate crusts.

Preservation of Mixed-Layer Traces Under steady-state conditions, biogenic structures produced in the mixed layer normally have very little preservation potential, owing to substrate fluidity and overprinting by transition-layer bioturbation. Mixed layer traces could be possibly preserved by very early diagenetic mineralization, as is described above for transition-layer burrows. However, in most cases, preservation of mixed-layer biogenic activity requires a non-steady state. Specifically, chemical or physical conditions must change periodically in ways that isolate mixed layer fabrics from subsequent intense overprinting. Some mixed layer ichnofabrics may be isolated when bioturbation ceases during extended episodes of anoxia (Savrda and Ozalas, 1993). More commonly, mixed layer traces emplaced in mud are preserved owing to episodic rapid deposition, which results in virtually instantaneous vertical translocation of

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the seafloor and hence the zone of most intense biogenic activity. This is addressed in greater depth below.

PRESERVATION IN HETEROLITHIC SOFTGROUND SUCCESSIONS So far, focus has been on factors controlling trace fossil preservation in muds that accumulate slowly and steadily in quiet-water settings. Here, attention is given to stratigraphic successions in which muds alternate with coarser beds, reflecting periodic variations in environmental energy. The effects of rapid depositional events associated with storms and turbidity currents in normally quiet settings are emphasized. However, heterolithic successions that form in response to higher frequency environmental dynamics are also addressed.

Pre- and Post-Depositional Traces and Toponomy Discussion of trace fossil preservation associated with event beds must distinguish between traces produced prior to event-bed deposition and those formed during or after event deposition, i.e., pre-depositional and post-depositional traces

Post-depositional Traces

epireliefs (epichnia) convex concave

(Seilacher, 1962). Discussion is also facilitated by terminology used to describe disposition of trace fossils relative to background mud, event beds, and their contacts; e.g., the toponomic or stratinomic classification schemes of Seilacher (1964) and Martinsson (1970) (Fig. 6.6). Pre-depositional traces may be preserved as fullrelief structures in background mud or as concave or convex hyporeliefs on event-bed soles. Postdepositional traces may be preserved in full-relief within event beds and (if vertically extensive enough) subjacent mud, but also as hyporeliefs or epireliefs on event-bed soles and tops, respectively (Fig. 6.6).

Preservation of Pre-Depositional Traces Storm and turbidite deposition may be preceded by event-related scour. The extent and quality of preservation of pre-depositional traces depend on the depth of pre-depositional erosion and its relationship to burrow stratigraphy in background muds. If pre-depositional scour completely removes the mixed layer, then only transition-layer structures will enter the stratigraphic record. Visibility of transitionlayer traces may be enhanced in several ways. Open burrows may be filled with contrasting event-bed sediments, resulting in bed-junction preservation of full-relief structures. Alternatively, transition-layer

Background Muds

full reliefs Event Sands

hyporelief

convex concave hyporeliefs (hypichnia) full relief Pre-depositional Traces

FIGURE 6.6 Relationship between post- and pre-depositional traces and toponomic preservational modes associated with event beds in heterolithic sequences (based on Seilacher, 1964; Martinsson, 1970). Hypo- and epireliefs are collectively referred to as semireliefs. Full-relief structures (indicated by stars) exemplify burrows that are more visible by virtue of bed-junction preservation.

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PRESERVATION IN HETEROLITHIC SOFTGROUND SUCCESSIONS

Preservation of Post-Depositional Traces Following event deposition, substrates may be impacted sequentially by four groups of bioturbators; (1) animals attempting to escape after burial, (2) organisms introduced via storm or turbidity currents (allochthonous tracemakers), (3) opportunistic organisms that take advantage of newly deposited sediments, and/or (4) normal fair-weather tracemakers that become reestablished upon resumption of background conditions (Frey and Goldring, 1992; Grimm and Fo¨llmi, 1994; Pemberton and MacEachern, 1997; Savrda and Nanson, 2003). In storm deposits, juxtaposition of trace fossils produced by these distinct organism groups commonly results in the development of mixed Skolithos–Cruziana ichnofacies assemblages (Figs. 6.9 and 6.10A). Ichnofossil assemblages produced in

Burial Preservation Background Muds

Tempestites

A

casting of surface structures

Turbidites

B

C Tidal Laminites

structures may be preserved as hyporeliefs resulting from casting of open burrows or previously filled, differentially scoured structures. If the transition layer is tiered, progressively deeper erosion results in preservation biases towards structures in deeper tiers. In the case of shallow or no pre-depositional erosion, preservation of transition-layer traces is minimally influenced by event deposition and is governed by factors outlined above for mudrock ichnofabrics. However, event deposition following limited or no scour elevates the preservation potential of mixed layer structures. Event deposition has two important effects. First, provided that event beds are thick enough, burial protects pre-depositional mixed layer structures from intense overprinting by post-depositional bioturbation. Moreover, casting of traces by event sediments may result in exquisite preservation as semireliefs (Figs. 6.7 and 6.8A,B). These structures include surface traces (in the case of no erosion) or shallow subsurface structures, such as the intricate graphoglyptid farming structures (in the case of shallow scour). Preservation of mixed layer structures in this way, referred to as burial preservation (Simpson, 1957; Hallam, 1975), is reflected in the examples of the Cruziana ichnofacies developed in storm-influenced shelf deposits (Figs. 6.7 and 6.8A,B), and in many cases is prerequisite for recognizing the typically deeper marine Nereites ichnofacies (Bromley and Asgaard, 1991) (Fig. 6.7B). Similar casting of shallow or surface structures is commonly manifest in the continental lacustrine Mermia ichnofacies (e.g., de Gibert et al., 2000).

casting of surface or shallow mixedlayer structures

hyporeliefs epireliefs

undertracks (cleavage relief)

FIGURE 6.7 Preservation of surface and/or shallow subsurface traces (pre-depositional) as semireliefs due to rapid burial by storm sediments (A), turbidites (B), and tidal laminites (C). Note the preservation of cleavage reliefs (undertracks) in thinly laminated strata, as shown in (C). Post-depositional and transition-layer burrows in sand and background mud are not shown.

storm and other event deposits by the first three groups of bioturbators can be referred to the Arenicolites ichnofacies (Bromley and Asgaard, 1991). Preservation potential of traces produced by each of the four organism groups is dependent on the extent of overprinting by the groups that succeed them. Bioturbation by the first three groups is generally not very intense, but the fourth group may substantially mix event beds in their upper portions and thereby reduce ichnologic fidelity (Fig. 6.9). Preservation potential of traces produced by the first three groups is improved if mixing by fair-weather trace makers is minimized by high event frequency (Orr, 1994) or by oxygen-deficient or otherwise unfavorable background conditions (Grimm and Fo¨llmi, 1994; Savrda and Nanson, 2003).

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A

B

C

D

FIGURE 6.8 Examples of surface/near-surface trace fossils preserved as semireliefs. (A) Cruziana and Rusophycus preserved as hyporeliefs on base of storm bed (Cambrian Rome Formation, Tennessee). (B) Asteriacites and other structures preserved as convex hyporeliefs on storm-bed base (Mississippian Hartselle Sandstone, Alabama). (C) Post-depositional Ophiomorpha preserved in semirelief on storm-bed base (Eocene Tallahatta Formation, Alabama). (D) Delicate traces preserved on bedding planes in tidal laminate sequences (Pennsylvanian Pottsville Formation, Alabama). Bar scales are 2 cm long in (A–C), 1 cm long in (D).

The visibility of those post-depositional traces that pass into the stratigraphic record is governed by factors previously addressed. Depending on organism behavior, post-depositional traces preserved in full-relief may be subject to bed-junction preservation (Figs. 6.9 and 6.10). Manifestation of intergenic traces—those produced by organisms that exploit or travel along lower and upper surfaces of event beds—may be improved by virtue of preservation as hyporeliefs or epireliefs (Fig. 6.8C).

Event-Bed Integrity Certain modes of preservation are dependent on preservation of bedding. Destruction of discrete beds and bedding planes by intense post-depositional biogenic mixing precludes the preservation of trace fossils as semireliefs. Whether or not an event deposit maintains its integrity in the stratigraphic record depends on a number of factors, the most important of which are depth of burrowing, rate of postdepositional bioturbation, and event-bed thickness

(Wheatcroft, 1990) (Fig. 6.9). The first factor is governed by post-depositional environmental conditions (e.g., benthic oxygenation) but also depends on geologic age. Thickness of the benthic boundary layer increased markedly during the early Phanerozoic in step with marine invertebrate evolution. Expectedly, preservation potential of discrete beds, and in particular the lower parts of event beds with associated semireliefs, improves with increasing event-bed thickness. In the cases where post-depositional bioturbation compromises the integrity of distinct beds, ichnologic fidelity is obviously reduced. However, incomplete or partial admixing of event sediments and background sediments commonly enhances the textural contrast between preserved structures and host sediment, thereby increasing visibility (Figs. 6.9, 6.10B). In cases of extreme mixing, burrow fills may provide the only evidence for depositional events. As in the ‘tubular tempestites’ described by Tedesco and Wanless (1991), the only record of storm deposition may be coarser, storm-derived passive fills within

PRESERVATION IN COARSE-GRAINED SUBSTRATES

Fair-weather Muds

Increasing Depth/intensity of Fair-weather Bioturbation

Decreasing Event Bed Thickness

D

tubular tempestites Th

C

B

Ar Sk E

Op

A

101

and high-energy events are relatively infrequent. Other heterolithic sequences may develop in environments wherein high-frequency variations in energy are the norm. Tidal laminite sequences in which millimeter to centimeter-scale alternation of finer and coarser sediments reflect diurnal or semidiurnal tidal cycles provide a good example. In associated tidal environments, organisms may produce a variety of surface tracks and trails and shallow subsurface burrows that would stand little chance of preservation under static conditions. However, environmental dynamics generally preclude the development of a thoroughly bioturbated mixed layer. Moreover, like the normal marine mixed layer traces preserved by event deposition, biogenic structures are cast during rapid deposition of tidal laminae, and hence they may be exquisitely preserved as semireliefs on bedding planes (Figs. 6.7C and 6.8D). In thinly laminated sediments, depression of subjacent thin laminae by tracemaker appendages may result in preservation as cleavage reliefs, or ‘undertracks’ (Seilacher, 1964) (Fig. 6.7C).

Impact of Lithification

FIGURE 6.9 Factors controlling preservation of postdepositional traces in sequences impacted by event deposition. Where fair-weather biogenic disruption of event-bed tops is limited (A), event-related traces are well preserved (escape structures, E; Skolithos, Sk; Arenicolites, Ar; Ophiomorpha, Op). Where biogenic disruption is moderate (B,C), preservation of event-related traces is limited by overprinting by fair-weather structures, the visibility of which may be enhanced by virtue of bed-junction preservation. Where disruption is intense, and where sand and mud are thoroughly admixed (D), event-related traces are destroyed. Visibility of fair-weather traces may be enhanced with increased textural/compositional contrast in admixed sediment and/or by event-related infilling of deep open burrows to form tubular tempestites (an example of concealed bed-junction preservation).

deeper parts of vertically extensive burrows (e.g., Fig. 6.10B). Such occurrences, wherein burrows are preserved but the original sedimentary beds that supplied burrow fill are not, exemplify what Simpson (1957) called concealed bed-junction preservation.

Other Heterolithic Successions Above discussion focuses on facies that develop in settings wherein quiet conditions are the norm

A variety of diagenetic processes may impact ichnofossil preservation in heterogeneous sedimentary successions, including preferential cementation and/or secondary mineralization of burrowed sediment. Sequences that are well lithified tend to split along bedding planes and thereby avail clear views of pre- and post-depositional traces that are disposed as semireliefs or cleavage reliefs. In contrast, traces preserved in sequences that are not fully lithified may be difficult if not impossible to recognize or access. This is due to the generally lower propensity for relatively unconsolidated sediments to split cleanly along lithologic contacts. Bedding-plane surfaces exposed by natural weathering and erosion (or by careful preparation by the ichnologist) generally do not reveal the same detail.

PRESERVATION IN COARSE-GRAINED SUBSTRATES Compared to muds, sand-dominated marine sequences generally reflect rapid deposition under more energetic conditions in shallow-water environments. There are exceptions, of course, since sands accumulate in a wide range of marine settings impacted by a variety of processes. Presence and behaviors of infaunal organisms, the extent to which they bioturbate substrates, and the ichnologic fidelity

102


Op

Op Th Th

A

B

FIGURE 6.10. Examples of storm-related ichnofabrics (Cretaceous Eutaw Formation, western Georgia). (A) Discrete storm bed with event-related traces (mainly Ophiomorpha, Op). Top of bed has been partly disrupted by fair-weather bioturbators. (B) Texturally hybridized muddy sand formed by intense disruption of thin storm bed(s) by fair-weather bioturbators. Large sand-filled burrows (Thalassinoides, Th) represent ‘tubular tempestites’ (Tedesco and Wanless, 1991) and exemplify concealed bed-junction preservation.

of resulting ichnofabrics vary as a function of environmental rigor, rates and frequencies of deposition, and frequency and depth of intermittent erosion. Hence, as with mud substrates, sweeping generalizations about ichnofossil preservation in coarser substrates are difficult to make. Nonetheless, many of the factors that impact ichnologic fidelity and trace fossil visibility can be exemplified by considering the Skolithos ichnofacies, which dominates many shallow marine and marginal marine sands.

Skolithos Ichnofacies The Skolithos ichnofacies characterizes slightly muddy to well-sorted sands deposited in unpredictable, moderate to very high-energy settings subject to episodes of both rapid deposition and erosion. Such substrates may or may not be characterized by shallow-tier suspension- and deposit-feeders, such as bivalves and worms (Bromley, 1996), but most are colonized by relatively deep burrowers, mainly suspension-feeding organisms. Consequently, trace fossil associations representing the Skolithos ichnofacies are typified by vertically extensive, sometimes branched, commonly lined, cylindrical and/or U-shaped dwelling burrows (e.g., Skolithos, Ophiomorpha, Arenicolites), some of which may reflect equilibrium movements in response to substrate aggradation and/or scour (e.g., Diplocraterion, Conichnus). Evidence for shallower tier bioturbation is relatively rare in these associations. In some cases, paucity of shallow-tier structures may indicate that conditions were unfavorable for shallower infauna. In others, it may reflect diminished ichnologic fidelity.

Periodic erosion or physical reworking of upper parts of substrates favors the preservation of the deeper tier traces (Bromley and Asgaard, 1991; Bromley, 1996). Skolithos ichnofacies sediments vary from very weakly to completely bioturbated. Bioturbation intensity depends on various factors, such as tracemaker population densities, types, rates, and depths of tracemaker activities, and the period over which environmental conditions are favorable for colonization, i.e., the colonization window (Pollard et al., 1993). Individual trace fossils are more evident and more easily studied where colonization windows were only briefly open. In these cases, bioturbation intensity is low and burrows clearly stand out from laminated or crosslaminated background fabrics (Fig. 6.11A). Where colonization windows were open longer, bioturbation is more thorough, overprinting of burrows may be intense, and ichnologic fidelity may be limited, particularly if deeply and densely emplaced elite trace fossils mask the biogenic activities of shallower dwelling and/or less prolific organisms. As with mud substrates, visibility of trace fossils in Skolithos ichnofacies is influenced by factors such as tracemaker behavior, diagenesis, and differential weathering. In partly or thoroughly bioturbated sands, trace fossil visibility is enhanced if organism behavior enhances the textural or compositional contrast between the resulting trace fossil and surrounding sediment. Maintenance of open burrows may lead to passive infilling with contrasting material. Construction of burrow walls (e.g., clay linings of Palaeophycus and pelleted linings of Ophiomorpha; Fig. 6.11A) or textural/mineralogic segregation of

PRESERVATION IN FIRMGROUNDS

A

C

103

B

D

FIGURE 6.11 Examples of preservation in Skolithos ichnofacies sands. (A) Clay-lined Ophiomorpha cutting across preferentially iron-stained, cross-laminated sand (tidal facies, Cretaceous Eutaw Formation, western Georgia). (B) Macaronichnus manifest by virtue of tracemaker segregation of dark and light sands into mantle and core, respectively (tidal inlet facies, Eutaw Formation, central Alabama). (C) Varying expression of ichnofabrics in a sand unit (Eocene Meridian Sand, western Alabama). Sand appears relatively featureless (center). Scraping away the weathering rind reveals obvious burrow-mottling (right), whereas slow differential erosion by surface runoff provides three-dimensional exposure of ichnofossils (left). (D) Close-up of trace fossils (e.g., Teichichnus and Ophiomorpha) exposed in (C). Bar scales in (A,B,D) = 2 cm. Lens cap near lower right corner of (C) is 5.5 cm in diameter.

sediment grains by selective sediment feeders, such as that manifest in distinct burrow mantles and cores of Macaronichnus (Fig. 6.11B), clearly improves trace fossil visibility. Variations in composition and texture, as well as the presence of mucus linings, may result in differential diagenesis. Burrows or burrow parts are commonly more or less susceptible to mineralization, cementation, and staining than host sediments, further enhancing their presence. Primary or diagenetically enhanced contrasts may be amplified in outcrop by differential erosion and weathering (Fig. 6.11C,D).

PRESERVATION IN FIRMGROUNDS Firmgrounds are stiff but unlithified substrates. Mechanisms for marine firmground development include (1) incipient synsedimentary cementation of

carbonates during periods of sediment bypass and/or nondeposition and (2) erosional exhumation of compacted muds. The former mechanism is exemplified in prelithification omission suites documented in some chalk sequences (Bromley, 1975). The latter mechanism operates in response to a variety of autocyclic processes (e.g., tidal channel migration), but it is particularly relevant in the formation of sequence stratigraphic surfaces (see MacEachern et al., Chapter 7). Because habitation is limited to organisms capable of excavating stiff sediments, bioturbation in firm substrates is typically heterogeneous. Firmground trace fossil assemblages, which correspond to the Glossifungites ichnofacies, are typified by vertically extensive, open burrows excavated by crustaceans (e.g., Thalassinoides), bivalves (Gastrochaenolites), and worms (Arenicolites). Owing in part to the lack of a surface mixed layer, ichnologic fidelity of firmground ichnofabrics is typically high.

104


Firmground muds

Concealed Bed-junction Preservation adhered

floating

casting by sand 1 erosion of sand 1 deposition of sand 2 casting by sand erosion of sand

Bed-junction Preservation casting by sand

FIGURE 6.12 Well-expressed firmground burrow systems (Thalassinoides) at coplanar sequence boundary/transgressive surface (oblique view of K–T boundary, western Alabama). Burrow fills (Paleocene sandy marl) contrast markedly with host sediment (Upper Cretaceous sandy chalk). Tape roll is 10 cm in diameter.

Moreover, firmground structures are typically very well manifest. Trace fossil visibility is enhanced by sharp, commonly scratched burrow walls and bed-junction preservation. Burrows are typically filled with coarser sediments that contrast markedly with the host sediment and the pre-omission softground ichnofabric preserved therein (Fig. 6.12). Burrows may be highlighted by preferential cementation of burrow fills or mineralization of burrow walls prior to burrow filling (Bertling, 1999). Additional mechanisms for firmground development have been recognized from studies of Cambrian sequences (Droser et al., 2002; Jensen et al., 2005). Well-preserved firmground trace fossils occur in thin marine mudrocks that are intercalated with silty or sandy storm deposits. In these cases, stiff mud formed due to the lack of mixedlayer bioturbation and also possibly to microbial sediment binding, rather than by erosion or cementation. Associated firmground traces, consisting mainly of shallowly emplaced, sharp-walled open burrows, owe their preservation to casting by coarser sediment from an overlying event bed (bed-junction preservation). Alternatively, they may be cast by sediment that bypassed the seafloor, reflecting two forms of concealed bed-junction preservation: floating preservation, whereby burrow casts are isolated in background mud, and adhered preservation, whereby burrows are attached to an event bed that was independent of and deposited

FIGURE 6.13 Bed-junction and concealed bed-junction preservation in Cambrian firmground mud (after Droser et al., 2002). Firmground conditions developed due to lack of mixed-layer bioturbation and, possibly, microbial substrate stabilization.

after the casting (Fig. 6.13).

event

(Droser

et

al.,

2002)

PRESERVATION IN HARD SUBSTRATES Hard substrates include (1) hardgrounds sensu stricto, formed by syndepositional cementation of carbonate sediments at or near the seafloor, and (2) rockgrounds, which are lithified substrates of various types that have been exhumed. Trace fossil assemblages produced in these substrates define the Trypanites ichnofacies. Assemblage character is controlled by substrate composition, environmental conditions, geologic age, and length of time that the colonization window is open (Bromley, 1994). Assemblages in hardgrounds may include relatively shallow bioerosion features (rasping and gnawing structures; e.g., Gnathichnus and Radulichnus) that comprise the Gnathichnus subichnofacies, as well as borings produced by more deep-seated bioeroders (e.g., Entobia and Gastrochaenolites) that define the Entobia subichnofacies (Bromley, 1994). Ichnologic integrity of assemblages in hard substrates, particularly those composed of carbonate, is controlled by the colonization window. As described by Bromley (1994), colonization of carbonate hardgrounds or rockgrounds follows a temporal succession. Microbes are the first to occupy newly exposed substrates. They are followed by shallow bioeroders responsible for various surficial structures (Gnathichnus subichnofacies), and then by the

PRESERVATION IN WOODGROUNDS

A

105

B

FIGURE 6.14 Borings (Gastrochaenolites) in carbonate hardground (age and origin of specimens uncertain). (A) Borings with sharp, partly mineralized walls. (B) Resistant boring casts weathering out in positive relief. Scale bars are 1 cm long.

excavators of deeper borings (Entobia subichnofacies). Because bioerosion processes are destructive to substrates, features of the Gnathichnus subichnofacies are normally lost during extended episodes of endolith colonization. Ichnologic fidelity is high only when the colonization window is shortened by rapid burial. Visibility of bioerosion structures is generally good. If preserved, traces of the Gnathichnus subichnofacies are manifest in negative relief on hardground surfaces. Like firmground burrows, borings have extremely sharp walls, which may be accentuated by diagenetic mineralization (Bertling, 1999; Ekdale and Bromley, 2001), and they are commonly filled with sediment that contrasts with the host substrate (Fig. 6.14A). Moreover, boring casts may be less susceptible than the host substrate to dissolution. In such cases, the three-dimensional geometry of borings, which otherwise is obscured beneath hard substrate surfaces, may be rendered in positive relief (Fig. 6.14B).

PRESERVATION IN WOODGROUNDS Woodgrounds include (1) composite wood substrates (xylic peatgrounds) characterized by the Teredolites ichnofacies (Bromley et al., 1984), and (2) isolated wood clasts and/or stumps (e.g., loggrounds; Savrda et al., 1993). Modern marginal marine woodgrounds host a variety of biogenic structures that include relatively shallow traces normally associated with other soft, firm, or hard substrate types, as well as relatively deeply excavated pholadid and teredinid bivalve borings (Teredolites) (Gingras et al., 2004). In contrast, ancient marine woodgrounds rarely contain identifiable ichnofossils other than Teredolites (Savrda et al., 2005).

Observed differences between modern and ancient woodground trace fossil assemblages may be related to real differences in environmental setting and associated communities of wood inhabitants. Alternatively, they may reflect the fact that modern wood substrates have not yet passed through the full succession of taphonomic filters. Shallower borings or burrows may have been emplaced in some ancient woodgrounds but were subsequently lost when outer parts of substrates were destroyed by pervasive bivalve bioerosion or by mechanical or chemical degradation (Savrda et al., 2005). In this regard, woodgrounds may be similar to lithic carbonate substrates. Preservation of shallowly emplaced woodground traces, like those of the Gnathichnus subichnofacies, may be limited to wood substrates that are buried after a brief period of colonization. As in other substrates addressed herein, tracemaker behavior, as well as subsequent sedimentologic and diagenetic processes may influence ichnofossil preservation in woodgrounds. As an example, some producers of Teredolites (i.e., teredinid bivalves) secrete a calcite lining along all or part of their borings. These linings may be the only evidence of boring activity in fossil woodgrounds, particularly if borings are unfilled and the substrate is highly compacted (Fig. 6.15). Manifestation of woodground borings is enhanced by casting of borings by sediment and/or diagenetic minerals (e.g., calcite, pyrite, silica) that contrast with ambient wood and are less susceptible to compaction (Fig. 6.15A). These factors are particularly important where mechanical and biodegradational processes have destroyed the original wood. Mats of filled or unfilled and compressed linings (ghost log-grounds; Fig. 6.15B) and reworked Teredolites casts and/or linings (Fig. 6.15C) provide the only evidence for the pre-existence of woodgrounds in some settings (Savrda et al., 1993).

106


A

B

C

FIGURE 6.15 Preservation of Teredolites in woodgrounds. (A) Sediment- and mineral-filled, lined and unlined Teredolites. (B) Casts and linings of Teredolites in a ghost log-ground. (C) Reworked sediment-filled Teredolites tube linings liberated from original wood substrates (A,C, Paleocene Clayton Formation, western Alabama; B, Cretaceous Mooreville Chalk, central Alabama). Bar scales = 1 cm.

¨ TTEN ICHNOFOSSIL-LAGERSTA Fossil-lagersta¨tten, deposits that contain extraordinary amounts of paleontologic information (Seilacher et al., 1985; Allison, 1988b), have counterparts in the trace fossil realm. In containing more paleobiological or paleoenvironmental information than normal, deposits characterized by unusually high ichnologic fidelity and/or trace fossil visibility can be regarded as ichnofossil-lagersta¨tten (Savrda and Ozalas, 1993; Mangano and Buatois, 1995; Forno´s et al., 2002). In the body fossil realm, lagersta¨tten fall into two basic categories. Conservation lagersta¨tten are those wherein exceptional preservation of fossils resulted from rapid burial (obrution deposits), diminished benthic oxygenation (stagnation deposits), early diagenetic mineralization, bacterial sealing (conservation traps), or some combination thereof. Concentration lagersta¨tten are those wherein fossils are unusually abundant, reflecting concentration or condensation by sedimentologic and biological processes. Suites of taphonomic factors that influence body fossils and ichnofossils are clearly not identical. Nonetheless, without too much twisting, ichnofossil-lagersta¨tten can be placed into the same genetic categories.

Conservation Ichnofossil-Lagersta¨tten As noted in various sections of this chapter, preservation potential of surface and shallow

subsurface traces is normally low. Exceptional preservation of tracks, trails, and shallow endogenic burrow systems requires relatively rapid casting by storm deposits (Cruziana ichnofacies), turbidites (Nereites ichnofacies), or other episodically introduced sediment (e.g., lacustrine Mermia ichnofacies). Similarly, preservation of shallow-tier bioerosion features (Gnathichnus subichnofacies) in lithic carbonate substrates (and possibly wood substrates) requires relatively rapid burial. Hence, deposits preserving these trace fossil components represent obrution ichnofossil-lagersta¨tten. Stagnation lagersta¨tten also have analogs in the ichnofossil realm. Exceptional preservation of mixed-layer ichnofabrics resulting from the onset of extended episodes of oxygen deficiency and consequent cessation of bioturbation represent one example (Savrda and Ozalas, 1993). However, reoxygenation episodes may also result in what can be considered ichnofossil-lagersta¨tten. Emplacement of transition-layer burrows into previously deposited dark, laminated mud commonly results in fabrics wherein preserved ichnofossils are manifest in exquisite detail (Fig. 6.3). Ichnologic versions of conservation traps are also common. These include deposits in which early diagenetic concretions preserve ichnologic elements that in unmineralized sediments were masked by compaction or are otherwise poorly expressed (Fig. 6.5). Similarly, deposits in which trace fossil preservation was enhanced by microbial substrate stabilization can be considered ichnofossil

107

ACKNOWLEDGEMENTS

conservation traps. Significant bioturbation normally precludes development of microbial mats. Nonetheless, microbially enhanced preservation of shallow burrows and other biogenic structures in ‘matgrounds’ (Seilacher, 1999) may be important, particularly in terminal Proterozoic and earliest Palaeozoic deposits (Gehling, 1999; Jensen et al., 2005).

Concentration Ichnofossil-Lagersta¨tten As commonly noted in introductory treatments of ichnology, trace fossils are far less susceptible than body fossils to physical reworking and transport. Hence, mechanical concentration of ichnofossils is not normally given much attention. However, some ichnofossils, by virtue of their early diagenetic mineralization (pyritized tubes), more resistant linings (Ophiomorpha), or more compact fills (Taenidium), can be physically liberated by erosion from host substrates, transported, and concentrated as lags (Baird, 1978; Balson, 1980; Brett and Baird, 1991; Savrda et al., 2000). Given that such reworked ichnofossils may provide the only evidence of the existence of a substrate and biogenic activities therein, resulting deposits can be considered as forms of concentration ichnofossil-lagersta¨tten. The concept of concentration ichnofossil-lagersta¨tten can be applied more liberally in other situations. It has been applied to deposits in which substrates have been concentrated—e.g., marine shelf deposits wherein abundant Teredolites-bored log-grounds accumulated in response to winnowing or sediment starvation (e.g., Savrda et al., 2005). Others have applied the concept to ichnofabrics developed across omission and/or condensation surfaces that preserve clear records of ecologic succession in response to evolving substrate consistency (Mangano and Buatois, 1995). Indeed, some firmground ichnofabrics warrant consideration as ichnofossil-lagersta¨tten based on enhanced trace fossil visibility alone.

CONCLUSIONS The taphonomic state of a trace fossil assemblage or ichnofabric is controlled by a variety of interacting factors that govern the entry of biogenic structures into the stratigraphic record (ichnologic fidelity) and/or the degree to which preserved ichnofossil elements are manifest therein (trace fossil visibility). Controlling factors generally fall within one of three categories: (1) physical environmental—e.g., substrate type, and

rates and frequencies of deposition; (2) ecologic—infaunal tiering and behavioral routines of tracemakers; and (3) diagenetic—preferential mineralization, general lithification, and weathering. Varying combinations of these factors result in preservation states ranging from poor to excellent. Regardless of whether an ichnofabric reflects limited preservation or represents an ichnofossil-lagersta¨tte, careful consideration of taphonomic aspects can help assess aspects of depositional regime, tracemaker palaeobiology, and post-depositional histories of substrates.

ACKNOWLEDGEMENTS I thank volume editor William Miller for inviting this contribution, and Tony Ekdale and Richard Bromley for reviews of an earlier version of this chapter. Acknowledgement is made to the Donors of the American Chemical Society Petroleum Research Fund for partial support of the research upon which this chapter is based.

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Chattannooga Shale (Upper Devonian) and experiments. Journal of Sedimentary Research, 69, 1041–1049. Locklair, R.E. and Savrda, C.E. (1998). Ichnology of rhythmically bedded Demopolis Chalk (Upper Cretaceous, Alabama): implications for paleoenvironment, depositional cycle origins, and tracemaker behavior. Palaios, 13, 423–438. MacNaughton, R.B. and Pickerill, R.K. (2003). Taphonomy and taxonomy of trace fossils: a commentary. Lethaia, 36, 66–70. Mangano, M.G. and Buatois, L.A. (1995). A conceptual framework of trace fossil-lagerstatten. Second International Symposium on Lithographic Limestones, Extended Abstracts, Lleida and Cuenca, Spain, July 9–16, pp. 103–105. Maples, C.G. (1986). Enhanced paleoecological and paleoenvironmental interpretations result from analysis of early diagenetic concretions in Pennsylvanian shales. Palaios, 1, 512–516. Martinsson, A. (1970). Toponomy of trace fossils. In: Crimes, T.P. and Harper, J.C. (Eds.), Trace Fossils, Geological Journal, Special Issue 3, pp. 323–330. Miller, W., III (2003). Paleobiology of complex trace fossils. Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 3–14. Morrow, D.W. (1978). Dolomitization of Lower Paleozoic burrowfillings. Journal of Sedimentary Petrology, 48, 295–306. Orr, P.J. (1994). Trace fossil tiering within event beds and preservation of frozen profiles: an example from the Lower Carboniferous of Menorca. Palaios, 9, 202–210. Pemberton, S.G. and MacEachern, J.A. (1997). The ichnological signature of storm deposits: The use of trace fossils in event stratigraphy. In: Brett, C.E. and Baird, G.C. (Eds.), Paleontological Events–Stratigraphic, Ecologic, and Evolutionary Implications, Columbia University Press, New York, pp. 73–109. Pickerill, R.K. (1994). Nomenclature and taxonomy of invertebrate trace fossils. In: Donovan, S.K. (Ed.), The Palaeobiology of Trace Fossils, John Wiley and Sons, Chichester, pp. 3–42. Pollard, J.E., Goldring, R., and Buck, S.G. (1993). Ichnofabrics containing Ophiomorpha: significance in shallow-water facies interpretation. Journal of the Geological Society of London, 150, 149–164. Savrda, C.E. and Bottjer, D.J. (1988). Limestone concretion growth documented by trace-fossil relations. Geology, 16, 908–911. Savrda, C.E. and Nanson, L. (2003). Ichnology of fair-weather and storm deposits in an Upper Cretaceous estuary (Eutaw Formation, western Georgia, USA). Palaeogeography, Palaeoclimatology, Palaeoecology, 202, 67–83. Savrda, C.E. and Ozalas, K. (1993). Preservation of mixed-layer ichnofabrics in oxygenation event beds. Palaios, 8, 609–613. Savrda, C.E., Ozalas, K., Demko, T.H., Huchison, R.A., and Scheiwe, T.D. (1993). Log-grounds and the ichnofossil Teredolites in transgressive deposits of the Clayton Formation (Lower Paleocene), western Alabama. Palaios, 8, 311–324. Savrda, C.E., Blanton-Hooks, A.D., Collier, J.W., Drake, R.A., Graves, R.L., Hall, A.G., Nelson, A.I., Slone, J.C., Williams, D.D., and Wood, A. (2000). Taenidium and associated ichnofossils in fluvial deposits, Cretaceous Tuscaloosa Formation, eastern Alabama, southeastern U.S.A. Ichnos, 7, 227–242. Savrda, C.E., Counts, J., McCormick, O., Urash, R., and Williams, J. (2005). Log-grounds and Teredolites in transgressive deposits, Eocene Tallahatta Formation (southern Alabama, USA). Ichnos, 12, 47–57. Scheiber, J. (2002). The role of an organic slime matrix in the formation of pyritized burrow trails and pyrite concretions. Palaios, 17, 104–109.

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Tedesco, L.P. and Wanless, H.R. (1991). Generation of sedimentary fabrics and facies by repetitive excavation and storm infilling of burrow networks, Holocene of South Florida and Caicos Platform, B.W.I. Palaios, 6, 326–343. Wetzel, A. and Bromley, R.G. (1994). Phycosiphon incertum revisited: Anconichnus horizontalis is its junior subjective synonym. Journal of Paleontology, 68, 1396–1402. Wheatcroft, R.A. (1990). Preservation potential of sedimentary event layers. Geology, 18, 843–845. Wilson, M.V.H. (1988). Paleocene #9. Taphonomic processes: information loss and information gain. Geoscience Canada, 15, 131–148.

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7 Uses of Trace Fossils in Genetic Stratigraphy James A. MacEachern, S. George Pemberton, Murray K. Gingras, Kerrie L. Bann, and Lynn T. Dafoe

SUMMARY : Trace fossils represent both sedimentological and paleontological entities and as such, constitute a unique blending of potential environmental indicators in the rock record. Trace fossils and trace fossil suites can be employed effectively to aid in the recognition and genetic interpretation of various discontinuity types. Ichnology may be employed to resolve surfaces of stratigraphic significance in two main ways: (1) through the identification of discontinuities using omission suites, comprising substratecontrolled ichnofacies (i.e., firmground Glossifungites Ichnofacies, hardground Trypanites Ichnofacies, and woodground Teredolites Ichnofacies) or palimpsest softground suites; and (2) through careful analysis of vertical softground ichnologic successions (analogous to facies successions). Integrating data derived from omission suites with paleoecological data from vertically and laterally juxtaposed softground ichnological suites greatly enhances the recognition and interpretation of potentially significant stratigraphic surfaces.

stratigraphy and to genetic stratigraphic sequences, is also vital in resolving the depositional environments of associated deposits, and in determining the allocyclic controls on the depositional systems. The advent of genetic stratigraphy created a new avenue of ichnological application (Pemberton and Frey, 1985; MacEachern et al., 1990, 1991a,b, 1992a,b; Savrda, 1991a,b; Pemberton et al., 1992a,b). Crimes (1975) summarized the role of trace fossils in stratigraphic analysis, as it was perceived at the time. Owing to the background of most ichnologists, it was perhaps inevitable that the pursued direction would be largely biostratigraphic. It was suggested that the Precambrian–Cambrian boundary could be defined on the basis of trace fossils, and that species of Cruziana had biostratigraphic zonation significance in otherwise unfossiliferous basins. Indeed, Crimes (1975) presented a table showing the known ranges of 30 trace fossil genera. Work, since, has demonstrated that these ranges are spurious, and were based on incomplete datasets. Analysis of the Cambrian Gog Group of Alberta also led Magwood and Pemberton (1990) to question the viability of the Cambrian–Ordovician ichnostratigraphic paradigm. Indeed, the well-established appreciation that ichnogenera are temporally long ranging and strongly facies controlled should have forewarned ichnologists that this was likely to be an unfruitful approach. However, the characteristics that make trace fossils unsuitable to biostratigraphy are the ones that make them indispensable to genetic stratigraphic analysis and facies reconstruction. Through the 1970s and 1980s, numerous articles were published on trace fossil suites that occurred at stratigraphic breaks. Bromley (1975) summarized

INTRODUCTION Genetic stratigraphy lies at the core of three main stratigraphic paradigms: genetic stratigraphic sequences (cf. Galloway, 1989a,b), allostratigraphy (cf. Walker and James, 1992), and sequence stratigraphy (cf. van Wagoner et al., 1990). The recognition of stratigraphic breaks is essential in any genetic stratigraphic paradigm, but is commonly a challenging task, particularly in subsurface analysis. Interpreting the origin of discontinuities, essential to sequence


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the extensive work done on trace fossils at omission surfaces, and presented the terminology ‘preomission,’ ‘omission,’ and ‘postomission’ to characterize the nature of the resulting juxtaposed suites. Such terminology remains as useful today as it was when conceived some 30 years ago. Bromley further showcased the nature of prelithification omission burrows (generally palimpsest softground and firmground suites) and postlithification borings (essentially hardground suites). The evolution of the substrate itself was also shown to result in an intermingled assemblage. This is particularly true of carbonate omission under conditions of slow deposition (e.g., condensed sections and hiatal surfaces in chalk). Data collected in the late 1970s and early 1980s led to the recognition of a number of substrate-controlled trace fossil suites associated with stratigraphic discontinuities. Hayward (1976) described a suite attributable to the Glossifungites Ichnofacies, developed along a submarine canyon margin incised into the Lower Miocene Nihotupu Formation, Tirikuhua Point, New Zealand. Kobluk et al. (1977) and Pemberton et al. (1980) described occurrences of the Trypanites Ichnofacies demarcating the Silurian–Devonian disconformity in Ontario, Canada. From data collected in 1979, Pemberton and Frey (1985) summarized the neoichnological expression of the Glossifungites Ichnofacies forming in transgressively exhumed salt marsh mudstones along the coast of Catherine’s Island. Fu¨rsich et al. (1981) evaluated softground, firmground, and remanie´ phases of colonization along a regional discontinuity at the Austin–Taylor (Upper Cretaceous) contact in Texas. Miller and Rehmer (1982) illustrated the role of trace fossils in ascertaining whether a sharp contact between two units represented a short-lived discontinuity or a major unconformity, using an assessment of the interface between the Lower Devonian Esopus Shale and the Carlisle Center Formation in New York. They were able to show that the Esopus Shale was largely unconsolidated at the time the Carlisle Fm was deposited and that what had hitherto been regarded as an unconformity was more likely to be no more than a depositional hiatus. Bromley et al. (1984) described an occurrence of the Teredolites Ichnofacies demarcating a channel base excavated onto a coal deposit of the Upper Cretaceous Horseshoe Canyon Formation, in Drumheller, Alberta, Canada. Saunders and Pemberton (1986) also documented the Teredolites Ichnofacies at a transgressive surface of erosion (TSE) in the Bearpaw–Horseshoe Canyon transition in Drumheller. Vossler and

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Pemberton (1988) indicated that suites attributable to the Glossifungites Ichnofacies are common at the bases of conglomerates of the Turonian Cardium Formation, incised into underlying marine mudstones. They argued that the discontinuity recorded, at the very least, a depositional hiatus, but that the surfaces coincided with major sequence stratigraphic breaks in the Cardium (cf. Plint, 1988 and Plint et al., 1988 for summaries of the unit’s stratigraphic architecture). Oppelt (1988) also identified suites of the Glossifungites Ichnofacies associated with transgressive erosion of subaerial delta plain deposits, recording the Lower Cretaceous Gething–Bluesky Formation contact in northeastern British Columbia. Jones and Pemberton (1989) summarized a Pleistocene occurrence of the Glossifungites Ichnofacies, from exhumed lagoonal muds beneath tidal channels of the Ironshore Formation, at Salt Creek, Grand Cayman. Similarly, Mańgano and Buatois (1991) summarized the role of ichnological suites in the evaluation of substrate consolidation of some Lower Cretaceous shallow marine carbonate deposits in the Aconcagua area of Argentina, with the aim of identifying discontinuities. Dam (1990) provided a groundbreaking evaluation of a shallow marine succession in East Greenland. There, the Lower Jurassic Neill Klinter Formation contains well-developed omission suites of Diplocraterion parallelum, excavated into coal capping delta plain deposits. Bromley and Goldring (1992) also summarized the character of firmground trace fossil omission suites associated with the Cretaceous–Paleocene unconformity in southern England. It is instructive to note just how early the routine recognition of palimpsest omission suites associated with stratigraphic discontinuities was. In essence, the ‘discovery’ that ichnology has a direct application to sequence stratigraphic analysis was more a case of awaiting a formal terminology that described the genesis of the discontinuities. What followed in the 1990s was more a cataloging of case studies that illustrated the role of omission suites and juxtaposed softground ichnological suites in the context of sequence stratigraphic analysis. In 1990, the International Association of Sedimentologists held its 13th International Sedimentological Congress in Nottingham, England, where a special meeting of ichnological specialists met to discuss current thinking in trace fossil analysis. There, MacEachern et al. (1990) presented a poster illustrating the utility of the Glossifungites Ichnofacies in delineating surfaces of sequence stratigraphic significance. MacEachern et al. (1991a) published these findings at the following American Association of Petroleum Geologists (AAPG) annual meeting in

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Dallas, Texas. Probably of even greater importance was the presentation of a talk and a poster at a NUNA Research Conference on high-resolution sequence stratigraphy, hosted by the Geological Association of Canada (MacEachern et al., 1991b). The meeting brought together a small but expert international group of researchers in sequence stratigraphy, many of who were introduced for the first time to the applications of ichnology. During the same period, Savrda (1991b) published an article on the application of ichnology to sequence stratigraphic studies, with a case study on the discontinuity separating the Upper Cretaceous Prairie Bluff Chalk and the Lower Paleocene Clayton Formation. In that study, Savrda recognized that the lowstand fluvial valley fill succession of the Clayton Formation, which sits on a Type 1 sequence boundary, lacked omission suites, but that suites attributable to the Glossifungites Ichnofacies were associated with a TSE that truncated the valley interfluve area. The downlap surface separating the transgressive systems tract of the Clayton Formation and the highstand systems tract of the Porters Creek Formation was likewise documented to contain firmground suites. Savrda (1991a) immediately followed this up with an article on the role of suites attributable to the Teredolites Ichnofacies in the demarcation of discontinuities that record sea-level dynamics. He was able to show the utility of such suites, which later would be regarded as log-grounds (Savrda et al., 1993), associated with transgressively generated stratigraphic breaks. In 1992, two publications came on the scene that established ichnology’s role in stratigraphic applications. First, the publication of the influential textbook ‘Facies Models: Response to Sea Level Change,’ edited by Walker and James (1992) facilitated the widespread dissemination of the role of ichnology in sequence stratigraphy. In that volume, Pemberton et al. (1992a) summarized the application of trace fossil analysis in recognizing a wide variety of discontinuities, and laid out the rationale for applying ichnofacies analysis to genetic stratigraphy. In the article, the authors argued that trace fossil suites could be employed to aid in the recognition of various discontinuity types, as well as to assist in their genetic interpretations. Ichnology was deemed to be effective in resolving surfaces that may have stratigraphic significance in two principal ways: (1) using substrate-controlled (e.g., Glossifungites, Trypanites, and Teredolites Ichnofacies) or softground palimpsest trace-fossil suites associated with colonization of the discontinuity; and (2) recognition of vertically and laterally juxtaposed ichnological suites that contravene Walther’s Law. They advocated that

the effectiveness of both approaches was greatly enhanced when used in tandem. Second, a Society of Economic Paleontologists and Mineralogists (SEPM) sponsored core workshop and volume, entitled ‘Applications of Ichnology to Petroleum Exploration,’ edited by Pemberton (1992) provided a number of subsurface case studies, many of which concentrated on the identification of discontinuities. Sedimentologists and stratigraphers working on subsurface problems were introduced to the refinement in interpretation accorded by integration of ichnology with conventional facies analysis. MacEachern et al. (1992a) concentrated on the recognition of transgressive discontinuities and of transgressive systems tracts from the Viking Formation of central Alberta. MacEachern et al. (1992b) evaluated the application of the Glossifungites Ichnofacies to the recognition of various stratigraphic discontinuities, though mainly from the Western Interior Seaway of Alberta. Several other papers in the volume addressed similar issues (e.g., Pemberton et al., 1992b; Raychaudhuri et al., 1992). Taylor and Gawthorpe (1993) attempted to tailor the established ichnofacies-based approach to the developing ichnofabric concept, with little refinement. They suggested 6 main ways in which trace fossils indicate key stratal surfaces: (A) facies change (environment); (B) salinity change (marine incursion); (C) salinity change (burrowed soil); (D) omission surface (firmground); (E) omission surface (hardground); and (F) paleosol (rooted shoreface). Of these, A–C and F correspond to juxtaposed softground suites that contravene Walther’s Law, and D and E correspond to suites attributable to the Glossifungites Ichnofacies and Trypanites Ichnofacies, respectively. This approach failed to provide advancements to the previously established concepts. In the succeeding decade, it became widely accepted that trace fossils are exceedingly useful in high-resolution sequence stratigraphic analysis (e.g., MacEachern and Pemberton, 1994; MacEachern et al., 1995, 1998, 1999a,b; Savrda, 1995; Ghibaudo et al., 1996; MacEachern and Burton, 2000; Savrda et al., 2001a,b; Bann et al., 2004, 2005; Gibert and Robles, 2005). In these and other papers, a wide range of sequence stratigraphic discontinuities were evaluated ichnologically, and trace fossil analyses were demonstrated to be effective in resolving details of the stratigraphic architecture of numerous shallow marine and marginal marine successions. Taylor et al. (2003) offered up a summary of the ichnofabric approach, with nine suggested key stratal surface types. They separated these surface types into those without environmental shift and those with


environmental shift. Most of those without environmental shift probably correspond to autocyclic depositional contacts between genetically related facies—their role as ‘key stratal surfaces’ appears inscrutable. Most of these require colonization in response to changes in environmental conditions but without accompanying erosion or deposition, though how this might be accomplished was not outlined. Only firmground bypass and hardground omission may have relevance to sequence stratigraphy, mainly as indicators of condensed sections, though they can also be generated autocyclically. Of those corresponding to key stratal surfaces with environmental shift, three correspond to specific occurrences of juxtaposed softground suites (of which the most significant corresponds to marine flooding surfaces (MFS)), and one of firmground omission (i.e., suites attributable to the Glossifungites Ichnofacies). Surprisingly, a large number of established discontinuity types, well documented by pubished case studies, are grouped together as ‘firmground exhumation’ with no further differentiation in Taylor et al. (2003). Such surfaces include amalgamated sequence boundary-flooding surfaces (e.g., valley fills, transgressive ravinement of interfluve areas, transgressively incised shorefaces), transgressive surfaces of erosion (e.g., tidal scour ravinement and wave ravinement), and submarine-generated incision surfaces generated by falling relative sea level (e.g., seaward extensions of sequence boundaries and regressive surfaces of erosion (RSE)). These encompass the bulk of sequence stratigraphic discontinuity types. Likewise, hardground omission or exhumation with environmental shift (i.e., suites attributable to the Trypanites Ichnofacies), or woodground omission and exhumation with environmental shift (i.e., suites attributable to the Teredolites Ichnofacies) were not addressed in Taylor et al. (2003). These oversights make the relevance of ichnofabric analysis to the delineation, characterization, and high-resolution correlation of sequence stratigraphic discontinuities elusive. Refinements in concepts and additions of case studies have prompted further review articles on the concept (e.g., Pemberton and MacEachern, 1995, 2005; Pemberton et al., 2001, 2004). The Pemberton et al. (1992a) article was translated into Spanish for the South American community in 1997 (Pemberton et al., 1997), and into Chinese three years later (Pemberton et al., 2000). Research continues to expand and refine the role of trace fossil analysis in the sequence stratigraphic evaluation of clastic and carbonate successions. Most workers recognize that to achieve this requires the full integration of

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trace fossil relationships with physical sedimentology and sequence stratigraphic techniques (e.g., Pemberton et al., 1992a, 2001, 2004; Pemberton and MacEachern, 1995, 2005; Savrda et al., 2001a,b; Bann et al., 2004). This chapter summarizes the main discontinuity types of sequence stratigraphic relevance, and some of the case studies that showcase the ways in which ichnology has refined our interpretation of the successions. Most of the case studies have been derived from extensive analysis of Cretaceous units of the Alberta Foreland Basin, but these are integrated with other published studies dealing with the ichnology of sequence stratigraphic discontinuities from other basin types and geologic age.

SUBSTRATE-CONTROLLED ICHNOFACIES One of the most important factors in the distribution of organisms in modern environments is substrate type (Fig. 7.1). Substrates may be categorized as: soupgrounds (water-saturated muds), softgrounds (muddy sediment with some dewatering); loosegrounds (sandy sediments wherein permanent burrows require stabilized margins); stiffgrounds (stabilized sediment wherein burrows are unlined); firmgrounds (firm, dewatered, commonly compacted sediment); hardgrounds (lithified substrates: variations include shellgrounds and rockgrounds formed by tectonically induced omission); and woodgrounds (including xylic peatgrounds and isolated log-grounds). Three substrate-controlled ichnofacies have been long established (cf. Ekdale et al., 1984): Glossifungites (firmground), Trypanites (hardground), and Teredolites (woodground). In clastic settings, most of these trace suites are associated with erosionally exhumed (dewatered and compacted or cemented) substrates and, hence, correspond to erosional discontinuities (Fig. 7.2). Depositional breaks, such as condensed sections, also may be semilithified or lithified presumably at their upper contacts (or downlap surfaces), and may be colonized without associated erosion. In general, however, the recognition of substrate-controlled ichnofacies may be regarded to be equivalent to the recognition of discontinuities in the stratigraphic record. Determining whether these discontinuities are autocyclically generated or allocyclically generated and hence stratigraphically important, is considerably more challenging.

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Soupground

Softground

Looseground

Stiffground

Nereites Zoophycos

Firmground

Hardground

Woodground

Zoophycos

Cruziana Mermia Skolithos Psilonichnus Scoyenia Glossifungites Trypanites Coprinisphaera Entobia Gnathichnus Teredolites

FIGURE 7.1 Relationship of substrate types and the distribution of ichnofacies (after Pemberton et al., 2004).

Trypanites Ichnofacies The Trypanites Ichnofacies (Fig. 7.3A) develops in fully lithified substrates such as hardgrounds, reefs, rocky coasts, beachrock, and other omission surfaces. Development of this ichnofacies could correspond to discontinuities that have major sequence stratigraphic significance. Trace fossil suites are characterized by: (1) substrate-normal, cylindrical to vase-, tear-, or Ushaped to irregular borings, recording the domiciles of suspension feeders or passive carnivores (Fig. 7.4A); (2) raspings and gnawings of algal grazers and similar organisms (mainly chitons, limpets, and echinoids); and (3) moderately low diversities of ichnogenera, although the borings and scrapings of individual ichnogenera may be abundant. In contrast to the Glossifungites Ichnofacies, the walls of the borings cut across grains in the substrate, rather than diverting around them.

Teredolites Ichnofacies The Teredolites Ichnofacies (Fig. 7.3B) consists of suites of borings and burrows in woody or xylic substrates. Woodgrounds differ from other substrates in three main ways: (1) they may be flexible instead of rigid; (2) they are composed of carbonaceous material instead of mineral matter; and (3) they are readily biodegradable (Bromley et al., 1984). Hence, the methods and reasons for boring into woodgrounds may be markedly different from those of other substrate types. Interpretations of depositional conditions, marine influence, etc. require knowledge as to whether the wood borings are associated with

colonization of an in situ xylic substrate, or record the borings of isolated logs. Log-grounds, in particular, accumulate because currents are capable of rafting woody materials, and it is essential to determine whether the borings were emplaced before or after the xylic material was transported to its site of deposition. Only the autochthonous forms (those generated on an intact substrate) comprise true members of the Teredolites Ichnofacies. Woodground suites may also be important in defining parasequence boundaries as well as amalgamated sequence boundaries and flooding surfaces (e.g., Savrda, 1991a; Savrda et al., 1993). All modern wood-boring bivalves occupy marine or only slightly salinity reduced marginal marine settings. The contention that the ichnogenus Teredolites may have occurred in freshwater settings of the Cretaceous and early Tertiary (e.g., Plint and Pickerill, 1985) has been reconsidered. The two ancient occurrences described in the article are associated with units containing hitherto unrecognized MFSs that interrupt the continental succession (A.G. Plint, pers. comm., 2005), and in the case of the Cretaceous Dunvegan Formation, are known to be associated with MFS (Plint, 2000). The Teredolites Ichnofacies is characterized by: (1) sparse to profuse, club-shaped borings (Fig. 7.4B), the walls of which are commonly ornamented with the texture of the host substrate (e.g., tree-ring impressions); (2) stumpy to elongate, subcylindrical excavations that locally branch (cf. Gingras et al., 2004) restricted to marine and marginal marine settings); and (3) shallower, sparse to profuse, nonclavate etchings (e.g., isopod borings in freshwater settings).


FIGURE 7.2 Schematic development of a Glossifungites Ichnofacies-demarcated erosional discontinuity in a clastic interval. (A) Muddy substrate is buried and dewatered. (B) Erosional exhumation results in the development of a firm substrate. (C) Colonization of the discontinuity surface by tracemakers of the Glossifungites Ichnofacies proceeds during a depositional hiatus. (D) Burial of firmground substrate and filling of omission structures.

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C FIGURE 7.3 Schematic block diagram of substrate-controlled ichnofacies. (A) Trypanites Ichnofacies. Traces include Echinoid grooves (Ec), Entobia (E), Gastrochaenolites (G), polychaete borings (P), Rogerella (R), Trypanites (T), and Ubiglobites (U ). (B) Teredolites Ichnofacies. Traces include Caulostrepsis (Ca), Entobia (En), Diplocraterion parallelum (Dp), Meandropolydora (Me), Psilonichnus (Ps), Rogerella (Ro), Teredolites clavatus (Tc), Teredolites longissimus (Tl), Trypanites (Tr), and Thalassinoides (Th). Black labels reflect genera recorded from both ancient and modern occurrences. White labels correspond to ichnogenera thus far encountered only from modern occurrences. (C) Glossifungites Ichnofacies. Traces include firmground Arenicolites (A), Bergaueria (B), Chondrites (Ch), Conichnus (C), Diplocraterion (D), Gastrochaenolites (G), Planolites (P), Psilonichnus (Ps), Rhizocorallium (Rh), Skolithos (S), Taenidium (Ta), Thalassinoides (Th), and Zoophycos (Z).


A

2 cm

B

2 cm

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2 cm

FIGURE 7.4 Substrate-controlled assemblages. (A) Modern expression of the Trypanites Ichnofacies, Bay of Fundy, New Brunswick; arrow shows Gastrochaenolites clavatus with bioglyphs. The tracemaker is the bivalve Zirfea pslsbyri. (B) Modern expression of the Teredolites Ichnofacies, a bored Douglas Fir, Willapa Bay, Washington. White arrow points to a teredinid bivalve (Bankia sp.) and the black arrow points to encrusting barnacles (Balanus sp.). (C) Modern expression of the Glossifungites Ichnofacies from a firmground in Willapa Bay, Washington. X-radiograph of the surface shows Arenicolites made by the amphipod Corophium (white arrow), Diplocraterion (spreite not visible) made by the polychaete Polydora (black arrow), and the top of a Thalassinoides system made by the mud shrimp Upogebia (gray arrow).

Glossifungites Ichnofacies The Glossifungites Ichnofacies (Fig. 7.3C) is environmentally wide ranging, but only develops in firm, unlithified substrates such as dewatered muds or compacted sands. Dewatering results from burial, and the substrates are made available to tracemakers when exhumed by later erosion (e.g., Pemberton and Frey, 1985). Exhumation can occur in terrestrial environments as a result of channel meandering or valley incision, in shallow-water environments as a result of migrating tidal and other channels,

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coastal erosion or erosive shoreface retreat, and in deep water, related to submarine canyon erosion (cf. Hayward, 1976; Pemberton and Frey, 1985; Savrda, 1991b; MacEachern et al., 1992a; MacEachern and Pemberton, 1994; Pemberton and MacEachern, 1995; Savrda et al., 2001a). Such horizons commonly form at bounding discontinuities and are critical in sequence stratigraphic reconstructions of the rock record (cf. Pemberton et al., 2004). The Glossifungites Ichnofacies is characterized by: (1) vertical, cylindrical, U-, or tear-shaped pseudo-borings and/or sparsely to densely branching dwelling burrows (Fig. 7.4C); (2) protrusive spreiten in some structures that develop mostly through animal growth (e.g., funnel-shaped Rhizocorallium and Diplocraterion (formerly Glossifungites)); and (3) low diversity, but commonly abundant individual structures. Firmground traces are dominated by vertical to subvertical dwelling structures of suspensionfeeding organisms (Fig. 7.5A). The presence of vertical shafts within shaly intervals is anomalous, as these structures are not capable of being maintained in soft, muddy substrates (Figs. 7.5A–D). Elements of the Glossifungites Ichnofacies are typically robust, commonly penetrating 20–100 cm below the associated discontinuity; they tend to be large in diameter (e.g., 0.5–1.0 cm) and are sharp-walled and unlined (Figs. 7.5A,C,D). Further evidence of substrate stability is the presence of scratch marks on the burrow walls (Fig. 7.5E), and the passive nature of burrow fills. The latter characteristic demonstrates that structures remained open after being vacated by the tracemaker, thus allowing material from subsequent depositional events to accumulate therein (Fig. 7.5G). The post-depositional origin of the Glossifungites Ichnofacies is clearly demonstrated by the ubiquitous cross-cutting relationships; firmground traces unilaterally cut the previously formed softground assemblage (Fig. 7.5D). Firmground ichnofossil suites also tend to reflect colonization in large numbers. In examples from the Cretaceous Western Interior Seaway, seven to fifteen firmground traces (Fig. 7.5F), most commonly Diplocraterion habichi, occur on bedding planes of 9-cm (3.5-inch) diameter cores. This corresponds to a density of between 1100 and 2300 shafts/m2. Comparable numbers are apparent in many modern firmgrounds (Gingras et al., 1999, 2000).

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A

E

C

B

F

D

G

FIGURE 7.5 Characteristics of trace fossils attributable to the Glossifungites Ichnofacies. (A) Ichnofossils are generally robust, dwelling burrows like this firmground Arenicolites marking a transgressive surface of erosion (TSE), Lower Cretaceous Viking Formation of Alberta, well 07-19-62-19W5, 1652 m. (B) Trace fossils are unlined and exhibit sharp walls, such as this Thalassinoides demarcating a discontinuity in the Upper Cretaceous Dunvegan Formation, well 06-11-62-03W6, 2523.6 m. (C) Traces cross-cut the original softground assemblage. Here, silty and sandy mudstones display a distal expression of the Cruziana Ichnofacies, truncated by a TSE. Firmground Skolithos has piped conglomeratic sandstone from the overlying transgressive lag. Lower Cretaceous Viking Formation, well 14-20-40-06W5, 2250.0 m. (D) Firmground Diplocraterion cross-cuts softground burrows at a transgressive ravinement surface, Bluesky Formation, well 02-23-75-13W6, 1772.5 m. (E) Ichnogenera commonly preserve scratch marks, such as this Diplocraterion at a transgressive ravinement surface, Upper Cretaceous Horseshoe Canyon Formation, Alberta. (F) Trace fossils such as these Diplocraterion habichi commonly occur in high densities. Upper Cretaceous Belly River Formation, well 08-07-21-25W4, 656.2 m. (G) Firmground burrows (e.g., Diplocraterion) are commonly filled with contrasting sediment piped down from above, Lower Cretaceous Viking Formation, well 05-06-41-06W5, 2304.0 m.

SUBSTRATE-CONTROLLED ICHNOFACIES AND THE ROLE OF AUTOCYCLICITY

SUBSTRATE-CONTROLLED ICHNOFACIES AND THE ROLE OF AUTOCYCLICITY In genetic stratigraphy, differentiation of breaks of autocyclic derivation from those of allocyclic origin is paramount. Autocyclic processes are part of the dynamic nature of the environment and reflect no widespread or fundamental change to depositional conditions. Hiatal surfaces or localized discontinuities may be generated but of limited temporal significance and distribution. Allocyclic processes are imposed upon the depositional settings by external forces (e.g., tectonics, eustasy, climate), and resulting discontinuities tend to record fundamental changes in depositional conditions that affect a number of environments. Such discontinuities tend to be of greater temporal significance and are widespread. Only surfaces corresponding to allocyclic changes in depositional conditions are of relevance to sequence stratigraphy. Differentiation of these surface types is, however, challenging and omission suites may be present at both. Gingras et al. (2001) showed that firmgrounds that record the greatest temporal breaks (more likely to be allocyclic) showed the greatest levels of firmness. Indeed, studies of recent environments have demonstrated that a continuum exists from highly compact, nearly lithified firmgrounds, to slightly dewatered and cohesive ‘stiffgrounds’ (e.g., Gingras et al., 1999, 2000, 2001). Bechtel et al. (1994) recognized similar ‘firmground’ omission burrows in point bars of the McMurray Formation containing inclined heterolithic stratification (IHS), which were attributed to autocyclic pauses in lateral accretion. In their study of Willapa Bay, Gingras et al. (2000, 2001) showed that shear strength of ‘firmgrounds’ varied considerably. Erosionally exhumed, deeply buried mudstones of the Pleistocene displayed shear strengths ranging from 108 to 109 pascals (Pa), based on a modified Brinell Hardness Test. Recent ‘firm’ cutbank margins of autocyclically migrating tidal creeks and tidal channels, on the other hand, yielded shear strengths of only 104–105 Pa. These latter surfaces are probably better characterized as stiffgrounds. Gingras et al. (2000, 2001) suggested that low shear strength ‘firmgrounds’ were related to temporally short erosional events, most likely of autocyclic origin. Such autocyclically generated omission surfaces tend to contain higher proportions of worm-generated dwellings (e.g., small-diameter Skolithos, Arenicolites, and Paleophycus with some Thalassinoides) and resulting suites show considerable compaction of the structures. Nearly lithified firmground

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substrates, on the other hand, tend to show crustacean- and bivalve-generated structures (e.g., robust Skolithos, Psilonichnus, Diplocraterion, Thalassinoides, Rhizocorallium, and Gastrochaenolites) that show little or no compactional modification. Autocyclic production of a highly firm substrate in the marine and marginal marine realm is generally difficult to accomplish. The eroding event must be capable of unroofing buried sediment without immediately leading to sediment accumulation on the exposed surface. In siliciclastic settings, this limits autocyclic shallow marine occurrences to the margins and bases of channels (e.g., tidal channels, tidal inlets, distributary channels, and estuaries), mudstones that are temporarily buried beneath large, periodically moribund bedforms (e.g., tidal ridges, tidal shoals, storm-mobilized bedforms), and high intertidal mudflats, which may endure long periods of subaerial exposure and desiccation around neap cycles. Another source of firm, shallowly buried substrates may be found in the foreshore of fine-grained sand beaches. There, wave pounding contributes to the repacking of sand grains, and results in surprisingly firm media. In arid settings, some intertidal siliciclastics may be prone to incipient calcite cementation, forming firmgrounds or even hardgrounds (Gruszczyn´ski, 1986). Carbonate settings are more susceptible to cementation during autocyclic exposure (e.g., beachrock), or to some occurrences of subaqueous cementation due to sediment starvation (e.g., some submarine hardgrounds). Bromley (1975) elegantly summarized progressive increases in substrate coherence and resulting changes in the character of omission suites for chalk and fine-grained limestone intervals. Such slowly accumulated carbonate units display overprinting of softground suites by firmground and eventually hardground omission suites, recording a number of discrete ichnocoenoses. Nevertheless, such periods of sediment starvation, and omission may be a response to Milankovitch-type climate cycles and of allocyclic origin (e.g., Savrda and Bottjer, 1989; Savrda, 1995). Surprisingly, deeper-marine settings are equally susceptible to autocyclic substrate-controlled suites as the shallow marine. Contour currents, oceanic currents, and even proximal turbidity currents may strip away surficial soupy muds (cf. Stow and Holbrook, 1984). The two former processes tend to provide a persistent source of energy that continuously removes sediment from the area, whereas the latter mostly may lead to sediment bypass in the vicinity of the truncated sediment, leaving only a thin veneer of sediment in its wake. Savrda et al. (2001a) described clinoform-toe deposits in slope settings off

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the New Jersey shelf with firmground (and likely some stiffground) suites of Thalassinoides, attributable to the Glossifungites Ichnofacies. They proposed that contour currents or other bottom currents exhumed consolidated mud substrates through a combination of erosion, sediment starvation, and bottom-current winnowing, probably facilitated or at least enhanced by increased bed roughness and particle liberation due to bioturbation of the substrate (Savrda et al., 2001a, b). Though in this case study the discontinuity surfaces could be tied to one or more sequence boundaries identified up-dip of these positions, the implication is clear—contour currents are probably an underappreciated autocyclic cause of firmgrounds and stiffgrounds in the deep sea. The foregoing is instructive. The ultimate test to differentiate autocyclic erosion surfaces from allocyclic discontinuities is regional correlatability. Autocyclic surfaces show limited areal extents and do not separate genetically unrelated facies successions. Allocyclic discontinuities, on the other hand, are marked by regionally mappable extents, separate genetically unrelated successions, and are probably more common in the marine and marginalmarine realm. It remains the responsibility of the geoscientist to determine the significance of any substrate-controlled suites encountered in the rock record, and not to blindly assign stratigraphic importance to them.

ICHNOLOGICAL APPLICATIONS TO GENETIC STRATIGRAPHY The applications of ichnology to genetic stratigraphy are mainly twofold. The most obvious use is in the demarcation of erosional discontinuities. The second use is subtler, and is concerned with the paleoenvironmental implications of the trace fossil suites, both with respect to the softground suites and the omission suites. Pemberton et al. (2004) and Pemberton and MacEachern (2005) recently summarized a number of case studies dealing with regional stratigraphic discontinuities demarcated by suites attributable to substrate-controlled ichnofacies. Most of the case studies were derived from extensive study of the Western Canada Sedimentary Basin, particularly in the Cretaceous. In several units, particularly the Lower Cretaceous Viking Formation, allocyclic discontinuities are widespread and abundant, corresponding to the

combination of tectonic and eustatic processes operating in the foreland basin at the time, as well as being characterized by generally low accommodation. Abundant and widespread discontinuities also appear to be associated with low accommodation icehouse periods in the Permian of Australia (cf. Bann et al., 2004; Fielding et al., 2006). There, the stacking of genetically unrelated ichnological suites and of discontinuities containing omission suites have proven instrumental in resolving the genetic stratigraphic architecture of intervals such as the Pebbley Beach Formation. These observations have been integrated with the published literature in other settings to showcase the similarities and differences that can be expected in the recognition of stratigraphically significant trace fossil omission suites.

Regressive Surfaces of Erosion (RSE) and Sequence Boundaries (SB) Although subaerial exposure and/or erosion during relative sea-level lowstand may produce widespread development of dewatered, firm or cemented substrates (corresponding to regressive surfaces of erosion (RSE) and sequence boundaries (SB)), most are unlikely to become colonized by substrate-controlled trace fossil suites unless the surfaces are subsequently exposed to marine or marginal marine conditions prior to burial. In most of the cases, deposition of significant thicknesses of nonmarine strata generally precludes development of these omission suites on the RSE or SB themselves. There are a number of scenarios, however, where such discontinuities may be preferentially colonized by tracemakers of palimpsest softground and substrate-controlled suites. Such settings include RSE developed beneath forced regressive shorefaces, SB underlying lowstand shorefaces, SB comprising submarine canyon margins, and some SB lying at the estuarine mouths of incised valleys, during late lowstand but prior to transgressive infill. These settings are conducive to colonization of the discontinuity, because the surfaces were excavated subaqueously in a marine or marginal marine environment. Suites attributable to the Glossifungites Ichnofacies can develop on subaqueously excavated sequence boundaries, such as those associated with forced regression and lowstand shorefaces (cf. Plint et al., 1988; Posamentier et al., 1992; Pemberton and MacEachern, 1995; MacEachern et al., 1999a),

ICHNOLOGICAL APPLICATIONS TO GENETIC STRATIGRAPHY

as well as incised lowstand submarine canyons (cf. Hayward, 1976). Forced Regressive and Lowstand Shorefaces In permanently subaqueous settings, a SB may be excavated at maximum lowstand (cf. Plint, 1988; Posamentier et al., 1992) prior to burial during progradation of lowstand shorefaces, or lowstand deltas (Fig. 7.6A), whereas a RSE may be developed beneath forced regressive shorefaces (Figs. 7.6B) during the early falling stage of sea level (cf. Hunt and Tucker, 1992, 1995; Helland-Hansen and Gjelberg, 1994; Mellere and Steel, 1995). Pemberton et al. (2004) summarized the details of forced regressive and lowstand ‘sharp-based’ incised shorefaces from an ichnological perspective, largely based on observations of the Lower Cretaceous Viking Formation in the Kaybob and Judy Creek fields of Alberta by MacEachern et al. (1992a,b), and Pemberton and MacEachern (1995). From a facies perspective, sharpbased shoreface successions generated in these two scenarios are virtually identical (Fig. 7.7). Both record allocyclic shoreline progradation with a concomitant decrease in accommodation space, although lowstand shorelines may experience some addition of accommodation during the latest stages of lowstand due to a reduction in the rate of sea-level fall. Both shoreface types also overlie erosional discontinuities cut by wave erosion, when facies that were originally deposited below fair-weather wave base were brought into the zone of wave attack due to relative sea-level fall. Forced regressive and lowstand shoreface basal discontinuities (RSE and SB, respectively) are probably excavated and available for colonization only above fair-weather wave base. Although erosion may persist as far seaward as storm wave base, such autocyclically generated scour surfaces are mantled by storm beds, and shielded from colonization. As such, seaward of fair-weather wave base, RSE and SB pass into what are known as non-erosional correlative conformities (CC) (Fig. 7.7). Such CC have a high preservation potential only in lowstand shorefaces of lowstand systems tracts; continued fall of relative sea level during forced regression facilitates the erosional removal of the CC outboard of the RSE (MacEachern et al., 1999a). During lowstand, however, the CC will either be buried by progradation of the lowstand shoreface, or overlain by offshore to shelf mudstones during ensuing transgression. Hence, the lowstand shoreface typically preserves the CC, and helps in the identification of the sequence boundary.

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Incised, Lowstand Submarine Canyons Sequence boundaries comprising submarine canyon margins are conducive to colonization of the discontinuity because the surface is excavated subaqueously in a marine or marginal-marine environment. There, high-energy sediment-gravity flows scour the canyon margins, but generally lead to little deposition. During periods of lowstand, in particular, the submarine canyons are principally zones of sediment bypass, and funnel sediment to the deep sea. There are few published ichnological assessments of ancient submarine canyon margins. Outcrops of the lower Miocene Nihotupu and Tirikohua Formations at Tirikohua Point, Northland, New Zealand display a submarine canyon margin, demarcated by a spectacular firmground trace fossil suite (Figs. 7.6C,D) referable to the Glossifungites Ichnofacies (Hayward, 1976). The underlying Nihotupu Formation consists of volcanogenically derived siltstones, sandstones and subaqueous mass-flow conglomerates, intruded by submarine andesite pillow–pile complexes. The underlying softground suite is sparse and sporadically distributed, characterized by localized individual occurrences of Thalassinoides, Planolites, and Scalarituba. These deposits are interpreted as turbidites that were emplaced at bathyal water depths within an inter-arc basin on the lower eastern flanks of the west Northland volcanic arc. The contact with the overlying Tirikohua Formation is sharp and erosional, and exhibits visible relief. The exhumed substrate is demarcated by a firmground omission suite that consists of Skolithos, Rhizocorallium, and Thalassinoides (Fig. 7.6D). Hayward (1976) interpreted the erosional discontinuity as a submarine canyon wall, excavated into bathyal to neritic inter-arc sediment gravity-flow deposits as a result of basinmargin tectonic uplift. Colonization of the canyon walls by the firmground tracemakers preceded the gradual burial of the canyon margins by neritic turbidite deposits of the Tirikohua Formation. The infill of the submarine canyon probably corresponds to late-stage relative sea-level lowstand and early transgression. Examples of submarine canyon incision with the development of trace fossil suites of the Glossifungites Ichnofacies have also been recognized in the subsurface. In the Miocene of the Nile Delta (Figs. 7.8A, B), canyon walls excavated during lowstand incision were colonized by arthropods that constructed robust Thalassinoides. The interpretation of the surface is critical to the correct correlation

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T

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FIGURE 7.6 Trace Fossils at Regressive Surfaces of Erosion (RSE) and Sequence Boundaries (SB). (A) Close-up photo of a regressive surface of erosion (RSE) at the base of an interpreted forced regressive shoreface. The RSE shows a palimpsest softground suite consisting of Skolithos (S), cross-cutting the original softground trace fossil suite. The incised shoreface in this locality has cut into bioturbated (BI 5) muddy sandstones containing Ophiomorpha (O), and Paleophycus (Pa), reflecting a proximal expression of the Cruziana Ichnofacies. Overlying proximal lower shoreface sandstones of the forced regressive shoreface contain sideritized mudstone rip-up clasts and Paleophycus (Pa). Kaybob Field, well 11-35-61-20W5, 1759.2 m. (B) Box shot of core from the Lower Cretaceous Viking Formation lowstand incised shoreface at Judy Creek. Base of the interval is to the lower left, and top to the upper right (T). In this proximal position, bioturbated (BI5) silty mudstones contain suites attributable to distal expressions of the Cruziana Ichnofacies, interpreted as lower offshore deposits. These are incised into with a SB and overlain by moderately to intensely bioturbated (BI4–5) silty sandstones containing ichnocoenoses corresponding to proximal expressions of the Skolithos Ichnofacies. The overlying sandstones are interpreted to record lower shoreface environments of a lowstand shoreface. The SB is demarcated by firmground Thalassinoides (arrows; see inset close up) of the Glossifungites Ichnofacies. Black bar in inset photo is 2 cm long. Judy Creek Field, well 02/10-19-63-11W5; 1423.4–1427.1 m. (C) Submarine canyon margin (SB) corresponds to the unconformable contact between the Lower Miocene Nihotupu and Tirikohua Formations at Tirikuhua Point, Northland, New Zealand. (D) Close-up of the SB in (C). The Glossifungites Ichnofacies here is characterized by firmground Rhizocorallium (R) and Thalassinoides (T).

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incremental sea-level fall

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FIGURE 7.7 Differentiation of forced-regressive, lowstand, and transgressively incised shoreface complexes. Sharp-based, discontinuity-bound (incised) shorefaces can be ascribed to one of the three sequence stratigraphic settings. Model 1 reflects forced regression (falling stage), showing the initial fall of relative sea level and the development of successive shorefaces overlying regressive surfaces of erosion (RSE). Note that correlative conformities (CC) may be produced seaward of each RSE, but progressive sea-level fall makes these susceptible to erosional removal. Model 2 shows the development of the lowstand shoreface, reflecting the most seaward position of the shoreline associated with the lowest position of sea level. The erosional component of the sequence boundary extends only as far seaward as fair-weather wave base (FWWB), where it passes into the correlative conformity (CC). Model 3 shows the rise of relative sea level. Transgression generates a low-energy flooding surface in basinal positions, passing landward into a transgressive ravinement surface (TSE). Where the surface cuts across or incises through the sequence boundary, it produces an amalgamated (composite) surface (FS/SB). Note that sea-level rise drowns and preserves the CC of the lowstand shoreface. During a pause in the rate of transgression, shoreline progradation occurs, producing a transgressively incised shoreface. In basinward positions, offshore mudstones deposited below fair-weather wave base may directly overlie erosional portions of the FS/SB, because the surface was cut when sea level was lower but deposition did not occur until after significant deepening (modified from MacEachern et al., 1999a).

of the canyon fill, and to the recognition of point-source turbidites. Fine-grained facies outside of the canyons are thoroughly bioturbated with Phycosiphon, Planolites, and Helminthoida. Similar facies within the canyon system reflect episodic mud turbidites and are virtually unburrowed (Pemberton et al., 2004). Similar characteristics are present in the Miocene units

of the Mississippi Canyon of the Gulf of Mexico (Figs. 7.8C–F)

Transgressive Surfaces Transgressive surfaces are manifest by (1) mainly non-erosional (MFSs), and (2) low relief, erosional

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S S Th Th SB

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FIGURE 7.8 Suites attributable to the Glossifungites Ichnofacies, associated with interpreted submarine canyon incision. (A) Firmground Skolithos (S), filled with contrasting sediment piped from an overlying unit, West Ahken-1 core, 4379.8 ft. (B) Sequence boundary (SB) at the base of submarine canyon fill characterized by firmground Thalassinoides (arrow), West Ahken Field, Nile Delta, West Ahken-1 core, 4375.3 ft. (C) Interpreted sequence boundary (SB) demarcated by firmground Skolithos (S) of the Glossifungites Ichnofacies at the base of an interpreted submarine canyon in the Mississippi Canyon, Gulf of Mexico. (D) Close-up photo of the firmground Skolithos (S) depicted photo C. (E) A deeper surface in the same sequence, demarcated by firmground Skolithos (S). (F) Close-up photo of the firmground Skolithos (S) depicted in photo E.

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Te Ph

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FIGURE 7.9 Trace fossils associated with marine flooding surfaces (MFSs) and transgressive surfaces of erosion (TSE). (A) A non-erosional MFS, separating upper offshore sandy mudstones below from lower offshore/shelf silty mudstones above. The sandy mudstones contain suites attributable to the archetypal Cruziana Ichnofacies, with Paleophycus (Pa), Diplocraterion (D), Asterosoma (As), Planolites (P), Phycosiphon (Ph), Teichichnus (Te), and Rosselia (Ro). The overlying silty mudstones contain trace fossil suites recording a distal expression of Cruziana Ichnofacies, and show Phycosiphon (Ph) and Teichichnus (Te). Lower Cretaceous Viking Formation, well 12-1739-27W4; 1604.6 m. (B) A proximal expression of a regionally extensive TSE in the Lower Cretaceous Viking Formation of Alberta, with a pebble lag passively infilling firmground Diplocraterion (D) and Skolithos (S) of the Glossifungites Ichnofacies. The omission suite penetrates siderite-cemented silty mudstones with visible Paleophycus (Pa) and Chondrites (Ch). Well 12-3140-02W5, 1860.8 m. (C) A proximal TSE, capped with a pebble lag that passively infills firmground Diplocraterion (D). The omission suite cross-cuts lower offshore silty mudstones with stacked tempestites, containing abundant Phycosiphon (Ph), Helminthopsis (H), and Chondrites (Ch) that comprise a distal expression of the Cruziana Ichnofacies. Well 09-1539-27W4; 1549.4 m.

(ravinement) surfaces. Ravinement surfaces are commonly referred to as transgressive surfaces of erosion (TSE) and may correspond to wave ravinement (typically beveled, flat, seaward-dipping erosional discontinuities) and tidal scour ravinement (variable, undulatory, and locally incised scour surfaces).

Non-Erosional Surfaces MFSs are typically abrupt contacts across which there is evidence of a relative increase in water depth (Fig. 7.9A). MFSs are typically characterized by abrupt juxtaposition of offshore, shelf, or prodelta mudstones on shallow marine sandstones, and are easily identified on geophysical well logs.

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Juxtaposed suites recording lower energy, more distal ichnofacies (e.g., Zoophycos Ichnofacies) overlying higher energy, more proximal ichnofacies (e.g., Skolithos Ichnofacies) are a strong indicator of relative deepening. These surfaces are commonly mantled with dispersed sand, granules or intraformationally derived rip-up clasts, indicating some erosion. Preservation of underlying stratigraphic markers indicates that the degree of erosion is minimal. Erosional Surfaces Transgressive surfaces of erosion (i.e., ravinement surfaces) P the most elegant manner of generating widespread, substrate-controlled assemblages, because the exhumed surfaces are produced within a marine or marginal marine environment (Fig. 7.9B,C). This favors firmground colonization by organisms during ravinement-surface excavation, and prior to the accumulation of significant thicknesses of overlying sediment. The recognition of discrete TSE is challenging on the basis of sedimentology alone, particularly in the intervals where sharp-based pebble stringers and thin, trough crossstratified, coarse-grained sandstones are intercalated with interbedded sandstones, siltstones, and shales (e.g., MacEachern et al., 1992b; Pemberton and MacEachern, 1995; Bann et al., 2004; Fielding et al., 2006). Some coarse-grained stringers could correspond to veneers on transgressive ravinement surfaces, but due to the abundance of such layers in transgressive successions, identifying those with regional stratigraphic significance is problematic. However, virtually every TSE incised into, or ravined across, shaly sediments exhibits suites attributable to the Glossifungites Ichnofacies. Many firmgrounds also appear to have been developed on siderite-cemented intervals within the shales. Whether the siderite is a consequence of the ravinement, a chemical response related to deep penetration by the tracemakers of the Glossifungites Ichnofacies, or that pre-existing, siderite-cemented bands formed resistant layers through which the TSE could not incise, is uncertain. In the latter case, soft-bodied fauna would presumably find it difficult or impossible to penetrate a cemented layer; endobenthos capable of exploiting such a cemented horizon would produce, if anything, suites of the Trypanites Ichnofacies. Transgressively Incised Shorefaces In the Cretaceous of Alberta, Canada, several Viking Formation oil and gas fields in central Alberta produce hydrocarbons from NW-SE trending, sharp-based sandstones interpreted as incised

shoreface deposits. Many of these shoreface deposits are believed to rest upon TSEs (see MacEachern et al., 1999a; Pemberton et al., 2004 for details). The facies that comprise these transgressive shoreface successions are virtually identical to those of the forced regression complexes. One of the main differences lies in the thickness of the offshore to upper shoreface succession; transgressive systems tend to be thicker due to the increased accommodation space available. The other principal difference between the forced regression complex and the transgressively incised shoreface complex lies in the erosional extent of the basal discontinuity (Fig. 7.7). In the transgressive scenario, lower and upper offshore deposits, reflecting deposition below fair-weather wave base, can overlie the erosional component of the basal discontinuity. Transgressive ravinement permits the generation of an erosional discontinuity that ultimately lies seaward of fair-weather wave base during the ensuing period of shoreface progradation, because the discontinuity was cut prior to shoreface progradation and while sea level lay at a lower position (MacEachern et al., 1999a). This relationship contrasts markedly with that associated with the RSE and SB, which pass into nonerosional CC seaward of fair-weather wave base. This difference facilitates discrimination of shorefaces and deltas generated during relative sea-level fall, from transgressively incised shorefaces and deltas deposited during relative sea-level rise (MacEachern et al., 1999a). Firmground omission suites attributable to the Glossifungites Ichnofacies commonly demarcate the TSE, even in positions where the overlying facies reflect deposition well below fair-weather wave base. In these positions, a coarse-grained lag is also commonly associated with the discontinuity. The TSE passes seaward into a non-erosional MFS. In settings characterized by intense burrowing, the contact may be obscured. Only the full integration of sedimentology, ichnology, and stratigraphy permits the reliable recognition and interpretation of the discontinuity. Deep-Sea Omission Suites and Condensed Sections In the deep sea, Savrda et al. (2001a,b) outlined firmground suites associated with sediment starvation, substrate bioturbation, and concomitant contour bottom currents along slope settings off the New Jersey shelf, suggesting this as the deep-water expression of transgression. There, the omission surfaces are associated with condensed sections and maximum transgression. Pemberton et al. (1992a) and Pemberton and MacEachern (1995) summarized some of the ichnological characteristics of condensed


sections, particularly in clastic units. Loutit et al. (1988) described most of the principal sedimentological, diagenetic/authigenic features, and micropaleontological characteristics of siliciclastic condensed sections. In most of the case studies, there is a close association between high total organic carbon and reduced oxygenation contents. Similar observations have been derived from the Cambro-Ordovician of the Baltic Shield (Lindstro¨m, 1963; Jenkyns, 1986); the Toarcian Jet Rock Shales of the UK (Morris, 1979, 1980), the Albian basal shales of the Shaftebury Formation of Alberta, Canada (Leckie et al., 1990); Late Albian Mowry Shale, Wyoming, USA (Byers and Larson, 1979; Jenkyns, 1980), the Turonian Awgu Shale, Benue Trough, Nigeria (Petters, 1978; Jenkyns, 1980), Upper Cretaceous Niobrara Formation (Savrda and Bottjer, 1989), and the Eocene–Oligocene boundary of Alabama, USA (Loutit et al., 1988). Trace fossil suites associated with condensed sections display reduced numbers, lowered diversities, smaller burrow diameters, and shallower levels of penetration into the substrate; features characteristic of oxygen-restricted ichnocoenoses (cf. Savrda and Bottjer, 1989, 1991; Martin, 2004 for a summary). Such scenarios record strongly oxygen-stratified basin settings, and are well developed in foreland basin settings. In contrast, trace fossil suites associated with condensed sections that formed on shallow water, well-oxygenated passive margins tend to show very different characteristics (cf. Savrda, 1995). Savrda’s extensive work in the Gulf Coast examples indicates that ichnological expressions at maximum flooding surfaces can be quite variable, both within and between depositional successions. In some chalk–marl rhythmite successions, maximum flooding surfaces are demarcated not by changes in substrate consistency, but rather by relatively abrupt vertical changes in softground ichnofabrics and accompanying lithologic characteristics (e.g., Locklair and Savrda, 1998). In settings such as those recorded by the Campanian Demopolis Chalk, facies are: (1) thoroughly bioturbated; (2) display diverse and locally high-density trace fossil suites comprising robust (e.g., burrow diameter and vertical extent) ichnogenera; (3) record diffusely burrow-mottled ichnofabrics, complexly overprinted by discrete ichnotaxa; and (4) bed junctions characterized by numerous piped zones. Slow rates of deposition in these well-oxygenated marl and chalk condensed sections lead to stacked tiers and composite ichnofabrics. Interestingly, common occurrences of Teredolites-bored allochthonous wood (including log-grounds) are also encountered in some condensed sections, recording transgressive inundation of forested coastal settings, and

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concentration of this wood debris due to sediment starvation (e.g., Savrda and King, 1993; Savrda et al., 1993). In other well-oxygenated condensed sections, maximum flooding surfaces are characterized by firmground omission (e.g., Glossifungites Ichnofacies) or even hardground ichnocoenoses, recording current winnowing and/or synsedimentary lithification generated by sediment starvation, increased bottom circulation, and non-deposition (Savrda, 1995). Submarine hardgrounds and associated suites referable to the Trypanites Ichnofacies commonly punctuate the record of carbonate shelves, recording their response to rapid transgression (cf. Coniglio and Dix, 1992). Bromley (1975) recognized numerous non-erosional (i.e., non-depositional) omission surfaces in Upper Cretaceous chalks of northwestern Europe, characterizing both shelf and slope settings. He was able to show transitions from prelithification suites (softground and firmground) and postlithification suites (hardground). Comparable expressions have been summarized from mid-Tertiary pelagic limestones of New Zealand (Lewis and Ekdale, 1992), where spatial variations from softground, firmground, hardground, and even rockground conditions are recorded by complicated composite ichnofabrics with complex tiering patterns. Such scenarios are probably characteristic of major marine transgression and condensed section development in the carbonate realm, though the role of Milankovitch-driven climatic cycles cannot be ruled out as a sole or contributing factor.

Amalgamated Sequence Boundaries and Marine Flooding Surfaces (FS/SB) Amalgamated sequence boundaries and transgressive surfaces (FS/SB) may correspond to coplanar surfaces or composite surfaces. Coplanar expressions are characterized by the sequence boundary as a discrete surface, but mantled with a MFS. Composite surfaces correspond to a discontinuity where the original sequence boundary has been erosionally removed by a TSE. The two discontinuities are challenging to differentiate, because the sequence boundary is typically erosional and the overlying facies record deepening. The presence of a winnowed lag, locally glauconitic may support associated transgressive erosion. Amalgamated sequence boundaries and transgressive surfaces either of coplanar or composite nature are commonly colonized by substrate-controlled tracemakers, and are widespread in many stratigraphic successions (Fig. 7.10).

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T P H

FS/SB

P

Th

r r

A

B

C

FIGURE 7.10 Glossifungites Ichnofacies that characterize amalgamated (coplanar and composite) sequence boundaries and flooding surfaces. (A) Rooted (r), incipient paleosols of the Lower Cretaceous Upper Boulder Creek Fm, interpreted as floodplain deposits, are transgressively eroded and overlain by a thin transgressive lag and brackish-water bay mudstones of the Paddy Formation. This composite FS/SB marks the interfluve of an incised valley, and is demarcated by firmground Thalassinoides (Th). Overlying brackish-water mudstones contain an impoverished trace fossil suite with Planolites (P) and exceedingly rare Helminthopsis (H). Well 08-13-69-11W6; 1907.2 m. (B) Box shot photo of core from the incised valley of the Crystal Field. Base of the core is to the lower left, and top to the upper right (T). Underlying lower offshore silty mudstones have been truncated by a sequence boundary, and overlain by a bay-line flooding surface, forming a coplanar FS/SB along the margins of the estuarine-incised valley. A firmground suite of Skolithos and Gastrochaenolites (arrow) demarcate the discontinuity (also, see inset close-up photo). The valley fill at this locality consists of sandy bay deposits onlapping the valley margins. Underlying trace fossil suites correspond to fully marine, distal expressions of the Cruziana Ichnofacies. Overlying bay deposits show stressed, brackish-water trace fossil suites. Well 04-01-46-04W5, 1802.1–1806.2 m. (C) Schematic model of incised valley surface types of both autocyclic and allocyclic origin, commonly demarcated by suites attributable to the Glossifungites Ichnofacies (modified after MacEachern and Pemberton, 1994).


Lowstand erosion events typically produce widespread firmground, hardground, and woodground surfaces, corresponding to RSE or SB. During flooding, the coplanar expression allows colonization of the discontinuity prior to burial. Omission suites may record ethological groupings more consistent with low-energy conditions, owing to the typically sheltered and/or distal expression of transgressive deepening (cf. MacEachern and Burton, 2000; Savrda et al., 2001a). In the case of composite surfaces, the following transgressive event is accompanied by erosion, generating a TSE that typically removes most or all of the lowstand deposits, and exposes the original discontinuity to marine or marginal marine conditions. During this phase of transgression, organisms are commonly able to colonize the re-exhumed substrate and typically record ethological groupings characteristic of higher energy conditions (cf. MacEachern et al., 1992a,b, 1999b). The most reliable means of discerning coplanar and composite surface types, however, is through high-resolution reconstructions of facies architecture and sequence stratigraphic correlation. Although such amalgamated surfaces may also include discontinuities at the bases of some transgressively incised shorefaces (e.g., E–T surfaces of Plint et al., 1988; FS/SB of MacEachern et al., 1992b, 1998, 1999a,b), most are associated with estuarine-incised valley systems. Fluvial valley fills generally indicate preservation of lowstand (typically late lowstand) deposits, and directly overlie the sequence boundary. They are separated from overlying estuarine fill by a MFS or TSE. In such settings, the vertical juxtaposition of brackish-water trace fossil suites above continental ichnocoenoses is a compelling indicator. In lowaccommodation settings, such as the Viking Formation, lowstand deposits either never accumulated (i.e., were zones of sediment bypass), have been removed by transgressive reworking, or have been reworked into transgressive deposits. In these cases, there is no lowstand systems tract and the sequence boundary and TSE (or MFS) have become amalgamated. These successions record estuarineincised valleys that are typically filled during ensuing transgression, and so overlie the initial transgressive surface within the valley. Amalgamated surfaces are also generated along valley margins, where little or no lowstand deposition occurs (locally characterized by pedogenic modification of interfluves). During transgressive fill of the estuary, bay margins may show bay line flooding surfaces that onlap the sequence boundary, or a transgressive ravinement surface (either wave ravinement or tidal scour ravinement) that generates a composite discontinuity. Some reserve

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the amalgamated term ‘FS/SB’ for amalgamated discontinuities developed on valley interfluves, where deposition did not occur until after transgressive infill of the valley and flooding across valley margins during continued relative sea-level rise (e.g., van Wagoner et al., 1990). This limitation of the term does not accommodate the various ways in which such amalgamated (both coplanar and composite) discontinuities may form. TSE Across Subaerially Exposed Surfaces Numerous units in coastal margin (e.g., delta plain and coastal plain) settings display surfaces that reflect initial subaerial exposure subsequently flooded and eroded during transgressive influx of brackish to marine waters. Such scenarios are conducive to the development of substrate-controlled ichnofacies that demarcate the discontinuities. The neoichnological appraisal of the Glossifungites Ichnofacies by Pemberton and Frey (1985) dealt with such a scenario, where transgressively exhumed salt marsh mud along the coast of Catherine’s Island, Georgia are colonized by bivalves and thalassinid shrimp, and buried by beach sand. In Alberta, the Lower Albian Mannville Group–Joli Fou Formation contact in the Kaybob Field of central Alberta is characterized by a regionally extensive FS/SB. Rooted, incipient paleosols developed in floodplain mudstones of the Mannville Group are cross-cut by robust, firmground Thalassinoides reflecting the Glossifungites Ichnofacies, passively filled with muddy sand and large siderite-cemented clasts. The overlying silty shales contain a distal expression of the Cruziana Ichnofacies and, more rarely, the Zoophycos Ichnofacies, recording deposition in lower offshore to inner shelf environments. The amalgamated surface corresponds to an interfluve (cf. van Wagoner et al., 1990) that was transgressively overrun during basinwide flooding of the Joli Fou Seaway. This transgression marks a major period of marine inundation of the Western Interior Seaway of North America. A similar occurence occurs in the Upper Boulder Creek-Paddy formation transition in west-central Alberta (Fig. 7.10A). Woodground surfaces are commonly colonized during such ravinement events. Bromley et al. (1984) described a mud-filled tidal channel that exhumed a xylic substrate of the coastal plain in the Upper Cretaceous Horseshoe Canyon Formation of Alberta. A monospecific suite of Teredolites clavatus occurs along the channel base, corresponding to the Teredolites Ichnofacies. Saunders and Pemberton (1986) described woodground Diplocraterion parallelum associated with transgression across coastal plain coals of the Upper Cretaceous Appaloosa Sandstone,

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Bearpaw–Horseshoe Canyon transition of Alberta. Dam (1990) described similar woodground expressions of Diplocraterion parallelum, associated with wave ravinement of a deltaplain coal horizon from the Lower Jurassic Neill Klinter Formation of East Greenland. Savrda (1991a) and Savrda et al. (1993) characterized woodground suites of log-grounds, some of which are probably referable to the Teredolites Ichnofacies, associated with transgressively generated discontinuities in the Lower Paleocene Clayton Formation of Alabama.

MacEachern et al., 1999b). This, coupled with the presence of substrate-controlled suites that demarcate erosional discontinuities (many of them allocyclic) within the valley fill (Figs. 7.10B,C), allows detailed mapping of valley components, and assists in the resolution of the sequence stratigraphic history of valley excavation and infill.

Estuarine-Incised Valley Complexes The bases and margins of transgressively filled incised valley complexes (i.e., estuaries) are commonly demarcated by firmground suites attributable to the Glossifungites Ichnofacies (Pemberton et al., 1992b; MacEachern and Pemberton, 1994; Pemberton and MacEachern, 1995). Lowstand deposits rarely dominate incised valley complexes except near their transgressive limits, since valleys are largely zones of sediment bypass during their incision (van Wagoner et al., 1990). Much of the sediment accumulation in valleys occurs during late lowstand and transgression, and is therefore characterized by estuarine (brackishwater) infill. Recognition of estuarine-incised valleys is typically facilitated by facies contrast between the facies into which the valley is incised and the brackish-water infill of the valley complex itself. In the case of the Viking Formation of Alberta, the estuarine valley complexes are incised into open marine parasequences, recording shelf to distal lower shoreface settings, making recognition relatively easy (Pemberton et al., 1992b; MacEachern and Pemberton, 1994). In the case of the Glauconite Formation, however, the estuarine valleys are incised into coastal margin brackish-water deposits, and filled with tidal–fluvial estuarine deposits, making delineation of valley successions challenging (MacEachern and Gingras, in press). Estuarine valley-fill successions are characterized by highly complex facies architectures that record incremental transgressive fill, variable estuarine subenvironments, common periods of valley re-incision, and the excavation of numerous internal discontinuities within the valley fill (Fig. 7.10C). Ichnology is ideally suited to help resolve the internal complexities of estuarine successions. Trace fossil suites are effective in differentiating salinity changes and more specifically, salinity reductions, which assist in the differentiation of fully marine, brackish-water, and freshwater deposits (e.g., Wightman et al., 1987; Beynon et al., 1988; Beynon and Pemberton, 1992; MacEachern and Pemberton, 1994; Gingras et al., 1999;

The main applications of ichnology to genetic stratigraphy are twofold. The most obvious use lies in the identification of substrate-controlled suites attributable to the Glossifungites, Teredolites, and Trypanites Ichnofacies, which demarcate erosional discontinuities corresponding to stratigraphically significant surfaces. The second use is subtler, and relies on trace fossil behaviors and their paleoenvironmental implications with respect to Walther’s Law. Juxtaposed softground suites that do not reflect originally adjacent depositional environments (i.e., successions of suites that contravene Walther’s Law) are highly effective in assisting the genetic stratigraphic assessment of the ancient record. Trace fossils, when used in conjunction with primary sedimentary structures, are useful in the delineation and interpretation of facies and facies associations. Given the spatial and temporal complexities in the genesis of stratigraphic discontinuities, continued refinement in the utility of ichnology is essential. The infaunal colonization of discontinuities yields critical information about the origin of the discontinuity and the paleoenvironmental conditions that followed. The close integration of ichnological characteristics with physical sedimentological facies analysis and sequence stratigraphic modeling is essential, in order to achieve high-resolution reconstructions of the ancient record.

CONCLUSIONS

ACKNOWLEDGEMENTS The authors would like to thank the Natural Science and Engineering Research Council of Canada (NSERC) for research funding; Discovery Grant 184293 to J.A. MacEachern, Operating Grant No. A0816 to S.G. Pemberton; and Discovery Grant (PRG) No. 238530-03 to M.K. Gingras. SGP would like to thank the Canada Research Chairs program for their support of his research. The authors are indebted to Dr. C.E. Savrda and Dr. K.R. Aalto for their thorough and constructive review of this manuscript.

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MacEachern, J.A., Bechtel, D.J. and Pemberton, S.G. (1992a). Ichnology and sedimentology of transgressive deposits, transgressively related deposits and transgressive systems tracts in the Viking Formation of Alberta. In: Pemberton, S.G. (Ed.), Applications of Ichnology to Petroleum Exploration: A Core Workshop, Society of Economic Palaeontologists and Mineralogists, Tulsa, OK, Core Workshop Notes, 17, pp. 251–290. MacEachern, J.A., Raychaudhuri, I. and Pemberton, S.G. (1992b). Stratigraphic applications of the Glossifungites Ichnofacies: delineating discontinuities in the rock record. In: Pemberton, S.G. (Ed.), Applications of Ichnology to Petroleum Exploration: A Core Workshop, Society of Economic Paleontologists and Mineralogists, Tulsa, OK, Core Workshop Notes, 17, pp. 169–198. MacEachern, J.A., Pemberton, S.G. and Zaitlin, B.A. (1995). A late lowstand to early transgressive coarse-grained tongue from the Viking Formation of the Joffre Field, Alberta: embayment complex or shoreface wedge? In: Swift, D.J.P., Snedden, J.W., and Plint, A.G. (Eds.), Tongues, Ridges and Wedges: Highstand Versus Lowstand Architecture in Marine Basins, Society of Economic Palaeontologists and Mineralogists Research Conference, Powder River and Bighorn Basins, Wyoming, June, pp. 24–29. MacEachern, J.A., Zaitlin, B.A. and Pemberton, S.G. (1998). Highresolution sequence stratigraphy of early transgressive incised shoreface and early transgressive valley/embayment deposits of the Viking Formation, Joffre Field, Alberta, Canada. American Association of Petroleum Geologists Bulletin, 82, 729–756. MacEachern, J.A., Zaitlin, B.A. and Pemberton, S.G. (1999a). A sharp-based sandstone succession of the Viking Formation, Joffre Field, Alberta, Canada: criteria for recognition of transgressively incised shoreface complexes. Journal of Sedimentary Research, 69, 876–892. MacEachern, J.A., Zaitlin, B.A. and Pemberton, S.G. (1999b). Coarsegrained, shoreline-attached, marginal marine parasequences of the Viking Formation, Joffre Field, Alberta Canada. In: Bergman, K.M. and Snedden, J.W. (Eds.), Isolated Shallow Marine Sand Bodies: Sequence Stratigraphic and Sedimentologic Interpretation, Society of Economic Paleontologists and Mineralogists, Tulsa, OK, Special Publication, 64, pp. 273–296. Magwood, J.P.A. and Pemberton, S.G. (1990). Stratigraphic significance of Cruziana: new data concerning the Cambrian–Ordovician ichnostratigraphic paradigm. Geology, 18, 729–732. Mańgano, M.G. and Buatois, L.A. (1991). Discontinuity surfaces in the Lower Cretaceus of the High Andes (Mendoza, Argentina): trace fossils and environmental implications. Journal of South American Earth Sciences, 4, 215–299. Martin, K.D. (2004). A re-evaluation of the relationship between trace fossils and dysoxia. In: McIlroy, D. (Ed.), The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis, Geological Society, London, UK, Special Publication, 228, pp. 141–156. Mellere, D. and Steel, R. (1995). Facies architecture and sequentiality of nearshore and ‘shelf’ sandbodies; Haystack Mountains Formation, Wyoming, USA. Sedimentology, 42, 551–574. Miller, M.F. and Rehmer, J. (1982). Using biogenic structures to interpret sharp lithologic boundaries: an example from the Lower Devonian of New York. Journal of Sedimentary Petrology, 52, 887–895. Morris, K. (1979). A classification of Jurassic marine shale sequences; an example from the Toarcian (Lower Jurassic) of

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8 The Application of Trace Fossils to Biostratigraphy Robert B. MacNaughton

especially helpful in Neoproterozoic and lower Paleozoic marine siliciclastic strata. Vertebrate trace fossils can be used to date and correlate Mesozoic continental strata. This chapter reviews the biostratigraphic advantages and limitations of trace fossils; describes the main applications of trace fossils in biostratigraphy; briefly discusses other, potentially useful trace-fossil groups; and offers suggestions for optimal utilization of trace fossils as a tool in biostratigraphy.

SUMMARY : The characteristics that make trace fossils valuable in sedimentology and paleoecology limit their usefulness in biostratigraphy. However, in certain situations they can be the sole source of biostratigraphic data or can usefully augment biostratigraphic data from other sources. Trace fossils have been applied successfully to detailed biostratigraphy in the basal Cambrian (various ichnotaxa) and the Cambrian–Ordovician transition (trilobite traces, especially Cruziana), and to the dating of deep-marine Cambrian deposits (Oldhamia) and continental Mesozoic strata (vertebrate tracks). Other trace-fossil groups with potential biostratigraphic applications include certain complex, deep-marine traces (graphoglyptids), Tertiary insect-produced traces, and some bioerosion structures. Reliable trace-fossil biostratigraphy relies on high-caliber systematic ichnotaxonomy, augmented by careful paleoenvironmental analysis, and can be conducted profitably in tandem with studies on the evolution of behavior.

LIMITATIONS AND ADVANTAGES OF TRACE FOSSILS IN BIOSTRATIGRAPHY Trace fossils have definite limitations as potential zone fossils. Ideally, zone fossils should have short stratigraphic ranges and be widely enough dispersed to permit correlation across multiple paleoenvironments. However, many common ichnotaxa are longranging (Crimes, 1975), and ichnofaunas can be strongly tied to depositional facies due to the marked influence of environmental limiting factors on benthic organisms and their behaviors. Also, some ichnotaxa apparently show different stratigraphic ranges in different paleocontinental realms. In Gondwana, Phycodes circinatus Richter apparently is restricted to the Lower Ordovician; in Laurentia, it is primarily Middle Ordovician (Fillion and Pickerill, 1990) but may range back to the Lower Cambrian (Magwood and Pemberton, 1990). A related problem is the mimicking of ichnotaxa by homeomorphs of different ages; examples of this are provided by

INTRODUCTION Trace fossils are better known for their use in sedimentology and paleoecology than for their application in biostratigraphy. Nevertheless, trace-fossil biostratigraphy (also referred as palichnostratigraphy) has been practiced since the nineteenth century. In the last forty years, trace fossils have come into their own as a means of dating and correlating numerous, otherwise sparsely fossiliferous or unfossiliferous successions. Invertebrate ichnofossils have proven


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Seilacher (1994; see also Magwood and Pemberton, 1990) and by Zonneveld et al. (2002). However, these limitations should not be over-emphasized. Some of the longest-ranging and least distinctive ichnotaxa—e.g., Palaeophycus, Planolites, Skolithos—provide useful first-appearance data for Ediacaran–Cambrian biostratigraphy (see below). Facies control and faunal provincialism are more severe versions of problems also seen with macrofossils and microfossils, and homeomorphy is not unique to trace fossils. It must also be emphasized that although many ichnotaxa cannot be tied to a specific producer, ichnotaxa are form taxa and their biostratigraphic utility arises from their empirically determined stratigraphic ranges, not from the identity of presumed tracemakers (Lockley, 1998a). Despite their limitations, trace fossils can offer advantages in biostratigraphy. They are common in many successions. In siliciclastic strata, trace fossils generally have higher preservation potential than body fossils and may be the sole source of biostratigraphic data. Soft- and firm-substrate traces are nearly always found in situ and reworked specimens are readily recognized. Many biostratigraphically useful ichnogenera have a distinctive appearance and can be identified readily by non-specialists (e.g., Cruziana, Oldhamia, Rusophycus, Treptichnus). Finally, trace fossils can survive tectonism and metamorphism that would obliterate body fossils, although such survivors may not be identifiable past the ichnogenus level.

A

CHARACTERISTIC APPLICATIONS OF TRACE FOSSILS IN BIOSTRATIGRAPHY The principal applications of trace-fossil biostratigraphy have been recognized for several decades or longer (see reviews by Crimes, 1970, 1975). Trace fossils are most useful for biostratigraphy when at least one of three conditions is met: 1. A distinctive trace-fossil morphology has a relatively short stratigraphic range. Selected examples include Oldhamia (Fig. 8.1A; discussed below), certain graphoglyptid trace fossils (also discussed below), Phycodes circinatus (discussed above), and Climactichnites (Fig. 8.1B). 2. Relatively rapid evolution of behavior or morphology within a group of tracemaking organisms yields a series of first and last appearances of ichnotaxa. The resulting ichnospecies ranges and range overlaps permit subdivision of the stratigraphic record. Examples (discussed later in this section) include ‘Cruziana’ stratigraphy—reflecting trilobite evolution—and Mesozoic vertebrate-footprint stratigraphy. 3. Several ichnotaxa appear in the stratigraphic record in an order reproducible from locality to locality, permitting the establishment of biozones based on first appearances. This characterizes the Neoproterozoic–Cambrian trace-fossil record (see below).

B

FIGURE 8.1 Examples of ichnotaxa with restricted stratigraphic ranges. (A) Oldhamia curvata Lindholm and Casey (Cambrian, British Mountains, northwestern Canada). Scale bar is 1 cm. Oldhamia occurs globally and is an Early to Middle Cambrian index fossil. Photograph by B. Rutley. (B) Climactichnites wilsoni Logan (Cambrian, Wisconsin). Scale bar is 10 cm. Climactichnites is common in cratonic North America and apparently is confined to the Dresbachian (Upper Cambrian) (Yochelson and Fedonkin, 1993). Photograph by the author.

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This section describes the four most common applications of trace-fossil biostratigraphy, each representing one of these classes. Literature citations generally emphasize recent research; references to relevant earlier contributions can be found in many of these articles.

Distinctive, Short-Lived Ichnotaxon: Oldhamia in Deep-Marine Cambrian Strata The ichnogenus Oldhamia has a very distinctive morphology (Fig. 8.1A), encompassing radiating, flabellate, or dendritic systems of very narrow burrows. It occurs almost exclusively in deep-marine Cambrian strata, where it is commonly the only agediagnostic fossil. Oldhamia has been considered an indicator fossil for the Cambrian since the nineteenth century and may have been the first ichnotaxon used for biostratigraphy. Although its status as a trace fossil was debated well into the twentieth century, it is now regarded as the product of deposit-feeding, vermiform organisms (Ruedemann, 1942). At least six ichnospecies are in common use (Lindholm and Casey, 1990; Hofmann et al., 1994) and recent work (Seilacher et al., 2005) suggests that at least eleven ichnospecies can be distinguished. Oldhamia-bearing localities are widely distributed, including sites in Argentina, Ireland, continental Europe, the North American Cordillera and Appalachians, and the Canadian Arctic islands (Lindholm and Casey, 1990; Hofmann et al., 1994). Although it generally does not occur with other agediagnostic fossils, most occurrences have been considered to be of Early Cambrian age, with some occurrences possibly ranging into the latest Ediacaran or the Middle Cambrian. Lindholm and Casey (1990) noted that North American occurrences are generally Early Cambrian, with a few latest Ediacaran localities; that European examples include both Early and Middle Cambrian occurrences; and that South American Oldhamia apparently are confined to the Early Cambrian. Rare Ordovician and Carboniferous specimens have been assigned to Oldhamia (Seilacher, 1974; Seilacher et al., 2005); these are morphologically and ichnotaxonomically distinct from ichnospecies of Oldhamia found in the Ediacaran and Cambrian. Currently, assemblages of Oldhamia are used for series-level biostratigraphy. However, Seilacher (1974) posited a trend from simple radiating structures to more complex forms during the history of the ichnogenus. More recently, Lindholm and Casey (1990) described a diverse set of Oldhamia ichnospecies from the tectonized Blow Me Down Brook

Middle Cambrian? Oldhamia flabellata

Oldhamia curvata

Oldhamia antiqua Lower Cambrian?

Oldhamia smithi

Latest Proterozoic?

Oldhamia curvata

Oldhamia radiata

FIGURE 8.2 Possible evolutionary history of Oldhamia, modified after Lindholm and Casey (1990); note uncertainty regarding precise stratigraphic ranges of ichnospecies. If this succession can be verified and calibrated, it may form the basis for biozones in deep-marine Cambrian strata.

Formation in Newfoundland, Canada. They suggested that two parallel trends could be recognized in their collections (Fig. 8.2): (1) Evolution from radial forms to dendritic and flabellate forms; (2) Evolution from radial forms to curving, double-fan-shaped forms. If these trends can be substantiated and documented in other successions, Oldhamia may provide the basis for a more detailed, deep-marine, Ediacaran? to Middle Cambrian trace-fossil biozonation. Further work is also needed to test how Oldhamia assemblages are influenced by paleoenvironmental factors; Lindholm and Casey (1990) attempted this only at a very basic level. If any new, Oldhamia-based biozones can be recognized, establishing their correlation with Cambrian platformal biozones should be a priority.

Evolution within a Group of Tracemakers: ‘Cruziana’ Biostratigraphy Trilobites are important index fossils through much of the Paleozoic, and their evolution is mirrored, to a diminished extent, in the stratigraphic record of trilobite-produced trace fossils. Of these, the most biostratigraphically useful is the bilobate, ribbon-like

138


ichnogenus Cruziana, the biostratigraphic potential of which was recognized in the late 1800s by the Canadian paleontologist G.F. Matthew (Fillion and Pickerill, 1990). Resting impressions, assignable to the ichnogenus Rusophycus, are somewhat less useful. Although some specimens of Cruziana and Rusophycus were produced by non-trilobite arthropods (e.g., Zonneveld et al., 2002), most specimens can be assigned to the work of trilobites (Seilacher, 1970). Detailed use of trilobite-produced traces in biostratigraphy dates to pioneering work in the 1960s and 1970s by T.P. Crimes and A. Seilacher. This section discusses the relatively detailed Cruziana biostratigraphy of the Upper Cambrian and Lower Ordovician, and the more generalized ‘Cruziana’ stratigraphy of the Cambrian through Carboniferous. Numerous workers (e.g., Crimes, 1970, 1975; Baldwin, 1977; Pickerill and Fillion, 1983; Fillion and Pickerill, 1990; Mańgano and Buatois, 2003; Knaust, 2004) have documented the succession of Cruziana ichnospecies in the Upper Cambrian and Lower Ordovician. The combination of first and last appearances and overlapping ranges of several ichnospecies (Fig. 8.3) corresponds closely to the bases of the Tremadoc and Arenig series, and also permits subdivision of the Tremadoc. Four ichnotaxa, widely reported from Gondwana, are especially important. Cruziana semiplicata Salter (Fig. 8.4A) extends from the Upper Cambrian into the upper part of the Tremadoc. It overlaps with Cruziana furcifera d’Orbigny (Fig. 8.4B) and Cruziana goldfussi (Rouault) (Fig. 8.4C),

Ichnotaxa

the overlap corresponding with the upper Tremadoc. The first appearance of typical Cruziana rugosa d’Orbigny (Fig. 8.4D), which roughly coincides with the last appearance of C. semiplicata, approximates the base of the Arenig—though small, atypical specimens of C. rugosa have been reported from the upper Tremadoc (Mańgano and Buatois, 2003). C. furcifera, C. goldfussi, and C. rugosa all extend at least to the Llanvirn (Fillion and Pickerill, 1990; Mańgano and Buatois, 2003). (Also, see Mańgano and Buatois, 2003, for an alternative view of the ichnotaxonomy of these three ichnospecies.) Two less common ichnotaxa may also be useful in this interval. Cruziana breadstoni Crimes and Cruziana tortworthi Crimes were both considered by Crimes (1970) to be lower Tremadoc forms. However, Pickerill and Fillion (1983) reported them from the same strata as C. furcifera and C. goldfussi, suggesting that C. breadstoni and C. tortworthi span much or all of the Tremadoc. Whereas most workers have focused on the Cambro–Ordovician transition, Seilacher (1970, 1991) drew on data from numerous, widely separated localities to erect a ‘Cruziana’ stratigraphy for Paleozoic, shallow-marine sandstones in the Gondwanan paleocontinent (Fig. 8.5). Although ‘Cruziana’ stratigraphy covers the Cambrian through Carboniferous, data for the Devonian and Carboniferous are currently too sparse to permit long-distance correlations (Seilacher, 1991). The scheme has been used for stratigraphic subdivision and correlation in the Paleozoic of North Africa and

Upper Cambrian

Tremadoc lower

Arenig

upper

Cruziana semiplicata Cruziana breadstoni Cruziana tortworthi Cruziana furcifera Cruziana goldfussi Cruziana rugosa

?

FIGURE 8.3 Stratigraphic ranges of ichnospecies of Cruziana in the Upper Cambrian and Lower Ordovician. Ranges are based on data in Crimes (1970, 1975), Baldwin (1977), Pickerill and Fillion (1983), Fillion and Pickerill (1990), and Mańgano and Buatois (2003). Cruziana furcifera, Cruziana goldfussi, and Cruziana rugosa continue at least to the Llanvirn. Pale-gray rangebar segment represents rare, atypical specimens of possible Cruziana rugosa reported from the Tremadoc of Argentina by Mańgano and Buatois (2003).


A

C

B

D

FIGURE 8.4 Key Cruziana ichnospecies for Upper Cambrian–Lower Ordovician biostratigraphy. Photographs by L. Buatois and G. Mańgano. All scale bars are 1 cm. (A) Cruziana semiplicata, Bell Island Group (Upper Cambrian), Bell Island, Newfoundland, Canada (Tu¨bingen Collection). (B) Cruziana furcifera, Mojotoro Formation (Arenig–Llanvirn), northwest Argentina. (C) Cruziana goldfussi, Khabour Quartzite (Lower Ordovician), Iraq (Tu¨bingen Collection). (D) Cruziana rugosa, Mojotoro Formation (Arenig–Llanvirn), Cordillera Oriental, Argentina. (Collections of Invertebrate Paleontology of the Universidad Nacional de Tucumań.)

139

140


pudica retroplana uniloba rhenana

lineata radialis

leifeirikssoni polonica

balsa

lobosa carbonaria costata

dispar nabataeica

arizonensis barbata

aegyptica carinata

M

salomonis

U

cantabrica fasciculata

L

petraea acacensis quadrata

Ordov.

U

L

omanica semiplicata breadstoni

Silurian

U

flammosa perucca

M

pedroana

U

L

Cambrian

Rusophyciform ichnospecies

L

tortworthi furcifera goldfussi imbricata rouaulti rugosa almadenensis

Devonian

Car.

Cruzianiform ichnospecies

L

FIGURE 8.5 ‘Cruziana’ biostratigraphy of the lower Paleozoic. Modified after Seilacher (1991, 1994). Cruzianiform and rusophyciform ichnotaxa are shown separately (see text). Names of ichnospecies are mostly as given by Seilacher (1994); no attempt has been made to correct the orthography of probable Rusophycus ichnospecies. Range data are presented in a digitized, series-by-series fashion that can hide details of some ranges: e.g., in the Upper Cambrian–Lower Ordovician (compare with Fig. 8.3) and in the Lower Cambrian (ichnospecies here are shown through the entire interval, whereas Cruziana is absent from most of the sub-trilobite Cambrian).

the Middle-East. It has proven particularly useful in the epicratonic ‘Nubian Sandstone’ facies, in which body fossils are rare, and has aided in recognition and dating of marine transgressions recorded in this succession (Seilacher 1991). Application of ‘Cruziana’ stratigraphy has been complicated by Seilacher’s (1970) decision to include both cruzianiform (furrowing) and rusophyciform (resting impression) traces within Cruziana. This decision has generally not been followed by other workers, who have retained the distinction between Cruziana and Rusophycus (e.g., Fillion and Pickerill, 1990). Thus the author who has contributed the most to the subject is not writing in quite the same ichnotaxonomic language as other workers. (In Fig. 8.5, cruzianiform and rusophyciform ichnotaxa are shown separately.) Additionally, Seilacher’s publications do not uniformly communicate the regional distribution of ichnospecies or the quality of independent biostratigraphic control on their occurrences throughout their paleobiogeographic ranges. Some of Seilacher’s ichnotaxa apparently are based on limited material from limited areas, and age control

may not always be optimal. For example, Cruziana omanica Seilacher originally was reported from two sites, one tentatively considered Ordovician, the other Upper Cambrian or Lower Ordovician (Seilacher, 1970); whereas, in a subsequent report it was shown as being questionably Upper Cambrian (Seilacher, 1991). A published compendium of the complete database (localities, ichnotaxa, lithostratigraphy, independent biostratigraphic data) underlying ‘Cruziana’ stratigraphy would aid in assessing the inter-regional applicability of this important biozonation. Currently, ‘Cruziana’ stratigraphy cannot be applied reliably outside regions that formerly comprised Gondwana (Seilacher, 1994). Magwood and Pemberton (1990) assigned material from the Lower Cambrian Gog Group of western Canada (Laurentia) to C. semiplicata, C. goldfussi, and C. rugosa. Some of this material may have been misidentified (Fillion and Pickerill, 1990) or may better be assigned to a homeomorphic ichnospecies, Cruziana pectinata Seilacher (Seilacher, 1994). Nevertheless, the work of Magwood and Pemberton (1990) emphasizes that little work has been done on the biostratigraphy of


B ASSEMBLAGES Ceratopsian Assemblage

Caririchnium Assemblage

210

Iguanodon Assemblage

Dinosaur Assemblage LATE

215

JURASSIC

230 CARNIAN Brasilichnium Assemblage Otozoum Assemblage Eubrontes-Grallator Assemblage

TRIASSIC

200

225

NORIAN

TRIASSIC

Sauropod-Theropod Assemblage

ASSEMBLAGES

205

220 150

AGE

RHAETIAN

Brachychirotherium Assemblage Oldest-known dinosaur tracks

235

240

MIDDLE

100

CRETACEOUS

Hadrosaur Assemblage

200

245

250

EARLY

A

PERIOD

The scientific study of fossil vertebrate tracks began in the 1820s, but vertebrate ichnofossils were little used in biostratigraphy until the latter half of the twentieth century (Sarjeant, 1975). The number of recorded continental vertebrate tracksites has increased dramatically since the 1960s; fossilized vertebrate footprints are now reported widely from the Carboniferous to Holocene (Lockley, 1998b). Biostratigraphic application of vertebrate tracks has grown apace with the rest of vertebrate ichnology.

Demathieu and Haubold (1972) suggested that fossilized vertebrate footprints in the Triassic of Europe could be used for correlation within Europe and with the United States and Africa. Since that work, numerous studies of Triassic tetrapod footprints have been published. These were summarized by Lucas (2003), who suggested that at least three stratigraphically restricted footprint assemblages can be recognized in the Triassic (Fig. 8.6B). In ascending order, these are: a chirothere assemblage of Olenekian–Ladinian (Early Triassic–early Middle Triassic) age; a dinosauriform assemblage of Ladinian (late Middle Triassic) age; and a dinosaur assemblage of Carnian–Rhaetian (Late Triassic) age. An earliest Triassic (Induan?) assemblage of EPOCH

Evolution within a Group of Tracemakers: Continental Vertebrate Traces

Distinctive track assemblages (Fig. 8.6A) can be recognized at various levels in the Triassic, Jurassic, and Cretaceous (Lockley, 1991), and these provide the basis for vertebrate trace-fossil biostratigraphy.

PERIOD

Cruziana and related ichnotaxa outside Gondwana (Seilacher, 1994). Faunal provincialism among Cruziana ichnospecies probably can be turned to advantage as a means of testing paleocontinental reconstructions (e.g., Seilacher, 1991; Knaust, 2004).

141

LADINIAN

ANISIAN

Dinosauriform Assemblage Chirothere Assemblage

OLENIKIAN INDUAN

FIGURE 8.6 (A) A compilation of stratigraphically restricted, Mesozoic vertebrate track assemblages; modified after Lockley (1991). Vertical axis is millions of years before present. (B) Triassic vertebrate footprint assemblages; modified after Lucas (2003). A possible earliest Triassic dicynodont-track assemblage is not shown (see text). Vertical axis is millions of years before present.

142


LOWER JURASSIC

dicynodont footprints may also be recognizable, though data are sparse. Overall, the track assemblages provide less stratigraphic resolution than Triassic tetrapod body fossils (Lucas, 2003). However, although the Late Triassic dinosaur assemblage permits only series-level correlation, the other three assemblages represent time-spans comparable to those of Triassic stages (Fig. 8.6B). The Triassic–Jurassic boundary corresponds to significant changes in the tetrapod ichnofauna. These changes are particularly well documented in the Newark Basin of eastern North America (Olsen, 1988; Silvestri and Szajna, 1993) but are also recorded elsewhere in North America, Europe, and Lesotho (Haubold, 1986; Rainforth, 2003). In the Newark Basin, the Triassic–Jurassic boundary (Fig. 8.7) is marked by the upsection disappearance of the ichnogenera Apatopus, Brachychirotherium, and Gwyneddichnium, and the appearance of Anomoepus, Ameghinichnus, and Eubrontes (Silvestri and Szajna, 1993). The study of Triassic–Jurassic vertebrate ichnogenera is complicated by ichnotaxonomic issues, including probable oversplitting of Lower Jurassic ichnospecies (Lockley, 1998a) and errors in the identification and documentation of

UPPER TRIASSIC

Eubrontes

Gwyneddichnium

Anomoepus

Apatopus

Ameghinichnus

Brachychirotherium

FIGURE 8.7 Vertebrate track ichnotaxa useful in delineating the Triassic–Jurassic boundary in the Newark Basin, Pennsylvania. Scale bars are 1 cm. Tracks are redrawn after Olsen (1988). This diagram is not a range chart; for detailed range data, see Olsen (1988) and Silvestri and Szajna (1993).

nineteenth-century type material from the Lower Jurassic of the Connecticut Valley (Rainforth, 2003). Recent ichnotaxonomic revisions have clarified biostratigraphic ranges. For example, the dinosaurian footprint Otozoum has been reported from the Triassic and the Jurassic. Rainforth (2003) demonstrated that Triassic occurrences should be assigned to Pseudotetrasauropus and that Otozoum is restricted to the Lower Jurassic. Middle and Upper Jurassic vertebrate tracks also have biostratigraphic potential. Late Jurassic assemblages of theropod tracks assignable to the ichnogenera Megalosauripus and Therangospodus are widespread and apparently restricted to the Oxfordian– Kimmeridgian boundary interval (Lockley et al., 1998). The Megalosauripus–Therangospodus assemblage has been recognized in North America, Europe, and Asia. At least three other widely distributed Middle and Upper Jurassic footprint ichnotaxa show similarly restricted stratigraphic ranges (Lockley, 1998b): Ravatichnus (Bajocian); Carmelopodus (Bathonian); and Dinehichnus (Kimmeridgian). Footprints are not the only vertebrate-produced trace fossils with biostratigraphic potential. Vertebrate coprolites (fossilized fecal material) also have been used in stratigraphic correlation (e.g., Johnson, 1934), a practice dubbed coprostratigraphy (Hunt et al., 1993). Studies in the Upper Triassic of the western USA indicate that vertebrate coprolites are useful in local and regional correlation and can be the basis of both range and acme zones (e.g., Hunt et al., 1993, 1998).

Succession of Ichnotaxon First Appearances: The Neoproterozoic–Cambrian Transition Trace-fossil diversity increased dramatically across the Neoproterozoic–Cambrian boundary (Fig. 8.8), and this is recorded particularly well in the siliciclastic-dominated strata that comprise many Neoproterozoic–Cambrian transitional sections. In many such sections, shelly micro- and macrofossils are rare or absent in the sub-trilobite Lower Cambrian. Seilacher (1956) recognized the importance of the increase in trace-fossil diversity and suggested that trace fossils could be used to recognize the base of the Cambrian in the absence of other fossil remains. This early insight was expanded upon in a series of articles by Crimes (1987, 1992, and references therein) that documented the trace-fossil record of many


143

Number of ichnogenera

120 100 80 60 40 20 0 E (49)

LC (86)

MC (76)

UC (80)

LO (94)

MO UO LS (113) (115) (104)

FIGURE 8.8 Bar graph of ichnogenus-level diversity of trace fossils in uppermost Neoproterozoic and lower Paleozoic, based on data compiled by Crimes (1992). Horizontal axis shows subdivisions of geological time (E = Ediacaran, LC = Lower Cambrian, MC = Middle Cambrian, UC = Upper Cambrian, LO = Lower Ordovician, MO = Middle Ordovician, UO = Upper Ordovician, LS = Lower Silurian), with total number of ichnogenera given in brackets for each subdivision. Note large increase in diversity from Ediacaran to Lower Cambrian; recent reassessments of the Ediacaran trace-fossil record (e.g., Jensen, 2003) suggest that this increase may be even more dramatic than shown here.

Neoproterozoic–Cambrian successions. The result was an impressive database of first-appearance and range data for numerous ichnotaxa, and the proposal (Crimes, 1987) that three trace-fossil biozones could be recognized in the Ediacaran to sub-trilobite Lower Cambrian. These biozones were based primarily on first-appearance data for relatively long-ranging ichnogenera, although some last-appearance and range data were also cited. Zone I (upper Ediacaran) was dominated by long-ranging, relatively simple traces, such as Helminthoidichnites, Palaeophycus, and Planolites. It also contained a number of unusual structures (e.g., Harlaniella, Palaeopascichnus, and Yelovichnus) that were restricted to the Ediacaran and were interpreted as trace fossils. The hallmark of Zone II was the advent of branching burrow networks, typified by Treptichnus (Phycodes) pedum (Seilacher) (Fig. 8.9A). Zone III saw the appearance of such arthropod-produced ichnotaxa as Rusophycus (Fig. 8.9B) and Cruziana (Fig. 8.9C). Detailed faunal lists for these zones were provided by Crimes (1992) in an article that also tabulated age ranges for numerous ichnotaxa in the Ediacaran–Cambrian

A

B

C FIGURE 8.9 Nominate ichnotaxa for sub-trilobite Cambrian trace-fossil biozones. Scale bars (lower right corners of photographs) represent 1 cm. (A) Treptichnus pedum (Seilacher), Chapel Island Formation (Lower Cambrian), Grand Bay, Newfoundland, Canada. Individual ‘probes’ of the burrow are indicated by arrows. (B) Rusophycus avalonensis Crimes and Anderson, Backbone Ranges Formation (Lower Cambrian), Mackenzie Mountains, northwestern Canada. (C) Cruziana tenella (Linnarsson), upper Mickwitzia sandstone (Lower Cambrian), Kinnekulle, Va¨stergo¨tland, Sweden. Photographs A and B by the author; photograph C by S. Jensen.

8. THE APPLICATION OF TRACE FOSSILS TO BIOSTRATIGRAPHY Ichnotaxa FAs and Characteristic Ichnotaxa

Typical Features of Ichnofauna

Cruziana tenella Zone

Cruziana ispp. (incl. C. tenella), Plagiogmus arcuatus

Arthropod furrowing traces appear. Large, back-filled burrows.

Rusophycus avalonensis Zone

Taphrelminthopsis circularis, Rusophycus ispp.

A rthropod resting traces appear. Large, bilobate furrowing traces.

Treptichnus pedum Zone

Treptichnus pedum, T. coronatum, Gyrolithes, Bergaueria

Diverse branching burrow systems. Anemone resting traces.

‘Simple burrows III’

Treptichnus isp. (nonT. pedum ), ‘Curvolithus’

First simple burrow systems. Traces with 3-lobed lower surface appear.

‘Simple burrows II’

Archaeonassa, Helminthoidichnites, Helminthopsis, Helminthorhaphe

Unbranched horizontal traces. Rare traces with open meanders.

‘?Simple burrows I’

Planolites

Earliest shallow infaunal traces.

Biozones

Sub-trilobite Lower Cambrian

interval. Although the status and ichnotaxonomy of several of the ichnotaxa have been questioned (see below), these tabulations are still useful. These zones were expanded upon in subsequent studies. Narbonne et al. (1987) documented the biostratigraphy of the Global Stratotype Section and Point (GSSP) for the base of the Cambrian System at Fortune Head, Newfoundland, Canada, and named formal biozones corresponding to the informal zones of Crimes (1987): Harlaniella podolica Zone (= Zone I); Phycodes pedum (now Treptichnus pedum) Zone (= Zone II); and Rusophycus avalonensis Zone (= Zone III). The base of the Cambrian System ultimately was defined at the lowest-known specimen of Phycodes (Treptichnus) pedum within the Fortune Head section. Subsequent workers have proposed additional biozones. In a study of the basal Cambrian of the Mackenzie Mountains, northwestern Canada, MacNaughton and Narbonne (1999) proposed that Zone III of Crimes (1987) could be subdivided into a lower Rusophycus avalonensis Zone and an upper Cruziana tenella Zone. Rusophycus appears below Cruziana in many basal Cambrian sections (Crimes, 1992), including the Fortune Head GSSP (Narbonne et al., 1987). The Neoproterozoic Zone I has also been subdivided; Jensen (2003) proposed that as many as three uppermost Ediacaran biozones could be recognized using simple trace fossils. The current trace-fossil biozonation for the Ediacaran–Cambrian transition is summarized in Fig. 8.10. Recently, several aspects of the Ediacaran–Cambrian trace-fossil record have been clarified. Several of the unusual ‘ichnotaxa’ restricted to the Ediacaran (e.g., Harlaniella, Palaeopascichnus, and Yelovichnus) have been shown not to be trace fossils (Jensen, 2003; Seilacher et al., 2003; Seilacher et al., 2005). However, these structures are probably of biological origin and may still be of value to biostratigraphy (Jensen, 2003). The range of Treptichnus ispp. relative to the Ediacaran–Cambrian boundary also has been reassessed. Specimens of Treptichnus isp. (non Treptichnus pedum) have been reported from uppermost Proterozoic strata in Namibia (Jensen et al., 2000) and Newfoundland (Gehling et al., 2001). This material differs in detail from Treptichnus pedum, but shows that simple treptichnids can be a feature of uppermost Ediacaran ichnofaunas (Fig. 8.10). Previously unrecognized specimens of Treptichnus pedum have been documented up to 4 m below the ratified base of the Cambrian in the Fortune Head GSSP (Gehling et al., 2001). Although the base of the Treptichnus pedum Zone does not coincide exactly with the defined base of the Cambrian System, this does not affect the utility

‘Upper’ Ediacaran

144

FIGURE 8.10 Upper Ediacaran to sub-trilobite Cambrian trace-fossil biozones, modified after Jensen (2003). Data for Cambrian biozones are from Crimes (1992) and MacNaughton and Narbonne (1999). Neoproterozoic biozones follow Jensen (2003), although their informal names are modified after MacNaughton and Narbonne (1999). The base of the ‘?Simple burrows I’ zone corresponds to the oldest reliable trace fossils in the stratigraphic record.

of Ediacaran–Cambrian trace-fossil biozones for correlation, and Treptichnus pedum ‘remains a reasonable indicator for the base of the Cambrian . . . ’ (Gehling et al., 2001, p. 213). Of potentially greater concern are the relative roles of environment and evolution in controlling the tracefossil record of the Neoproterozoic–Cambrian transition. In view of the global transgression that occurred at that time, it has been suggested that the recognized succession of biozones may have resulted as transgression produced a vertical succession of successively more distal facies, each with a distinctive (ichno)fauna (Brasier, 1979). Higher-frequency changes in relative sea-level can also influence the distribution of appropriate environments and, thus, of lithofacies within a depositional sequence, lessening the resolution of correlations based on trace fossils (Lindsay et al., 1996). To address the former issue, MacNaughton and Narbonne (1999) analyzed the ichnology, sedimentology, and high-resolution sequence stratigraphy of Ediacaran–Cambrian strata in northwestern Canada.

Ct

15

Ct

13 12

sb

sb

Ra

sb

Ra

Tp Ra

11 sb

10

Ra

9

Tp

Ra

8

Tp

Tp

Ra Ra Ra

Ra

7

Tp

Ra

6

Ra

Ra

5

Tp

Tp

Tp

sb

sb

4

sb

3 2 1

sb

sb

sb

sb

sb

BIOZONE

SYSTEM CAMBRIAN

16

145

stressed, marginal-marine environments generally provided a reliable indication of Cambrian vs. Ediacaran age, but were unreliable at the level of biozones. However, biozones could be recognized consistently in strata deposited in open-marine settings, supporting the view that evolution was the primary control on the vertical distribution of trace fossils (Fig. 8.11). Several biostratigraphically significant ichnotaxa, including Treptichnus and Rusophycus, occurred in a variety of marine and marginal-marine facies. Similarly integrated studies should be undertaken for other Ediacaran–Cambrian successions. At present, it can be noted that the original base of the Treptichnus pedum Zone in the Fortune Head GSSP did not correspond to a major facies change (Narbonne et al., 1987), nor does the first appearance of T. pedum as determined in more recent studies of the GSSP (Gehling et al., 2001).

OTHER POTENTIALLY USEFUL ICHNOTAXA EDIACARAN

Ct

Rusophycus avalonensis

VAMPIRE

17

14

BACKBONE RANGES

Ct

‘simple burrows’ T. pedum

Ct

18

Cruziana tenella

Ct

18+

INGTA

OFFSHORE TRANSITION DISTAL SHELF

L. SHOREFACE

SHOREFACE

BEACH

MOUTH BAR

INTERDISTRIBUTARY

FLUVIAL

AEOLIAN

SEQUENCE

FORMATION

OTHER POTENTIALLY USEFUL ICHNOTAXA

FIGURE 8.11 Time–environment matrix for Ediacaran– Cambrian trace-fossil biozones recognized in the Mackenzie Mountains, northwestern Canada, modified after MacNaughton and Narbonne (1999). High-resolution depositional sequences are shown on vertical axis; interpreted depositional environments are shown on horizontal axis. Trace-fossil assemblages are shown for each environment on a sequence-by-sequence basis: sb = ‘simple burrows’ assemblage; Tp = Treptichnus pedum assemblage; Ra = Rusophycus avalonensis assemblage; Ct = Cruziana tenella assemblage. Gray boxes indicate environments not represented in a given depositional sequence; diagonal lines indicate barren strata. Base of Cambrian, as determined from trace fossils, is within sequence 5. This is independently constrained by a latest Ediacaran, negative carbonisotope excursion recorded in sequence 1 and by Cambrian small shelly fossils in sequence 6. Trace-fossil assemblages from offshore-transition (shelf) and distalshelf lithofacies provide a consistent biozonation, whereas those from marginal-marine lithofacies are less reliable. For additional discussion, see MacNaughton and Narbonne (1999).

They demonstrated that environmental limiting factors were a significant secondary control on the distribution of trace fossils within depositional sequences. Trace-fossil assemblages associated with

The preceding discussion does not exhaust the biostratigraphic potential of trace fossils. Examples of ichnotaxa with limited stratigraphic ranges and distinctive morphologies are scattered throughout the literature. However, such ichnotaxa will be of little practical help if range data are not compiled into useful compendia. Discussion of stratigraphic ranges should be included as a standard component of ichnotaxonomic monographs, as is being done for the revised trace-fossil volume of the Treatise on Invertebrate Paleontology, currently in preparation (Rindsberg, A. pers. comm., 2005). Databases of stratigraphic range information are an important component of developing additional, trace-fossilbased biostratigraphic schemes. Computerization permits such databases to be updated and accessed readily. Extensive data compilations feature in several recent publications that give a sense of the biostratigraphic potential of several groups of trace fossils.

Graphoglyptids Graphoglyptids are trace fossils encompassing a variety of shapes, including nets, spirals, star-like forms, and meanders, commonly of significant complexity. They occur overwhelmingly as positiverelief features preserved on the soles of turbidites. Uchman (2003, 2004) has presented compilations of the stratigraphic ranges for numerous graphoglyptid ichnospecies, the majority of which are Cretaceous or younger. Although many graphoglyptid ichnotaxa

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are relatively long-ranging, a number of them are apparently restricted to one or two systems. In particular, ichnospecies of Dictyodora may be useful in the Lower Palaeozoic, where other biostratigraphic data can be sparse in deep-marine successions (Uchman, 2004).

Hard-Substrate Ichnotaxa Recent data compilations dealing with microborings (Bromley, 2004; Glaub and Vogel, 2004) and macroborings (Bromley, 2004) suggest that although many bioerosion ichnotaxa are long-ranging, some are apparently restricted to one system and may have potential as index fossils. Further work is required to test the biostratigraphic utility of these ichnotaxa (Glaub and Vogel, 2004). The published compilations are at a coarse resolution and it is unclear how useful first-appearance data for bioerosion structures might be for biostratigraphy. Bioclaustrations, which are distinct from bioerosion structures, are dwelling structures produced when endosymbionts locally hinder the growth of their host organism’s skeleton. A review by Tapanila (2005) indicates that several bioclaustration ichnotaxa have relatively short (seriesor stage-level) stratigraphic ranges, but the known stratigraphic record of these structures is sparse.

Insect-Produced Traces Genise (2004) has reviewed the ichnotaxonomy and stratigraphic distribution of numerous ichnotaxa attributable to insects and found primarily in Cretaceous and younger strata. Several of these distinctive structures have relatively restricted stratigraphic ranges and many show a stratigraphic range similar to that of their likely producers. Insects tend to be widely dispersed, which may enhance the biostratigraphic potential of their trace fossils.

are consistently developed. Detailed measured sections are essential for facies analysis and sequencestratigraphic study, and the stratigraphic position of collected and observed trace fossils should be recorded accurately on the measured sections. Detailed lithofacies and paleoenvironmental analysis are essential for recognizing environmental—as opposed to evolutionary—controls on the composition and distribution of ichnofaunas. Environmental limiting factors are always a control on the distribution of ichnofossils and, as a result, similar ichnofaunas do not necessarily indicate similar ages. Indeed, through much of the stratigraphic record, similar ichnofaunas (especially at the ichnogeneric level) are more likely to indicate similar environmental conditions than similar ages. Sequence-stratigraphy and related methods provide insight into any transgressive–regressive cycles that may have controlled the availability of lithofacies suitable for production and preservation of trace fossils. High-resolution sequence stratigraphy can also provide an independent stratigraphic framework against which trace-fossil successions can be compared. Careful, detailed ichnotaxonomy is essential; whenever possible, trace fossils should be identified to the level of ichnospecies or ichnosubspecies. Oversplitting of ichnotaxa can lead to erroneous biostratigraphy if combined with incautious correlation. If an ichnotaxon is known only from a single locality or region, it may be the product of oversplitting. It should be used for biostratigraphy only after careful review of its systematic ichnotaxonomy. By contrast, excessive lumping of ichnotaxa can mask useful biostratigraphic data. Age assignments based on poorly preserved material are likely to be incorrect and should be made cautiously. Awareness of the influence of taphonomic history on ichnotaxonomic assignments is essential.

CONCLUDING DISCUSSION TOWARD RELIABLE TRACE-FOSSIL BIOSTRATIGRAPHY In view of the difficulties inherent in using trace fossils for biostratigraphic correlation, the following guidelines are suggested as insurance against misapplication. Detailed collecting should be undertaken and every effort made to examine both bedding-plane and cross-sectional outcrop exposures. Studying multiple sections through a stratigraphic interval helps to document whether trends in ichnofaunal composition

Trace fossils are unlikely to be applied to biostratigraphy except in parts of the stratigraphic record where they are the sole source of biostratigraphic data or where they usefully augment data available from other fossils, but in such situations they may be invaluable. When other biostratigraphic data are available but sparse, trace-fossil biostratigraphy can help calibrate and test more traditional biostratigraphic methods. Trace-fossil ranges should be integrated with independent biostratigraphic and geochronologic data whenever possible.

ACKNOWLEDGEMENTS

Compendia of range data are helpful in studying behavioral evolution and evolutionary paleoecology, and thus trace-fossil biostratigraphy works well in tandem with such studies. Useful data can flow both ways between these disciplines. For example, the database compiled by Crimes (1987, 1992) for biostratigraphic purposes subsequently was the basis of published discussions of the evolutionary history of the Ediacaran–Cambrian transition (Crimes, 1994). By contrast, work by Uchman (2003, 2004) has been concerned mainly with the evolutionary paleoecology of graphoglyptids, but may also have biostratigraphic implications. In rare cases, a distinctive trace fossil can be tied to a likely producer, providing important information on the tracemaker’s behavior and functional morphology. For example, when Fortey and Seilacher (1997) suggested that C. semiplicata was probably produced by trilobites of the genus Maladioidella, the concurrent ranges of the trace and the trilobite were key evidence in making the connection. Thus reliable stratigraphicrange data for ichnotaxa can help document behaviors of specific organisms. Finally, because solid ichnotaxonomy is essential to good trace-fossil biostratigraphy, the two disciplines should proceed hand-in-hand. Ideally, specialists in trace-fossil biostratigraphy should also be trenchant ichnotaxonomists. At the very least, trace-fossil biostratigraphers should hold ichnotaxonomists in high regard, whilst spurring them on to ever greater feats of monograph writing.

ACKNOWLEDGEMENTS Thanks are due particularly to G.M. Narbone for spurring and encouraging my interest in tracefossil biostratigraphy. This chapter directly benefited from helpful conversations or correspondences with the following persons: L. Buatois, W. Hagadorn, S. Jensen, G. Mańgano, A. Rindsberg, and J.-P. Zonneveld. Buatois, Jensen, and Mańgano also provided photographs reproduced in this chapter. Photographs by the author were taken during fieldwork with G. Narbonne or W. Hagadorn. Helpful reviews by J. Utting (GSC internal review), S. Jensen, and R. Pickerill improved the manuscript. M. Peterson, E. Hau, and B. Rutley provided technical assistance. This manuscript was prepared as part of Geological Survey of Canada Project Y08. Earth Sciences Sector Contribution 2005328.

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Pickerill, R.K. and Fillion, D. (1983). On the Tremadoc-Arenig and Lower-Upper Tremadoc boundaries in the Bell Island Group, Conception Bay, eastern Newfoundland. Maritime Sediments and Atlantic Geology, 19, 21–30. Rainforth, E.C. (2003). Revision and re-evaluation of the Early Jurassic dinosaurian ichnogenus Otozoum. Palaeontology, 46, 803–838. Ruedemann, R. (1942). Oldhamia and the Rensselaer grit problem. New York State Museum Bulletin, 327, 5–17. Sarjeant, W.A.S. (1975). Fossil tracks and impressions of vertebrates. In: Frey, R.W. (Ed.), The Study of Trace Fossils, Springer-Verlag, New York, pp. 283–324. Seilacher, A. (1956). Der Beginn des Kambriums als biologische Wende. Neues Jarbuch fu¨r Geologie und Palaöntologie Abhandlungen, 103, 155–180. Seilacher, A. (1970). Cruziana stratigraphy of ‘non-fossiliferous’ Palaeozoic sandstones. In: Crimes, T.P. and Harper, J.C. (Eds.), Trace Fossils, Seel House Press, Liverpool, pp. 447–476. Seilacher, A. (1974). Flysch trace fossils: evolution of behavioral diversity in the deep-sea. Neues Jarbuch fu¨r Geologie und Palaöntologie Monatshefte, 233–245. Seilacher, A. (1991). An updated Cruziana stratigraphy of Gondwanan Palaeozoic sandstones. In: Salem, M.J., Hammuda, O.S. and Eliagoubi, B.A. (Eds.), The Geology of Libya—Volume IV, Elsevier, Amsterdam, pp. 1565–1581. Seilacher, A. (1994). How valid is Cruziana stratigraphy? Geologisches Rundschau, 83, 752–758. Seilacher, A., Buatois, L.A. and Mańgano, M.G. (2005). Trace fossils in the Ediacaran–Cambrian transition: behavioral diversification, ecological turnover and environmental shift. Palaeogeography, Palaeoclimatology, Palaeoecology, 227, 323–356. Seilacher, A., Grazhdankin, D. and Legouta, A. (2003). Ediacaran biota: the dawn of animal life in the shadow of giant protists. Paleontological Research, 7, 43–54. Silvestri, S.M. and Szajna, M.J. (1993). Biostratigraphy of vertebrate footprints in the Late Triassic section of the Newark Basin, Pennsylvania: reassessment of stratigraphic ranges. In: Lucas, S.G. and Morales, M. (Eds.), The Nonmarine Triassic, New Mexico Museum of Natural History & Science Bulletin 3, pp. 439–445. Tapanila, L. (2005). Palaeoecology and diversity of endosymbionts in Palaeozoic marine invertebrates: trace fossil evidence. Lethaia, 38, 89–99. Uchman, A. (2003). Trends in diversity, frequency and complexity of graphoglyptid trace fossils: evolutionary and palaeoenvironmental aspects. Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 123–142. Uchman, A. (2004). Phanerozoic history of deep-sea trace fossils. In: McIlroy, D. (Ed.), The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis, Geological Society Special Publication 228, pp. 125–139. Yochelson, E.L. and Fedonkin, M.A. (1993). Paleobiology of Climactichnites, an enigmatic Late Cambrian fossil. Smithsonian Contributions to Paleobiology, 74, 74 pp. Zonneveld, J.-P., Pemberton, S.G., Saunders, T.D.A. and Pickerill, R.K. (2002). Large, robust Cruziana from the Middle Triassic of northeastern British Columbia: ethologic, biostratigraphic, and palaeobiologic significance. Palaios, 17, 435–448.

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9 Trace Fossils and Marine Benthic Oxygenation Charles E. Savrda

paleoceanographic conditions and to understand and predict the distribution of potential hydrocarbonsource rocks. The use of trace fossils in interpreting paleo-redox conditions centers on the identification of ichnocoenoses (ecologically pure assemblages of ichnofossils inferred to derive from the work of distinct infaunal communities; Bromley, 1990) that can be tied to relative levels of benthic oxygenation. Recognition and application of oxygen-related ichnocoenoses (ORI) have been described in previous studies (e.g., Savrda and Bottjer, 1986, 1987, 1989a,b, 1991, 1994; Savrda, 1992, 1995, 1998a,b; Ozalas et al., 1994; Martin, 2004). The objectives of this chapter are to (1) summarize the genesis and stratigraphic manifestation of ORI, (2) exemplify the use of ORI in deciphering temporal oxygenation histories of, and spatial gradients within, marine basins, and (3) highlight some of the potential limitations and applications of the ichnologic approach.

SUMMARY : Benthic oxygenation strongly influences the character of infaunal communities and the ichnofabrics they produce in marine mud substrates. Trace fossil diversity and size parameters (burrow diameters, vertical penetration depths) provide the basis for recognizing oxygen-related ichnocoenoses, the stratigraphic distribution of which can help reconstruct temporal changes and spatial gradients in paleo-oxygenation. Although the trace fossil approach has some limitations and can be further refined, ichnologic proxies for benthic oxygenation can be applied effectively towards a better understanding of paleoceanographic conditions in ancient basins and the hydrocarbon-source potential of marine mudrocks deposited therein.

INTRODUCTION Benthic oxygenation is an important oceanographic parameter. It reflects aspects of oceanic circulation, some of which may be climate mediated (e.g., upwelling intensity and thermohaline density stratification), and controls the quantity and preservational state of organic matter in marine sediments. Oxygenation is also one of the most important factors influencing the character and activities of benthic organisms, particularly in quiet marine basinal settings. Fortunately, responses of infauna to variations in benthic oxygenation may be preserved in the trace fossil record. Hence, ichnofabrics in pelagic and hemipelagic muds can serve as proxy indicators of paleo-oxygenation and, in turn, help to reconstruct

OXYGEN-RELATED ICHNOCOENOSES (ORI) Ichnocoenoses in Well-Oxygenated Substrates Well-oxygenated, marine hemipelagic/pelagic substrates typically exhibit a burrow stratigraphy or tiering that is manifest in ichnofabrics preserved in the stratigraphic record. These substrates can be divided into two main components based on the character of concurrent biogenic activity (Berger et al., 1979; Ekdale et al., 1984); the surface mixed layer


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Mixed Layer

Historical Layer

LOD

DOL

LOD

Transition Layer

Ichnotaxa:

Chondrites

Zoophycos

Thalassinoides

FIGURE 9.1 Burrow stratigraphy in well-oxygenated pelagic/hemipelagic substrates and resulting ichnofabrics and ichnocoenosis. Historical layer ichnofabrics include homogeneous or burrow-mottled backgrounds (shown as solid white or gray) and discrete transitionlayer structures (drawn as dotted, dashed, or solid figures). Assemblage of transition-layer ichnofossils is diverse (only three ichnotaxa are shown here for simplicity) and includes large, vertically extensive structures. Note that under persistently well-oxygenated conditions, the ichnocoenosis represented in historical layer ichnofabrics remains unchanged. Nonetheless, transition-layer burrows are more clearly manifest in lighton-dark (LOD) and dark-on-light (DOL) piped zones wherein all or part of the sediment within structures contrasts with host sediments.

and transition layer (Fig. 9.1). The mixed layer, up to 15 cm thick, is a relatively fluid zone of continuous bioturbation by organisms that may produce surface tracks and trails and various endogenic locomotion, dwelling, feeding, and gardening structures. However, under steady-state conditions, traces produced within the mixed layer are normally not preserved due to low sediment shear strengths and overprinting by transition-layer traces (see Chapter 6). The transition layer is characterized by heterogeneous mixing by organisms that live and/or feed at greater depths (several decimeters) below the seafloor. In well-oxygenated substrates, transition-layer ichnofossil suites are diverse and include a variety of burrows, burrow systems, and complex spreite structures. These structures, many of which are passively or actively filled with sediment derived at or near the sediment–water interface, vary widely in size but include burrows with relatively large diameters (up to several centimeters). As the mixed and transition layers migrate upward in pace with deposition, sediments eventually pass below the benthic boundary layer into the historical layer. Historical layer ichnofabrics (i.e., those that enter the stratigraphic record) consist of two components: (1) homogeneous or vaguely burrow-mottled backgrounds produced during passage through the surface mixed layer; and (2) a suite of superimposed structures emplaced during subsequent passage through the transition layer (Fig. 9.1). As long as oxygenation levels and the community of bioturbating organisms remain the same, these two temporally disjunct ichnofabric components comprise a single ichnocoenosis. Ichnocoenoses generated under welloxygenated conditions are characterized by highdiversity assemblages of transition-layer structures that include relatively large, vertically extensive forms (Fig. 9.1). The visibility of transition-layer structures within historical-layer ichnofabrics depends on the degree of compositional contrast between burrow fills and host sediment. Where sediment type is unchanging, contrast is typically low. Visibility of many structures is naturally enhanced in sequences characterized by stratal color variations caused by temporal changes in sediment composition (e.g., clastic vs. carbonate content, organic carbon content). Transition-layer burrows are well expressed at bed transitions, or piped zones. In dark-on-light (DOL) piped zones, lighter colored mixed-layer background fabrics are overprinted by transition-layer structures that, at least

MANIFESTATION OF ORI IN VERTICAL SEQUENCES

in part, were passively or actively filled with overlying darker sediment. In light-on-dark (LOD) piped zones, darker mixed-layer fabrics are cut by structures wholly or partly filled with lighter sediments derived from above (Fig. 9.1).

Response to Changes in Oxygenation As recognized in earlier studies of modern oxygendeficient settings (e.g., Rhoads and Morse, 1971; Pearson and Rosenberg, 1978; Savrda et al., 1984), the character of infaunal communities and their activities vary with changes in bottom-water oxygenation. As oxygen concentrations decline, bioturbating infauna become less diverse due to the progressive loss of larger and more active organisms that typically have higher oxygen requirements. Oxygen flux into the substrate via burrow irrigation and wholesale sediment- and pore-water advection is commonly limited, resulting in reduced burrowing depths of most infaunal organisms. Although general burrow stratigraphy remains unchanged as oxygenation varies, responses of the infauna are reflected by ichnological features. Predictably, as bottom-water oxygenation decreases, temporally or spatially within a basin, the thickness of the mixed layer should decrease, and diversity, diameter, and penetration depths of transition layer structures should generally decline. Eventually, if oxygen levels drop below a critical threshold, bioturbation ceases altogether and primary, laminated fabrics (laminites) are preserved. Oxygen-related changes in infaunal communities result in the production of different ichnocoenoses that are manifest in historical layer ichnofabrics. Oxygen-related ichnocoenoses (ORI) generated under progressively lower oxygen concentrations are characterized by progressively lower diversity assemblages of smaller diameter, more shallowly penetrating transition-layer burrows (Figs. 9.2 and 9.3). Notably, these ichnologic changes are typically accompanied by a progressive increase in organic carbon contents and consequent sediment darkening.

MANIFESTATION OF ORI IN VERTICAL SEQUENCES Expression of ORI in the stratigraphic record is highly variable. Where intercalated with laminites reflecting anoxic conditions (Fig. 9.2), oxygenation

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event beds typically have two distinct parts: (1) a thoroughly bioturbated interval (primary stratum) overlying (2) a very well-defined piped zone. Thoroughly bioturbated intervals are those that were subject to mixed layer bioturbation during the oxygenation episode. In the case of very short-lived episodes, this interval mainly reflects the mixing of previously laminated sediments to a finite depth governed by degree of oxygenation. Ichnofabrics are typically homogeneous to diffusely mottled, and they lack the transition-layer burrows that characterize normal historical layer ichnofabrics (e.g., primary stratum at 1 in Fig. 9.2). In the case of extended oxygenation episodes, bioturbated intervals thicken in response to seafloor accretion, and their lower parts may develop normal historical layer ichnofabrics as transition-layer burrowers migrate upward in pace with sedimentation (e.g., primary stratum at 2 in Fig. 9.2). Piped zones beneath thoroughly bioturbated intervals are characterized by laminated background fabrics (Fig. 9.2). They record the emplacement of transition-layer burrows into sediments that were far enough below the sediment–water interface to preclude mixed layer bioturbation during the oxygenation episode. Transition-layer structures in piped zones are typically better expressed than in superjacent bioturbated intervals, owing to greater color contrast between ichnofossils and host sediment. Consequently, they are particularly useful in recognizing ORI. Generally, with increasing magnitude of oxygenation episodes, thickness of piped zones increases, as do the diversity and size of ichnofossils preserved therein (Fig. 9.2). Recognition of ORI within thoroughly bioturbated intervals may be more complicated, because ORI overlap, producing more complex or compound ichnofabrics (Fig. 9.3). Temporal increases in oxygenation and hence bioturbation depth result in overprinting by both mixed layer and transition-layer bioturbators. Temporal decreases in oxygenation lead to reduced bioturbation depths; hence, overprinting is not as extensive. Differences in organic carbon content (and sometimes other constituents) result in sediment color variations among ORI, facilitating the recognition of piped zones. In these piped zones, transitionlayer structures representing one ichnocoenosis are superimposed on fabrics that reflect an earlier formed ichnocoenosis. Increases and decreases in oxygenation levels are typically reflected by LOD and DOL piped zones, respectively (Fig. 9.3).

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n atio gen y 3 x O 2 1

Mixed Layer

Transition Layer A Historical Layer

3

Piped Zone

B 2

Piped Zone

C 1

Piped Zone

Chondrites

Zoophycos

Thalassinoides

Ichnocoenoses 1 2 3

FIGURE 9.2 Ichnofabrics associated with different oxygen-related ichnocoenoses (ORI) (1–3) in sequences wherein bioturbated layers are interbedded with laminites. As oxygen levels decrease (from ORI 3 to ORI 1), diversity, size and vertical extent of transition-layer structures decrease. (A–C) schematically show the relative extent to which earlier formed fabrics (in this case, laminites) are destroyed by mixed layer bioturbation and overprinted by earliest emplaced transition-layer structures (piped zones). In the oxygenation curve, lines 1–3 represent progressively higher oxygen levels required for the establishment of ichnocoenoses 1–3, respectively.

CASE STUDY—CRETACEOUS BRIDGE CREEK LIMESTONE n

atio

gen

Oxy

1

2

3

A 3

2

B

A 3

B 2 C 1

C

1

FIGURE 9.3 Composite historical layer ichnofabrics produced by changes in oxygenation and resulting succession of ichnocoenoses (1–3). Overprinting of one ichnocoenoses by another within bioturbated intervals is commonly well manifest in piped zones. (A–C) schematically show the relative extent to which earlier formed fabrics are overprinted by mixed layer and transition-layer bioturbation associated with ichnocoenoses 3, 2, and 1, respectively, as conditions change through time. Oxygenation curve is constructed as in Fig. 9.2.

Whether associated with laminites or occurring in thoroughly bioturbated sequences, ichnofabrics can be interpreted in the context of vertical stacking of ORI. ORI stacking patterns, in turn, can be used to decipher temporal oxygenation histories (Figs. 9.2 and 9.3).

CASE STUDY—CRETACEOUS BRIDGE CREEK LIMESTONE Ichnologic criteria have been used to interpret oxygenation histories recorded in a wide array of

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Phanerozoic marine mudrocks. Such applications are particularly well exemplified by studies of the Cretaceous (Cenomanian–Turonian) Bridge Creek Limestone, as described in the synopsis below. The reader is referred to previous articles (Pratt, 1984; Savrda and Bottjer, 1994; Savrda, 1998a) for more detailed ichnologic discourse on this unit. The Bridge Creek Limestone, part of the Greenhorn Formation, was deposited in distal offshore settings of the Western Interior foreland basin during a major phase of transgression (Elder and Kirkland, 1985; Elder et al., 1994). This unit is characterized by decimeter-scale alternation of highly bioturbated, organics-poor limestones and laminated to bioturbated, relatively organics-rich marlstones and calcareous shales. Carbonate rhythms have been attributed to climate-driven clastic dilution cycles (e.g., Hattin, 1971; Pratt, 1984; Arthur and Dean, 1991; Pratt et al., 1993; Elder et al., 1994) or carbonate productivity cycles (e.g., Eicher and Diner, 1991; Ricken, 1994). Minor lithologic elements include altered volcanic ashes (bentonites) and calcarenites. Ashes and prominent limestones can be traced over broad areas and help define lithochronozones within the basin. Bioturbated intervals in the Bridge Creek Limestone are characterized by one or more of four ichnocoenoses. These are defined on the basis of recurring trace fossil assemblages containing one or more of seven trace fossil types (Fig. 9.4A): Chondrites, both small and large Planolites, Taenidium(?), Zoophycos, or Zoophycoslike structures, Teichichnus, and Thalassinoides. Trace fossil diversity, burrow diameters, and burrow-penetration depths (judged on the basis of vertical extents of burrows as well as piped zone thicknesses) increase from ORI 1 through ORI 4 (Fig. 9.4A), reflecting progressively higher levels of benthic oxygenation. Interpreted paleo-oxygenation curves constructed from the vertical disposition of laminites and the four ORI as observed in core reveal the following patterns: (1) a general, long-term decrease in benthic oxygenation through the period of Bridge Creek deposition; (2) a high-amplitude redox-cyclicity defined by the recurrence of ichnocoenoses 3 and 4, which generally correspond to thin limestones; and (3) a higher frequency, lower amplitude redox cyclicity generally defined by the alternation of laminites with ichnocoenoses 1 and/or 2 in thicker marlstone/calcareous shale interbeds (only the latter two patterns are evident in the short interpreted oxygenation curve in Fig. 9.4C). The covariation of oxygenation and carbonate contents in the Bridge Creek likely records combined redox/dilution cycles reflecting climate-mediated variations in clastic sediment supply and water-column stratification in

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the basin Savrda (1998a). Spectral analyses of ichnologic and sedimentologic data (e.g., organic C) indicate that these cycles were driven by Milankovitch orbital forcing (Sageman et al., 1997). Comparison of oxygenation curves generated for Bridge Creek lithochronozones expressed at different sites in the basin (now in Colorado and Kansas; see Fig. 9.4B) illustrate the potential utility of ORI in recognizing spatial changes in benthic redox conditions (Fig. 9.4C; also see Savrda, 1998a, Figs. 4–6). Oxygenation levels during limestone deposition appear to have been high and relatively invariant across the deepest part of the basin. In contrast, during clastic-dominated phases, oxygenation levels were generally depleted but lower toward the east. The latter trend may be related to differences in the relative influence of distinct Tethyan and Boreal water masses between the eastern and western sides of the basin (see Slingerland et al., 1996). Whatever the cause of the temporal and spatial changes in oxygenation during deposition of the Bridge Creek Limestone, there is a close link between ORI and organic carbon preservation. Both the amount and quality of organic matter (as assessed via whole-role pyrolysis; see Pratt, 1984) are lowest in sediments characterized by ichnocoenoses 4, progressively increase in sediments with lower ichnocoenosis rank (3 ! 1), and are highest in unbioturbated laminites. These relations demonstrate the potential use of ORI to evaluate the distribution of potential hydrocarbon-source rocks.

POTENTIAL LIMITATIONS AND FUTURE DIRECTIONS A number of limitations or potential problems should be considered when attempting to employ ichnologic data as proxies for benthic oxygenation. These include (1) the time-averaging inherent to the trace fossil record, (2) potential variability in the responses of infauna to changes in oxygenation, (3) the influence of parameters other than oxygen availability on organisms and their activities, and (4) poor trace fossil preservation or expression. Interpreted oxygenation curves (e.g., those in Fig. 9.4C) are necessarily time-averaged records of redox conditions. Records of short-term redox cycles or events are not preserved because bioturbation is a penetrative process that destroys parts of previously formed ichnofabrics. The extent of time averaging depends on depth of bioturbation, particularly mixed layer thickness, and sedimentation rate, which

controls how quickly pre-existing fabrics are buried and isolated from a subsequent bioturbation regime. For sequences deposited under well-oxygenated conditions and at typical pelagic/hemipelagic sedimentation rates (5–50 cm/ky), only lower frequency changes (those occurring over periods of 104 year or longer) can be detected in the trace fossil record. Predictably, temporal resolution of the record improves as benthic oxygenation levels and bioturbation depths decline, and as sedimentation rates increase (Savrda and Bottjer, 1991; Savrda, 1992). The ichnologic approach as described herein is based on the assumption that marine benthic communities and trace-making activities respond systematically and in the same way to changes in oxygenation levels in all marine environments. However, recent studies along modern oxygen gradients indicate that macrofaunal responses to changes in oxygen availability in some settings may be more complex than previously assumed. Studies of oceanic oxygen-minimum zones (OMZ) indicate that bioturbation may be intense at extremely low levels of oxygenation (Levin et al., 2003), that certain ichnologic parameters (e.g., maximum burrow diameters, bioturbation depths) do not necessarily correlate with oxygen levels (Smith et al., 2000), and that, under certain conditions, benthic food supply may have a greater influence than oxygen on infaunal activity and resulting traces, particularly where symbiont-bearing organisms are important (Levin et al., 2000). The trace fossil record in marine mudrocks may also be influenced by other environmental parameters that are independent of, or may influence, substrate oxygenation. The trace fossil approach is most easily applied to mudrocks deposited in settings that are minimally influenced by physical events. Tempestite and turbidite deposition may exterminate or modify the behaviors of resident benthic fauna. Alternatively, they may introduce allochthonous organisms (‘doomed pioneers’ of Grimm and Fo¨llmi, 1994) or those acclimated to different substrate types (Kern and Warme, 1974; Pemberton and MacEachern, 1997). These processes complicate ichnofabrics and may mask the background signal of oxygenation. Substrate consistency can also impact both tracemaker behavior and ichnofossil preservation. In soupy clay-rich muds, lack of shear strength may limit the ability of organisms to produce or maintain open burrows and to aerate substrates. Hence, porewater oxygen concentrations may be low, further impacting the benthos, despite well-aerated bottom waters (Savrda and Bottjer, 1994). Substrate consistency has been considered by some

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POTENTIAL LIMITATIONS AND FUTURE DIRECTIONS Ch Ps Ta Zo Pl Te Th

B

WY

NB

CO Portland #1

0 108°

Portland

200

41°

KS 39°

Bounds #1

400 km

OK TX

37°

104° Interpreted O2 curves 1 2 3 4 1 2 3 4

Bounds

4 LS 10

C LS 9

3

~1

m

LS 8

2

LS 7

cm cm

1

A

0 2 4 6 8 10 12 Burrow diameter (mm) Burrow depths (cm)

B

C

FIGURE 9.4 Oxygen-related ichnocoenoses (ORI) and inferred oxygenation histories for part of the Bridge Creek Limestone. (A) Characteristics of Bridge Creek ichnocoenoses. Ichnofossil diversity, maximum burrow diameters, and burrow-penetration depths increase from ORI 1 through ORI 4. Ch—Chondrites, Ps—small Planolites, Ta—Taenidium(?), Zo—Zoophycos or Zoophycos-like structures, Pl—large Planolites, Te—Teichichnus, and Th—Thalassinoides. (B) Location of two cores in central Colorado and western Kansas from which oxygenation curves were constructed for the Bridge Creek Limestone. (C) Generalized stratigraphic columns and interpreted oxygenation curves for an 4-m-thick interval of the lower Bridge Creek Limestone in two cores. LS7–LS10 are prominent limestones, and B and C are bentonite beds. In oxygenation curves, 1–4 reflect oxygenation levels necessary to support development of ORI 1 through 4 (more complete oxygenation curves for the two cores are provided in Savrda, 1998a).

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(e.g., Hattin, 1986; Sageman, 1989; Wignall, 1993) to be the principal control over ichnofabric development and ichnocoenosis character in some mud-dominated sequences, including the Greenhorn Formation described above. Distinguishing the relative effects of substrate consistency and bottom-water oxygenation may be problematic and requires future consideration. Obviously, the ichnologic approach is difficult to apply if distinct trace fossils are not well expressed. In some strata, especially clay-rich mudrocks, ichnofabrics appear homogeneous to diffusely burrowmottled; discrete trace fossils are absent or rare. This may be related to limited compositional and textural contrast between structures and host sediments. Alternatively, lack of distinct traces may be related to substrate conditions. Soupy substrates are not favorable for the production of distinct burrows, and those traces that are produced may be obscured by subsequent mechanical compaction. Notably, compaction of fluid substrates that were bioturbated by shallow ‘substrate swimmers’ may result in fabrics that, without careful examination, may be erroneously identified as laminites (Lobza and Scheiber, 1999; Scheiber, 2003). Some of the potential problems with the ichnologybased approach may be circumvented by further investigations of modern oxygen-deficient marine systems. Trace fossil criteria for evaluating oxygenation histories can be refined via studies of faunal responses and adaptations (including symbiosis; see Levin et al., 2003) to, and ichnologic manifestations, of spatial and temporal changes in bottom- and porewater oxygenation, substrate character, food resources, and other physio-chemical parameters in a broader range of modern environments. Sedimentary successions deposited in ancient epicontinental basins are locally petroliferous and a common focus of paleoceanographic studies. Hence, future investigations should include relatively rare modern epeiric basin analogs wherein organism responses to and ichnologic records of environmental change presumably differ, perhaps substantially, from those recognized in more thoroughly studied oceanic OMZ. Other problems encountered in applying the ichnologic approach to decipher paleo-oxygenation levels, such as poor expression of ichnofossils, likely to have no solution. However, the inability to recognize all traces and to assign them ichnotaxonomic names does not preclude the use of ichnofabrics in assessing oxygenation histories. Even relatively simple bioturbation indices can be used as proxies for benthic oxygenation levels and, when placed within a detailed chronostratigraphic framework, can provide

valuable information on global and regional oceanic circulation modes and their relations to climate change (e.g., see Behl and Kennett, 1996). Quaternary marine sediments, stratigraphic successions recovered during deep-sea drilling (i.e., in DSDP, ODP, and IODP cores), and land-based sections of Phanerozoic marine mudrocks possess an untapped wealth of ichnologic data that in the future can and should be applied in the studies of paleo-oxygenation and associated paleoceanographic parameters.

CONCLUSIONS Responses of marine infauna to changes in benthic oxygen availability may be reflected in the trace fossil record. As oxygenation declines, ichnofossil diversity and size parameters (burrow diameters, vertical penetration depths) generally decrease, resulting in the production of distinct ichnocoenoses. Stratigraphic distribution of ORI can be employed to reconstruct spatial gradients and time-averaged histories of paleo-oxygenation in marine basins. Even with its limitations, some of which may be eased by further integrated studies of modern oxygendeficient settings, the ichnologic approach has a broad range of potential applications, including evaluation of palaeoceanographic processes and events and appraisal of marine mudrock hydrocarbon-source potential.

ACKNOWLEDGEMENTS The author’s work on the relationships between paleo-oxygenation and trace fossils in the stratigraphic record was completed mainly during the period 1984–1998 with support from NSF, ACS-PRF, DOE, and USGS. The author thanks editor William Miller for the opportunity to review this subject, and Molly Miller and Sally Walker for critiques of an earlier version of this chapter.

References Arthur, M.A. and Dean, W.E. (1991). A holistic geochemical approach to cyclomania: examples from Cretaceous pelagic limestone sequences. In: Einsele, G., Ricken, W. and Seilacher, A. (Eds.), Cycles and Events in Stratigraphy, SpringerVerlag, New York, pp. 126–166.

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Behl, R.J. and Kennett, J.P. (1996). Brief interstadial events in the Santa Barbara Basin, NE Pacific, during the past 60 kyr. Nature, 379, 243–246. Berger, W.H., Ekdale, A.A. and Bryant, P.F. (1979). Selective preservation of burrows in deep-sea carbonates. Marine Geology, 32, 205–230. Bromley, R.G. (1990). Trace Fossils–Biology and Taphonomy, Special Topics in Palaeontology, Unwin-Hyman, London, 3, 280 pp. Eicher, D.L. and Diner, R. (1991). Environmental factors controlling Cretaceous limestone–marlstone rhythms. In: Einsele, G., Ricken, W. and Seilacher, A. (Eds.), Cycles and Events in Stratigraphy, Springer-Verlag, New York, pp. 79–93. Ekdale, A.A., Muller, L.N. and Novak, M.T. (1984). Quantitative ichnology of modern pelagic deposits in the abyssal Pacific. Palaeogeography, Palaeoclimatology, Palaeoecology, 45, 189–223. Elder, W.P. and Kirkland, J.I. (1985). Stratigraphy and depositional environments of the Bridge Creek Limestone Member of the Greenhorn Limestone at Rock Canyon Anticline near Pueblo, CO. In: Pratt, L.M., Kauffman, E.G. and Zelt, F.B. (Eds.), FineGrained Deposits and Biofacies of the Cretaceous Western Interior Seaway: Evidence for Cyclic Sedimentary Processes, Society of Economic Paleontologists and Mineralogists, Field Trip Guidebook, Tulsa, Oklahoma, 4, pp. 122–134. Elder, W.P., Gustason, E.R. and Sageman, B.B. (1994). Correlation of basinal carbonate cycles to nearshore parasequences in the Later Cretaceous Greenhorn seaway, Western Interior, U.S.A. Geological Society of America Bulletin, 106, 892–902. Grimm, K.A. and Fo¨llmi, K.B. (1994). Doomed pioneers: Allochthonous crustacean tracemakers in anaerobic basinal strata, Oligo-Miocene San Gregorio Formation, Baja California Sur, Mexico. Palaios, 9, 313–334. Hattin, D.E. (1971). Widespread, synchronously deposited, burrowmottled limestone beds in Greenhorn Limestone (Upper Cretaceous) of Kansas and southeastern Colorado. American Association of Petroleum Geologists Bulletin, 55, 412–431. Hattin, D.E. (1986). Carbonate substrates of the Late Cretaceous sea, central Great Plains and southern Rocky Mountains. Palaios, 1, 347–367. Kern, J.P. and Warme, J.E. (1974). Trace fossils and paleobathymetry of the Upper Cretaceous Point Loma Formation, San Diego, California. Geological Society of America Bulletin, 85, 893–900. Levin, L.A., Gage, J.D., Martin, C. and Lamont, P.A. (2000). Macrobenthic community structure within and beneath the oxygen minimum zone, NW Arabian Sea. Deep-Sea Research II, 47, 189–226. Levin, L.A., Rathburn, A.E., Gutie´rrez, D., Munõz, P. and Shankle, A. (2003). Bioturbation by symbiont-bearing annelids in near-anoxic sediments: implications for biofacies models and paleo-oxygen assessments. Palaeogeography, Palaeoclimatology, Palaeocology, 199, 129–140. Lobza, V. and Scheiber, J. (1999). Biogenic sedimentary structures produced by worms in soupy, soft muds: observations from the Chattanooga Shale (Upper Devonian) and experiments. Journal of Sedimentary Research, 69, 1041–1049. Martin, K.D. (2004). Re-evaluation of the relationship between trace fossils and dysoxia. In: McIlroy, D. (Ed.), The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis, Geological Society of London, Special Publication, London, 228, pp. 141–156. Ozalas, K., Savrda, C.E. and Fullerton, R.R. (1994). Bioturbated oxygenation-event beds in siliceous facies of the Monterey Formation (Miocene), California. Palaeogeography, Palaeoclimatology, Palaeocology, 112, 63–83.

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Special Publication, Oxford (by Blackwell Scientific), 19, pp. 195–210. Savrda, C.E., Bottjer, D.J. and Gorsline, D.S. (1984). Development of a comprehensive oxygen-deficient marine biofacies model: evidence from Santa Monica, Santa Barbara, and San Pedro basins, California continental borderland. American Association of Petroleum Geologists Bulletin, 68, 1179–1192. Scheiber, J. (2003). Simple gifts and buried treasures–implications of finding bioturbation and erosion surfaces in black shales. The Sedimentary Record, 1(2), 4–8. Slingerland, R., Kump, L., Arthur, M.A., Fawcett, P.J., Sageman, B.B. and Barron, E.J. (1996). Estuarine circulation in the Turonian Western Interior seaway of North America. Geological Society of America Bulletin, 108, 941–952. Smith, C.R., Levin, L.A., Hoover, D.J., McMurtry, G. and Gage, J.D. (2000). Variations in bioturbation across the oxygen minimum zone in the northwest Arabian Sea. Deep-Sea Research II, 47, 227–257. Wignall, P.B. (1993). Distinguishing between oxygen and substrate control in fossil benthic assemblages. Journal of the Geological Society of London, 150, 193–196.

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10 Climatic Control of Marine Trace Fossil Distribution Roland Goldring, Gerhard C. Cadeé, and John E. Pollard

realm for the Caenozoic and Pleistocene. We discuss the difficulties of extending this further back in geological time. Trace fossils, with the exception of those utilised in Palaeozoic ichnostratigraphy, and footprint stratigraphy, are notable for their long stratigraphic ranges, and sedimentological research has focussed on the ichnofacies concept and the relative constancy of the Seilacherian ichnofacies through the Phanerozic. Ichnotaxa are also generally regarded as having wide geographical extent as well as long time ranges, though there are notable exceptions, as with most traces of Cruziana (below). This is undoubtedly, in part, attributable to the more equable climates that prevailed over much of the Phanerozoic, as well as the recognition that individual long-ranging ichnotaxa were formed by a variety of different animals. For example, the common upright tubular trace Skolithos could be reasonably attributed to a variety of annelids and probably to some crustaceans. However, there are rare to uncommon ichnotaxa, and others that are more common, that have more restricted distributions. For example, Diplocraterion of decimetre(s) depth and width, is known from the Cambrian to the Miocene. But specimens with these dimensions are unknown from modern environments, and it may be hinted that the originator may be known off tropical deltas such as the Niger, but not its burrow. Diplocraterion is, of course, generally recognised as the work of a range of animals, and at present it is impossible to recognise any general climatic control in its distribution. Climatic effects on trace fossil distributions will obviously be most apparent in marginal marine

SUMMARY : Marine trace fossils are not generally considered to be useful as climatic indicators, because of their usually long stratigraphic ranges, and because ichnotaxa may have been formed by a variety of different animals. However Ophiomorpha is today formed only in tropical/subtropical sediments. This appears to have been the case in older sediments, back at least to the early Caenozoic. The burrows of spatangoid echinoids forming Scolicia and Bichordites have a wider range (temperate to tropical). Together, and with regard to a few other trace fossils (Diplocraterion, Lingulichnus, Renichnus, and possibly Cruziana) these two conspicuous trace fossils offer small but significant climatic indications, if certain safeguards regarding identification are observed.

INTRODUCTION At present the biota of coastal and shallow-offshore waters display immense differences as one passes from equatorial towards polar regions. This is compounded by differences in the distributions between the northern and southern hemispheres. However, such differences are less marked in the sediments of past ages, and when trace fossils are selected, differences that might be attributed to climate are relatively few or absent. This problem has been addressed by Goldring et al. (2004), though it has long been recognised that continental trace fossils do show marked climatic control (Hasiotis, this volume). In this chapter, we attempt to use certain trace fossils as indicators of climate in the marine


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and neritic facies, because of the greater diversity and disparity present in the equivalent environments than in pelagic facies. To establish such effects in the fossil record it is necessary to show that one is dealing with ichnological differences between similar depositional environments that are of similar age. It is also an important attempt to demonstrate that absence of an ichnotaxon is due to climatic rather than to other palaeoecological factors. Absence of an ichnotaxon from a facies in which it would be expected to occur, may be due to real absence (impossible to prove positively), or apparent absence, due to hydraulic factors (i.e., it was once there, but was removed by penecontemporaneous erosion), or apparent absence due to loss of identity by reworking and obscuring by other animals and plants. It is in the last situation that the role of tiering in aggradational settings is significant, because the traces of deeper-tier burrows tend to overprint and eliminate the activities of shallow-tier bioturbators from the rock record, leading to a distinct bias in the ichnofabric and preferential preservation as elite traces. In this chapter, we discuss first the constraints and problems of the recognition of climatic control of trace fossils, then review aspects of the distributions and ichnology of typical crustaceans and spatangoid echinoids, and certain other trace fossils, before considering some case histories and drawing conclusions.

CONSTRAINTS ON RECOGNITION OF CLIMATIC CONTROL OF TRACE FOSSILS The correct identification of the trace fossil is most important. Trace fossils are often and notoriously difficult to identify, because of poor preservation and/or incompleteness. Here, we refer to traces that are often poorly preserved, and may exhibit taphonomic irregularities. If the identification is doubtful then the least that can be asked for is this doubt to be indicated in the conventional way. Size is also significant, because it may relate to a quite different producer, or reflect ecological aspects (for instance, change of habitat during ontogeny). In some instances, minute traces of robust and ‘normally’ larger traces have been given positive identification. It would be useful to consider the size limitation of the producer, and the consequences of a poor identification. If the significance of a trace fossil is to be extended it is also important to attempt to relate it to

the colonisation surface, though too often this has been lost. Another qualifying aspect for identification is the architecture of the burrow system. Too often an identification has been given based on a burrow fragment. But the diagnosis of the ichnotaxon will have included the architecture. Again, only a suitable qualifier is required. Modern distributions may show significance applicable to the fossil record. For instance Cadeé (2001), in a section of his review article on the sediment dynamics of bioturbating organisms in the coastal zone, drew attention to the modern latitudinal variation in bioturbation, and certain changes in the diversity of groups of organisms with latitude. We extend this discussion to include the shoreface which is of greater geological significance. But lack of information prevents extension to arctic shoreface settings. Cadeé (2001) considered two aspects that might be applied to modern bioturbated sediments: first, that the overall degree of sediment reworking between arctic coasts and warm coasts increased more than fivefold. But such measurements cannot be applied to fossil examples, where sedimentation rate and event stratigraphy greatly influence the degree of bioturbation (Taylor et al., 2003). It has been shown that the beginning of the Mesozoic witnessed a massive increase in the depth of bioturbation (Ausich and Bottjer, 1982). Second, Cadeé (2001) referred to, and expanded on, the increase in diversity of coastal life from high to low latitudes. Diversity is not readily or reliably applied to ancient bioturbated sediments, because the effects of salinity, and the colonisation window have to be eliminated (Taylor et al., 2003), and because ichnodiversity is quite distinct from the diversity of body fossils. But changes in diversity through a succession are most useful, especially when applied to the recognition of marginal marine facies. To apply diversity change to ancient sediments requires extensive relatively contemporaneous examples. Cadeé (2001) drew attention to the lack of a diverse fauna of callianassids and crabs and their activities from arctic and temperate coasts in contrast to their richness in warm waters. This is of much geological interest because the trace fossils formed by these crustaceans are so conspicuous and distinct in the fossil record though body fossils are uncommon. Independent criteria that may be used to assess palaeoclimate of an ichnological section are: overall palaeogeography palaeoclimate;

and

regional

ICHNOLOGY OF CERTAIN CRUSTACEANS

facies, especially those that are climatically sensitive: reefs, marine evaporites and glaciogenic; information from associated body fossils, particularly diversity, and information from modern and ancient associations in carbonates (forams-molluscs, chlorozoan); morphological factors such as shell thickness, growth banding in plants, corals and shells, and geochemistry/isotope geochemistry of shells; abundance (frequency)—a complex ecological factor, but one that may be of value when the overall picture is taken.

ICHNOLOGY OF CERTAIN CRUSTACEANS The well-known and conspicuous trace fossils Ophiomorpha (Figs. 10.1B and 10.2), Thalassinoides and Spongeliomorpha can be attributed to the work of thalassinidean crustaceans, or thalassinid-like crustaceans with some confidence. In Thalassinoides the margin of the burrow is smooth, while in Spongeliomorpha the margin displays distinct bioglyphs. Closely similar or identical structures, and their makers, are well known from modern sediments. Also, in some instances body fossils that could have formed the trace have been found within, or closely associated with geologically older burrows. The latter is not a complete proof: the body fossils could have been lodgers (commensals), or slipped into the burrows as dead carapaces. Further the three trace fossils range back to the early Mesozoic, and must have been constructed by many different species over this length of geological time. Thalassinoides (unlined burrow) ranges still further back to the Ordovician, and it has been suggested that trilobites may have been responsible, in some instances carapaces of Asaphus are common within the burrow system. Dworschak (2000) reviewed the present-day latitudinal distribution of thalassinidean species, which show the highest diversity between 30–408N and 20–308S (Fig. 10.3). Thalassinideans are unknown from coastal and shoreface sediments in latitudes higher than about 708N and 508S. Many species construct substantial burrow systems to appreciable depths (partially reviewed by Bromley, 1996). The architecture of modern and fossil crustacean burrows is relatively unknown. This is because of the large dimensions of many, which are too deep to be dug out and too deep for plastic casting techniques to

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penetrate fully. The overall extent of many fossil burrows also remains uncertain because of the difficulty in fully excavating these from the rockface, together with the extensive cross-cutting by later systems. Not only has the architecture of Ophiomorpha, Thalassinoides and Spongeliomorpha not been fully explored, but the details of the burrow lining (when present) are also uncertain. The burrow architecture seems to be of a general form (type 4 of Griffis and Suchanek, 1991), of deep burrow systems with a maze or boxwork of galleries, with some expansions at junctions to form turning points. Other features have been described, but do not add to the general model. In modern settings, type 4 burrows are found only in the burrows of Calichurus major and a few other tropical taxa (Dworschak and Ott, 1993). The burrows of many modern crustaceans are commonly, but not invariably, lined (when excavating a relatively loose substrate). The lining can be of several types: mucus, which is unlikely to be preserved; a mud lining (see Bromley, 1996), which may be of different thickness in different taxa; a mud lining pressed into the burrow margin (tamping), or a pelleted lining, associated with type 4 burrow (Griffis and Suchanek, 1991). The pellets are inserted by the animal into the burrow margin, and then smoothed off on the inside (Frey et al., 1978). Type 4 burrows are distinguished by the absence of sediment mounds (unlikely in trace fossils), restricted apertures, and a deep reticulate system of shafts and galleries (Curran and White, 1991; Curran, 1994; Chapter 14). It is the pelletal lining that is so readily observed in the fossil record. Such traces are often referred to Ophiomorpha, even though the diagnostic burrow architecture of Ophiomorpha may not be apparent. The pellets of Ophiomorpha vary considerably in composition between occurrences, though without apparent facies change. Most commonly they are of muddy sand (as described by Frey et al., 1978), in which case they do not compact. In other cases they may be more muddy, or rich in plant debris, and may become strongly compacted on burial (Pollard et al., 1993). Five other ichnotaxa may also be considered. The upright spiral Gyrolithes (Fig. 10.2C) may lead into one or other of the three ichnotaxa. It generally does not have a pelletal lining. The sinuous Sinusichnus (Fig. 10.2D) (de Gibert et al., 1999) from the Pliocene of the northwestern Mediterranean, which has an unlined burrow, was probably constructed by a decapod crustacean. Pliocene examples of Psilonichnus (Fu¨rsich, 1981), with a Y, J, or U-form burrow were linked to Pholeus (Nesbitt and Campbell, 2002), and to thalassinideans

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FIGURE 10.1 (A) Diagram to show the formation of meniscate backfill by the modern, globular echinoid (Echinocardium cordatum) in longitudinal and transverse (centre) section, and a wedge-shaped echinoid (Schizaster). Spines are shown diagrammatically. An active respiratory shaft (funnel), and an abandoned shaft indicate advance of Echinocardium. (B) Composite diagram of an Ophiomorpha–Planolites-mottled ichnofabric, with restricted shaft, constricted aperture, and lined, top-lined and unlined portions of shafts and galleries.

(Gingras et al., 2000), though Frey et al. (1984) interpreted similar burrows as the work of the ghost crab Ocypode (ocypodid). The upright bow-form burrow Glyphichnus (Fig. 10.4B), with crustaceantype bioglyphs, from lower Caenozoic sediments, may be linked with certain Cylindrichnus (Goldring et al., 2002). Associated Meyeria sp. (Glypheoidea) were probably responsible for Lower Cretaceous examples. Thalassinoides, Ophiomorpha, and Spongeliomorpha may all be present in one specimen to form a compound trace fossil, reflecting the need of the constructor to deal with the burrow margin in different ways. Clearly, with a firm substrate the organism only needs to render the margin attractive/unattractive to intruders or microorganisms. The common observation in sandy sediments is for a pellet-lined upper section of the burrow system to pass down to unlined or top-lined galleries, reflecting passage into a firmer level. Some species of callianassid thalassinideans appear to colonise a range of substrates: sand, sandy mud, and silty mud. Those that pellet-line their burrows and live in coastal sands, or in sandy shoreface settings (Fig. 10.1B), appear to have a restricted

FIGURE 10.2 (A) Ophiomorpha passing down into unpelleted ‘Thalassinoides’. (B) Ophiomorpha with Teichichnus-like spreite. (C) Gyrolithes (adapted from Frey et al., 1978). (D) Sinusichnus, Pliocene, Baix Ebre Basin, northeast Spain. Scale bar 1 cm.

latitudinal range. Thus, on western Atlantic coasts, Callichurus major, forming Ophiomorpha-type burrows, does not today extend north of the North Carolina–South Carolina state boundary (about 348N)

ICHNOLOGY OF CERTAIN CRUSTACEANS

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FIGURE 10.3 Global map with indications of modern latitudinal distributions of Callichurus major, thalassinideans, infaunal echinoids and lingulids. (1) 708N–508S, northern and southern limits of thalassinidean, and northern limit of infaunal echinoids. (2) 348N–278S, northern and southern limits of Callichurus major (Dworschak, 2000). (3) 428S probable southern limit of infaunal echinoids. Crosses represent occurrences of Lingula; circles represent occurrences of Glottidia (simplified from Emig et al., 1987).

FIGURE 10.4 (A) Ophiomorpha nodosa in Palaeocene estuarine sands in the Twyford Member, Reading Formation at Knowl Hill, Reading, UK (hammer head 16 cm). (B) Glyphichnus penetrating unconformity surface into Upper Cretaceous Chalk. Palaeocene, Reading Formation at Pincent’s Kiln, Reading, UK. Scale bar 10 cm.

or, south of southern Brazil (about 278S) (Dworschak, 2000) (Fig. 10.3). Thalassinideans in muddier sediment are present at higher latitudes, e.g., Callianassa subterranea in the North Sea, and their burrows, which are not pellet-lined, may be referred to Thalassinoides or, possibly, Spongeliomorpha. The question is whether modern distributions can be applied to ancient occurrences, because different taxa will have been responsible (at least at lower orders). Another question that must also be posed is

whether the recognised ichnospecies of Ophiomorpha (Frey et al., 1978; Miller and Curran, 2001), distinguished on the form and arrangement of the pellets lining the burrow margin, had the same or different ecologies, e.g., O. nodosa, O. annulata, and O. irregulaire. Tentatively, we suggest that occurrences of pellet-lined burrows in shoreface, lower beach and estuarine sandy sediments represent complex constructions in warm tropical to subtropical environments by decapod crustaceans. Although there is little likelihood for

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confusing Ophiomorpha and Thalassinoides, it is useful to keep in mind the nature of the substrate associated with each occurrence. The Upogebiidae appear to have a similar latitudinal range to the Callianassidae (Dworschak, 2000). The burrows are of type 5 (Griffis and Suchanek, 1991) (relatively simple Y-shaped), and of the form generally referred to the ichnotaxon Psilonichnus. The type ichnospecies, P. tubiformis is unlined, as are other ichnospecies, though P. upsilon (Frey et al., 1984) and P. lutimuratus (Nesbitt and Campbell, 2002) have a distinctive mud lining. More complex double U-form pelleted upogebiid burrows are known from the Bahamas (Curran and Martin, 2003).

(Kanazawa, 1995). Sand dollar activity has not yet been recorded from ancient sediments. Echinoid burrows are found in lower beach, upper and middle shoreface settings, and, off the Georgia coast in offshore relict sands, as well as deeper water environments (below). The latitudinal distribution of shallow marine infaunal spatangoids extends from the tropics to 708N (North Cape) for African and European species (Hayward and Ryland, 1990), and to at least 428S (Fig. 10.3), thus considerably greater than that of crustaceans forming pellet-lined burrows.

SPATANGOID ECHINOID ICHNOLOGY

DISCUSSION ON MODERN DISTRIBUTIONS OF INFAUNAL ECHINOIDS AND OPHIOMORPHA-FORMING CRUSTACEANS

There are two common trace fossils that can be attributed to spatangoid locomotion and feeding (Fig. 10.1A). Bichordites refers to traces made by Echinocardium-type spatangoids, with a single drain, and Scolicia (and associated preservational variants) to Spatangus-type echinoids, with a double drain. ‘Scolicia’ is often used for a trace (without drain) in much older strata, when it is likely to have been formed by gastropods. The less common resting and rather more deeply burrowing trace Cardioichnus may be found in close association with Scolicia or Bichordites. The meniscate backfilled burrows can be up to 8 cm in width. The drain may not always be readily apparent. Smaller but similar backfilled burrows (up to 2 cm diameter) have been referred to Taenidium, in which there is no drain. It is not possible to differentiate further between Bichordites and Scolicia, but it might just be feasible to recognise test shape from the shape of the menisci of the backfill, e.g., relative burrowing depth (Kanazawa, 1995). Burrowing echinoids evolved rapidly in the Caenozoic, though many Mesozoic echinoids were able to plough through the sediment. The oldest deepwater Scolicia, that is reasonably attributable to an echinoid, is from the Tithonian (latest Jurassic), though the age of the oldest shallow-water threedimensional back-filled burrow that can be related to an echinoid is much less certain, probably because of the low preservation potential (below). Spatangoid echinoids burrow to depths not more than 20 cm, and mostly shallower (Fig. 10.1A). Their burrows can be very abundant as well as prominent, especially in relatively poorly sorted sandy sediment

The present latitudinal distributions of infaunal echinoids and burrowing crustaceans would seem to offer opportunities for application to fossil occurrences, especially because of their distinctive traces. But there are several problems, not only with respect to the well-known difficulty of extending modern ecologies to those of fossil taxa. It is important to understand the preservation potential and regional facies distribution of the traces. We thus address ecological aspects, and the sedimentologically related aspects of tiering and tier preservation. Perhaps the first consideration is in respect of the salinity tolerance of each group: echinoids being stenohaline are normally excluded from estuarine environments, while crustaceans enjoy a wider salinity tolerance. Where infaunal echinoids and burrowing crustaceans are present in the same general area such as the southern North Sea and Georgia coast (Do¨rjes, 1972), they tend to occupy different specific areas, with different sediment characteristics, and penetrate to different tier levels. Two distinct infaunal activities are represented: locomotion/feeding traces by echinoids, and more or less permanent to semipermanent dwelling structures by crustaceans. The latter require wall stabilisation and thus the availability, either in suspension, within the sediment, or at the sediment–water interface, of fine-grained mud or organic matter. Both groups construct burrows to an appreciable depth, but while many fossil and modern crustacean, burrows extend to a metre or more, and which may be regarded as deep-tier structures, echinoid burrows are found at a relatively shallow tier. Thus under conditions of more or less continuous sediment

OPHIOMORPHA AND SPATANGOID TRACE FOSSILS

aggradation, it is to be expected that spatangoid traces would be readily overprinted by other deeper traces, and possibly eliminated from the fossil record. Preservation of shallow tiers may be favoured by several situations (Taylor et al., 2003) in which event beds are particularly involved (we do not refer to tier preservation associated with geochemical changes, such as oxygenation). Below a distal turbiditic event bed, or storm event bed, where little (minimal) penecontemporaneous erosion had taken place prior to the event sedimentation. This is the classic situation for the preservation and casting of pre-event, shallow graphoglyptids on the soles of distal turbidites. Close to the upper surface of event beds, where the event bed was colonised temporarily prior to the renewal of ‘normal’ sedimentation. In inclined heterolithic sedimentation, with thin amalgamated, or closely spaced event beds, where little erosion, and little sedimentation took place between successive events. In association with large-scale, cross-stratification, with impure packstone event units (0.1–1.0 m thick), as described from Rhodes and Italy (below) where the ‘events’ represent grain-flow avalanching off the edge of a prograding platform. Similar preservation is to be expected under avalanching in other situations. A further problem for the preservation of echinoid burrows is that they are subject to amensalism by other bioturbators. Although forming relatively deep burrows in the lower beach and shoreface they must maintain a connection with the substrate surface by constructing a ventilation shaft, which must be regularly replaced as the animal progresses forward (Fig. 10.1A). Any obstruction to this upwardly built shaft is disadvantageous to the animal below. Burrowing echinoids would be inhibited from colonising areas with pellet-lined shafts of Ophiomorpha, or lined tubes of Skolithos (cf. sand mason Lanice). On the other hand, population disturbance by the activity of the burrowing echinoid Brissopsis lyrifera had a marked negative effect on overall diversity. We also note the effect on deep-water spatangoids on the preservation of Zoophycos, with truncation of the initial stages of construction. We restrict our discussion to shallow marine environments and facies, because arthropod and echinoid distributions in modern deep water, basinal environments have not yet been fully analysed in respect of ecological parameters. Furthermore, it has

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been suggested that turbidites with Ophiomorpha may have been formed in cold deep water by relocated producers (Fo¨llmi and Grimm, 1990), which may have originated in shallow tropical or subtropical waters. Off the Georgia coast (Do¨rjes, 1972), where Callichurus major is common in the beach environments, the echinoid Moira bioturbates medium- to coarse-grained relict sand, that may be too clean for thalassinidean burrowing. In contrast, in the southern North Sea Callianassa subterranea occupies silty mud, whereas Echinocardium cordatum occupies fine to medium-grained sand. In the Gulf of Gaeta (Mediterranean) Echinocardium cordatum is recorded, but no extensive activity by thalassinideans. The spatial separation of modern echinoids and thalassinideans seems to be related to substrate preference, but it might be expected that pellet-lined burrows would be formed in sandy substrates in the North Sea if higher temperatures were present! The thalassinideans present in the North Sea forms Thalassinoidestype burrows, but not Ophiomorpha. We have few data from modern coastal waters, and there are probably many more records available from the Pacific and Indian oceans. We can tentatively recognise three latitudinal zones in modern coasts and shoreface settings: In the tropics and subtropics (latitudes 0–358) where pellet-forming thalassinidean, and burrowing echinoids are present, though in different facies. In temperate latitudes (358–668) where spatangoid echinoids are present with Thalassinoidesproducers (in different facies), but not Ophiomorpha producers. In arctic latitudes (668–908) where neither groups are present, and the principal bioturbators are annelids and bivalves. We can apply this model to Pleistocene and Caenozoic occurrences with a certain degree of confidence, depending on the data available, but with caution to Cretaceous and older settings in respect of the distribution of Ophiomorpha producers.

OPHIOMORPHA AND SPATANGOID TRACE FOSSILS Examples of Tertiary and Pleistocene occurrences of Ophiomorpha and spatangoid trace fossils (Table 10.1) were documented by Goldring et al. (2004). These gave

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FIGURE 10.5 (A) Bichordites Miocene, Bateig Fantasia, Bateig Hill, Alicante, Spain. Slab cut parallel to stratification. (B) Scolicia at the base of the transgressive Early Oligocene Aldinga Formation at Port Willunga, South Australia. Hammer graduated in 5 cm intervals.

TABLE 10.1 Occurrences of Bichordites/Scolicia and Ophiomorpha in Tropical/Subtropical, Temperate and Arctic Climatic Zones in the Caenozoic. For Most, the Palaeoclimate can be Corroborated from Associated Body Fossils (from Goldring et al., 2004 with additions) Arctic

Pliocene, Alaska (Eyles et al., 1992)

Temperate

Eocene/Oligocene, South Australia (Goldring et al., 2004) Pliocene, Washington State, USA (Campbell and Nesbitt, 2000) ?Pleistocene, Washington State, USA (Gingras et al., 2000) Pleistocene, Mediterranean (D’Alessandro and Massari, 1997) ?Pleistocene, Korea (Kim and Heo, 1997)

Tropical/subtropical

Eocene, southern England (Pollard et al., 1993) Oligocene, New Zealand (Ward and Lewis, 1975) Miocene, Amazonia, Brazil (Gingras et al., 2002) Miocene, Austria, Denmark and Poland (Radwanski, 1977, Uchman and Krenmayr, 1995) Miocene, Alicante, Spain, Mediterranean (Goldring et al., 2004) Miocene, Patagonia, Argentina (Buatois et al., 2003) Miocene, Delaware, USA (Miller et al., 1998) Pliocene, northwestern Mediterranean (de Gibert and Martinell, 1998) Pleistocene (Tyrrhenian), Tunisia (Plaziat and Mahmoudi, 1988) Pleistocene, Jamaica (Pickerill et al., 1993) Pleistocene, Bahamas (Curran and Martin, 2003) Pleistocene, North Carolina (Curran and Frey, 1977)

convincing evidence for tropical and subtropical, temperate and arctic climates. Figure 10.4A shows abundant O. nodosa as galleries and shafts in estuarine sands (Twyford Member, Reading Formation) in southern England: an estuarine environment. No echinoid’s burrows are present, or would be expected in such a setting, though tropical. Figure 10.5A shows extensive Bichordites probably attributable to Maretia, producing the extraordinary architectural stone known

at Bateig Fantasia, from the tropical Miocene of the Alicante region of southern Spain. Ophiomorpha nodosa is occasionally present, and commonly so in interbedded units. Figure 10.5B shows abundant Scolicia in the coolwater, sand-rich calcarenites above a flooding surface marking the base of the transgressive Early Oligocene at Port Willunga, South Australia. Goldring et al. (2004) observed some contradictory occurrences.

OPHIOMORPHA AND SPATANGOID TRACE FOSSILS

(1) In the Lower Miocene of Patagonia (Argentina), Ophiomorpha nodosa is prominent in shoreface silty sandstones of Chubut Province (Buatois et al., 2003), and a diverse suite of trace fossils is present in associated lower shoreface sediments. Scolicia is recorded. The authors suggested that the climatic signature was cold temperate due to polar currents, based on independent analysis of microfossil elements, and cetacean and penguin skeletal remains. This would appear to question our model. However, the palaeoclimatic model for the Middle Miocene of the area (Valdes et al., 2000) predicts warmer conditions, not dissimilar from those of the Miocene of the Mediterranean area (above). Also, evidence from insect trace fossils in palaeosols, fossil plants and mammals in the contemporary Punturas Formation in inland Patagonia at the same latitude indicates a tropical to subtropical climate (Bown and Laza, 1990). (2) Eyles et al. (1992) described Pliocene? glacially influenced continental shelf and slope trace fossils from the Yakataga Formation of Alaska. We are not convinced by their identification of Ophiomorpha (Eyles et al., 1992, fig. 10), or that the back-filled burrow (op. cit. fig. 11) is attributable to echinoid activity. Thus, their ichnoassemblages may be better interpreted as attributable to annelid and molluscan activity in an arctic setting. (3) Campbell and Nesbitt (2000) have provided a convincing account of an active margin, storm-flood influenced Pliocene estuary fill in Washington State, USA, grading to shelfal (basinal) muddy sediments. While the shelfal sediments contain echinoid burrows, more proximal sandy, estuarine sediments contain Psilonichnus latimuratus. Campbell and Nesbitt (2000) recorded only rare Ophiomorpha. Psilonichnus appears to have a wider latitudinal distribution than Ophiomorpha, and as Campbell and Nesbitt (2000) note, its producers appear to have a tolerance to lower salinity. The ichnogenus may even occur in coastal terrestrial environments. (4) In the Pleistocene of Washington State, USA, Gingras et al. (1999, 2000) compared the modern trace-forming biota from Willapa Bay with the trace fossils in closely similar Pleistocene estuarine sediments. Ophiomorpha was recognised as of common occurrence in several Pleistocene facies. This appears to refute our model, as it is unlikely that subtropical conditions reached to 478N, even during warmer interglacials.

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Thalassinoides and ‘Ophiomorpha-like’ burrows were recognised from the modern sediments at Willapa Bay and linked to Upogebia pugettensis and Callianassa californiensis, though it has been noted that the former lines its burrow with mud and mucus, and the latter does not line its burrow. Only the Pleistocene deposits contain Ophiomorpha associated with bay sediments. Although the authors do not explain whether the Pleistocene deposits represent glacial or interglacial sedimentation, we suggest that they may represent interglacial sedimentation, warmer than at present. (5) The Pleistocene of the Mediterranean offers a number of examples of shallow water, shoreface facies, several of which show abundant traces due to burrowing echinoids. D’Alessandro and Massari (1997), in a comprehensive and integrated study of the Pliocene and Pleistocene deposits in southern Italy, showed that the Middle Pleistocene (Calcarenite della Casarana) contains a cool-water (foram-molluscan) fauna including Arctica islandica. Facies 1 includes metre-scale cross-stratification with laminatedto-bioturbated calcarenitic event beds. The bioturbated intervals are 5–10 cm thick, with Bichordites isp., while the laminated part can be much thicker. In some intervals the bioturbated beds are complex and up to a metre thick. The laminated-to-bioturbated units represent grain flow avalanche deposits, subsequently burrowed. Ophiomorpha is recorded as very rare and of peculiarly small size. No climatic indication is warranted. The clinoform stratification is truncated by a unit (up to 2 m thick) of fine-grained calcarenites, intensely bioturbated by Thalassinoides boxworks. The Calcarenite della Casarana as a whole represents coarse sediments deposited at relatively lower sea-level during forced regression. (6) Large-scale cross-stratification in grainstones to packstones was described by Hanken et al. (1996) from the Pleistocene Cape Arkhangelos calcarenite facies of the Rhodes Formation of Rhodes. The unit represents a spectacular, and unusual example of such stratification, which forms large asymptotic clinoforms in beds with dips up to 308. The facies is composed of event beds, from less than 10 cm to over 1 m thick, each fining upwards. The beds represent grain-flow avalanches on clinoforms constructed at the outer margin of a shallow water, carbonate sand body, that was prograding into deeper water. The beds are intensely bioturbated by Echinocardium, that

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FIGURE 10.6 (A) Lingulichnus Lower Carboniferous, Weston-super-Mare, UK. Scale bar 1 cm (referred to as ‘pipe-rock’ in Whittaker and Green, 1983). (B) Renichnus on oyster valve. Miocene, Lorca Basin, Spain. Scale bar 1 cm.

forms winding traces of Bichordites. Ophiomorpha nodosa is absent, but is recorded from lower units of the Rhodes Formation, as are large corals, and which are of late Pliocene age, and represent warm water sedimentation. Ophiomorpha is well known from ancient crossstratified siliciclastic and carbonate sands, though commonly relatively sparse (Pollard et al., 1993). There are several possible explanations for the absence of crustacean activity cross-cutting echinoid burrows in the clinoform stratification of Rhodes: (a) temporal exclusion as in the deep sea (above); (b) the short duration of the colonisation window between successive avalanches. In this context, it is useful to note the high rate of bioturbation that echinoid activity can attain. The rate of progress of the spatangoid producers has been estimated by Kanazawa (1995) as up to one metre per day (for Lovenia in an aquarium), though Bromley (1996) suggested somewhat lower rates for species of Echinocardium. In association with clinoform sedimentation each avalanche became well bioturbated before the next. Avalanche frequency is likely to have been of tidal periodicity, or at most, of storm frequency. Hanken et al. (1996) did not refer to the lateral extent of avalanche units, but are likely to have been only a few metres in width (not substantially different from those widely observed on subaerial dunes). This would have allowed colonisation to take place by lateral

migration. Such high rate of bioturbation would have prevented colonisation by the Ophiomorpha producer; and (c) climatic control. Hanken et al. (1996, figs. 8, 14) interpreted the Cape Arkhangelos as representing highstand sedimentation, but this is somewhat inimical for a cool-water (glacial) interval, and may be better attributed to local tectonic activity. With infaunal echinoid trace fossils not being recorded prior to the Tithonian (Tchoumatchenco and Uchman, 2001) (and mostly later), their usefulness as climatic indicators is stratigraphically limited.

OTHER TRACE FOSSILS OF POSSIBLE CLIMATIC SIGNIFICANCE A few other types of trace fossil may be candidates as climatic indicators. Large-size Diplocraterion have already been referred to (above).

Lingulichnus Lingulid brachiopods are familiar as long time ranging ‘living fossils’ ( > 410 Ma, Zonneveld and Pemberton, 2003) and today occur in a variety of shoreline and shoreface habitats in tropical and warm temperate climatic zones, approximately 408N–408S (Fig. 10.3) (Emig et al., 1987). However, neither the shells nor the trace fossils (Lingulichnus) occur

CONCLUSIONS

commonly in post-Triassic strata (Kowalewski, 1996; Zonneveld and Pemberton, 2003), possibly due to taphonomic factors such as shell thickness or obliteration of the burrows by competitive bioturbators. In the late Palaeozoic (e.g., Dinantian and Silesian, UK Fig. 10.6A; Silesian, USA and UK), Lingulichnus occurred in equatorial environments, while in the Triassic (e.g., France: Gall, 1971; Emig et al., 1987; UK: Pollard, 1981 and Canada: Zonnefeld and Pemberton, 2003) the ichnogenus was found in sediments formed in palaeolatitudes 15–208N. At least in Palaeozoic to Triassic sediments Lingulichnus may be regarded as a climatic indicator.

Renichnus Bromley (2004) listed the stratigraphic ranges of traces due to bioerosion, and noted the systematic increase in diversity over geological time. In most of the instances the host substrate or rock substrate will provide better climatic evidence. Renichnus (Fig. 10.6B), the fixation marks of vermetid gastropods, is a suitable climatic indicator for tropical to subtropical climates since the Miocene (Radwanski, 1977).

Cruziana Numerous ichnospecies of Cruziana have been recognised (Seilacher, 1991), most of which can be reasonably attributed to trilobite activity. The well-known Cambrian–Carboniferous (particularly late Cambrian–Silurian) ‘Cruziana’ stratigraphy of Gondwana is a useful and important tool. Provinciality of the several Cruziana groups is well marked (Fortey and Cocks, 2003; Mańgano and Droser, 2004), especially the distinction between polar West Gondwana (southern Europe and North Africa) and East Gondwana (Australasia) in ‘tropical’ latitudes in the Lower Ordovician. But translating these as climatic indicators is less clear. Climatic gradients in the pre-Upper Ordovician are uncertain. Possibly the eurypterid trackways (Palmichnium and Petalichnus) in marginal marine sediments of the Ordovician of South Africa represent tropical to subtropical climate.

CONCLUSIONS Our analysis of a number of Caenozoic and Pleistocene occurrences of echinoid and crustacean burrows, together with modern examples suggests a general model of climate control for this geological

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interval. We tentatively recognise three latitudinal zones in modern coastal and shoreface settings: Tropical and Subtropical Zone where thalassinideans forming pellet-lined burrows, and burrowing echinoids are present, though in discrete facies. Temperate Zone where spatangoid echinoids are present with facially separated Thalassinoides producers, but not Ophiomorpha producers. Arctic Zone where neither group is present, and the principal bioturbators are annelids and molluscs. Although we have referred to relatively few examples, and with differing degrees of confidence, our model for climatic distribution of shallow marine trace fossils appears to be robust. There are anomalous examples from the Pliocene and Pleistocene. The Pliocene example we regard as probable misidentification of both the crustacean and echinoid traces, though we must hold judgement on the Pleistocene example from Washington State. The occurrence of O. nodosa in Italy in association with Arctica islandica is also anomalous, but the size and overall morphology of the trace fossils are atypical. The association of Ophiomorpha in apparently cold-temperate sediments in the Miocene of Patagonia is anomalous, but the palaeoclimate model suggests much warmer conditions than those suggested by the micropalaeontological data. Other trace fossils that have climatic significance include Renichnus (formed by tropical to subtropical vermetid gastropods), Lingulichnus (low latitudes in Upper Palaeozoic to Triassic) and possibly, large-size Diplocraterion (in tropical latitudes). The climatic significance of Cruziana ichnospecies is uncertain, though provinciality is well marked. We also tentatively suggest that these assessments may be applied to deep water (turbiditic) occurrences. We recognise the problem of extending the Scolicia–Ophiomorpha zonation further back in the geological record (to include Mesozoic occurrences of Ophiomorpha) because of the problems in knowing what the constructor(s) were, and whether they were capable of forming a pellet lining to the burrow. We also raise some of the questions that need to be addressed by ichnology: the types and methods of construction of burrow linings, turbiditic distributions of Ophiomorpha and related crustacean traces, and the ecological tolerances of spatangoid echinoids. We also emphasise the necessity for careful identification of ichnotaxa, and the identification of the sedimentary surface actually colonised.

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ACKNOWLEDGEMENTS We are grateful to Tina D’Alessandro (University of Bari) and Jordi de Gibert (University of Barcelona) and Richard Jenkins (South Australian Museum, Adelaide) who contributed to the extended version of this chapter (Goldring et al., 2004). We also thank Jordi de Gibert for supplying a figure of Sinusichnus, and Michael Talbot (University of Bergen) for supplying a figure of Renichnus. Al Curran and an anonymous reviewer are thanked for their helpful and constructive reviews.

References Ausich, W.I. and Bottjer, D.J. (1982). Tiering in suspension-feeding communities on soft substrata throughout the Phanerozoic. Science, 216, 173–174. Bown, T.M. and Laza, J.H. (1990). A Miocene termite nest from southern Argentina and its paleoclimatological implications. Ichnos, 1, 73–79. Bromley, R.G. (1996). Trace Fossils: Biology, Taphonomy and Applications, 2nd edition. Chapman and Hall, London, pp. 85–105. Bromley, R.G. (2004). A stratigraphy of marine bioerosion. In: McIlroy, D. (Ed.), The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis, Geological Society, London, Special Publications, 228, pp. 455–479. Buatois, L.A., Bromley, R.G., Mańgano, M.G., Bellosi, E., and Carmona, N. (2003). Ichnology of shallow marine deposits in the Miocene Chenque Formation of Patagonia: complex ecologic structure and niche partitioning in Neogene ecosystems. Asociacioń Paleontolo´gica Argentina. Publicacioń Especial, 9, 1–11. Cadeé, G.C. (2001). Sediment dynamics by bioturbating organisms. In: Reise, K. (Ed.), Ecological Comparisons of Sedimentary Shores, Ecological Studies, 151, pp. 127–148. Campbell, K.A. and Nesbitt, E.A. (2000). High-resolution architecture and paleoecology of an active margin, storm-flood influenced estuary, Quinault Formation (Pliocene), Washington. Palaios, 15, 553–579. Curran, H.A. (1994). The palaeobiology of ichnocoenoses in Quaternary, Bahaman style carbonate environments: the modern to fossil transition. In: Donovan, S.K. (Ed.), The Palaeobiology of Trace Fossils, John Wiley, New York, pp. 83–104. Curran, H.A. and Frey, R.W. (1977). Pleistocene trace fossils from North Carolina (U.S.A.) and their Holocene analogues. In: Crimes T.P. and Harper, J.C. (Eds.), Trace Fossils 2, Geological Journal, Special issue, 9, pp. 139–162. Curran, H.A. and Martin, A.J. (2003). Complex decapod burrows and ecological relationships in modern and Pleistocene intertidal carbonate environments, San Salvador Island, Bahamas. Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 229–245. Curran, H.A. and White, B. (1991). Trace fossils of subtidal to dunal ichnofacies in Bahaman Quaternary carbonates. Palaios, 6, 498–510.

D’Alessandro, A. and Massari, F. (1997). Pliocene and Pleistocene depositional environments in the Pesculuse area (Salento, Italy). Revista Italiana de Paleontologia e Stratigrafia, 103, 221–258. de Gibert, J.M. and Martinell, J. (1998). Ichnofabrics of the Pliocene marginal marine basins of the northwestern Mediterranean. Revista de la Sociedad Geolo´gica de Espanã, 11, 43–56. de Gibert, J.M., Jeong, K., and Martinell, J. (1999). Ethologic and ontogenetic significance of the Pliocene trace fossil Sunusichnus sinuous from the northwestern Mediterranean. Lethaia, 32, 31–40. Do¨rjes, J. (1972). Georgia coastal region, Sapelo Island, U.S.A.: sedimentology and Biology. VII, Distribution and zonation of macrobenthic animals. Senckenbergiana Maritima, 4, 183–216. Dworschak, P.C. (2000). Global diversity in the Thalassinidea (Decapoda). Journal of Crustacean Biology 20, Special number 2, 238–245. Dworschak, P.C. and Ott, J.A. (1993). Decapod burrows in mangrove-channel and back reef environments at the Atlantic barrier Reef, Belize. Ichnos, 2, 277–290. Emig, C.E., Gall, J.C., Pajaud, D., and Plaziat, J.C. (1987). Re´flexions critiques sur l’ećologie et la syste´matique des lingules actuelles et fossiles. Geobios, 11, 573–609. Eyles, N., Vossler, S.M., and Lagoe, M.B. (1992). Ichnology of a glacially-influenced continental shelf and slope; the late Cenozoic Gulf of Alaska (Yakataga Formation). Palaeogeography, Palaeoclimatology, Palaeoecology, 94, 193–221. Fortey, R.A. and Cocks, L.R.M. (2003). Palaeontological evidence bearing on global Ordovician–Silurian continental reconstructions. Earth-Science Reviews, 61, 245–307. Frey, R.W., Howard, J.D., and Pryor, W.A. (1978). Ophiomorpha: its morphologic, taxonomic, and environmental significance. Palaeogeography, Palaeoclimatology, Palaeoecology, 23, 199–229. Frey, R.W., Curran, H.A., and Pemberton, S.G. (1984). Tracemaking activities of crabs and their environmental significance: the ichnogenus Psilonichnus. Journal of Paleontology, 58, 333–350. Fo¨llmi, K.B. and Grimm, K.A. (1990). Doomed pioneers: gravityflow pioneers and bioturbation in marine oxygen-deficient environments. Geology, 18, 1069–1072. Fu¨rsich, F.T. (1981). Invertebrate trace fossils from the Upper Jurassic of Portugal. Communiques Serviços Geologicos de Portugal, 67, 53–168. Gall, J.C. (1971). Faunes et paysages du Gre`s a` Voltzia du Nord des Vosges. Essai paleóećologique sur le Bundsandstein supe´rieur. Me´moires Service Carte geólogique Alsace et Lorraine Strasbourg, 34, 318 pp. Gingras, M.K., Pemberton, S.G., Saunders, T., and Clifton, H.E. (1999). The ichnology of modern and Pleistocene brackish-water deposits at Willapa Bay, Washington: variability in estuarine settings. Palaios, 14, 352–374. Gingras, M.K., Hubbard, S.M., Pemberton, S.G., and Saunders, T. (2000). The significance of Psilonichnus at Willapa Bay, Washington. Palaios, 15, 142–151. Gingras, M.K., Ra¨da¨nen, M., and Ranzi, A. (2002). The significance of bioturbated inclined heterolithic stratification in the southern part of the Miocene Solimoes Formation, Rio Acre, Amazonia Brazil. Palaios, 17, 591–601. Goldring, R., Gruszczynski, M., and Gatt, P.A. (2002). Bow-form burrow and its sedimentological and paleoecological significance. Palaios, 17, 622–630. Goldring, R., Cadeé, G.C., D’Alessandro, A., de Gibert, J.M., Jenkins, R., and Pollard, J.E. (2004). Climatic control of trace fossil distribution in the marine realm. In: McIlroy, D. (Ed.), The Application of Ichnology to Palaeoenvironmental and

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11 Climatic Controls on Continental Trace Fossils Stephen T. Hasiotis, Mary J. Kraus, and Timothy M. Demko

Much information already exists on the palaeoclimatic significance of palaeosols and plant, invertebrate, and vertebrate body fossils (e.g., Parrish, 1998; Retallack, 2001; and references therein); however, continental trace fossils have been under-utilized for this purpose (e.g., Voorhies, 1975). A well-defined relationship exists between biodiversity, soils, environment, and hydrology and their distribution in modern climate zones, which can be applied to suites of trace fossils and palaeosols (e.g., Whittaker, 1975; Lydolph, 1985; Aber and Melillo, 1991; Retallack, 2001). Climate and biota are two of the five major factors in soil formation. Climate ultimately determines net primary productivity (NPP) as well as diversity and distribution of terrestrial and aquatic organisms via the amount and seasonality of precipitation, temperature, and solar insolation with respect to latitudinal position (Lydolph, 1985). The robust correlation between modern climates, soils, ecosystems, and biodiversity suggests that there is a strong association between palaeoclimate, palaeosols, and ichnodiversity in the rock record (e.g., Parrish, 1998; Retallack, 2001; Hasiotis, 2004; and references therein). Continental trace fossils and ichnocoenoses in ancient, weakly to strongly pedogenically modified sediment (palaeosols) have been hypothesized to indicate zonations and fluctuations of the groundwater profile, the seasonality of precipitation, and the spatial and temporal variability in palaeohydrologic regime for a local or regional area of extent. This hypothesis is based on palaeoclimatic and palaeohydrologic evidence from palaeosols, geochemical data, and the sedimentary deposits in which trace fossils suites are found (e.g., Ahlbrandt et al., 1978; Bown, 1982; Bown and Kraus, 1983; Smith, 1987;

SUMMARY : A well-defined relationship exists between modern biodiversity, soils, environment, hydrology, and climate zones. Preserved patterns in tiering relationships of continental trace fossils and their association with different types of palaeosols in Mesozoic to Recent deposits represent their formation in Ever-Dry, Dry, Wet–Dry, Wet, and Ever-Wet palaeoclimates. Ichnofossils in Ever-Dry palaeoclimates are not present; however, in Dry palaeoclimates they occur as rare, weak to intensely bioturbated bedding plane exposures with very little vertical tiering in Entisols, Inceptisols, and Aridisols. As precipitation and moisture increases within Wet–Dry palaeoclimates, so does ichnofossil diversity, abundance, and tiering in Entisols, Inceptisols, Aridisols, Spodosols, Alfisols, and Ultisols. Wet palaeoclimates are characterized by deep to shallow tiers in Entisols, Inceptisols, Spodosols, Alfisols, Ultisols, Histosols, and Oxisols, depending on the amount of water in the system. As the amount of perennial water increases in the system, the tiers become ever shallower. Ever-Wet palaeoclimates have very shallow tiering, where all tiers are compressed to the near-surface in Entisols, Inceptisols, Spodosols, Alfisols, Ultisols, Histosols, and Oxisols.

INTRODUCTION The purpose of this chapter is to propose hypotheses for the palaeoclimatic relationship between trace-fossil suites (ichnocoenoses) and pedogenically modified deposits in continental strata since the Mesozoic, using criteria that characterize the climatic distribution of modern biota and soils.


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DISTRIBUTION OF ORGANISMS AND THEIR TRACES—ICHNOFOSSILS

Hasiotis and Bown, 1992; Hasiotis and Mitchell, 1993; Smith et al., 1993; Hasiotis and Dubiel, 1994; Groenewald et al., 2001; Hasiotis, 2002, 2004; Hembree et al., 2004; Radies et al., 2005; Kraus and Hasiotis, 2006). Suites of trace-fossil associations within a particular type of palaeosol can be referred to as ichnopedologic associations. With few exceptions, trace-fossil suites (ichnocoenoses) and associations (collection of overprinted ichnocoenoses) have not yet been characterized for different palaeoclimates in different periods of geologic time during which various terrestrial and freshwater organisms evolved. An adequate amount of information from Mesozoic and Cenozoic strata, however, does exist to predict the different types of ichnopedologic associations that might be present in continental strata for distinct palaeoclimates.

DISTRIBUTION OF ORGANISMS AND THEIR TRACES—ICHNOFOSSILS Precipitation and temperature are the major factors that determine the global distribution of organisms on continents. The most limiting factor for all life is water availability and is a major control of its distribution (e.g., Aber and Melillo, 1991; Hasiotis, Chapter 16). Most biodiversity today is found in the tropics along the equator. Biodiversity decreases with increasing latitude through the subtropics, drastically declines in the deserts or horse latitudes, and dramatically increases in temperate zones. Biodiversity again decreases towards the poles, which are, in essence, cold deserts (e.g., Whittaker, 1975; Aber and Melillo, 1991). The biodiversity pattern from the equator to the poles follows that of NPP, which is the total net amount of carbon production for plant growth and is also related to temperature and precipitation. In a landscape, microbes, plants, and animals are distributed vertically and laterally according to their physiological needs or tolerances to water, soil moisture, salinity, ecological associations with other organisms, and ultimately by climate (e.g., Wallwork, 1970; Whittaker, 1975; Hasiotis and Bown, 1992). The organisms may be terrestrial in habitat and live above, on, and below the soil surface but above the water table. Some organisms are amphibious and restricted to shorelines of water bodies. Other organisms are aquatic and live in freshwater rivers, lakes, and the saturated zone within soils, or live in temporary to permanently hypersaline water bodies. Still other organisms have phases of their life cycle that include both terrestrial and aquatic habitats.

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The remains of most organisms, however, are not preserved in the exact place where they lived, with most remains are reworked, out of ecological context, and taphonomically diminished prior to fossilization (e.g., Behrensmeyer and Kidwell, 1993). Traces of these organisms, alternatively, have a higher likelihood of preservation and can serve as in situ indicators of their one-time existence in a particular environment of a landscape preserved in the geologic record (Hasiotis, 2002). These ancient landscapes can be interpreted from the mosaic of deposits that represent different palaeoenvironmental settings. Organisms found preserved in the burrows they constructed and lived also represent in situ evidence. These occurrences are uncommon in the geologic record with some exceptions that include deposits formed during highly seasonal climates during the Permian and Triassic (e.g., Smith, 1987; Hasiotis and Mitchell, 1993; Groenewald et al., 2001; Hembree et al., 2004, 2005). The occurrence of articulated vertebrate and invertebrate remains within burrows can provide a valuable palaeoclimatic information base of their relationship. Overall, invertebrates and their traces are most useful in delineating hydrologic profiles and ecological partitions in the geological record (Fig. 11.1) (e.g., Hasiotis and Bown, 1992; Hasiotis, 2002). Most invertebrates are classified as insects and fall into the Coleoptera, Isoptera, and Hymenoptera. Invertebrates inhabiting terrestrial and aquatic environments include: (1) insects and arachnids; (2) soft-bodied annelids and oligochaetes; (3) mollusks; and (4) crustaceans. Many of these invertebrate groups have trace-fossil records that extend back into the Mesozoic or earlier (e.g., Ekdale et al., 1984; Hasiotis, 2002; Rasnitsyn and Quicke, 2002). Root patterns indicate the behavior of plants with respect to water absorption, nutrient collection, and consistency of the medium into which they penetrate (Pfefferkorn and Fuchs, 1991), and are useful for delineating hydrologic profiles in the geological record (e.g., Kraus and Hasiotis, 2006). Roots push their way through sediment as they grow, and continue to re-grow throughout the life of the plant. They typically take the path of least resistance, follow cracks and pre-existing burrows, and react to changes in soil moisture, chemistry, and consistency (e.g., Pfefferkorn and Fuchs, 1991; Retallack, 2001). Rhizoliths—the preserved traces of plant roots—are useful for palaeoenvironmental interpretations. This is particularly so when they are associated with trace fossils of terrestrial and aquatic invertebrates, which used roots for shelter, food, and burrowing pathways. Rhizolith morphology, however, is not plant specific

Interstitial water Phreatic Hydrophilic Zone Phreatic water (groundwater)

Distal Floodplain Cp

Hb

Vtb

F

Rh

Increase groundwater height Decrease biodiversity and biotic exchange

Rh

Fp

An

Rh - Rhizocorallium

Cp - Coprinosphaera

St - Steinichnus

Ck - Cochlichnus Ce - Celliforma

Tm - Termite nest T/Rh - Termite nest in rhizolith Un - Undichnia

F - Fuersichnus

Ut - U-tube-ghost

Fp - Footprints

Uts - U-tube

G - Gastropod trail

Vb - Vertical burow

Hb - Horizontal burrow

Vtb - Vertebrate burrow

Hu - Horizontal U-tubes

Wp - Wasp nest/cocoon

Proximal Lacustrine

AMB

P

Hu

P

Tm Hb

T/Rh Rh

Ca

Vb

Ck

Ca Ca

Ce

Fp

Ut

Rh

Un AMB

T/Rh

Ca

T/Rh

Ca

Ce

Hb

P

Rh Rh

AMB

Distal Lacustrine

St

F

AMB Rh

Rh

Decrease nutrient availability

P - Planolites

At - Ant nest

G

Rh

Cp

Decrease biodiversity

Km - Kouphichnium

AMB - Adhesive meniscate burrow

P

Ca

Decrease biotic exchange

An - Ancorichnus

Ca - Camborygma

Increase soil moisture

Transitional Environments Shallow Water Table Settings

substratum surface

KEY

Hydrophilic Phreatic water (groundwater)

Fp

Increase organic matter

Point where the groundwater table intersects the landsurface = paludal to lacustrine conditions

Hygrophilic Vadose water

Decrease O2--increase CO2

Decrease organic matter

Capillary water

Decrease in trace fossil depth and tiering

Proximal Floodplain

Rh

Decrease biodiversity and biotic exchange

Water Table

Rivers and Lakes

Uts Uts

Ca Vb

Ut

P

Rh

P Ce Ce

G

Rh

Hb

Hb

Ut Rh

At

Cp

At

P Wp At

Tm AMB

Un

Km

Rh

Vb

At

AMB

P

Vb T/Rh

Ca

FIGURE 11.1 Relationship between trace-making organisms, soil formation, and the groundwater profile. Soil formation, depth, and diversity of burrowing organisms are controlled mainly by the groundwater profile and its fluctuations, as well as other soil characteristics. Block diagrams are examples of different types and depths of traces made by plants and animals in different environmental settings (modified from Hasiotis, 2002, 2004).

11. CLIMATIC CONTROLS ON CONTINENTAL TRACE FOSSILS

Capillary water

Terraphilic Vadose well-drained

Increase soil compaction

intermediate to the lower Hygrophilic part

Increase relative humidty

Vadose upper part water

Decrease O2 exchange

Vadose Zone


Terraphilic

Decrease O2--increase CO2

Soil water

Floodplain and Supralittoral environments

soil surface


Epiterraphilic

Increase O2 concentration

Footprints, trackways, surface nests

No soil formation takes place in sediments beneath the saturated zone

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Soil formation zone = function of climate, topography, biota, parent material, & time Contributing factors = (1) magnitude & frequency of depositional events (2) rate of sedimentation & accumulation (3) distance from sediment-water source (4) grounwater profile & its fluctuation

SOIL FORMATION AND PALAEOSOLS

but is ecophenotypic (i.e., root patterns produced by specific environmental conditions) and relates specific information about substrate moisture, texture, and compaction (e.g., Pfefferkorn and Fuchs, 1991; Kraus and Hasiotis, 2006). Vertebrates are useful in delineating environmental conditions, especially when used in conjunction with plant and invertebrate trace fossils. Vertebrate tracks and trackways are not as sensitive as invertebrate or plant trace fossils to environmental conditions because vertebrates can cross over many environments with different biophysicochemical characteristics (e.g., Wallwork, 1970; Hasiotis, 2004). Vertebrate burrows, however, contain more significant in situ palaeoenvironmental information pertaining to the groundwater profile and climate parameters such as precipitation and temperature as well as their seasonality and extremes. These burrows are even more useful when they contain the animals that constructed them (e.g., Smith, 1987; Groenewald et al., 2001). Vertebrates live in burrows as transient to periodic fauna in order to escape extremes in temperature and moisture, and for dwelling or reproduction (e.g., Voorhies, 1975; Smith, 1987; Groenewald et al., 2001; Hasiotis et al., 2004).

SOIL FORMATION AND PALAEOSOLS Soil formation (pedogenesis) modifies nearly all media that comprise the landscape (Fig. 11.1), including crystalline and sedimentary bedrock and transported sediments (e.g., Jenny, 1941; Brady and Weil, 2002). In general, parent material, biota, topography, climate, and time are the five soil-forming factors that determine what type of soil will form in a particular area (Jenny, 1941). Soil formation occurs at different rates, and with different results, based on the magnitude and frequency of depositional events, distance from sediment source, parent material, position and fluctuation of the groundwater profile, inherent local topography, composition of biotic communities, and the climate with regard to temperature and precipitation (e.g., Bown and Kraus, 1987; Brady and Weil, 2002). The results of pedogenesis comprise a range of soil features that indicate maturity and relative age (e.g., Jenny, 1941; Retallack, 2001). The broad range of biophysicochemical conditions and soil types indicates the high degree of spatial and temporal heterogeneity in continental environments, resulting in conterminous microcosms, each with unique physical, chemical, and biologic

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properties (Fig. 11.1) (e.g., Wallwork, 1970; Whittaker, 1975; Aber and Melillo, 1991; Brady and Weil, 2002). Soils are weakly, moderately, or strongly developed, and can be simple, compound, or cumulative in nature (e.g., Kraus, 1999; Retallack, 2001). Soils are assigned to one of twelve soil orders based on soil properties that characterize their development, which result from the most influential of the soil-forming factors (e.g., Brady and Weil, 2002). More than one type of soil can form in a small area depending on the characteristics of each soil-forming factor. For example, different soils can form under the same climate because of differences in parent material, biota, and duration of formation (i.e., time). Soils considered as immature and poorly developed include Entisols, Inceptisols, Andisols, Gelisols, Histosols, and Vertisols (Brady and Weil, 2002). Entisols are recent, immature soils with little or no horizonation and abundant, original parent material characteristics. Entisols form in any climatic areas with active deposition or erosion, and occupy about 16% of the present-day land area. Inceptisols are found in all climates and show incipient soil horizons, particularly of an illuviated zone. They cover more than 9% of the land area, and are similar to, but with more formation time than Entisols. Andisols are relatively immature soils, make up less than 1% of the present-day land area, and are characterized by parent materials of volcanic ash and cinders. They are organic-rich and dominated by silicate weathering products such as allophone and imogolite. Gelisols are characterized by permafrost and frost churning, and are otherwise similar to Entisols and Inceptisols. They cover about 9% of the present-day land area in places where temperatures remain below freezing for more than two consecutive years. Histosols are soils composed mostly of organic material in various states of degradation and have little or no profile development. They occupy about 1% of the present-day land area, principally in tropical, temperate, and polar climates where moist to wet anaerobic conditions persist for long periods of time to allow the build up of organic material. Vertisols are typically dark soils that occupy about 2.5% of the present-day land area and are characterized by shrink–swell clays that undergo wetting and drying periods. Their shrink–swell properties keep them from developing horizons, producing abundant and large slickensides termed pseudoanticlines or mukkara. Aboveground, a threedimensional pattern of polygonal high and low topography is produced above the mukkara, termed gilgai. They are found mostly in semiarid to subhumid, warm climates with seasonally distributed precipitation.

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Soils considered well developed and moderately mature, mature, or extremely old include Aridisols, Spodosols, Mollisols, Alfisols, Ultisols, and Oxisols (Brady and Weil, 2002). Aridisols are moisture-deficient soils, such that no more than 90 consecutive days of plant growth can take place, and contain horizons with accumulations of soluble salts. They occupy about 12% of the present-day land area where the surface is covered by a mosaic of bare ground, and drought-adapted, small shrubs and bunch grasses. Mollisols are moderately mature soils with calciumrich organic matter, dense root systems, and horizonation. They occupy about 7% of the present-day land area and form under seasonally humid, temperate climates. Spodosols form on mostly coarse-grained, acidic parent material and are easily leached, such that an illuviated, organic-rich horizon forms under an eluvial, thin leached horizon. They occupy about 3% of the present-day land area and form under coniferous forests in cold to temperate, moist climates. They do occur in subtropical to tropical climates, but are rare. Alfisols are moderately leached, mature soils with an illuviated clay (argillic) horizon that forms in cool to hot, humid climates. They occupy about 10% of the present-day land area and support grasslands or deciduous forests. Ultisols are more highly weathered, acidic, and mature than Alfisols, indicating that they are older. They occupy about 9% of the present-day land area and form in warm to tropical, moist climates. Oxisols are the most highly weathered, mature soils with a thick, leached horizon of hydrous iron- and aluminum-oxide clays, indicating that they are older. They occupy about 8% of the present-day land area and form in hot, tropical climates with moist conditions year-round. The recognition of these soil orders in the geologic record is not uniform because early diagenesis and burial diagenesis have various effects on the original soil properties (e.g., Retallack, 2001). Another problem that arises from the use of modern soil taxonomy with respect to palaeosols is that there is no way to know the exact number of days or months that soils were dry, moist, or saturated. Many soil suborders and further divisions in soil taxonomy are based on the duration and amount of moisture in the soil. For the purposes of this chapter, identification to soil order is reasonable, based on many physicochemical characteristics. Entisols and Inceptisols are the easiest to recognize as palaeosols because very little of the original characteristics are lost. Vertisols are readily identified by their mukkara and gilgai structures. Histosols become coal deposits of varying thickness based on the original soil thickness. Oxisols should also be relatively easy to identify, based on their

highly leached soil features and properties, such as the presence of hydrous oxide minerals. Plinthic textures associated commonly with Oxisols also occur in Ultisols and Alfisols, which might make their discrimination challenging. Mollisols, however, are difficult to identify in the geologic record because they loose their dominant, organic-rich horizon and appear more similar to Alfisols and Ultisols. Aridisols, if preserved under appropriate conditions are easily identified; however, accumulations of soluble salts may be lost during fluid migration following burial. Gelisols may be difficult to identify once any features of frost wedging or churning are blurred or lost because of climate change or burial. The volcaniclastic sediments of Andisols will likely to devitrify during burial diagenesis and be mistaken for one of the other soil orders representative of weak soil development.

SOIL-WATER BALANCE: LINKING SOIL, BIOTA, AND CLIMATE Climate, soil, and biota are linked together through the soil-water balance in an environment (Thornthwaite and Mather, 1955). Water availability is more important than precipitation because the amount of water available for plant growth controls the abundance and diversity of plants, which forms the basis for the food pyramid, and supports lower and higher trophic levels. All levels of life that occupy the landscape above- and belowground in continental ecosystems depend on water, which is ultimately controlled by climate (e.g., Wallwork, 1970; Whittaker, 1975). The effects of climate on soil-water balance can be measured through the soil-water budget (Fig. 11.2), which is equal to the gain, loss, and storage of soil water in a column of soil (Thornthwaite and Mather, 1955; Strahler and Strahler, 1989). There are several components of the soil-water balance. Evapotranspiration (E) is defined in two ways. Actual evapotranspiration (Ea) is the actual rate at which water vapor is returned to the atmosphere from the ground and by plants, and is also termed water use. Potential evapotranspiration (Ep) is the water vapor flux under ideal conditions of complete ground cover by plants, uniform plant height and leaf coverage, and an adequate water supply; this is also termed water need. These values have been calculated for land surfaces of the entire globe based on air temperature, latitude, and time of year (Thornthwaite and Mather, 1955). Intensity and duration of solar radiation received by the landscape is determined by latitude

CLIMATE

and the season. As a consequence, water need for a particular environment may be greater or lesser than the amount actually used. Soil-water shortage (D) occurs when Ea < Ep, and soil-water surplus (R) occurs when Ea > Ep. Surplus will result in (1) runoff from excess water or retarded infiltration and (2) groundwater flow through the vadose zone to the phreatic zone. Precipitation (P) is mainly the delivery of moisture to the environment, but may also be in the form of fog or mist which occurs along the coasts of most continents (e.g., Thornthwaite and Mather, 1955; Lydolph, 1985; Lancaster, 1989; Strahler and Strahler, 1989). Moisture used by plants is termed utilization (G); if it is not used, it is termed recharge (+G) and will pass eventually through to the phreatic zone and become part of the groundwater outflow as a form of runoff (R). Soil-water storage (S) is the sum of available water in the soil column available to plants and animals, and also affects soil formation, nutrient cycling, and overall biodiversity (e.g., Thornthwaite and Mather, 1955; Whittaker, 1975; Strahler and Strahler, 1989). Water delivered to the soil through precipitation and runoff becomes part of the soil-water belt (Fig. 11.2), which is part of the groundwater profile (Strahler and Strahler, 1989; Hasiotis, Chapter 16). The thickness of each zone in the groundwater profile is dependent upon the water-table depth, which reflects the soil-water balance. The upper vadose zone is the depth reached by most plant roots and associated biota in general. The intermediate vadose zone typically marks a depth too great for water to be returned to the atmosphere by evaporation. The phreatic zone is generally out of reach for most organisms in most environments (e.g., Thornthwaite and Mather, 1955; Wallwork, 1970).

CLIMATE Climate is the source of energy and water that controls the distribution and diversity of plants and animals (e.g., Whittaker, 1975), plays a major role in soil formation (e.g., Brady and Weil, 2002), and impacts the degree and rate of nutrient cycling (e.g., Wallwork, 1970; Odum, 1971). Nutrient cycling is regulated by the detritivore-dominated soil biota, and their interactions are mainly responsible for maintaining the fitness of an ecosystem (Wallwork, 1970; Odum, 1971; Aber and Melillo, 1991). It is these organisms that are most likely to leave trace fossils in alluvial, palustrine, lacustrine, eolian, and

177

volcaniclastic environments, formed under different climates (e.g., Hasiotis, 2004, Chapter 16). Climate is defined as weather sequences over long periods of time for a certain region, characterized by latitude and by large-scale air motions and airmass interactions. The criteria used to define climate consists of short- and long-term records of: (1) temperature; (2) precipitation; (3) atmospheric humidity; and (4) wind direction and speed. Climate is also affected by orographic effects and proximity to large water bodies (e.g., Lydolph, 1985; Ruddiman, 2001). All regions on Earth contain tangible indicators of climate, including biodiversity (microbes, plants, and animals), soil type, and depositional systems that interact to form the landscape (e.g., Lydolph, 1985). These are all dependent on climate for their development, and are also expressed as: (1) above- and belowground biologic activity; (2) soil formation; (3) local to regional hydrology and topography; and (4) the continentality and latitude of the region (Brady and Weil, 1999). The integration of these empirical and quantitative physical, biological, and chemical elements represents the totality of the climate for a region (Lydolph, 1985). A modified version of the Ko¨ppen climatic classification is currently used in climatology because it is simple, useful, and is based on (1) moisture and (2) temperature (Lydolph, 1985; Ruddiman, 2001). Climatic regions are identified as Tropical, Dry, Temperate, Boreal, and Polar. Each type is subdivided to characterize the type of vegetation, amount of humidity, temperature, presence of ice, and other regional climate indicators. For the purposes of this chapter, traditional climate classification schemes are too cumbersome and complicated to be applied to building ichnopedologic associations for palaeoclimate interpretations. For example, temperature and its variation at the time an ichnopedologic association was formed are difficult to accurately assess, as it is for most continental deposits (e.g., Parrish, 1998). Modern climate classification schemes take into account the amount of humidity in the air, however, humidity cannot be measured directly in ichnopedologic associations, or in most of the geologic record. In some instances, however, humidity can be inferred by the type of body fossils and trace fossils, sedimentary facies, and by geochemical characteristics of the rocks (e.g., Parrish, 1998). In geologic time, the exact months or time of the year when precipitation is delivered, which is necessary to distinguish between summer and winter maxima (e.g., of precipitation or temperature), cannot be established directly from the rocks, and must be inferred from global climate models (e.g., Parrish, 1998). Since the main concern of this chapter

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FIGURE 11.2 Climate, soil, and biota are linked together through the soil-water balance in an environment. The effects of climate on soil-water balance (A,B) can be measured through the soil-water budget (C), which is equal to the gain, loss, and storage of soil water in a column of soil (taken and modified from Strahler and Strahler, 1989).

CLIMATE

is to use organism behavior as palaeoclimatic indicators through time, the major factor that controls the distribution of biodiversity—water—will be used to develop a simplified palaeoclimate classification scheme that can be tested with ichnopedologic associations. The most limiting factor for life is water availability (e.g., Wallwork, 1970; Odum, 1971; Lydolph, 1985). Most water in the environment is delivered in the form of precipitation, however, the amount and intensity of solar radiation will determine the effectiveness of the precipitation delivered to that environment (Brady and Weil, 2002). Effective precipitation (EP) is determined by the temporal distribution of precipitation, moisture loses from evapotranspiration, and the temperature (Lydolph, 1985). EP can be used as a proxy for the relationship between precipitation and temperature for a particular region and also takes into account the seasonality of precipitation, which is important for all climate types. Equally as useful are Precipitation/Evapotranspiration (P/E) ratios that also serve as indicators of EP (e.g., Thornthwaite and Mather, 1955; Lydolph, 1985). For example, P/E < 1 indicates a water deficit in the environment, whereas P/E > 1 reflects a water surplus, and P/E = 1 suggests a balance between surplus and deficit of moisture in an environment (e.g., Lydolph, 1985).

Simplified Categories of Climate and Palaeoclimate Modern and ancient climates can be viewed from a simplified perspective of being Ever-Dry, Dry, Wet–Dry, Wet, and Ever-Wet (Fig. 11.3). Ever-Dry climates are defined for the most part by the total lack of precipitation where P E to P >> E, which is common for settings with closed canopy forests. Ever-Wet climates are defined by abundant precipitation and available water throughout the year, where P >> E to P >>> E, which is common for settings with dense rainforests and swamps, as are found in the Amazon and in parts of Indonesia and Malaysia. Climate types that fall into these categories include Wet equatorial and Wet coastal (e.g., Lydolph, 1985; Strahler and Strahler, 1989). Each climate type can be characterized by a unique set of soil-water budgets (Thornthwaite and Mather, 1955; Lydolph, 1985; Strahler and Strahler, 1989), showing periods of surplus, deficit, and recharge (Fig. 11.3). Each soil-water budget graphically contains the amount of precipitation, temperature, and potential evapotranspiration per month (Thornthwaite and Mather, 1955). From these, the periods of water use, water deficit, storage withdrawal, surplus, and recharge can be determined. The surplus and deficits in the soil-water cycle are controlled by annual precipitation, solar radiation, evapotranspiration losses, and changes in soil moisture (Thornthwaite and Mather, 1955). Soil-water budgets indicate the seasonal variation in water available for organisms, as well as for soil-forming and landscape-shaping processes (e.g., Brady and Weil, 2002). Above- and below-ground biodiversity and soils are the products of long-term, soil-water cycles and together reflect the soil-water balance for a particular area (Fig. 11.3). For example, the soil-water budget for the interior Sahara Desert runs a major deficit of water all year long (e.g., Thornthwaite and Mather, 1955; Strahler and Strahler, 1989) and has been so for several million years. The biodiversity and NPP for these regions of the Sahara are miniscule compared to the subtropics and tropics of South America, Africa, and the Malay Peninsula, which have the richest biodiversity and greatest NPP (e.g., Whittaker, 1975; Strahler and Strahler, 1989). The latter settings also have a year-round water surplus even during periods of relatively little precipitation (e.g., Thornthwaite and Mather, 1955; Strahler and Strahler, 1989). Empirical data based on observations of the modern distribution of trace-making continental organisms (e.g., Cloudsley-Thompson, 1962; Krishna and Weesner, 1970; Wallwork, 1970; Spradberry, 1973; Michener, 1974; Whittaker, 1975; Ahlbrandt et al., 1978; Crawford, 1981, 1991; Hobbs, 1981; Louw and Seely, 1982; Glinski, and Lipiec, 1990; Ho¨lldobler and Wilson, 1990; Hasiotis and Mitchell, 1993;

180 11. CLIMATIC CONTROLS ON CONTINENTAL TRACE FOSSILS

FIGURE 11.3 formation.

Distribution of soil-water, ichnodiversity, and climate in relation to temperature, water, NPP, biodiversity, and soil

ICHNOPEDOLOGIC ASSOCIATIONS AS CLIMATE INDICATORS: ORGANISM BEHAVIORS AND PALAEOSOLS

Merritt and Cummins, 1996; Hasiotis, 2002) suggests that a different pattern of biodiversity would be recorded in geologic record if only the traces of organisms (i.e., no body fossils) were preserved (Fig. 11.3). The trace-making communities and the strata (sediments and soils) in which they occur is representative of time-averaged, soil-water cycles for specific areas, all of which are controlled by climate. These ichnopedologic associations can be used to predict the type(s) of burrowing behaviors and patterns that might be present in similar palaeoclimates. In general, Ever-Dry climates contain the lowest ichnodiversity; however, an increase in ichnodiversity might be expected in Dry climates due to the greater amount of moisture. Wet–Dry climates show a major increase in ichnodiversity; however, ichnodiversity appears to taper off as the climate becomes increasingly wet. This decrease in ichnodiversity indicates higher moisture levels and shallower water tables in the environments, such that fewer organisms leave deeply penetrating, elaborate, and taxa-specific structures below ground. Wet climates show a continued decrease in ichnodiversity, and is likely to be the the lowest in Ever-Wet climates due to the nearly saturated ground conditions year round. This generalized trend in ichnodiversity is in contrast to the biodiversity in Wet and Ever–Wet climates where most of the organisms live above ground and in trees (e.g., Wilson, 1992). Overall, the greatest ichnodiversity recorded in continental deposits is most likely to be in the seasonally wetter Wet–Dry climate types. The two main likely reasons for this pattern in ichnodiversity are (1) more availability of belowground ecospace for organisms to inhabit and (2) organisms whose lifestyles require both better drained (i.e., drier) or moister (i.e., wetter) conditions would be recorded in sediments and soils, and likely to be preserved in the rock record.

ICHNOPEDOLOGIC ASSOCIATIONS AS CLIMATE INDICATORS: ORGANISM BEHAVIORS AND PALAEOSOLS Ichnopedologic associations in the sedimentary record provide a way of linking trace-making biota and palaeosols to the ancient soil-water balance of the palaeoclimate that controlled their occurrence and distribution. Since extant organisms and organism behaviors are intrinsically linked to the communities and ecosystems they inhabit, ichnofossils and palaeosols must represent the climatic setting in terms of the moisture input and output. Thus, ichnopedologic

181

associations should indicate the palaeoclimatic setting under which they were formed. They have the potential to be used as in situ proxies for palaeoclimate, especially when used in conjunction with other palaeobiological, sedimentological, and geochemical proxies of palaeoclimate. Ichnopedologic associations are potentially as variable in the geologic record as they are today. Trace fossils found in simple, compound, or cumulative, poorly to well-developed palaeosols in terrestrial settings will occur with a wide variety of palaeosol characteristics and trace-fossil tiering relationships (e.g., Fig. 11.1). Trace fossils occurring in permanent aquatic settings will not be found associated with pedogenic characters. Thus, their ichnopedologic associations will contain a small variety of trace-fossil tiering relationships in bioturbated, non-pedogenically modified sediments (Hasiotis, 2004; Chapter 16). Organisms such as crayfish, termites, ants, bees, wasps, beetles, soil bugs, rodents, lizards, freshwater and terrestrial gastropods, freshwater bivalves, caddisflies, mayflies, and craneflies excavate or construct tubes, burrows, or nests that are useful indicators of the relative amount of water or moisture in the system (Fig. 11.4; see also Fig. 11.1). The ecologic and reproductive strategies of organisms represented by trace fossils can also be used to help discern the overall amount of precipitation delivered to an area via climate versus groundwater, fog banks, and other externally derived sources of water. The trunks and roots of plants are also useful as indicators of the relative amounts of moisture and its depth with respect to seasonal variations of the groundwater profile (see Fig. 11.1) within the soil (e.g., Klappa, 1980; Pfefferkorn and Fuchs, 1991; Retallack, 2001; Kraus and Hasiotis, 2006). Several examples of burrowing organisms with trace-fossil records extending back into the Mesozoic are presented here to illustrate how their trace fossils can be used to interpret the relative amounts of moisture in a palaeoenvironment of a particular palaeoclimatic setting. Crayfish (Fig. 11.5) construct burrows in, adjacent to, and within the banks and bottom sediments of water bodies, and away from water bodies where they excavate down through the soil to a position below the water table (e.g., Hobbs, 1981; Hasiotis and Mitchell, 1993; Hasiotis and Honey, 2000). They are not found typically beyond 448N–S. Crayfish in perennial water bodies construct only horizontal or very shallow subvertical burrows. Crayfish burrows are abundant where there is ample water in the subsurface, and can commonly reach 3–4 m in depth. As precipitation decreases and becomes more

Dry

Wet–Dry

Wet

Wetter

Drier

Features

Ever-Wet

182

Climates Ever-Dry

Ichnodiversity

increases w/increase in bioturbation and rhizoturbation

Disrupted bedding Tree stumps and roots Roots Crayfish burrows

shallow, few few-many, mainly shallow

shallow, buttressed, stilts neumatophores shallow, numerous, with all sizes

increasing abundance & depth increasing depth, become shallower & continuous with increased rainfall

few, short, rarely deep

abundant, shallow to deep, deeper

shallow

Termite nests

small, shallow

deep, confined

large, extensive, nests w/galleries

shallow, small

mostly in trees

Ant nests

small, shallow

moderate depth, confined nests

large, deep, extensive, complex nests

shallow, small

mostly in trees

Bee nests

few, shallow

Wasp nests

few, shallow

Scoyenia Steinichnus Coprinisphaera

larger, deeper, increased diversity of nests abundant, increasing depth & diversity of cocoons and nests

shallower nests shallower to arboreal nests

soil moisture levels of 100% & high relative humidity air–sediment–water interface in local areas of high water presence of vegetation & grazing organisms

Scaphichnium

soil moisture 10–15%, & seasonality of precipitation

Cylindricum

soil moisture ~50%, subaerial exposed surfaces near water bodies

Backfilled horizontal tubes

mostly in trees mostly in trees

soil moisture close to 100%, near air–sediment–water interface

Clam traces

perennial freshwater bodies

Caddisfly traces


Mayfly & Cranefly tubes


FIGURE 11.4 Continental ichnofossil climate indicators. Associations of modern organisms and their burrows, as well as trace fossils in the geologic record indicate relative amounts of moisture and palaeoclimate.


wet interdunes

very shallow, rare shallow, rare, sparse

ICHNOPEDOLOGIC ASSOCIATIONS AS CLIMATE INDICATORS: ORGANISM BEHAVIORS AND PALAEOSOLS

B

A

C

1m

chamber

B

A A

chimney

vadose zone

A

C. symplokonomos

wa

chamber

shaft

te

Camborygma litomomos

rt

ab le

phreatic zone

Cross section of crayfish burrows through aa alluvial channel-overbank environment

B

B C. eumekenomos

tunnel

kms E

D

5 cm

5 cm

F

G

5 cm

FIGURE 11.5 Crayfish burrows. (A,B) Modern crayfish burrow casts of short burrows (A; rock hammer for scale) where the water table is close to the surface, and deep burrows (B; hole is 2 m in depth) where the water table is deep within the substratum. (C) Schematic diagram showing how crayfish burrow morphology and depth varies with the position of the water table. (D,E) Crayfish burrows in the Upper Triassic Chinle Formation. (D) Short, complex burrows (lens cap = 5 cm) represent where the water table was about 30 cm below the palaeosurface. (E) Deep, simple burrows (lens cap in lower left hand corner of photo = 5 cm) represent where the water table was about 2 m below the palaeosurface. (F) Crayfish burrow (lens cap = 5 cm) from the Upper Jurassic Morrison Formation where the burrow was in the bottom of a pond or chute channel. (G) 2-m-deep crayfish burrows in the Upper Paleocene Fort Union Formation, Wyoming.

183

184


seasonal, deep burrowing crayfish in floodplain settings are no longer found, and only those that live in perennial water bodies are present. Some crayfish will construct burrows after their seasonal water body disappears. In these instances, the water bodies are seasonal and the water table remains relatively near to the surface. Deep crayfish burrows are absent in Dry and Ever-Dry climates because the water table is too deep to reach, and lifestyle and burrow maintenance is impossible to sustain (e.g., Hobbs, 1981; Horwitz and Richardson, 1986). Conversely, crayfish burrows are mostly absent in most Wet and Ever-Wet climates because there is no need for moderate to deep burrowing, as the phreatic zone is at or above the surface (e.g., Hobbs, 1981). Most termite species (Fig. 11.6) are found in tropical and subtropical regions with fewer species to about 448N and 408S (e.g., Krishna and Weesner, 1970). Their nests are very useful as indicators of palaeoclimate because they have a higher preservation potential then their body fossils (e.g., Hasiotis, 2003). In Tropical Wet–Dry climates, depending on the termite species, nests can be quite extensive and large, extending above and below ground (Noirot, 1970; Noirot and Darlington, 2000). Hotter and drier climates have progressively smaller termite nests, and include nests constructed within the dead wood of trees (e.g., Krishna and Weesner, 1970; Lee and Wood, 1971). They do not occur where there is no vegetation. In Wet and Ever-Wet climates, termite nests live mostly above ground and are constructed on or within trees (e.g., Krishna and Weesner, 1970). A similar pattern is also seen in the distributions and sizes of ant nests (Fig. 11.7), however, they are not as elaborately constructed or as visible above the ground surface as termite nests (e.g., Ho¨lldobler and Wilson, 1990; Hasiotis, 2003). Ants can live in colder as well as hotter climates than termites, and some species do not construct permanent nests but move from place to place ravaging everything in their path (e.g., Ho¨lldobler and Wilson, 1990). This type of behavior would not likely to be preserved. Freshwater bivalves live in perennial water bodies that are well oxygenated and of low turbidity (e.g., Parrish, 1998). The dwelling–suspension–feeding traces of bivalves can be expected to be in any climate where there was a perennial water body, though this is maximized in settings characterized by Wet–Dry to Ever–Wet climates. Few rivers or lakes persist into areas with Ever-Dry or Dry climates (e.g., Lydolph, 1985; Parrish, 1998). Ichnopedologic associations also co-occur with other palaeoclimatic indicators (Fig. 11.8) in the sedimentary record (e.g., Sellwood and Price, 1994).

For example, the aerial extensive and thick eolian and evaporite deposits are indicative of Ever-Dry to Dry climates. They are found in Wet–Dry climates as well but are smaller and much less abundant (Parrish, 1998). The degree and depth of leaching, stability of rock fragments, types of soil structures, and authigenic clay minerals are indicative of the climate in which they formed (e.g., Brady and Weil, 2002). The thickness and aerial extent of plant accumulations are contingent upon the climate and the relative position of the water table (Parrish, 1998).

PREDICTIONS OF ICHNOPEDOLOGIC ASSOCIATIONS OF PALAEOCLIMATE Ichnopedologic associations and trace-fossil tiering relationships are postulated to show distinct patterns for Ever-Dry, Dry, Wet–Dry, Wet, and Ever-Wet palaeoclimates, based on distribution patterns of extant organism behaviors and as well as trace fossils (see Fig. 11.1; also see Hasiotis, Chapter 16).

Ichnopedologic Associations Indicating Ever-Dry palaeoclimates Ichnopedologic associations of continental settings in Ever-Dry palaeoclimates are predicted to show little or no bioturbation (Fig. 11.9). This palaeoclimate type would have the lowest NPP and be nearly devoid of life due to extreme diurnal temperatures, and the lack of water and nutrients in the environment. Palaeosols should be classified primarily as Entisols and rarely as Aridisols due to the lack of precipitation and the continually shifting winds that reshape the land surface. Trace fossils, if present, would indicate organisms that have evolved special adaptations to exist in exceedingly harsh settings (e.g., Crawford, 1981, 1991). Trace fossils are expected to include very rare shallow rhizoliths of single plants, mainly horizontal burrows and trails of opportunistic (r-strategist) organisms that have little or no tiering (epiterraphilic and rare terraphilic) behavior. Exceptions to this pattern might occur when water is abundant for an extended period of time, and would produce wetter signatures in sedimentary facies than normally associated with Ever-Dry climates. Examples of such scenarios include desert oases (e.g., Smith et al., 1993), perennial rivers that run through arid regions (e.g., Nile River-Sahara; Lydolph, 1985), fog banks associated with coastal deserts (e.g., Namibia) (Lancaster, 1989), or a shift in climate from Ever-Dry or Dry to Dry or Wet–Dry palaeoclimates

PREDICTIONS OF ICHNOPEDOLOGIC ASSOCIATIONS OF PALAEOCLIMATE

B

A

5 cm

C

D

5 cm

F

E

6 cm

6 cm

H

G

5 cm

FIGURE 11.6 Termite nests. (A) Giant termite nest from the area around Pretoria, South Africa, where precipitation is around 1500 cm/year. Nest is 3 m tall. (B) Termite nest (lens cap = 5 cm) from an area south of Katherine, Australia, where precipitation is about 300 cm/year. (C,D) Termite nest (lens cap = 5 cm) from an area south of Alice Springs, Australia, where precipitation is around 200 cm/year. (E,F) Lower Jurassic Claron Formation termite nests showing distribution (E) and close-up (F) of one kind of internal nest architecture, consisting of cemented chambers and galleries (lens cap = 6 cm). (G) Spherical termite nest in sandstone of the Eocene-Oligocene Jebel-Qatrani Formation, Fayum, Egypt, showing internal nest architecture (scale in centimeters). (H) Internal architecture of lined chambers and galleries of the Miocene termite nest ichnofossil Syntermesichnus (coin 2.5 cm), southern Argentina.

185

186


A

B 10 cm

5 cm

C

6 cm

E

5 cm

D

F

5 cm

6 cm

G

10 cm

FIGURE 11.7 (A) Chambers and galleries of an ant nest constructed in the laboratory. (B) Chambers and galleries of a modern meat ant nest exposed in a bank along the Ross River, an ephemeral dryland river (lens cap = 5 cm). (C) Cross section through an abandoned meat ant nest in a longitudinal bar of the Umbum River, Simpson Desert, Australia (lens cap = 6 cm). (D) Cross section through an active meat ant nest in an extra-channel splay deposit of the Umbum River, Simpson Desert, Australia. (E) Ichnofossil complex showing mainly chambers and few galleries interpreted as an ant nest, Upper Jurassic Morrison Formation, Utah (lens cap = 6 cm). (F) Ichnofossil complex showing mainly chambers and few galleries interpreted as an ant nest in Miocene distal alluvial deposits, near Mequineza, Spain (lens cap = 6 cm). (G) Ichnofossil complex showing interconnected chambers and galleries interpreted as an ant nest in the Paleocene–Eocene Claron Formation, Utah.

Climates Types Ever-Dry

Wet–Dry

Dry

Wet

Drier

Features

Ever-Wet

Wetter

thin sandsheets

Eolian units

Ergs

Evaporites

Ca+, Ba+, Na+, K+ precipitants

coastal and lacustrine dune fields

Palaeosols Depth of weathering and leaching Intensity of bioturbation Fe–Al nodules and thick quartz-rich horizon

Bauxites/Oxisols

Laminar and nodular silicic structures Gypsum-cemented light-colored horizon

Gypcrete (>10 cm thick)

Pedogenic carbonate

thick, continous layers

moderate/nodular

After Sellwood and Price, 1994

Silcrete

deep, dispersed, nodules

shrinking/swelling clays, slickensides, pseudoanticlines Pedogenic clay

clay-rich, slickensided, >10 cm clay-rich, mottles of gray, yellow, orange, red; Fe–Al nodules

Clay Minerals Rock/pebble stability and dominance Disrupted bedding Plant accumulation layers (in place) Color mottling

Kaolinite, Smectite, Palygorskite, Sepiolite Dolomite, Limestone

Sandstone, Siltstone, mixed

Smectite, Kaolinite

Vermiculite, Kaolinite, Smectite

Sandstone, Granite, Basalt

Kaolinite, Smectite, Geothite

Kaolinite, Geothite, Lepidocrocite Gibbsite, Hematite Gibbsite

Granite, Quarzite

Quartzite, Chert


undifferentiated pedogenic modification of substrate

disrupted bedding with few roots and burrows thin, isolated, very rare

thin, patchy, organic-rich, with fine-grained sediment

thick coal

increase in soil color and mottling from orange towards reds towards strong blues, greens, and grays

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FIGURE 11.8 Palaeoclimatic indicators. Associations of different types of pedogenic products and features, authigenic minerals, climate-sensitive deposits, rock types, and weathering products can be used to indicate the relative amounts of moisture and the palaeoclimate.

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(e.g., Bordy et al., 2004; Hasiotis, 2004), similar to areas influenced by the present-day Intertropical Discontinuity (e.g., Sahel Region of Africa; Nicholson and Flohn, 1990). Ichnopedologic associations should display higher ichnodiversities and abundances, with the possible presence of terraphilic, hygrophilic, and hydrophilic behaviors, as well as other palaeo-indicators of a wetter climate.

abundances and uncommon occurrences of shallow, surface rhizoliths. Palaeosols are classified as Entisols, Inceptisols, or Aridisols depending on the depositional environment. One type of ichnopedologic association would have rare and weakly bioturbated strata with very little vertical tiering, and show a slightly greater diversity and abundance of trace fossils compared to the Ever-Dry palaeoclimate. Other ichnopedologic associations comprise intensely bioturbated strata of opportunistic (r-strategist) organisms with possible shallow to moderate, epiterraphilic to hydrophilic vertical tiering, and a greater ichnodiversities and abundances compared to ichnopedologic associations of drier conditions within the Dry palaeoclimate setting. One particular pattern represents bursts of activity due to episodic precipitation events or overland flooding events that allow local, transported, and opportunistic organisms to complete or begin new life cycles. Exceptions to these ichnopedologic patterns might occur when water via direct precipitation or runoff is more abundant for an extended period of time, producing wetter signatures in typically drier sedimentary facies. Ichnopedologic associations

Ichnopedologic Associations Indicating Dry Palaeoclimates A number of ichnopedologic associations are predicted for continental settings of Dry palaeoclimates due to the greater amounts of precipitation delivered to the system (Fig. 11.9). Palaeoenvironments typically have very low NPP from the lack of water and nutrients, and extreme temperatures. This would likely to be reflected in low ichnodiversities and abundances. Any trace fossils present represent organisms adapted to harsh conditions (Crawford, 1981, 1991). Vegetation is patchy and discontinuous, represented by low

EVER-DRY TO DRY CLIMATES: ICHNOPEDOLOGIC CHARACTERS Ephemeral rivers & hypersaline lakes

Eolian reworked alluvial, palustrine, lacustrine environments Moisture contribution mainly from overland flow

Springs and seeps, fresh to saline Epiterraphilic

Increase soluable salt concentration

Deep water table ~20- >100 m

soil surface - Rare, intensely bioturbated upper surfaces

Capillary water

Terraphilic - Terraphilic tiers dominate

Vadose well-drained

- Specialized and complex burrows and burrow systems dominate; adaptations to heat & moisture deficits - Root depth shallow to very shallow; larger vegetation closer to shallow water table

?

- Lack of Hygrophilic and Hydrophilic tiers

Point where the groundwater table intersects the landsurface Sharp gradients in groundwater profile

Hygrophilic Vadose water


Entisols and Aridisols dominate - profiles typical also of inceptisols; soil features of special conditions - accumulations of calcium carbonate, gypsum, sodium, and other salts - formation of silcretes, calcretes, gypcretes, and other duripans

Increase soil moisture Increase groundwater height Increase biodiversity and biotic exchange Increase in hydrophilic and hygrophilic tiering

FIGURE 11.9 Ever-Dry to Dry palaeoclimate characteristics.

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should display higher ichnodiversities and abundances, with the possible presence of terraphilic, hygrophilic, and hydrophilic behaviors, as well as other palaeo-indicators of a wetter climate. If water becomes more abundant for an extended period of time, ichnopedologic associations will resemble those of Wet–Dry palaeoclimates (see the next section).

Ichnopedologic Associations Indicating Wet–Dry Palaeoclimates Numerous ichnopedologic associations are predicted to be found in continental settings of Wet–Dry palaeoclimates because of the range of overall precipitation amounts and the variety of depositional environments by more water in the system (Fig. 11.10). NPP ranges from low to high, depending on the overall amount of EP, and is indicated by low to high ichnodiversities and

abundances. As moisture increases, so does ichnodiversity, abundance, and tiering. Vegetation covers the landscape surface as nearly complete, short ground-cover plants at the lower end of precipitation within Wet–Dry palaeoclimates. With increasing amounts of precipitation come other types of vegetation, including mixed ground cover, multistory, open canopy forests. The latter vegetation types are found at the upper end of precipitation within Wet–Dry palaeoclimates. Such settings are equivalent to savannah to mixed savannah-woodland. Palaeosols are classified as Entisols, Inceptisols, Aridisols, Vertisols, or Alfisols at the drier end of Wet–Dry palaeoclimates depending on the parent material, development, and duration for formation. At the wetter end of Wet–Dry palaeoclimates, Entisols, Inceptisols, Spodosols, and Alfisols are present as well as Ultisols and Oxisols, particularly where sedimentation is minimal for long periods of time. More clay-rich and better-developed palaeosols could be seasonally saturated, and develop gleyed

WET–DRY CLIMATES: ICHNOPEDOLOGIC CHARACTERS

Seasonal to Perennial rivers & lakes

Alluvial, palustrine, lacustrine environments with moderate to little eolian modification

fresh to hypersaline water bodies

Moisture contribution from direct precipitation and overland flow Epiterraphilic

Increase soluable salt concenttration

soil surface

Seasonal fluctuation great

Springs and seeps, fresh to saline

- Tiering depth increases with increased moisture Capillary water

Terraphilic - Terraphilic and hygrophilic tiers dominate

Vadose well-drained

- Simple to complex burrows and nests dominate; diversity and tiering indicate amount of moisture and precipitation delivery to environment - Root depth shallow to moderate depths; larger vegetation closer to shallow water table - Increasing dominance of Hydrophilic and Hydrophilic tiers closer to water bodies; increased moisture

Point where the groundwater table intersects the landsurface ? Hygrophilic Vadose water

Sharp to low gradients in groundwater profile away from water bodies Hydrophilic Phreatic water (groundwater)

Pedogenic Characteristics - entisols and inceptisols in areas with high sedimentation rates; gleyed to plinthic fabrics


- accumulations of calcic to argillic horizons, and duripans

Increase groundwater height

- vertic structures indicate desiccation; true vertisols also

Increase biodiversity and biotic exchange

- wetter areas with features of gleying, palustrine carbonate accumulations, heavily rooted with carbon preservation

Increase in hydrophilic and hygrophilic tiering

FIGURE 11.10

Wet–Dry palaeoclimate characteristics.

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to plinthic pedogenic fabrics, depending on the position, sedimentary characteristics, and soilforming processes in palaeolandscapes. Ichnopedologic associations of continental settings in Wet–Dry palaeoclimates are characterized by shallow to deep, epiterraphilic to hydrophilic tiering in palaeosols adjacent and lateral to water bodies. Ichnodiversity and tiering depth of opportunistic (r-strategist) and equilibrium (k-strategist) species increases with increasing moisture in the palaeosol to about 37% moisture in the vadose zone (e.g., Willis and Roth, 1962; Hasiotis and Bown, 1992). The depth and density of rhizolith patterns also increase with increasing moisture in the palaeosol to levels similar to that for burrowing animals (e.g., Retallack, 2001; Kraus and Hasiotis, 2006). As the amount of perennial water in the system increases, the tiers become shallower and compressed, such that hygrophilic to hydrophilic behavioral zones are near to or above the palaeosurface. Ichnopedologic associations of continental settings in the drier part of Wet–Dry palaeoclimates are characterized mainly by shallow to intermediate, epiterraphilic to terraphilic tiering in environments proximal and distal to water bodies. Ichnopedologic associations of continental settings in the equable and wetter part of Wet–Dry palaeoclimates are characterized predominantly by shallow to deep, epiterraphilic to hydrophilic tiering proximal and distal to water bodies. Ichnopedologic associations of continental settings in the wettest part of Wet–Dry palaeoclimates are characterized by shallow to intermediate, epiterraphilic to hydrophilic tiering proximal and distal to water bodies. Many variations can be expected in the ichnopedologic patterns briefly outlined for Wet–Dry palaeoclimates, based on spatial and temporal quantity of soil moisture and water in the environment. In general, as the amount of water in the system increases (i.e., wetter end of Wet–Dry palaeoclimates), the shallower and more compressed the ichnofossil tiers of ichnopedologic associations become, such that the hydrophilic behavioral zone is located near to the palaeosurface and the terraphilic and hygrophilic zones are very thin or absent. Areas of slightly higher topographic relief, however, have better drained conditions and deeper ichnofossil tiering. Palaeosols are better drained, leached, and illuviated, giving soils the appearance of greater development and maturity. Areas of slightly lower topographic relief will have more poorly drained conditions, and correspondingly shallower ichnofossil tiering. Palaeosols in these areas are wetter, more organic rich, and less illuviated, giving soils the appearance of

greater immaturity and slower development. In both the cases, variations in ichnopedologic associations are caused by intra-basinal landscape variability rather than by such extra-basinal variability as climate change with respect to precipitation, temperature, or latitudinal position.

Ichnopedologic Associations Indicating Wet Palaeoclimates Ichnopedologic associations of continental settings in Wet palaeoclimates are predicted to reflect high moisture conditions year-round, indicating abundant annual rainfall associated with high humidity (Fig. 11.11). These conditions would produce high NPP and EP; evidence for this would be preserved primarily by abiotic pedologic features (see Fig. 11.8). Vegetation covers the landscape surface as complete mixed-ground cover and multistory, open-canopy forests to multistory, closed-canopy forests, which are equivalent to mixed savannah-woodland to tropical rainforests. Palaeosols are classified as Entisols, Inceptisols, Alfisols, Spodosols, Ultisols, and Oxisols. Better developed, more mature palaeosols have deeply weathered profiles and organic-poor horizons. Finer grained, clay-rich palaeosols are mostly wet and seasonally saturated, developing mottled, gleyed, or plinthic pedogenic fabrics, depending on the sedimentary characteristics and soil-forming processes in the palaeolandscape setting. Ichnopedologic associations are characterized by all tiers, and range from shallow to deep, epiterraphilic to hydrophilic tiers, depending on the amount of water in the system and topographic relief. As the amount of moisture in the system increases, however, ichnodiversity and tiering decrease and become compressed (shallower) due to higher soil-moisture and water-table levels. Ichnofossil abundances could be high due to optimal conditions for organisms adapted to those conditions. Organisms with epigeal and arboreal lifestyles increase, due to more highly saturated ground conditions. Variations in the ichnopedologic patterns are expected for Wet palaeoclimates based on spatial and temporal abundance of soil moisture and water in the environment, as well as the topographic relief in the landscape. Ichnopedologic associations should differ according to variations in sediment texture, topographic relief, magnitude and frequency of flooding events, and drainage conditions caused by variability in moisture delivery and intra-basinal landscape morphology.

191


WET TO EVER-WET CLIMATES: ICHNOPEDOLOGIC CHARACTERS Alluvial, palustrine, lacustrine environments with nearly saturated palaeosols

Perennial rivers & lakes

Moisture contribution from direct precipitation and overland flow

Springs & seeps Epiterraphilic

soil surface Vadose imperfectly drained Capillary water

Vadose water

low nutrient availability

mobile cations leached

soluable salts removed

low moisture fluctuation

deep, intense weathering

Terraphilic

Hygrophilic

Hydrophilic

Point where the groundwater table intersects the landsurface

Phreatic water (groundwater)

Gentle gradients in the groundwater profile

- Shallow tiering, with all tiers compressed to the near-surface, particularly in areas of high soil moistrue and water table

- Hygrophilic & hydrophilic tiers dominate

- Tiering depth decreases with increased moisture

- Root depth shallow to surficial

- Ichnofossil diversity and abundance low; arboreal lifestyles increase

Pedogenic Characteristics

- saturated, gleyed, and plinthitic mottled soils; histosols present with organic accumulation

Increase soil moisture Increase groundwater height

- clay-sized particles dominated by hydrous oxides of Fe and Al; intense leaching Increase biodiversity and biotic exchange - low activity clays; water moves freely through profile

Increase in hydrophilic and hygrophilic tiering

- ultisols and oxisols dominate except where active sedimention forms entisols and inceptisols

FIGURE 11.11

Wet to Ever-Wet palaeoclimate characteristics.

Ichnopedologic Associations Indicating Ever-Wet Palaeoclimates Ichnopedologic associations in continental settings in Ever-Wet palaeoclimates are also predicted to reflect abundant moisture year-round with high humidity and annual rainfall (Fig. 11.11). These conditions preserve the highest NPP and EP; evidence for this would be preserved by abiotic pedologic features and organic matter accumulations (see Fig. 11.8). Vegetation covers the landscape surface as multistory, closed-canopy tropical rainforests. Palaeosols are classified as Entisols, Inceptisols, Alfisols, Spodosols, Ultisols, and Oxisols. Organic plant accumulations in areas with high water-table levels and anaerobic conditions produce Histosols. Better-developed, mature palaeosols have deeply weathered profiles and organic-poor horizons. Finer grained, clay-rich palaeosols are predominantly wet and seasonally to annually saturated, developing mottled, gleyed, or plinthic pedogenic fabrics,

depending on the sedimentary characteristics and soil-forming processes in palaeolandscape setting. Ichnopedologic associations are characterized by all tiers, and mostly compressed to the near-surface, with the water-table level lying close to, at, or above the surface in many areas. Hygrophilic and hydrophilic behaviors are dominant. Many areas do not have a well-developed terraphilic zone compared to other palaeoclimate settings, except in better drained, topographically higher areas of the landscape. Ichnodiversities are the lowest and tiering the shallowest, compared to similar settings in other palaeoclimate settings due to the high soil-moisture and water-table levels. Ichnofossil abundances should be high, reflecting optimal conditions for organisms adapted to such environments. Organisms with epigeal and arboreal lifestyles are dominant owing to very moist ground conditions. Variations in the ichnopedologic patterns for EverWet palaeoclimates would record spatial and temporal variations of soil moisture and water in the

192


environment, largely as a function of topography. Drier (better drained) ichnopedologic associations would be found in such topographically higher areas as natural levees and rare shoreline or coastal dune fields.

Testing Hypotheses to Develop New Proxies of Palaeoclimate and Climate Change With basic concepts, patterns, and hypotheses in place, these proposed trends in climate-sensitive, ichnopedologic associations can be tested in Mesozoic and Cenozoic continental deposits. It will be necessary to calibrate ichnopedologic associations to extant biota and the soils in which they played a role in developing for specific climates. Simultaneously, these should also be tested rigorously in present-day climate settings to confirm the observations and patterns gleaned from empirical data of modern biotic–soil–climate associations. Such parallel testing is necessary to insure that progress is made in developing ichnopedologic associations that more accurately reflect the biophysicochemical conditions of continental environments that control the spatial and temporal distribution of organism behaviors. The current redefined Scoyenia ichnofacies is dysfunctional because it is too broadly defined, and can be applied to every continental environment, including the occurrence of palaeosols. The Coprinisphaera, Mermia, and Termitichnus ichnofacies (e.g., Genise et al., 2000; Buatois and Mańgano, 2004) are also broadly defined and poorly formulated because they do not represent well any recurring facies associations of any particular sedimentary, palaeoenvironmental, or palaeopedogenic characteristics, or any palaeoclimatic setting. The goal is to produce climate-sensitive ichnopedologic associations that accurately integrate the biophysicochemical factors that control the spatial and temporal heterogeneity of palaeosols and their ichnodiversities and tiering. If the basic patterns of the ichnopedologic associations can be falsified, then revised or new hypotheses should be generated and re-tested until climate-sensitive ichnopedologic associations are developed. Such ichnopedologic associations may or may not be recurring through time because of differential evolution of terrestrial and aquatic organisms and ecosystems through the Phanerozoic. These ichnopedologic associations will have a major impact on the continental ichnofacies paradigm by eventually replacing the archetypal and cumbersome ichnofacies of old. Overwhelming data already exists (e.g., Stanley and Fagerstrom, 1974;

Ahlbrandt et al., 1978; Bown, 1982; Bown and Kraus, 1983; Smith 1987; Curran and White, 1991; GierlowskiKordesch, 1991; Curran, 1992; Smith et al., 1993; Bown et al., 1997; Groenewald et al., 2001; Bordy et al., 2004; Hasiotis, 2002, 2004; Hembree et al., 2004; Kraus and Hasiotis, 2006) to demonstrate that one or even two ichnofacies—Coprinisphaera and Termitichnus—cannot be the namesake for all palaeosols. The type and maturity of palaeosols are completely ignored and many of the ichnotaxa can be found in both ichnofacies, as well as in ichnofacies representing marine-organism behaviors and palaeoenvironments. Defining an ichnofacies as occurring in palaeosols is of little use because palaeosols are so variable in all aspects of their genesis, character, and significance that the original purpose of integrating trace fossils and palaeosol is lost. The ichnofacies paradigm may not have any application to the continental realm because the spatial and temporal heterogeneity of environments and climates renders such a paradigm ineffective. The continental realm is in need of a new paradigm that will properly incorporate patterns of bioturbation (one of the five soil-forming factors) and pedogenesis with the biophysicochemical controls and processes that reflect environmental and climatic conditions.

CONCLUSIONS Global climate change and its impact on Earth’s biodiversity and ecosystems are at the forefront of scientific debate and international government policy-making in the twenty-first century. The best archival record of how life and ecosystems react to global cooling or warming lies in the geologic record. Unfortunately, much of the focus has been on the latest Cenozoic (e.g., Parrish, 1998; Ruddiman, 2001). This is because ice cores, tree rings, corals, pollen, and other archives of climate are the best preserved and most continuous in the sedimentary record in the last million years or so. The record of palaeoclimate in deep geologic time is also important, however, because it provides a record of climate change over long periods of time and an archive of the biotic and ecosystem responses to these perturbations (e.g., Parrish, 1998; Retallack, 2001). Palaeontologic, lithologic, and geochemical evidence are traditionally the major indicators of deep-time palaeoclimate and of global change. Fossils, classified as direct, nearest living-relative, and empirical-morphologic palaeoclimatic indicators,

ACKNOWLEDGEMENTS

are used as sensitive indicators of palaeoclimate through the concepts of taxonomic and ecophenotypic uniformitarianism and palaeobiogeography (Parrish, 1998). Palaeosols have also been used to interpret the record of palaeoclimates where they are well studied and understood (e.g., Parrish, 1998; Retallack, 2001). Yet, continental trace fossils, which occur in many palaeosols (Hasiotis, 2000, 2002), have been under-utilized for this purpose (Voorhies, 1975). This is because trace fossils have neither been linked effectively to the deposits in which they are found, nor have they been considered as potential biotic archives of palaeoclimate data. This chapter provides an opportunity to explore these under-utilized archives of palaeoclimate through ichnopedologic associations that have local and regional significance. The hypotheses of climate-sensitive ichnopedologic associations presented here are meant as a catalyst for future testing of these potential palaeoclimatic indicators. It is also meant to encourage studies that integrate neoichnological with pedologic and climatic studies, in order to develop new deep-time palaeoclimatic proxies. Continental trace fossils represent not only in situ hidden biodiversity, but they also record sediment interactions that were strongly influenced by palaeoclimate. A better understood relationship between trace fossils, palaeosols, and palaeoclimate can yield more accurate interpretations from the continental sedimentary record. Ichnopedologic associations may prove to be extremely valuable in deposits where more traditional palaeoclimate data are sparse. New information gleaned from ichnopedologic associations can only enhance existing palaeoclimatic interpretations, particularly when combined with other palaeontologic, lithologic, and geochemical data. Integration of enhanced datasets to build the next generation of deep-time palaeoclimate models from the bottom–up will provide a new look at old data, in order to assess the response and feedback of continental biota and ecosystems through time.

ACKNOWLEDGEMENTS We are grateful to William Miller III for inviting us to provide this contribution to the book. We are indebted to the students of University of Kansas IchnoBioGeoScience research group for stimulating indepth research and discussions on the organism–medium interactions. Hasiotis thanks

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Dick Beerbower for provocative conversations concerning the use of continental trace fossils for reconstructing ancient environments and climates. James MacEachern and Kerrie Bann provided helpful comments and suggestions that greatly improved the chapter. We thank Brian Platt and Jon Smith for their help preparing this chapter for publication. Stephen T. Hasiotis acknowledges support from National Science Foundation Grant EAR-02293000. Mary J. Kraus acknowledges Support from National Science Foundation Grants EAR-0000616 and 0228858.

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Hasiotis, S.T. and Mitchell, C.E. (1993). A comparison of crayfish burrow morphologies: Triassic and Holocene fossil, paleo- and neo-ichnological evidence, and the identification of their burrowing signatures. Ichnos, 2, 291–314. Hasiotis, S.T., Wellner, R.W., Martin, A. and Demko, T.M. (2004). Vertebrate burrows from Triassic and Jurassic continental deposits of North America and Antarctica: their palaeoenvironmental and paleoecological significance. Ichnos, 11, 103–124. Hembree, D.I., Martin, L.D. and Hasiotis, S.T. (2004). Amphibian burrows and ephemeral ponds of the Lower Permian Speiser Shale, Kansas: evidence for seasonality in the midcontinent. Palaeogeography, Palaeoclimatology, Palaeoecology, 203, 127–152. Hembree, D.I., Hasiotis, S.T. and Martin, L.D. (2005). Torridorefugium eskridgensis (new ichnogenus and ichnospecies): amphibian aestivation burrows from the Lower Permian Speiser Shale of Kansas. Journal of Paleontology, 79, 583–593. Hobbs, Jr. H.H. (1981). The Crayfishes of Georgia, Smithsonian Contributions to Zoology, No. 166, Smithsonian Institution Press, Washington, D.C., 166 pp. Ho¨lldobler, B. and Wilson, E.O. (1990). The Ants, The Belknap Press, Cambridge, 732 pp. Horwitz, P.H.J. and Richardson, A.M.M. (1986). An ecological classification of the burrows of Australian freshwater crayfish. Australian Journal of Marine and Freshwater Research, 37, 237–242. Jenny, H. (1941). Factors of Soil Formation, McGraw-Hill Publishers, New York, 288 pp. Klappa, C.F. (1980). Rhizoliths in terrestrial carbonates: classification, recognition, genesis, and significance. Sedimentology, 26, 613–629. Kraus, M.J. (1999). Palaeosols in clastic sedimentary rocks: their geologic applications. Earth Science Reviews, 47, 41–70. Kraus, M.J. and Hasiotis, S.T. (2006). Significance of different modes of rhizolith preservation to interpreting palaeoenvironmental and palaeohydrologic settings: examples from Paleogene palaeosols, Bighorn basin, Wyoming. Journal of Sedimentary Research, 76, 633–646. Krishna, K. and Weesner, F.M. (1970). Biology of Termites, Volume 2, Academic Press, New York, 643 pp. Lancaster, N. (1989). The Namib Sand Sea—Dune Forms, Processes and Sediments, A.A. Balkema, Rotterdam, The Netherlands, 192 pp. Lee, K.E. and Wood, T.G. (1971). Termites and Soil, Academic Press, London, 251 pp. Louw, G. and Seely, M. (1982). Ecology of Desert Organisms, Longman Group Limited, London, 194 pp. Lydolph, P.E. (1985). The Climate of Earth, Rowman and Allanheld Publishers, Totowa, NJ, 402 pp. Merritt, R.W. and Cummins, K.W. (Eds.) (1996). An Introduction to the Aquatic Insects of North America, 3rd edition. Kendall/Hunt Publishing Company, Iowa, 862 pp. Michener, C.D. (1974). The Social Behavior of the Bees, Harvard University Press, Cambridge, MA, 418 pp. Nicholson, S. and Flohn, H. (1990). African environmental and climatic change and the general atmospheric circulation in late Pleistocene and Holocene. Climatic Change, 2, 313–348. Noirot, C. (1970). The nests of termites. In: Krishna, K. and Weesner, F.M. (Eds.), Biology of Termites, Academic Press, New York, pp. 73–125. Noirot, C. and Darlington, P.E.C. (2000). Termite nests: architecture, regulation, and defense. In: Abe, T., Bignell, D.E. and Higashi, M. (Eds.), Termites: Evolution, Sociality, Symbioses,

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12 The Trace-Fossil Record of Vertebrates Stephen T. Hasiotis, Brian F. Platt, Daniel I. Hembree, and Michael J. Everhart

SUMMARY: The trace-fossil record of vertebrates contains behavioral evidence of fish, amphibians, reptiles, dinosaurs, mammals, and birds in continental, transitional, and marine paleoenvironments since the Devonian. The study of vertebrate trace fossils includes tracks, trails, burrows, nests, and such feeding traces as bite marks, coprolites, gastroliths, and regurgitalites. Behaviors recorded by these traces include various kinds of (1) locomotion, (2) dwelling, (3) aestivation, (4) breeding and nesting, as well as (5) acts of feeding, which also result in (6) digestion, (7) regurgitation, and (8) defecation. These trace fossils represent the interaction between a vertebrate and a medium, which includes softgrounds, firmgrounds, hardgrounds, plants, and other animals. Humans also have a trace-fossil record, and, like other vertebrates, produce numerous trace fossils that result from different kinds of behavior.

Interpretation of the origin of vertebrate trace fossils is based largely on their comparison to structures produced by modern vertebrates as a result of specific behaviors and media. Such comparisons permit vertebrate trace fossils to be used as proxies for biodiversity at the class, ordinal, or familial levels, as well as for such trophic levels as herbivory, insectivory, carnivory, or saprivory. Vertebrate–media interactions are valuable for interpreting ancient environmental, ecological, and climatic settings in the geologic record when used in conjunction with plant and invertebrate body and trace fossils, the syn- and post-depositional history of the enclosing strata, as well as other proxies that measure change in the geosphere, biosphere, and atmosphere. The major sections of this chapter are organized according to the main topics and animal groups under study within vertebrate ichnology. The chapter begins with a review of general concepts and methods in vertebrate ichnology. The following sections provide reviews of modern and ancient traces produced by different vertebrate behaviors. Locomotion traces produced in terrestrial and aquatic environments since the Devonian are reviewed, including the methodology for description and measurement of each major trace-type. Vertebrate burrows and nests in modern and ancient environments are reviewed and summarized in a diagram charting the record of these traces since the Devonian. Ichnological evidence of feeding behaviors is reviewed for marine and continental vertebrates, with a focus on the Mesozoic. Behaviors and trace fossils produced by Late Pliocene to Holocene hominids are also reviewed. While often disregarded as true trace fossils by ichnologists,

INTRODUCTION The purpose of this chapter is to review the ichnology of vertebrates and the impact of vertebrate activity on continental, transitional, and marine deposits. Fish, amphibians, reptiles, dinosaurs, mammals, and birds have all produced different types of trace fossils. Vertebrate trace fossils include tracks, trails, burrows, nests, and such trophic-interaction (e.g., feeding, hunting, and defense) traces as bite marks, coprolites, gastroliths, and regurgitalites. These trace fossils represent the interaction between a medium (e.g., sediments, soils, lithified materials, animals, plants, etc.) and organism behavior.


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hominid trace fossils are used by archaeologists and anthropologists to study the evolution of hominid form, cognitive skills, and behavior. The chapter is concluded with a discussion of future directions in vertebrate ichnology.

VERTEBRATE ICHNOLOGY: CONCEPTS AND METHODS Vertebrate ichnology is more than just the study of footprints and trackways, which most research and the general public has focused on historically (e.g., Thulborn, 1990; Lockley, 1991; Lockley and Hunt, 1995; Lockley and Meyer, 2000). Vertebrate ichnology includes the study of tracks, trails, burrows, nests, predation and scavenging marks, coprolites, gastroliths, regurgitalites, and other types of trace fossils produced by lower and higher vertebrates. Traces older than 10,000 years (i.e., Holocene) are considered as true trace fossils. Those younger than this, but not from the present day, should be considered subfossils because they, too, record organism–media interactions useful for interpretation of the past. Vertebrate trace fossils represent the interaction between an animal and a media, which includes softgrounds, firmgrounds, hardgrounds, plants, and other animals. Behaviors recorded by these interactions include various kinds of (1) locomotion (repichnia), (2) dwelling (domichnia, aedificichnia), (3) aestivation, (4) breeding and nesting (calichnia), as well as such acts of (5) feeding (fodichnia) as predation, herbivory, and scavenging that result in (6) digestion, (7) regurgitation, and (8) defecation (e.g., Ekdale et al., 1984; Bromley, 1996). Simple to complex burrow systems that represent multiple, simultaneous behaviors and uses, are classified as polychresichnia (Hasiotis, 2003). Like other vertebrates, hominids also have a trace-fossil record that results from different behavior–substrate interactions although these have been studied traditionally in the discipline of archaeology. Traces produced by humans include tracks, dwellings, roadways, rock art, cave drawings, carvings, and primitive tools (e.g., Fagan, 2000). A single animal can produce one or more kinds of traces based on different types of behavior listed earlier (e.g., Ekdale et al., 1984). For example, a prairie dog (Fig. 12.1) can produce footprints, trackways, and extensive burrow systems. In and around their burrows may be evidence of herbivory on plant material, scavenging marks on bones, and even cannibalism, all resulting in scat or feces. Vertebrate burrows preserved in different media textures and

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consistencies will show different expressions of preservation. Erosion of these structures prior to burial will also produce a different pattern than a complete burrow or burrow system. These conditions may result in the same type of trace fossil receiving different ichnotaxonomic names. Plants, invertebrates, and vertebrates may produce tubular structures that are similar morphologically and may be confused easily with each other. Extinct taxa like therapsids (e.g., Smith, 1987) constructed simple to complex burrows that are similar in morphology to modern burrows of various mammals, reptiles, birds, and crustaceans (Fig. 12.2). Many of these burrows, however, have subtle surficial morphologic characters that are useful to distinguish one from the other (e.g., Groenewald et al., 2001; Miller et al., 2001; Hasiotis et al., 2004). Caution must be exercised when studying the morphology of vertebrate burrows because they may be intersected or interconnected with other burrows or rhizoliths. Vertebrate burrows are a part of complex benthic (aquatic) and soil (terrestrial) ecosystems and are prone to cross-cutting by burrows produced by other organisms. In soils, many animals will construct their burrows near shrubs and trees so that the true burrow system might be difficult to distinguish from the traces of large roots. Soft, flexible, and rigid eggs are not true trace fossils because they are internally precipitated by the female and are not the direct result of behavior that involves some other media (e.g., Hirsch, 1994). In most cases, eggs are the product of behavior (i.e., copulation), but some amphibians and reptiles can reproduce asexually if males are not present or the population is stressed (e.g., Policansky, 1982). In addition, an embryo cannot grow or survive outside the egg environment (e.g., Hirsch, 1994). This differs from cocoons spun by insect larvae. Insect larva cocoons are trace fossils because they are selfconstructed by either manipulating secreted fluids or using those fluids to bind other media together (e.g., Gullen and Cranston, 1994).

LOCOMOTION TRACES: TRAILS, TRACKS, AND TRACKWAYS Footprints, trackways, and trails provide nearly unequivocal evidence of the posture and locomotion of an animal. All terrestrial and aquatic vertebrates exhibit one or more kinds of locomotion behaviors that can be preserved as trace fossils, including

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12. THE TRACE-FOSSIL RECORD OF VERTEBRATES

manus

Gnaw marks pes

Feces

Prairie Dog (Cynomys)

Footprints

Burrow entrance

Burrow network (plan view)

1m Burrow (lateral view)

1m FIGURE 12.1 Multiple traces are produced by a single vertebrate. For example, one prairie dog produces many kinds of traces, including burrows, feces, gnaw marks, and footprints.

crawling, walking, trotting, running, and swimming.

loping,

galloping,

Description and Measurement of Terrestrial Locomotion Traces Locomotion traces of limbed tetrapods consist of sequences of impressions of the feet (pes) and hands (manus), and any other parts of the tracemaker that contacted the sediment. Each impression that represents a single footstep is referred to as a footprint, ichnite, or track (Leonardi, 1987). Three or more successive footprints from the same animal define a trackway (Leonardi, 1987; Thulborn, 1990).

Tracksites are areas where multiple trackways are present. The morphology of locomotion traces is a function of foot shape, body and tail motion and control, substrate consistency, and tracemakerlocomotion dynamics and posture (Brand, 1996; Demathieu and Demathieu, 2002). Thus, the footprints of a single tracemaker may not resemble each other exactly or provide accurate depictions of the trackmaker’s feet. These disparities must be taken into account when assigning ichnotaxonomic names (Demathieu and Demathieu, 2002). Well-preserved footprints are described by the number of digits: 5 = pentadactyl, 4 = tetradactyl, 3 = tridactyl, 2 = didactyl, 1 = monodactyl

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A

Architectural Morphology

Reference cylinder diameter Reference cylinder

B

Axis of coiling

Shaft

Tunnel

Ramp angle

Whorl height

Vertical

Scratches

Terminal chamber

Horizontal

Axis of reference cylinder

Whorl width

Ridge Surficial Morphology

FIGURE 12.2 Architectural and surficial morphological features of vertebrate burrows and burrow systems.

(Lockley and Hunt, 1995). Footprints are also described in terms of the nature of contact between foot and sediment: (1) plantigrade tracks preserve the impression of a complete manus or pes, (2) semiplantigrade tracks lack a heel impression, (3) digitigrade tracks contain impressions of the entire digit length, and (4) unguligrade tracks contain impressions only of the tips of the distal phalanges (Leonardi, 1987). Measurements of distances and angles of track features from a standard set of landmarks on each footprint (Fig. 12.3A) are important for identification and comparison to other tracks (Leonardi, 1987). The most common track measurements are track length and width, digit length, and partial and total divarication of digits (Figs. 12.3B,C). Trackways are described by the manner of locomotion. Quadrupedal (4-legged) trackways contain manus and pes impressions, whereas bipedal (2-legged) trackways contain only pes impressions. Vertebrates that produce trackways with both quadrupedal and bipedal locomotion are referred as facultatively quadrupedal or bipedal, depending on the dominance of tracks that comprise the trackway. Common trackway measurements include internal and external trackway width, stride length, pace length, pace angulation, and the angle of divarication from the trackway midline (Fig. 12.4A). Care should be taken to measure actual distances rather than apparent distances resulting from sedimentological features caused by animal–sediment interaction (Lockley et al., 2004).

Many tetrapod trackways contain tail traces, especially trackways of quadrupedal amphibians and reptiles. Because tail traces are surficial features, their presence indicates that the tracks are true tracks preserved on the original surface (Haubold et al., 2005). Tail traces can also be used to interpret tail movement during locomotion; tail movement is important for balance in some tetrapods, especially bipedal dinosaurs (Gillette and Thomas, 1985; Platt, 2005). A system for measuring and classifying tetrapod-tail traces is proposed by Platt (2005) (Fig. 12.4B). The classification system divides tetrapod-tail traces into tail impressions—no evidence of forward movement, protracted tail traces—present for at least one complete stride length, and abbreviated tail traces—present for less than one complete stride length (Platt, 2005).

Interpretation of Terrestrial Locomotion Traces Three methods are used to identify trackmakers: modern analogs, morphological comparisons, and predictive methods (Smith and Farlow, 2003). Modern analogs involve comparison of ancient tracks to similar tracks of extant animals. Morphological comparisons correlate ancient footprint morphology to the skeletal morphology of similarly aged taxa; this is the most common method of trackmaker identification (Smith and Farlow, 2003). Predictive methods are used

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FIGURE 12.3 (A,B) Morphological features and measurements of vertebrate tracks. FL = footprint length, FW = footprint width; dl = digit length; dw = digit width; p/sl = palm/sole length; p/sw = palm/sole width; ppd = length of the phalangeal portion of the digit; fl = free length. (C) Typical landmarks and measures of angles of vertebrate tracks; roman numerals refer to digit numbers. (D) Common measurements, terminology, and sedimentary structures of vertebrate tracks in cross section.

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A

B expulsion rims w pe

)

Glenoacetabular distance Pace length (manus)

Stride length (pes) δ

Trackway midline

Distance between manus and pes

Pace length (pes)

α

Tail-trace midline

w γ

β

d

original ground surface

Tail-trace baseline

ce Pa

us an

(m

Stride length (manus)

e(

c Pa

s)

ε

Intermanus distance Pace width (manus) Interpedes distance Pace width (pes) External trackway width

a p

C

cg mg α axis w’

β

a’

w a

mg λ

FIGURE 12.4 (A) Typical landmarks and measures of distances and angles of vertebrate trackways; = pace angulation of manus; = pace angulation of pes; = divarication of manus from midline; = divarication of pes from midline. (B) Morphological features and measurement of vertebrate-tail traces in cross section and plan view; w = tail-trace width; d = tail-trace depth; l = tail-trace wavelength; a = tail-trace amplitude; e = angle of divarication of tail-trace midline from tail-trace baseline. (C) Measurements and descriptions of fish trails. cg = central groove; mg = marginal grooves; a = amplitude; a’ = amplitude as defined by Trewin (2000); p = phase difference; w = width of groove pairs; w’ = separation of one set of marginal grooves measured perpendicular to direction of travel; = angle created by the intersection of the axis and a line connecting adjacent points of maximum displacement; = angle created by the intersection between the axis and a line representing the main trajectory of the marginal groove; l = wavelength.

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for animals with known body fossils but no known footprints. Body fossils are used to reconstruct foot morphology, from which a hypothetical footprint is produced. Trackmaker identification should not be based solely on the age of the track. For example, Carboniferous tetrapod tracks are attributed often to amphibians; however, reptiles were present at this time as well (Lockley and Hunt, 1995). Most amphibians produce morphologically similar tracks, which commonly have tetradactyl or pentadactyl manus and their pentadactyl pes arranged in quadrupedal trackways. Amphibian tracks are generally plantigrade, yet variations in sediment and behavior can produce tracks that range from plantigrade to digitigrade (e.g., Brand, 1996). Reptile tracks are more diverse than amphibian tracks. In general, manus and pes tracks of basal reptiles are pentadactyl and range from plantigrade to digitigrade in quadrupedal trackways. The footprints of certain reptile groups have diagnostic criteria based on distinct track morphologies. Based on predictive methods, pterosaur tracks are characterized by (1) manus prints lateral to pes prints; (2) pes prints four times longer than wide; and (3) penultimate phalanges are the longest. Many tracks attributed to pterosaurs, however, do not meet all of these criteria (Padian, 2003). The most distinctive dinosaur footprints are the crescent-shaped manus and rounded, digitless to pentadactyl pes prints of sauropods and the tridactyl footprints of theropods and ornithopods. Two types of sauropod trackways are recognized: wide-gauge, which have high pace widths, and narrow-gauge, which have smaller pace widths (Lockley and Hunt, 1995). Theropod tracks are characterized by (1) claw marks, (2) well-defined phalangeal pads, (3) pes prints longer than wide, (4) total divarication 2% of Corg content) in the NW African continental margin, large, lowdiverse biodeformational structures occur. They represent a low degree of behavioural specialization (Wetzel, 1983b).

CHANGES THROUGH GEOLOGICAL TIME AND EVOLUTIONARY ASPECTS It is obvious that environmental conditions can affect evolutionary processes of organisms, including bioturbators and tracemakers. Vice versa, in some cases organisms can influence environments. Trace fossils represent one of the most important records of macroinfaunal changes in Phanerozoic deep-sea environments. Studies on their diversity have been undertaken since the 1970s, but a flood of new data prompts revisions of the older approaches. The basic parameter is the diversity through time; Seilacher (1974, 1977b, 1978) considered this for 16 selected formations. McCann (1990) used 34 formations, but lumped some units together inappropriately, for instance, the Jurassic–Tertiary flysch of the Polish Carpathians, which includes several formations deposited in different basins (Ksia˛z_ kiewicz, 1977). Orr (2001) considered 50 formations within the Ordovician–Carboniferous interval. Uchman (2004a) considered 151 flysch formations for the entire Phanerozoic and revised them with respect to ichnotaxonomy in a consistent way. The considered formations differ not only in thickness, stratigraphic range, facies and exposure, but also in the amount of attention they have received from researchers. This problem is, however, difficult to avoid. Abundance can be measured by the number of formations in which a given trace fossil occurs. There is no consensus on changes of diversity of deep-sea trace fossils through geological time. There is also no uniform method to estimate trends in diversity. Seilacher (1974, 1977b, 1978) considered their number of ichnospecies. McCann (1990) analysed the numbers of both ichnospecies and of ichnogenera. Orr (2001) considered only ichnogenera in Cambrian–Carboniferous formations. Apart from the number of ichnogenera in a particular formation,

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he used the ‘average diversity—calculated by period’ as a parameter. Crimes (1974) documented a sharp increase in the number of ichnogenera in Cretaceous–Tertiary flysch deposits, but suggested that this could be an artefact partly caused by ‘more detailed studies’ on formations of this age. According to Seilacher (1974, 1976), the diversity of deep-sea trace fossils increased through the Phanerozoic with a rapid acceleration in the Cretaceous. Subsequently, Seilacher (1977b) evoked a gradual increase of diversity of ‘flysch ichnocoenoses’ through the Phanerozoic, but later (Seilacher, 1978) proposed a ‘mid-Cretaceous diversity burst’ (see also Frey and Seilacher, 1980). These views were tested by McCann (1990) who concluded that the increase of diversity was neither gradual in most of the Phanerozoic nor rapid in the Cretaceous. According to Orr (2001), the diversity of deep-sea trace fossil assemblages show a distinct increase from the Cambrian to Ordovician, and latter differences are considered as ‘not obvious’. The curve constructed by Uchman (2004a) (Fig. 15.11) is based on formations showing maximal diversity of ichnogenera. The diversity curve displays distinct changes through the Phanerozoic, with peaks in the Ordovician–Early Silurian and Early Carboniferous, a depression in the Permian—older Late Jurassic, a peak in the Tithonian–Aptian, a depression in the Albian, and the maximum peak in the Eocene. The contribution of graphoglyptids rose gradually up to the end of the Mesozoic, with a peak in the Paleocene–Eocene and a depression in Oligocene. The diversity changes were influenced mostly by competition for food, bottom water temperatures, sediment oxygenation, and also, indirectly, by changes of the frequency of flysch deposits (i.e., suitable deep-sea habitats). There is no clear influence of the major biotic crises, such as the Ordovician/Silurian, Frasnian/Famenian, Triassic/Jurassic, and Cretaceous/Tertiary on the diversity of deep-water trace fossils except for the lower rank Eocene/Oligocene crisis. However, the Ordovician/Silurian, Cretaceous/Tertiary and Paleocene/Eocene crises influenced graphoglyptid ichnodiversity and their relative abundance (Uchman, 2003). The decrease of diversity since the Late Carboniferous was probably caused by the Gondwanan glaciations and then reinforced by the Permian/Triassic extinction. The recovery took a long time, and the diversity remains low until the end of Jurassic, although the newest data from Oman (Wetzel et al., in review) shows that in the Tethyan refuges the diversity can be high already in the Late Triassic.

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15. DEEP-SEA ICHNOLOGY: DEVELOPMENT OF MAJOR CONCEPTS

FIGURE 15.11 Diversity curve of deep-sea ichnogenera (the dashed line shows some less documented portions of the curve), curves showing contribution of graphoglyptids in ichnoassemblages, relative abundance of new graphoglyptid ichnospecies, and a chart showing the number of graphoglyptid ichnogenera in the Phanerozoic (upper portions of the columns express ichnogenera reservedly included in graphoglyptids). Based on Uchman (2003, 2004a).

The diversity of graphoglyptid trace fossils, which are the most characteristic component of the deep-sea Nereites ichnofacies (Seilacher, 1967; Frey and Seilacher, 1980), was analysed by Uchman (2003) (Fig. 15.11). Diversity was low from the Cambrian to the Middle Jurassic, with a low peak in the Ordovician followed by a drop in the Silurian. In the Late Jurassic, after the late Palaeozoic low, the graphoglyptid diversity started to increase gradually and markedly in the Late Cretaceous, probably during the Turonian. It dropped again in the Paleocene, and subsequently increased to a maximum in the Eocene. The Oligocene was marked by a sharp decrease in graphoglyptid diversity and frequency, followed by an increase in the Miocene (Uchman, 2003). The Late Cretaceous radiation of graphoglyptids may be correlated with global changes in plankton and organic matter circulation. The ichnologic radiation was probably delayed in the Lower Cretaceous by the widespread anoxia at that time. The Eocene (total number of ichnotaxa) or Paleocene (total number of ichnotaxa/Ma) peak of the diversity of graphoglyptids and the Eocene peak of frequency of graphoglyptids are related to the common occurrence of oceanic oligotrophy in the Late Paleocene and Early Eocene (Uchman, 2003). Graphoglyptids display an increase of complexity with time (Seilacher, 1977a),

showing a distinct acceleration in the Late Cretaceous, when the farming activity of their tracemakers became a common feeding strategy. Morphometric analyses of Paleodictyon display trends in size and shape throughout the Phanerozoic, and these changes are related to phyllogenitic changes of their tracemakers (Uchman, 2003). Furthermore, individual ichnotaxa display interesting changes through time. In general, Zoophycos migrated to the deep-sea in Jurassic (Bottjer et al., 1988, Olivero, 2003), however, with some exceptions like the case from Miocene shelf sediments (Pervesler and Uchman, 2004). Ophiomorpha rudis (Ksia˛z_ kiewicz, 1977) and O. annulata (Ksia˛z_ kiewicz, 1977) occur in the flysch sediments since the Tithonian and document invasion of large crustaceans to the deep-sea (Tchoumatchenco and Uchman, 2001). Some of the ichnospecies, such as those of the Palaeozoic Dictyodora (Benton, 1982b) have relatively narrow stratigraphic ranges and can be used in stratigraphy (Uchman, 2004a) (Fig. 15.12). As shown by their relationship with tuffite layers, beds that contain characteristic trace fossils occupy the same stratigraphic position and can be used for delineation of ichnostratigraphic units within a basin (Pien´kowski and Westwalewicz-Mogilska, 1986).

DEEP-SEA FINE-GRAINED NON-TURBIDITIC SEDIMENTS

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The Nereites ichnofacies has time constraints. It can be distinguished from the Ordovician, when graphoglyptids colonized the deep-sea (Orr, 2001). A specific trace fossil association related to shallow burrowers, epifaunal traces and surface structures associated with microbial mats occurs in the Vendian–Cambrian (Buatois and Mańgano, 2003). The Ophiomorpha rudis ichnosubfacies can be distinguished since the Tithonian, when its index taxon first occurred in flysch deposits (Tchoumatchenco and Uchman, 2001).

DEEP-SEA FINE-GRAINED NON-TURBIDITIC SEDIMENTS

FIGURE 15.12 Stratigraphic ranges of Dictyodora ichnospecies based on Uchman (2003). In the lower part, Dictyodora liebeana Geinitz in horizontal section, turbiditic mudstone, 192P1 (housed in the Jagiellonian University), Kulm facies, Olsˇovec quarry, Moravia, Czech Republic.

Different deep-sea fine-grained non-turbiditic sediments occupy large areas of recent deep seafloors (Davies and Gorsline, 1976). The ichnology of their fossil equivalents was little known for a long time. Relatively much information derives from the deepsea Upper Cretaceous chalk, where the sediment is totally bioturbated and its ichnoassemblage is dominated by Zoophycos (Ekdale and Bromley, 1983, 1984). Other information comes from various calcareous and non-calcareous mostly Cretaceous to Neogene sediments (Ekdale, 1977, 1978, 1980b, 1985b; Okada, 1980; Gaillard, 1984; Wetzel, 1987; Savrda and Bottjer, 1994; Monaco and Uchman, 1999; Miller, 2000). Such sediments commonly contain Chondrites, Planolites, Teichichnus, Phycosiphon and Zoophycos. Similar ichnofabric occurs in radiolarites (Kakuwa, 2004). Trace fossils in sediments deposited below the CCD are less diverse and less well preserved than those above the CCD (Ekdale et al., 1984a, pp. 248–253). Tiering patterns in such sediments are determined on the basis of cross-cutting relationships between trace fossils, where those from deeper tiers cross-cut those from shallower tiers and mutual cross-cutting implies co-existence in a tier (Bromley and Ekdale, 1986; Bromley, 1990, 1996; Ekdale and Bromley, 1991). Horizontal lamination in such sediments is usually related to anoxic conditions, and the successive occurrence of Chondrites, Planolites, Thalassinoides and Zoophycos, and additionally increase in their individual size is interpreted as improvement of oxygenation (Bromley and Ekdale, 1984; Savrda and Bottjer, 1986, 1994). In some formations, the changes of oxygenation can be attributed to Milankovitch cyclicity (Erba and Premoli Silva, 1994; Savrda, 1998).

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NEOICHNOLOGY Neoichnological researches in the deep-sea were left behind in comparison to other environments mostly because of logistic and financial constraints and the relatively small number of researchers interested in this aspect. One of the simplest techniques is the photography of the deep seafloor. In the 1940s and early 1950s, the photographs showed benthic life activity, such as trails, holes and mounds, in great abundance (e.g., Emery, 1953). In the following years, there was a great effort to identify traces and their tracemakers, encountered and photographed on the seafloor surface (Laughton, 1961, 1963; Owen and Emery, 1967). Heezen and Hollister (1971) illustrated the diversified surface traces to be found in different parts of the oceans. Further publications revealed more details (e.g., Hollister et al., 1975; Ekdale and Berger, 1978; Kitchell et al., 1978a,b; Young et al., 1985) and the researches were summarized by Gage and Tyler (1991, pp. 337–360). Kitchell and Clark (1979) distinguished seven biofacies in the deep-sea Arctic on the basis of surface traces showing that each physiographic province displays a characteristic biofacies, but with patchy distribution of traces. Some of the traces have been studied in detail, like the echiuran burrows (Ohta, 1984; Vaugelas, 1989; Bett and Rice, 1993; Bett et al., 1995). Discovery of graphoglyptid traces referred to Paleodictyon, Urohelminthoida, Spirorhaphe and Cosmorhaphe on the surface of deep-sea pelagic sediments (e.g., Rona and Merill, 1978; Ekdale and Berger, 1978; Ekdale, 1980a; Gaillard, 1991) finally proved their deep-sea origin. New technologies of illumination, photographing, and presentation, including the IMAX cinema appeared (see Reed, 2002 for review). Surficial traces, however, have little chance to be preserved because of subsequent bioturbation and erosion (Wheatcroft et al., 1989; Gage and Tyler, 1991). Most of the trace fossils are produced within sediment, and observations of recent subsurface tracemaker activity remains difficult. Subsurface observations of subfossil burrows were made in box cores in submarine canyons off southern California (Bouma, 1965) and in the Mediterranean region (Hesse et al., 1971). Further research on box cores (Ekdale and Berger, 1978; Wetzel, 1981, 1983a,b, 1984) produced new data, also by means of X-ray radiography. From this research grew the concept of mixed, transitional and historical layers (Berger et al., 1979; Ekdale et al., 1984a,b) discussed in the former sections. The traces

observed in the box cores can be several, even thousands of years old, and therefore their neoichnological aspect is limited. In rare cases, traces can be well dated, such as the Nereites in the South China Sea that were formed after the 1991 ash eruption of Mt. Pinatubo as judged from their relation to the ash layer (Wetzel, 2002). Neoichnological experimentation with deep-sea animals is difficult, mostly because of special requirements necessary to maintain their life activity. However, results from experiments using shallowwater fauna produce very good results and in some cases they can be transferred to the deep-sea trace fossils, for instance those showing that Scolicia and Bichordites are produced by irregular echinoids (Bromley and Asgaard, 1975; Kanazawa, 1995; Bromley et al., 1997) and that Protovirgularia is produced by bivalves (Seilacher and Seilacher, 1994). The effect of biological mixing of sediment was noticed since the beginning of exploration of the deepsea, but more detailed researches were undertaken in the 1960s. Goldberg and Koide (1962) studied the influence of biological mixing on the distribution of radionuclides. Laughton (1963) proposed quantitative estimation of sediment disturbance by burrowing benthos. Eventually, more accurate estimations were obtained about the rate of sediment mixing, effects of bioturbation on sediment geochemistry and diagenesis, and sediment stability (for review see Wheatcroft et al., 1989; Gage and Tyler, 1991, pp. 353–360). Other lines of research have approached the determination of the distribution of traces and tracemakers. For instance, Kitchell et al. (1978a,b) investigated deep-sea surface traces in Arctic and Antarctica and concluded that there is no relationship between shape of traces (from random to meandering and spiral), food content and bathymetry. Alternatively, predation and competition can influence the shape (Kitchell, 1979). These results are in opposition to some achievements of palaeoichnology, for instance to the ichnofacies model (see Gage and Tyler, 1991, pp. 347–351, for discussion). Wetzel (1981) presented changes in the distribution of subfossil traces offshore of NW Africa, and later from slope to continental rise turbiditic and pelagic sediments in the Sulu Sea Basin (Wetzel, 1983a).

FURTHER PERSPECTIVES It seems that the greatest barrier in the further development of deep-sea palaeoichnology lies in the

ACKNOWLEDGEMENTS

recent state of deep-sea neoichnology. There is still a hidden world of animals burrowing under the seafloor surface, which is accessible to a very limited degree. Complex neoichnological research should be undertaken in different deep-sea environments in order to recognize and identify at least some tracemakers, their burrowing and overall behaviour and distribution. Probably, laboratory experiments using different deep-sea invertebrates will bring rapid advances in this matter and tracemakers will become less enigmatic. Special expeditions using submersible vehicles should be undertaken. Proper employment of robots for resin casting, for example, would be a significant forward step in furthering ichnological recognition in the deep sea. Quantitative data should promote understanding of the precise distribution of tracemakers and their traces. Other achievements are expected in the recognition of trace fossils, especially from periods that are poorly represented in the available data. This especially concerns turbiditic and other deep-sea sediments of the Cambrian, Devonian and the Upper Carboniferous–Jurassic, which have been studied only in a few places (Uchman, 2004a). A consistent and precise ichnotaxonomy is necessary for this purpose.

ACKNOWLEDGEMENTS Research by the author benefited from the Alexander von Humboldt Foundation, Jagiellonian University (DS funds), Komitet Badan´ Naukowych (Poland), Swiss National Science Foundation and CEEPUS grants. A visit to the Paris Museum National d’Histoire Naturelle was sponsored by the ColParSyst Program (2004). R.G. Bromley corrected a preliminary version of the manuscript. C. Gaillarad and an anonymous reviewer provided critical remarks.

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16 Continental Ichnology: Fundamental Processes and Controls on Trace Fossil Distribution Stephen T. Hasiotis

INTRODUCTION

SUMMARY : Continental biota are related to sediment through feeding, dwelling, locomotion, reproduction, and searching behavior evident as tracks, trails, burrows, nests of animals, and rooting patterns of plants. Such vestiges are preserved in the geologic record as trace fossils. The lateral and vertical distribution of modern trace-making organisms within an environment is controlled by sediment characteristics, soil moisture, water-table levels, ecological associations, and more. Trace fossils in the geologic record can be used to interpret the palaeoenvironmental, palaeoecologic, palaeohydrologic, and palaeoclimatic settings because a well-defined relationship exists between climate, hydrology, soils, environment, and all biodiversity. Trace fossils also relate information about soil formation and development, the type of biologic activity, topography of the landscape and its relationship to groundwater profile, and duration of time that a body of sediment has been stable at the surface with respect to sedimentation rate. Thus, trace fossils in the continental realm are proxies for: (1) biodiversity in terrestrial and aquatic palaeoenvironments not recorded by body fossils; (2) above- and below-ground palaeoecological associations; (3) palaeosol formation; (4) palaeohydrology and palaeo-groundwater profiles; and (5) seasonal and annual palaeoclimate indicators and climate change.

The purpose of this chapter is to bring attention to the fundamental controls and processes that are unique to continental ichnology. These are necessary to understand if trace fossils are to be used effectively to interpret the palaeoenvironmental, palaeohydrologic, palaeoecologic, and palaeoclimatic settings of continental deposits. Herein are discussed new directions in continental ichnology that focus on understanding the distribution of ancient terrestrial and aquatic trace-making organisms in continental deposits. The term continental is emphasized here to replace non-marine because continental refers to the processes that control the deposition and modification of sediments and other media, and to the distribution of life on land and its waters (Hasiotis and Bown, 1992). The term non-marine is inappropriate since it is not an objective term to express the biological and physicochemical factors that control organism behavior on the continent. Terms like terrestrial and freshwater are too restricted in meaning to be used as inclusive descriptors of the continent, its organisms, behaviors, and its trace fossils. Terrestrial is inadequate because it refers to land above water, or on Earth. Freshwater is insufficient because it only denotes aquatic life in water with a salinity of


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THE CONTINENTAL REALM

0–5 ppt (e.g., Ward, 1992), including rivers and lakes, but excludes hypersaline and saline–alkaline waters that are found commonly on the continent; it also ignores life on land. These terms, however, do have an appropriate place in continental ichnology as descriptors of environments that are predominantly above the water table (i.e., terrestrial) and environments where the water table is above the land surface most of the time (i.e., aquatic). The best approach to determine what factors and processes likely control the diversity, abundance, and distribution of continental trace fossils is to study the relationship of modern trace-making terrestrial and aquatic biota with the habitats and environments in which they live (e.g., Chamberlain, 1975; Voorhies, 1975; Hasiotis and Bown, 1992; Hasiotis, 2002). Continental environments contain a great diversity of above- and below-ground trace-making organisms (e.g., Wallwork, 1970; Whittaker, 1975; Wilson, 1992). These organisms are directly and indirectly related to sediment, soils, and other media through feeding, dwelling, locomotion, reproduction, escaping, and searching behavior evident as tracks, trails, burrows, nests, and borings of animals and root patterns of plants in terrestrial and aquatic environments. Borings differ from burrows in that an organism has to mechanically cut into or remove the matrix of lithified sedimentary or crystalline rocks to produce a trace (e.g., Ekdale et al., 1984). These organism behaviors and media (i.e., sediment, soil, wood, bone, and lithified and crystalline rocks) interactions are controlled by biological and physicochemical factors and processes characteristic of and unique to continental environments (Hasiotis and Bown, 1992; Hasiotis, 2000). Only after the relationship between organism behaviors, burrow morphology, media characteristics, biological and physicochemical factors, and environmental processes are identified and understood, can trace fossils be used more accurately to interpret continental deposits (Hasiotis, 2002, 2004). Although studies of continental trace fossils have increased markedly during the last few decades, most approaches are still founded on concepts and principles developed for marine organism behavior and ichnology, including the use of ichnofacies (e.g., Buatois et al., 1998; Genise et al., 2000; Miller et al., 2002; Buatois and Mańgano, 2004; Genise et al., 2004). As an artifact of this approach, continental trace-fossil studies have yielded interpretations and associations between ichnofossils and behavior, paleosols, and organism evolution that do not accurately reflect processes that operated in continental systems or that controlled organism behavior and its distribution.

269

The solution to this problem is to link trace-making behavior and organism-media interactions (i.e., neoichnology) in modern continental environments to associations and patterns between ichnofossils and sedimentary fabrics (i.e., palaeoichnology). Such linkages should provide more accurate interpretations of the processes and factors that influenced organism behavior and its distribution in deep geologic time (e.g., Chamberlain, 1975; Hole, 1981; Smith, 1986; Hasiotis and Mitchell, 1993; Villani et al., 1999; Vittum et al., 1999; Brake et al., 2002; Hasiotis, 2002, 2003, 2004; Hembree and Hasiotis, 2006; Kraus and Hasiotis, 2006). A similar strategy was used by German scientists at Senckenberg Institute in Wilhelmshaven during several decades of study of North Sea tidalflats to link the significance of biogenic structures and modern sediments to the preservation of trace fossils in ancient strata (e.g., Richter, 1920; Ha¨ntzschel, 1935, 1975; Reineck, 1955, 1958; Hertweck and Reineck, 1966; Schafer, 1972).

THE CONTINENTAL REALM In order to understand and interpret better the behavior and significance of continental ichnofossils, sedimentary environments and their biological and physicochemical attributes should be properly characterized in an integrated context. Ancient sedimentary environments are understood best by evaluating modern continental depositional settings and the factors and processes that control the distribution of trace-making organisms. The depositional settings of the continental realm represent a mosaic of landscapes with high spatial and temporal heterogeneity of water, soil development, and environmental stability (e.g., Wallwork, 1970; Whittaker, 1975; Aber and Melillo, 1991). Continental landscapes produced by heterogeneity contain a hierarchy of organisms as populations, communities, ecosystems, and biomes, all of which are influenced strongly by environment, topography, ecology, hydrology, and climate (Whittaker, 1975; Aber and Melillo, 1991; Jones and Lawton, 1995). The vertical and lateral distributions of trace-making biota within a sedimentary environment are also influenced in the same manner.

Spatial Variability of Water: Terrestrial, Aquatic, and Periaquatic Settings The continental realm (Fig. 16.1) is dominated by alluvial (fluvial and overbank), lacustrine, palustrine,

270

16. CONTINENTAL ICHNOLOGY: FUNDAMENTAL PROCESSES AND CONTROLS ON TRACE FOSSIL DISTRIBUTION

CONTINENTAL REALM: BIOPHYSICOCHEMICAL FACTORS ALLUVIAL

LACUSTRINE

PALUSTRINE

EOLIAN

VOLCANICLASITC

SUBDIVISIONS BASED ON: WATER TABLE & MOISTURE AVAILABILITY SPATIAL COMPONENTS: TERRESTRIAL

PERIAQUATIC WELL-DRAINED

AQUATIC: LOTIC (running water) IMPERFECTLY DRAINED

AQUATIC: LENTIC (standing water) POORLY DRAINED

TEMPORAL COMPONENTS: PEDOGENESIS

PERENNIAL AQUATIC (constant)

INTERMITTENT AQUATIC (frequent)

EPHEMERAL (rarely)

BIOLOGICAL COMPONENTS: EPITERRAPHILIC

TERRAPHILIC

HYGROPHILIC

HYDROPHILIC

FIGURE 16.1 Continental realm: biophysicochemical factors. Diagram depicts the spatial and temporal variability of continental environments and the organisms that inhabit it (see also Figs. 16.2 and 16.3).

eolian, glacial, and volcanoclastic deposition. The subenvironments within continental depositional systems have varying amounts of water for varying amounts of time, manifested physically and chemically in different ways. Although sediments accumulate or are removed by water-lain (liquid and solid), wind-blown, or air-fall (volcanoclastic) processes, they inevitably spend variable amounts of time beneath the water table. The water table is the boundary between the vadose (unsaturated) and phreatic (saturated) zones of the groundwater profile (Fig. 16.2). The vadose zone is where the pore space in sediment contains air and water. This zone can be subdivided into the soil water, and the upper and intermediate vadose zone. The phreatic zone is where pore space is saturated, and also includes the capillary fringe (Driscoll, 1986). A standing body of water occurs where the phreatic zone intersects the ground surface. This water will flow if there is a gradient on the landscape. A perched water table occurs in areas that are imperfectly or poorly drained, as well as in areas associated with flowing water, like stream or river (Driscoll, 1986). Terrestrial subenvironments are well, imperfectly, or poorly drained depending on sediment texture

and the amount of water input and output (Fig. 16.1). Water input and output are controlled ultimately by climate. Soil, biota, and climate are linked through the soil–water balance in terrestrial environments (Thornthwaite and Mather, 1955). There are several components of the soil–water balance (see also Hasiotis, this volume). Evapotranspiration (E) is defined as actual evapotranspiration (Ea)—the actual rate at which water vapor is returned to the atmosphere from the ground and by plants and potential evapotranspiration (Ep)—the water vapor flux under ideal conditions of complete ground cover by plants, uniform plant height and leaf coverage, and an adequate water supply. Effective precipitation (EP) is the temporal distribution of precipitation, moisture losses from evapotranspiration, and temperature (Lydolph, 1985). EP is a proxy for the relationship between precipitation and temperature for a particular region and takes into account also the seasonality of precipitation. Water availability in terrestrial environments affects the depositional setting, soil formation, nutrient cycling, and overall biodiversity (Jenny, 1941; Thornthwaite and Mather, 1955; Whittaker, 1975; Strahler and Strahler, 1989).


Hb

Fp

Rh

Vb

Vb


AMB

St - Steinichnus

Ck - Cochlichnus

Tm - Termite nest

F - Fuersichnus

T/Rh - Termite nest in rhizolith Un - Undichnia


Fp - Footprints

Ut - U-tube

G - Gastropod trail

Vb - Vertical burow

Hb - Horizontal burrow

Vtb - Vertebrate burrow

Hu - Horizontal U-tubes

Wp - Wasp nest/cocoon

Proximal (shallow) Aquatic

Transitional Environments Shallow Water Table Settings

Fp

An

P

P

St

F

Hu Rh P

Hb

T/Rh

Ca

Vb

Ck

Ca Ca

Ce

Ca

AMB T/Rh

Uts

Rh

Ce

G

Rh

Hb

Hb

Ut

P Uts

Ca Vb

Ce Vb

Ut Un

Ca

T/Rh

Ce

Fp

Rh

Vb

P

Distal (deep) Aquatic

G

Tm Rh

Hb

Decrease nutrient availability

Rh - Rhizocorallium

Cp - Coprinosphaera

Rh AMB

Decrease Biotic Exchange

P - Planolites

At - Ant nest

Ce - Celliforma Increase Groundwater Height

Rh Vb

Rh

Decrease Biodiversity

Km - Kouphichnium

AMB - Adhesive meniscate burrow

Ca - Camborygma

Increase Soil moisture

Vb Rh

AMB

Increase organic matter

KEY An - Ancorichnus

P Rh

Cp

Vadose water

Decrease O2--Increase CO2

Decrease Organic matter

F

Ca

Rh

Vtb

Hygrophilic

Decrease in trace fossil depth and tiering

Proximal Floodplain Cp

Point where the groundwater table intersects the landsurface = paludal to lacustrine conditions

substratum surface


Distal Floodplain


Interstitial Phreatic water Zone

Increase O2 concentration

Capillary water

Water Table

Capillary water

Vadose well-drained

Increase soil compaction

Hygrophilic

Increase relative humidty

intermediate to the lower part


Vadose upper part water

Increase Soil moisture

Terraphilic

Rivers and Lakes

Terraphilic

Decrease O2--Increase CO2

Soil water

Vadose Zone

Floodplain and Supralittoral environments

soil surface


Epi-Terraphilic

Footprints, trackways, surface nests

Ut Rh

At

Cp

At

P

Vb Wp At

Tm AMB

Vb

Un

Km

Rh

At

AMB

P

Vb T/Rh

Ca

271

FIGURE 16.2 Groundwater profile and organism behavior. The groundwater profile is composed of the vadose and phreatic zones, which vary spatially and temporally across a depositional system. The distribution of biota is controlled, in part, by the groundwater profile as well as the characteristics of the substratum and the environmental settings (see Figs. 16.1 and 16.3). The categories of organism behavior and biophysicochemical factors are superimposed on the groundwater profile. Block diagrams below depict examples of trace fossils and organisms that occupy the landscape at a particular space and time.

272


Sediments that are found the vast majority of time above the water table are referred to as terrestrial environments and include alluvial floodplain and playa, dune and dry interdune, epilittoral and supralittoral, and volcanoclastic subenvironments (Hasiotis and Bown, 1992; Hasiotis, 2002). Sediments that are found the vast majority of time below the water-table level that intersects the land surface are referred to as aquatic environments and include streams, rivers, and overbank lakes and ponds, and littoral to profundal subenvironments (e.g., Hasiotis and Bown, 1992; Hasiotis, 2002). Surface sediments found the vast majority of time near to (above or below) or at the water-table level are referred to as periaquatic environments (Ginsberg, R. personal communication, 2004). These include palustrine (swamp) and transitional or shoreline subenvironments (Hasiotis and Bown, 1992; Hasiotis, 2002). Thus, aquatic, periaquatic, and terrestrial subenvironments can be further subdivided and defined by the spatial and temporal variability of the groundwater profile (Fig. 16.2). Continental environments contain a mosaic of juxtaposed aquatic, periaquatic, and terrestrial subenvironments. Transitions between these subenvironments are gradational or abrupt, and all may be present within a small area. For example, a mosaic of terrestrial, periaquatic, and aquatic subenvironments exist together in a 50 m2 area in the Robinson Tract of the University of Kansas Field Station and Ecological Reserve, each with microbes, plants, animals, and soils that would leave a unique suite of evidence indicating the amount of water present for that particular climate setting.

Temporal Variability of Water and Environmental Stability Terrestrial, periaquatic, and aquatic subenvironments vary greatly in aerial extent over very short periods of time (see Figs. 16.1–16.3). For example, aquatic subenvironments are perennial, intermittent, or ephemeral in nature. Periaquatic subenvironments are variably moist to wet, but can become aquatic or terrestrial over short periods of time for variable lengths of time. When subaerially exposed, periaquatic settings can undergo soil formation (see Fig. 16.4). Temporal variability of water in a system is due to the amount contributed by direct precipitation, overland flow from runoff, or groundwater input (e.g., Driscoll, 1986; Ward, 1992; Hasiotis, 2004), and ultimately controlled by climate (Thornthwaite and

Mather, 1955). The amount of water input into a depositional system will influence direct sediment accumulation rates and local groundwater profile, and hence, the environmental stability of the landscape (Hasiotis, 2000, 2002). For example, the frequency and magnitude of flooding events in alluvial depositional systems determines the rate at which sediment accumulate. These events are controlled by local and regional weather patterns with precipitation inputs that may cause local or downstream flooding if precipitation occurs in an area over an extended period of time. Flooding raises the groundwater level depending on the input of direct precipitation and runoff, as well as the degree of saturation of the soil prior to the event. Subenvironments prone to frequent flooding have lower environmental stability and higher levels of disturbance compared to subenvironments distal to flood-prone areas (Odum, 1971). This variability in moisture in an environment can be seasonal, annual, decadal, and centurial in scale. Such variability can produce short- to long-term bodies of water in terrestrial settings, and raise and lower lake levels through time at similar scales (Fig. 16.3B).

Continental Environments and their Media Alluvial, lacustrine, and eolian environments (Fig. 16.3) can be subdivided based on major sedimentological processes and physical characteristics that produce such distinct subenvironments as channels, floodplains, shorelines, splays, dunes, and interdunes (Reineck and Singh, 1980). Volcanoclastic environments deliver sediment primarily by air-fall deposition, which are then modified by wind or water. Palustrine environments can occur in any of the depositional environments, defined by the position and fluctuation of the water table. All subenvironments can be further subdivided according to their (1) depositional energy; (2) magnitude and frequency of flooding experienced; (3) topographic relief; (4) groundwater profile and drainage conditions; (5) sediment texture; (6) type and degree of pedogenic modification; (7) environmental stability vs. disturbance; (8) oxic vs. disoxic vs. anoxic conditions; (9) salinity; (10) temperature; and (11) ionic strength in the water. Finer scale divisions based on these characteristics represent the spatial and temporal heterogeneity in continental environments that are necessary to put into perspective when evaluating trace-fossil suites or associations.

273


A. ALLUVIAL ENVIRONMENTS

Oxbow lakes/ponds

Distal Floodplain

Terrestrial

Crevasse-splay/avulsion

Aquatic

Levees

Channels

Proximal floodplain

Chutes

Distal floodplain

Oxbow lakes

Crevasse-splays after water recedes

Ponds associated with splays and seasonal floods

Channel

A

Levee/Bank

Proximal Floodplain

A' Vegetation and soil Wet Season water table level Dry Season water table level

A'

A

Sedimentation rate decreases Soil Maturity increases Disturbance decreases Biodiversity increases Soil moisture variability increases Ecological Tiering increases

B. LACUSTRINE ENVIRONMENTS Terrestrial

Alluvial-Supralittoral Lacustrine Deep Water Table Settings Supralittoral Lacustrine Dune fields

Aquatic

Levees Proximal floodplain Distal floodplain Crevasse-splays after water recedes

Channels Chutes Oxbow lakes Ponds associated with splays and seasonal floods

Supralittoral Dunes Dry Interdunes

Littoral Pelagic Profundal

Alluvial-Supralittoral Lacustrine High Water Table Settings

Proximal Lacustrine

A'

Vegetation and soil Wet Season water table level Dry Season water table level

Distal Lacustrine

Supralittoral

Epilittoral

Channel

A

Littoral

Sublittoral

A

A'

Soil Maturity decreases Disturbance increases Biodiversity decreases Environmental Stability decreases Grain size decreases Depositional energy increases

Soil Maturity increases Biodiversity increases Disturbance increases

C. EOLIAN ENVIRONMENTS Terrestrial

Extradune with encroaching erg over pedogenically modified sand sheet, dunes, or alluvial environments

Aquatic

Wet Interdune

A

Wet Interdunes Channels Chutes Oxbow lakes Dry Interdunes Ponds associated with splays and seasonal floods Vegetation and soil Extaduneal areas Springs, lakes associated with above the water wetter periods or regional Wet Season water table level table ground water discharge Dry Season water table level Dunes Stoss Lee

Dune

Environmental Stability decreases Ecological Tiering increases Depositional energy increases

Dry Interdune

A' Dune

Wet interdune

A

Dry interdune

Dune

A'

Depositional energy Soil moisture variability Water table depth Soil Maturity Environmental Stability Disturbance Biodiversity Ecological Tiering

increases increases increases decreases decreases decreases decreases

decreases decreases decreases increases increases high increases increases

increases increases increases decreases decreases low decreases decreases

decreases decreases decreases increases increases high lower increases increases

increases increases increases decreases decreases high decreases decreases

Dune

decreases decreases decreases increases increases low increases increases

FIGURE 16.3 Abiotic controls on the lateral and vertical distribution of biota in (A) Alluvial, (B) Lacustrine, and (C) Eolian environments. Volcanoclastic depositional environments deliver sediment primarily by air-fall deposition, which are then modified by one of the three depositional systems above. Palustrine environments can occur in any of the four depositional environments above.

274


TIME CLIMATE Forming voids Back-filling Forming and destroying peds Regulating soil moisture

Mounding Producing special constituents

Soil Body

Regulating movement of water and air in soil

Regulating biota

TE NTMA RIAL RE PA

RAPHY POG TO

Mixing (faunal pedoturbation)

Regulating plant litter Regulating animal cycling Regulating animal litter BIOTA

Constant

Variable

Products

FIGURE 16.4 Soil-forming factors (modified from Hole, 1981; Hasiotis, 2000). Diagram depicts the relationship of the five soil-forming factors, of which time is constant and topography, climate, biodiversity, and parent material are variable. The resultant fabric is a soil body that is constantly modified by the factors, of which biota play a major role by actively modifying the soil body.

The greatest ichnodiversity is in alluvial environments (Fig. 16.3A) and is predicted to be in distal and proximal floodplains. Channel and pond environments will have the least ichnodiversity because water and depositional-energy levels are most variable. They also have a lower diversity of organisms compared to terrestrial settings. Such deposits as though produced by crevasse-splay and avulsion processes are laid down on normally terrestrial, proximal, and distal floodplains. These extra-channel deposits will contain aquatic trace-fossil associations contemporaneous with flooded environments. These aquatic associations will be overprinted by terrestrial trace-fossil associations when the groundwater and hydrologic profiles return to normal conditions after flooding. The combined trace-fossil associations may show a higher diversity, but it is inappropriate to treat these trace fossils as one association because they were generated under several different conditions. The extra-channel deposits become part of the floodplain and, depending on the rate of accumulation, may preserve characteristics of the event or be obliterated by pedogenesis. Overall, terrestrial alluvial settings will have a greater diversity and abundance of trace fossils because they are the most stable portion of continental environments.

The greatest ichnodiversity in lacustrine environments (Fig. 16.3B) is predicted to be in epilittoral to supralittoral environments. Littoral environments will have the least ichnodiversity since they are most variable due to fluctuations in water levels and depositional energy levels. These environments also include palustrine subenvironments that record both aquatic and terrestrial behaviors. They also have a lower diversity of organisms compared to terrestrial settings. Sublittoral and profundal environments predictably have a comparably lower ichnodiversity because of a lower diversity of organisms that inhabit benthic-aquatic settings, as well as having bottom conditions not normally conducive to a wide range of epifauna or infauna habitation. Overall, terrestrial settings of lacustrine environments have greater ichnodiversities and abundances of trace fossils because they offer more stable environmental conditions. Exceptions to this are shoreline areas where dune fields may accumulate due to high winds that constantly shift landward and lakeward. Overall, aquatic settings in the continental realm are depauperate compared to terrestrial settings. Innovations in deep-water bioturbation patterns similar to those in permanent marine abyssal plain settings (e.g., Paleodictyon and other complex graphoglypid traces) were lost when lakes eventually filled with sediment or went dry through time because of changes in


climate or drainage patterns (e.g., Hasiotis, 2002, 2004). Such innovations never fully developed because they could not be used or maintained in channel or palustrine settings to which these organisms would have to re-adapt and compete for ecospace. The greatest ichnodiversity in eolian environments (Fig. 16.3C) is predicted to be in wet interdune environments. The dune environment is constantly shifting and harsh, and will not contain or preserve much bioturbation. Preservation potential of traces fossils is the most important factor because in dune environments the wind is constantly reworking these deposits and any tracks, trails, or burrows might be produced in the sediments. Dry interdune environments may be more stable than the dune; however, the lack of water prevents most organisms from living there. Ichnodiversity will be higher in environments juxtaposed to eolian environments that eventually become overrun by these erg-scale systems. These mixed eolian–fluvial environments contain ichnodiversities and abundances that record both large-scale processes. Exceptions to these patterns in eolian environments occur when they experience additional moisture than normal or record a major climate change that alters the whole system.

Soils and Paleosols: Products of Spatial and Temporal Variability on the Landscape Nearly all of the continental realm is modified by soils, which are referred to as paleosols when preserved in the geologic record (Retallack, 2001). Soil formation (Jenny, 1941; Brady and Weil, 2002) is influenced by the parent material, biota, topography, climate, and time (Fig. 16.4). Soils are not primary deposits but are the result of postdepositional modifications of the bedrock or sediments in alluvial, palustrine, lacustrine, eolian, glacial, and volcanoclastic environments. Soils are the result of spatial and temporal variability in depositional processes in sedimentary environments (e.g., Bown and Kraus, 1987). Soils develop at different rates with different results based on the magnitude and frequency of depositional events, distance from sediment source, parent material, position and fluctuation of groundwater profile, and inherent local topography. Soil development is strongly effected by the composition of biotic communities, climatic setting with regard to temperature and precipitation, and time in terms of sediment accumulation rate and how long

275

sediment is exposed to the other soil-forming factors (Hasiotis, 2004). The effect of biota can be observed in soilprofile development and used to measure the role of an organism’s activity in soil-forming processes (Fig. 16.4). Microbes, plants, and animals initiate and promote soil development in freshly deposited sediments, as well as in existing soils, by mounding, mixing, forming voids, backfilling voids, forming and destroying peds; by regulating soil erosion, regulating water, air movement, plant litter, animal litter, nutrient cycling, and biota; and by producing special constituents (Thorpe, 1949; Hole, 1981). The spatial and temporal variability in the groundwater profile (see Figs. 16.2 and 16.3) will have a major influence on soil development, including organism activity. Soil development is arrested in aquatic settings or is retarded in periaquatic settings (Jenny, 1941; Brady and Weil, 2002). The diversity of soilforming biota markedly decreases in these types of settings because the greatest diversity of organisms lives in terrestrial settings (Wallwork, 1970; Wilson, 1992). The type, depth, and degree of bioturbation will also change because aquatic organisms become more dominant. The type of soil formed will encompass the (1) type of climate; (2) amount of time parent material is exposed to the soil-forming factors; (3) frequency and magnitude of depositional events; (4) mineralology, texture, and depth of the parent material; and (5) type and diversity of biota present. Soils are weakly, moderately, or strongly developed, and can be simple, compound, or cumulative in nature. Soils are classified in soil orders, in increasing maturity, as Entisols, Inceptisols, Andisols, Gelisols, Histosols, Vertisols, Aridisols, Mollisols, Spodosols, Alfisols, Ultisols, or Oxisols, based on the extent of interactions of the five soil-forming factors (Brady and Weil, 2002).

Other Types of Media in the Continental Realm Other types of media contain traces of organisms besides the sediments found in continental depositional environments. The tissues of plants, including leaves, stems (bark and cambium), and roots, also serve as sites for other organisms to bore into for food, shelter, reproduction, or a combination of behaviors (Ekdale et al., 1984; Hasiotis, 2002, 2004). Organisms with these behaviors can be considered inhabitants of xylic (plant or wood) grounds.

276


Stromatolites and biolaminates are media that can have other organisms living on their surfaces or be bored (Ekdale et al., 1984; Hasiotis, 2002, 2004). Some organisms, termed endobionts even have the ability to prevent the microbial community from growing over the top of them, producing a cylindrical pit where the endosymbionts lives. Such lithified media as sandstone, mudrock, and limestone can also be bored by organisms living in terrestrial and aquatic environments (e.g., Mikula´sˇ and Cı´lek, 1998; Hasiotis, 2004). These types of substrata are considered hardgrounds because lithification of the matrix does not allow an organism to push aside grains to construct a burrow, but rather forces an organism to produce a boring (e.g., Ekdale et al., 1984). The bones of organisms can also serve as substrata in which organisms can leave their micro- or macroscopic traces. These traces include bite marks, insect borings, fungal borings, as well as pathologies produced by injuries or disease.

TERRESTRIAL AND AQUATIC BIOTA: TRACEMAKER CLASSIFICATION AND BEHAVIOR The continental realm contains the greatest diversity of life on Earth today, composed mostly of insects, other arthropods, higher plants, and a lesser diversity of vertebrates, non-arthropod invertebrates, fungi, and protists (Wilson, 1992). The vast majority of these and other continental organisms are terrestrial in habitat and, in one way or the other, play a role in soil formation (Thorpe, 1949; Hole, 1981; Wilson, 1992). There is a strong likelihood that a similar relationship in biodiversity existed as far back as the Mesozoic (e.g., Retallack, 2001; Hasiotis, 2004). The traces produced by continental biota serve as proxies that record body size, presence in the media, type of activity, effects on the media, and habitat preference (Wallwork, 1970; Hasiotis, 2000, 2004). The original classifications were developed for organisms living in soils, but they can be extended to aquatic organisms and to trace fossils.

Organism Size Organisms are classified as microfauna (20–200 mm), mesofauna (200 mm–1 cm), and macrofauna (>1 cm) according to size (Fig. 16.5A; Wallwork, 1970). Although there is a considerable range of body sizes of trace-making organisms, many taxonomic groups occupy fairly distinct size ranges. Most organisms

living in the soil are easily overlooked because the bulk of biodiversity and biomass are micro- and mesofauna (Wallwork, 1976; Wilson, 1992).

Presence in the Media The presence of organisms in different media varies widely and is classified according to their degree of time spent in it (Fig. 16.5B). The amount of time spent in a medium by organisms and their developmental stages varies greatly for many different reasons (Wallwork, 1970; Hole, 1981; Eisenbeis and Wichard, 1987). Organisms that live above the surface of a medium and have minimal impact on it are referred to as epigeon. Organisms that have a transient to periodic interaction with a medium are referred to as geophiles, and those with permanent interaction are referred to as geobionts. Transient fauna are adult forms of organisms that use a medium for temporary shelter or refuge during periods of inactivity. Temporary fauna are represented by the distinct stage or stages of development (egg->nymph or juvenile->adult; egg->larva->pupa->adult) a medium as one active life stage, from which an adult emerges and joins the epigeon as another active life stage. Periodic fauna spend a greater amount of time within a medium and, thus, have a much closer relationship to it. Here all life stages are completed within a medium where the organisms spend most of their lives, however, the adults will emerge to join the epigeon, mate, and begin the cycle again. Permanent faunas complete all life stages belowground and rarely appear at the surface. Accidental faunas are animals that live aboveground but fall, blow, or wash into a medium, and contribute the least to soil formation and soil ecosystems (Hole, 1981).

Type of Activity Organism behavior, particularly for those that burrow, can be divided into two main types of activities: locomotion and feeding (Fig. 16.5C). Others consider locomotion, feeding, and reproduction as the main behaviors (e.g., Odum, 1971; Aber and Melillo, 1991), however, it is rare that direct evidence of the act of reproduction is preserved but indirect evidence in the form of excavated and constructed structures (i.e., burrows) are often preserved (Genise et al., 2000; Hasiotis, 2000, 2002, 2003, and references therein). All behaviors are linked because animals use locomotion while feeding or to avoid being eaten, and to look for mates and construct nests. Locomotion is the process by which meso- and

277

TERRESTRIAL AND AQUATIC BIOTA: TRACEMAKER CLASSIFICATION AND BEHAVIOR MACROFAUNA MESOFAUNA 100 um 2 mm 20 mm Bacteria Fungi Nematoda Protozoa Rotifera Acari Collembola Protura Diplura Symphyla Enchytraeidae Chelonethi Isoptera Opiliones Isopoda

MICROFAUNA & - FLORA

A. ORGANISM SIZE MICROFAUNA

MESOFAUNA

MACROFAUNA Insecta Decapoda

Ostracoda Opiliones Chelonethi Diploura

Amphibia

Protura Collembola Araneida Acari

Chilopoda Diplopoda

Amphipoda Chilopoda Diplopoda

Insectivora Tardigrada Rotifera

Isopoda

Enchytraeidae Lumbricidae

Nematoda 0.02

0.04

0.08

Megadrili (earthworms) Coleoptera Araneida

Mollusca

Protozoa

0.16 0.32

0.64

1.3

2.6

5.2

10.4

20.8

41.6

83.2

Mollusca 1

2

4

8

16

organism length in mm

32

um

64 128 256 512

1

2

4

organism body width

8 16

mm

32

B. ORGANISM PRESENCE IN SUBSTRATUM

Adult

Aerial, Arboreal, and Epigeol Plants and Animals

Egg

Geophiles Terminology from Wallwork (1970)

Juvenile Juvenile Egg

Adult

Adult

soil surface

Adult Egg Transient

Juvenile

Egg

Geobionts

Adult

Juvenile

Temporary

Periodic

Juvenile

Egg

Accidental

Egg

Adult

Epigeon Geobionts Terminology from Eisenbeis & Wichard (1987)

Increased impact on the substratum

Epigeon

Juvenile

Permanent

Increased degree of bioturbation and mixing depth

C. ORGANISM ACTIVITY

Reproducing

Locomotion

Feeding

Burrowing Excavators Raking Pushing Pulling Carrying Forcing Ingestors Crawling

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Feeding Carnivores (1st, 2nd, 3rd order) Predators Parasites Herbivores (Phytophages) Aboveground (green plants & wood) Root system feeders Detritivores Saprophages Coprophages Xylophages Necrophages Omnivores

Microphytic Feeders

FIGURE 16.5 Trace-maker classification and behavior (modified from Hasiotis, 2000). (A) Organism size, with examples given for length and body width. (B) Organism presence in a medium, divided into the epigeon, geophiles, and geobionts. Geophiles include transient, temporary, and periodic biota, while Geobionts are also known as permanent biota. (C) Organism activity, mainly divided into locomotion and feeding activities for burrowing organisms (Wallwork, 1970), however, others consider reproduction as a separate behavior from locomotion and part of the major organism activities (Odum, 1971).

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macrobiota move over or through a medium, and more than one method may be used. Excavators use appendages for raking, pushing, pulling, or carrying media out of the burrow, or by forcing media into the burrow wall to dig tunnels. Pushers push or wedge themselves through the litter and upper horizons of loose media with a negligible amount of excavation. Ingesters use peristalsis to force themselves mouthfirst, mostly eating their way through a medium (e.g., Wallwork, 1970; Hasiotis, 2000). Feeding emphasizes the functional relationships between different organisms linked together in a common food chain within an ecosystem (e.g., Wallwork, 1970; Odum, 1971). Carnivores are composed of predators and parasites of other animals. Herbivores feed on above-ground green plants, woody material, and below-ground root systems. Detritivores (saprophages), feed on dead and decaying organic material, and includes fecal-feeders (coprophages), wood-feeders (xylophages), and carrion-feeders (necrophages). Omnivores (miscellaneous feeders) are not restricted in their feeding habits and fit easily in any of the categories. Microphytic feeders are those animals that feed on fungal hyphae and spores, algae, lichens, and bacteria (e.g., Wallwork, 1970).

Habitat Preference The habitat preference of modern organisms varies laterally and vertically in terrestrial and aquatic environments (see Figs. 16.2 and 16.3). Alluvial, palustrine, lacustrine, volcanoclastic, and eolian environments provide a wide variety of microhabitats (Wallwork, 1970; Hasiotis and Bown, 1992). Continental biota are distributed vertically and laterally in an environment according to their physiological needs for, or tolerance to, water, soil moisture and gases, salinity, light, oxygenation, carbon dioxide levels, media consistency, degree of ionic concentration, and salinity of water or media, total dissolved solids, sunlight, and pH, as well as evolved ecological associations with other organisms (e.g., Wallwork, 1970; Ward, 1992). These variables are, in turn, regulated by the regional climate in terms of seasonality of precipitation and temperature, amount of solar insolation, and weather patterns (e.g., Lydolph, 1985; Aber and Melillo, 1991). Arboreal (tree-dwelling), epigeal (aboveground), and fossorial (belowground) habitats can be partitioned into microhabitats within terrestrial environments, of which many organisms interact with one or more. Pelagic and benthic (epiand infaunal) habitats form microhabitats within aquatic environments including many organisms

which also interact with one or more. Such organisms as mayflies, dragonflies, and stoneflies occupy both terrestrial and aquatic habitats, based on their life cycle (e.g., Ward, 1992). The size, shape, and interconnectedness of voids, media texture, groundwater profile, and compactness dictate which organisms can live within a particular medium. These properties change with time because the biophysicochemical and hydrologic factors in the environment change with respect to sediment accumulation rate, magnitude and frequency of depositional events, soil drainage, hydrologic regime, and climate (e.g., Bown and Kraus, 1987; Hasiotis, 2000, 2002; Retallack, 2001).

Effects on the Sediments Epigeon, geophiles, and geobionts have multiple effects on a medium (Hole, 1981) by manipulating media and regulating processes that form and destroy media, while interacting as part of the ecosystem operating that medium (e.g., Thorpe, 1949; Wallwork, 1970; Hole, 1981). Organisms also affect a medium (see Soils and Paleosols and Fig. 16.4) by excavating and constructing shallow to deep and simple to complex burrows, burrow systems, and nests. Plants, via their trunks and roots, produce shallow to deep, simple to complex root patterns distinguished by their bushy, dispersed, tuber, tapering, or rectilinear branching forms (e.g., Odum, 1971; Retallack, 2001). Microbes construct microscopic structures that repeat in space and time to produce such macroscopic structures as stromatolites and biolaminates (e.g., Ekdale et al., 1984; Hasiotis, 2004). Animals, plants, and microbes also bioerode lithified media by mechanically or chemically removing mineral or rock fragments to produce mostly simple and shallow borings (e.g., Ekdale et al., 1984; Mikula´sˇ, and Cı´lek, 1998; Hasiotis, 2004). Thus, tracks, trails, burrows, nests, borings, and rooting patterns of continental organisms preserved in a medium, record the type of organism, habitat preference, type of activity (i.e., locomotion, feeding, and reproduction), degree of presence, and their effect on a medium. Organisms interact in many ways in above and below-ground habitats, and their behaviors are linked to the soil-forming factors. The more time and the more phases of a life cycle spent within a medium by organisms the more destruction and mixing takes place (Wallwork, 1970; Hasiotis, 2000). Together with other soil-forming factors, organisms play a major role in pedogenically modifying a medium that is seasonally to perennially

SYNTHESIS: CONTINENTAL ICHNOCOENOSES

(i.e., continuously) above the water table (e.g., Retallack, 2001; Hasiotis, 2002, 2004).

Tiering in the Continental Realm Organisms and their behaviors are distributed vertically in a medium in terrestrial and aquatic environments on the biological and physicochemical characteristics discussed in previous sections. The depth of tiering of organism traces is deepest in terrestrial environments and controlled mostly by the groundwater profile (e.g., Hasiotis, 2002, 2004). The depth of tiering of organism traces is shallowest in aquatic environments and controlled mostly by bottom-water oxygen, redox conditions in sediment, and an organisms ability to modify its microenvironment (e.g., Odum, 1971; Ekdale et al., 1984; Ward, 1992; Hasiotis, 2004; M. Gingras personal communication, 2006). The traces of modern terrestrial and aquatic organisms and the trace fossils from continental deposits can be placed into one of four behavior groups that indicate different space, trophic use, and moisture zones of the groundwater profile (see Fig. 16.2). These categories are based on the vertical and lateral spatial distribution of extant organisms and their physiological requirements for water, also known as tiering (Hasiotis and Dubiel, 1994; Hasiotis, 2000). Organisms living or moving on the land surface produce Epiterraphilic traces. These include arboreal, epigeal, or fossorial trackway-making organisms, as well as transient, temporary, and periodic organisms. Organisms living above the water table in the uppermost parts of the soil–water profile down to the upper part of the vadose zone construct Terraphilic traces. These include transient, temporary, and periodic organisms that have low tolerance for areas of prolonged high moisture levels, can tolerate short periods of 100% soil moisture, and can live in areas with relatively little available water. Organisms living within the upper, intermediate, and lower portions of the vadose zone with specific physiological and reproductive soil moisture requirements construct Hygrophilic traces. This category includes transient and temporary organisms living aboveground but burrow to this level for reproduction. These organisms obtain oxygen from the soil atmosphere. Periodic organisms are also included in this category. Hydrophilic traces are constructed by periodic and permanent organisms that live below the water table within a soil and below the sediment in open bodies of water where the water table intersects the land surface to form rivers and lakes. These organisms obtain

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oxygen from the water, and some can obtain oxygen via the atmosphere at the air–water interface within the burrow. They can also use high levels of soil moisture to keep their gills wet for short periods of time. This category includes organisms that burrow downward from a subaerially exposed surface to the water table at depth, and maintain an open burrow from the surface to some position below the water table.

Tiering in the Rock Record Although the position of the ancient water table and soil moisture zones are not directly preserved in the rock record, they can be approximated by integrating sedimentologic (primary and secondary sedimentary structures), paleopedologic (mottling, ped structure, micromorphology, texture, and soil geochemistry), geochemical (stable isotopes, redoximorphic conditions), and ichnologic evidence (see Figs. 16.6 and 16.7). For example, insects and crustaceans have burrowing behaviors that reflect the specific subaqueous or subaerial portions of terrestrial and aquatic environments. The depths of these traces, their crosscutting relationships with other traces (e.g., tiering), and their decrease in abundance within a profile, approximate the position of ancient soil-moisture zones and the palaeo-water table level. These traces occur in deposits whose primary and secondary sedimentary structures or pedogenic features preserve characteristics of the environment in which the organism was burrowing. Integration of physical, biogenic, and chemical evidence provides information about the paleohydrology (e.g., Kraus and Hasiotis, 2006). In turn, ichnologic evidence is integrated with other physical and geochemical evidence to interpret the climate at a particular time and place (e.g., Hasiotis and Dubiel, 1994; Hasiotis, 2000, 2004).

SYNTHESIS: CONTINENTAL ICHNOCOENOSES Continental environments and their trace fossils are better suited for classification or categorization as the behavioral proxies of biological community assemblages or ichnocoenoses (see Fig. 16.2). Localized remnants of above- and below-ground, trace-making, ecological communities are preserved as trace-fossil associations or ichnocoenoses. An ichnocoenosis contains tiered trace fossils of arboreal, epigeal, and fossorial organisms that lived together and had

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FIGURE 16.6 (A) Backfilled burrow of a cicada in colored layers of sand constructed in the laboratory. The cicada was collected from the field in a soil about 45 cm below the surface, equivalent to the hygrophilic zone. (B) Backfilled burrows in the Upper Jurassic Morrison Formation, near Naturita, Colorado, interpreted to be in the hygrophilic zone of a palaeosol. (C) Bivalve in its burrow in 10 m of water in Lake Tanganyika, near Kigoma, Tanzania; dark color of bivalve was permanently below the sediment-water interface. (D) Bivalve resting burrows (hydrophilic) seen from the bottom of the bed of a fluvial sandstone in the Upper Jurassic Morrison Formation, Cleveland Lloyd quarry, Utah. (E) Cast of a modern crayfish burrow from the University of Kansas Ecological Research Station, near Lawrence, where the water table is within 1 m of the surface. (F,G) Trace fossils interpreted to be crayfish burrows (hydrophilic) from palaeosols in the Upper Triassic Chinle Formation near Moab, Utah; cross-section (F) and plan (G) view of the outcrop showing circular-diameter, cylindrical burrows within welldeveloped, mottled palaeosol fabric. The palaeo-water table here was about 2 m below the palaeosurface.

SYNTHESIS: CONTINENTAL ICHNOCOENOSES

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FIGURE 16.7 (A) Cast of a wolf spider burrow (terraphilic) from the Ross River area, Simpson Desert, Australia. (B) Pleistocene trace fossil interpreted as a wolf spider burrow from the Neales River area, Simpson Desert, Australia. (C) Shallow cross-section into a meat ant nest (terraphilic) showing meat ants pouring out of domal chambers (dark circles and highly compressed ovals) and a few galleries (subhorizontal and vertical tunnels extending and going between the chambers) in an overbank splay deposit from the Umbum River area, Simpson Desert, Australia. (D) Miocene trace-fossil complex interpreted as an ant nest with domal chambers (dark circles and highly compressed ovals) and a few galleries (subhorizontal and vertical tunnels extending and going between the chambers) in proximal floodplain deposits, Piraces, Spain.

transient, temporary, periodic, or permanent relationships with the substratum. Ichnocoenoses are named for the most abundant or significant pedoecologicalmodifying behavior(s) in that ichnocoenosis and subenvironment. If crayfish burrows are the dominant trace fossils for a particular ichnocoenosis, the tracefossil association would be called the Camborygma

ichnocoenosis. Crayfish burrows would denote a saturate zone within 1–5 m of the surface within seasonal, imperfectly drained substratums. If caddisfly cases are the dominant trace fossils for a particular ichnocoenosis, the trace-fossil association would be called the Tektonargus ichnocoenosis. Caddisfly cases would denote an aquatic environment with gentle

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currents and abundant plant debris and other aquatic insects for the caddisfly larvae to feed on. If spherical termite nests are the dominant trace fossils, the tracefossil association would be called the Termitichnus ichnocoenosis. This type of nest denotes areas with ample vegetative material for termites that expand their nests by building new nest centers connected by a gallery system. The application of this approach produces a mosaic of juxtaposed ichnocoenoses, each with unique physical, chemical, and biologic properties characterized not only by the trace fossils present, but by crosscutting relationships with each other and their sedimentologic, pedogenic, and geochemical co-constitutes. For instance, in Fig. 16.2, a few examples of ichnocoenoses are provided and modeled after examples from the Upper Jurassic Morrison Formation in the western interior of the United States (Hasiotis, 2004). The ichnocoenoses are placed in the appropriate position below the diagram with the behavioral groups superimposed on the general representation of the groundwater profile for the continental realm. For alluvial deposits, two examples of ichnocoenoses are provided for the distal floodplain and three examples are provided for the proximal floodplain. For alluvial and lacustrine environments, three examples for transitional, shoreline environments, three examples for proximal aquatic settings, and three examples of distal aquatic settings are provided. Many more can be constructed for these and other deposits in the Morrison Formation (Hasiotis, 2004). The most important trend to note is that the diversity, depth, and tiering of trace fossils decreases toward shoreline and aquatic settings. Also important to note is that the terraphilic and hygrophilic behavioral zones are literally compressed out of the environments because the soil-moisture and water-table level in sediments increase towards periaquatic and aquatic environments. Interestingly, the epiterraphilic zone can continue to a water depth in aquatic settings where terrestrial organisms can produce footprints on the surface of the sediment in subaqueous settings. Ichnocoenoses could be used to develop a hierarchy of trace-fossil associations with community and ecological significance, indicating the high degree of spatial and temporal heterogeneity that exists in most continental environments. This hierarchy may become part of an ichnofacies scheme, or replace it altogether, in order to reflect better the nature of processes and life in the continental realm. A newly constructed hierarchy based on ichnologic, palaeontologic, sedimentologic, palaeopedologic, and geochemical data will track the evolution of terrestrial and aquatic ecosystems through geologic time. The new hierarchy

can assess the response of different portions of continental ecosystems to such perturbations as climate change, extraterrestrial impacts, superplume activity, caldera collapse, and tectonic reconfiguration.

CONCLUSION: TWO DISTINCT PARTS BUT ONE ICHNOLOGY Although continental and marine trace fossils and bioturbation patterns may generally appear similar, their genesis and significance are distinctly different because the biological and physicochemical conditions that influence the organism behaviors are specific to those depositional realms, as well as the behaviors themselves (e.g., Hasiotis and Bown, 1992; Hasiotis, 2002, 2003, 2004). For example, a burrow composed of backfilled menisci of minimally altered sediment alternating with pelleted sediment, assigned to the ichnogenus Taenidium, was produced by a deposit-feeding marine organism (e.g., Ekdale et al., 1984). A burrow composed of tightly backfilled bundles of adhesive menisci of minimally altered sediment (AMB) found in a paleosol, however, was produced by a terrestrial organism moving frequently through the soil in the vadose zone while feeding occasionally (e.g., Hasiotis and Bown, 1992). Although these two trace fossils are similar because of their meniscate backfill, their detailed internal and external morphologies, genesis, constructors, and significance are distinctly different. The interpretation of Taenidium is based on the behavior of marine organisms and physicochemical conditions of the sediment common in marine environments. The interpretation of AMB is based on experiments designed to test the burrowing ability of insects with respect to soil types and variable soil moistures common to terrestrial environments (e.g., Willis and Roth, 1962; Hasiotis and Bown, 1992; Hasiotis, 2004). If all backfilled burrows were interpreted as the product of deposit-feeding, sediment-ingesting aquatic organisms, then this would lead to incorrect interpretations of organism behavior and paleoenvironmental settings for continental deposits (e.g., Miller et al., 2002; Buatois and Mańgano, 2004; Genise, 2004; Genise et al., 2004). Thus, terrestrial and aquatic trace fossils and their relationship to the sedimentary and palaeopedogenic characteristics of the strata must be incorporated in an integrative and iterative process to understand more accurately their significance in the continental realm. Comparison of trace fossils to the structures of

ACKNOWLEDGEMENTS

modern continental organisms and the biological and physicochemical conditions and characteristics of its microenvironment provide the most appropriate explanation to interpret: (1) behavior and mode of construction of a trace fossil; and (2) the significance of the trace fossil with respect to the environmental, hydrologic, ecologic setting of the strata. In the example provided earlier, the sedimentary and palaeopedogenic characteristics of the trace-fossilbearing strata suggest that AMB was constructed by an organism living within the unsaturated zone of a palaeosol. The morphology of the burrow would indicate that the organism was moving and stopping frequently to produce the morphology of AMB. A simple comparison to modern fossorial insects shows the interpretation of the burrow morphology, behavior, and environmental conditions to be accurate (e.g., Hasiotis and Bown, 1992; Hasiotis, 2002). In the geologic record, trace-fossil-tiering relationships produced by above- and below-ground, tracemaking organisms preserve evidence of the seasonal fluctuations of the groundwater profile, which are linked intrinsically to the local and regional depositional setting, topography, hydrology, and climatic conditions. Because a well-defined relationship exists between climate, hydrology, soils, and biodiversity, continental trace fossils can be used to indicate such climatic parameters as temperature, precipitation, evapotranspiration, and solar radiation (see Hasiotis et al., Chapter 11). Similar controls also have an impact on soil formation, and include topography, parent material, biologic activity, and time. Therefore, trace fossils in continental deposits can be used as ancient proxies for: (1) hidden biodiversity not recorded by body fossils in terrestrial and aquatic settings; (2) above- and below-ground ecological associations; (3) soil formation; (4) hydrology and groundwater profiles; and (5) seasonal and annual climate indicators and climate change.

ACKNOWLEDGEMENTS I am grateful to William Miller III for inviting me to provide this contribution to the book. I am indebted to the students of University of Kansas IchnoBioGeoScience Research Group for stimulating research and discussions on the breadth and depth of organism-media interactions. Comments and suggestions provided by Murray Gingras greatly improved the chapter. We thank Brian Platt and

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Jon Smith for their help in preparing the chapter for publication.

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17 Invertebrate Ichnology of Continental Freshwater Environments Luis Alberto Buatois and Marıá Gabriela Mańgano

facies analysis by providing a summary of the ichnology of fluvial and lacustrine environments. Third, we discuss the potential contributions of the ichnofabric approach to the study of continental ichnofaunas. Fourth, we address the sequence stratigraphic significance of freshwater ichnofaunas. Fifth, we review examples of individual ichnotaxa in marine vs. continental realms. Sixth, we discuss the presence of freshwater ichnofaunas in environments that are not strictly continental but marginal marine. In this chapter we stress the importance of a combined approach to the study of continental ichnofaunas in space and time, using sedimentologic, stratigraphic, paleoecologic and paleobiologic datasets. Analysis of terrestrial ichnofaunas in paleosols is beyond the scope of this chapter, but excellent reviews have been recently published (Genise, 2004; Genise et al., 2004a).

SUMMARY : The study of continental ichnofaunas has shown an explosive development during the last decade. At present, three continental archetypal ichnofacies are accepted: the Scoyenia, Mermia, and Coprinisphaera ichnofacies. Integration of ichnologic, sedimentologic, and paleobiologic information is very useful in facies analysis and sequence stratigraphy of continental successions.

INTRODUCTION Continental invertebrate ichnology has experienced a remarkable development during the last fifteen years. Extensive research has resulted in the construction of an expanding dataset and the proposal of archetypal ichnofacies (e.g., Smith et al., 1993; Bromley, 1996; Buatois and Mańgano, 1995a, 2004; Genise et al., 2000, 2004a,b; Genise, 2004). Also, the potential and limitations of the ichnofabric approach to the study of continental ichnofaunas have been addressed in a number of studies (Buatois and Mańgano, 1998; Genise et al., 2004a; Buatois et al., in press a). Additionally, various studies attempt to evaluate temporal and spatial trends in trace fossil distribution (Buatois and Mańgano, 1993a; Genise and Bown, 1994a,b; Buatois et al., 1998a; Labandeira, 2002; Genise, 2004). In this chapter we will review our present knowledge on freshwater ichnofaunas, essentially those produced by invertebrates. First, we briefly evaluate the archetypal continental ichnofacies defined. Second, we stress the utility of biogenic structures in

CONTINENTAL ICHNOFACIES The ichnofacies concept was proposed by Seilacher (1967) and subsequently refined in a series of papers (e.g., Frey and Seilacher, 1980; Frey and Pemberton, 1984, 1985; Bromley, 1990, 1996; Pemberton et al., 1992, this volume; Bromley and Asgaard, 1993; Gibert et al., 1998; Buatois et al., 2002). Seilacherian or archetypal ichnofacies are trace fossil assemblages that recur through long intervals of geologic time and are characteristic of a given set of environmental conditions (Frey and Pemberton, 1984, 1985). A key component of the ichnofacies concept is their archetypal nature. This implies that peculiar local Copyright ß 2007, Elsevier B.V.

Trace Fossils: Concepts, Problems, Prospects

285


286

17. INVERTEBRATE ICHNOLOGY OF CONTINENTAL FRESHWATER ENVIRONMENTS

assemblages that do not exhibit recurrence in the stratigraphic record under a similar set of environmental conditions do not qualify as ichnofacies. Any potential ichnofacies should be based on a series of examples carefully selected from the ichnologic record, rather than a mere list of theoretical assemblages or documentation of local examples. Seilacherian archetypal ichnofacies should not be confused with ichnocoenoses. An ichnocoenosis refers to a group of biogenic structures that results from the work of a single community and, therefore, is a very different concept than ichnofacies and is applicable to different scale analysis (Bromley, 1990). Some authors (e.g., Hasiotis, 2004) have criticized the ichnofacies concept on these grounds, but the ichnofacies model is based upon recurring ichnocoenoses and trace fossil assemblages (Bromley et al., in press). A common misunderstanding is the assertion that if a particular trace fossil assemblage or ichnocoenosis cannot readily be ascribed to one ichnofacies, then the ichnofacies model is not valid. As noted by Pemberton et al. (1992), the ichnofacies model is analogous to facies models and, accordingly, archetypal ichnofacies are produced through a ‘distillation’ process that concentrates the diagnostic features of various ichnofaunas and eliminates the local peculiarities or the ‘noise’ of the particular examples. As in the case of facies models, an ichnofacies serves as a norm for purposes of comparison, framework, and guide for future observations, predictor in new situations, and basis for interpretation. Of course, at a local scale, discrete ichnofacies may be subdivided into different assemblages with paleoecological and paleoenvironmental implications, integrating sedimentologic and ichnologic datasets (MacEachern et al., 1999; McIlroy, 2004). In shallow marine clastic successions, this approach has resulted in models of onshore–offshore ichnofacies gradients that have been extremely useful in refining environmental zonations (e.g., MacEachern et al., 1999). Additionally, the addition of concepts and methods derived from the ichnofabric approach, such as the recognition of the taphonomic factors involved in the shaping of particular ichnofacies (Bromley and Asgaard, 1991), should be taken into account to produce more robust models. The ichnofacies model has been expanded into the continental realm in recent years. In his original model, Seilacher (1967) recognized only one ichnofacies for continental environments, the Scoyenia ichnofacies. He proposed the Scoyenia ichnofacies for ‘nonmarine sands and shales, often red beds, with a distinctive association of trace fossils’ and referred to a previous schematic illustration of this ichnofauna (Seilacher, 1963, Fig. 17.7), which included meniscate

burrows, arthropod trackways, and bilobed traces, as well as several physical sedimentary structures (e.g., desiccation cracks). Frey et al. (1984) noted that the Scoyenia ichnofacies subsequently was used as a catchall for all assemblages of continental trace fossils. However, the Scoyenia ichnofacies has precise environmental implications because it occurs in lowenergy continental deposits periodically exposed to air or inundated, intermediate between aquatic and nonaquatic (Frey et al., 1984; Frey and Pemberton, 1984, 1987). The fact that the Scoyenia ichnofacies was only one of the recurrent trace fossil assemblage of continental environments and that continental environments are as diverse as marine settings has been acknowledged by ichnologists long ago. However, it was not until recently that studies addressing the problem of recognizing additional continental ichnofacies were published (e.g., Smith et al., 1993; Buatois and Mańgano, 1995a; Bromley, 1996; Genise et al., 2000). At present, three continental archetypal (i.e., Seilacherian) ichnofacies are accepted: the Scoyenia, Mermia, and Coprinisphaera ichnofacies (Fig. 17.1 and Table 17.1). The former two occur in fluvio-lacustrine environments and are, therefore, discussed herein. The latter is present in palaeosols and its analysis is beyond the scope of this paper (see Genise et al., 2000 and Genise, 2004). In addition, the marine Skolithos ichnofacies may occur also in highenergy continental environments (Buatois and Mańgano, 1995a, 1998; Melchor et al., 2003). Continental ichnofacies have been addressed in more detail in a series of chapters (e.g., Buatois and Mańgano, 1995a, 1998, 2002, 2004; Genise et al., 2000; Genise, 2004; McIlroy, 2004). A common misconception is to assume a direct correlation between ichnofacies and depositional environments. Ichnofacies are not indicators of sedimentary environments but reflect sets of environmental factors. As Frey et al. (1990) put it, ichnofacies are not intended to be paleobathymeters. A wellknown example is the occurrence of the Skolithos ichnofacies, typical of foreshore to upper-foreshore settings, in lower-shoreface to offshore tempestites and deep-marine turbidites (e.g., Crimes, 1977; Pemberton and Frey, 1984; Pemberton and MacEachern, 1997). The Cruziana ichnofacies, though typical of lower-shoreface to offshore deposits, may be present in shallower settings, commonly intertidal flats of tide-influenced shorelines (e.g., Mańgano et al., 2002; Mańgano and Buatois, 2004a,b). Regardless of the depositional environment involved, it is a precise set of environmental conditions that is indicated by a specific ichnofacies. This situation is also the rule rather than the exception for continental ichnofacies.

287

ICHNOLOGY OF FLUVIAL SYSTEMS

Coprinisphaera ichnofacies Scoyenia ichnofacies Skolithos ichnofacies

Mermia ichnofacies

+ + + + + + + + + +

+

+

+

+

+

FIGURE 17.1 Ichnofacies Mańgano (2004).

+

+

+

model

of

+

+

+

continental

The Scoyenia ichnofacies (Fig. 17.2) may occur in lake margins, floodplains, and wet interdunes (Frey et al., 1984; Buatois and Mańgano, 1995a). The Mermia ichnofacies (Fig. 17.3) indicates permanently subaqueous freshwater conditions, this being typical of a lacustrine basin, but also of a freshwater body formed in a floodplain basin or even a fjord setting affected by a strong discharge of freshwater (e.g., Buatois et al., 2001; Buatois and Mańgano, 2002, 2003; Pazos, 2002). In these cases, water availability is a fundamental control in trace fossil distribution (GierlowskiKordesch, 1991) and sediment water content strongly influences substrate degree of consolidation. The role of substrate consolidation as controlling trace fossil preservation has been emphasized in a series of recent papers (e.g., Buatois et al., 1997a; Buatois and Mańgano, 2002, 2004) and the concept of taphonomic pathways has been introduced (Buatois and Mańgano, 2004). Accordingly, the Scoyenia and Mermia ichnofacies can be seen, at least in some sense, as taphofacies sensu Bromley and Asgaard (1991). As in the case of substrate-controlled ichnofacies in marine carbonates (e.g., Bromley, 1975), a single continental bed may represent the activity of more than one substratecontrolled suite, revealing the presence of composite ichnofacies (Buatois and Mańgano, 2002, 2004; Keighley and Pickerill, 2003). In the case of terrestrial assemblages, such as the Coprinisphaera ichnofacies (Fig. 17.4), climate plays a significant role, representing a first order control, regardless of the specific depositional environment (Genise et al., 2000). The Coprinisphaera ichnofacies indicates paleosols developed in paleoecosystems of herbaceous communities, which may range from dry and cold to humid and warm climates, but developed

+

+

+

+

environments.

After

Buatois

and

in a wide spectrum of depositional systems subject to subaerial exposure, such as alluvial plains, desiccated floodplains, and eolian deposits, reflecting the capacity of insects to nest in varied sedimentary environments. This and other potential terrestrial ichnofacies are controlled by ecologic parameters (e.g., vegetation, climate, and soil) rather than by depositional processes.

ICHNOLOGY OF FLUVIAL SYSTEMS Information on the ichnology of fluvial deposits is summarized in Table 17.2 based on 80 data entries. Commonly, trace fossils are not abundant in fluvial successions. It is not uncommon to find thick successions of fluvial deposits that are unbioturbated or in which trace fossils are restricted to certain beds and depositional surfaces. In addition, monospecific suites are the rule rather than the exception. However, where present, trace fossils may occur in profuse densities. As noted by D’Alessandro et al. (1987), trace fossil distribution in fluvial settings is largely a function of variability in stream discharge and the amount of time between depositional episodes. Trace fossils have been recorded more commonly in meandering deposits than in braided systems (Table 17.2). This may reflect in part, more favorable preservational conditions in abandoned channels and associated floodplain settings. A few ichnofaunas have been mentioned in anastomosing and ephemeral deposits, but this sparse record most likely reflects lack of studies. The Scoyenia ichnofacies indistinctly occurs in deposits of any fluvial style, but the Mermia

Ichnofacies Coprinisphaera

Characteristics Dominant nesting structures and subordinate feeding structures.

Composition Coprinisphaera, Monesichnus,

Implications Paleosoils related to ecosystems of herbaceous

Fontanai, Teisseirei, Celliforma,

communities, varying from dry and cold (i.e.

coprophagan scarabs, nests and cells of bees, wasp nests, ant nests, coprolites, meniscate burrows, vertebrate footprints and

Uruguay, Palmiraichnus, Ellipsoideichnus, Rosellichnus,

steppes) to humid and warm weather conditions (i.e., subtropical savannas).

root structures. Termite nests are rare. Mammalian burrows,

Chubutolithes, Attaichnus,

Dominance of hymenopteran traces sug-

commonly produced by rodents, constitute one of the most

Parowanichnus,

gests increased dryness, and the presence of

common vertebrate structures. Associations show moderate to

Syntermesichnus, Tacuruichnus

termite nests is indicative of higher humid-

relatively high ichnodiversity and high abundance, particularly

ity conditions. It is present in paleosols

in mature paleosoils. The complex tiering structure records the

formed in different sedimentary environ-

varying depths of the different groups of producer insects.

ments including alluvial plains, desiccated

deposits, which reflects insect capacity to colonize different substrates. Meniscate feeding structures, locomotion structures (both track-

Scoyenia, Taenidium, Beaconites,

ways and continuous trails) and cylindrical to irregular vertical

Diplichnites, Umfolozia,

origin deposited in low energy areas. They

burrows. Mixture of invertebrate, vertebrate, and plant traces.

Mirandaichnium,

include both slightly submerged sediments

Invertebrates are mainly detritus-feeders, deposit-feeders or

Diplopodichnus, Cruziana,

which are periodically emerged and sub-

predators. Vertebrates are predators or herbivorous. Vertebrates traces in this ichnofacies involve mainly bird and mammalian

Rusophycus,

aerial sediments which are periodically submerged. Intermediate continental envir-

tracks. Ichnodiversity of structures resulting from invertebrates

onments between aquatic and non-aquatic.

is generally low though some traces may be abundant. Vertebrate

Typical fluvial-lacustrine transitions. Typical

footprints may be diverse and abundant around water bodies.

environments include floodplains, ponds,

Likewise, some Paleozoic associations show a high diversity of

lake margins, ephemeral lakes and humid

arthropods trackways. Mermia

Sandy to argillaceous sediments of continental

Predominant horizontal to subhorizontal grazing and feeding traces

interdunes. Mermia, Gordia, Helminthopsis,

Permanent subaqueous conditions. Well-

caused by mobile detritus-feeders. Subordinate occurrence of locomotion traces. Generally high to moderate ichnodiversity.

Cochlichnus, Helminthoidichnites,

oxygenated unconsolidated fine-grained lacustrine substrates of low energy.

Poorly specialized grazing patterns show very rudimentary

Treptichnus, Circulichnis,

Sedimentation rate is usually low. However,

feeding strategies and include trails displaying overcrossing,

Vagorichnus

these environments may be periodically

simple meandering trails, and sinusoidal, curved and straight

affected by turbidity or underflow currents.

trails. Feeding structures show zig-zag, circular geometries or

Although archetypal associations to distin-

form systems with more varying morphologies. Fish trails may

guish shallow and deep lakes seem difficult

also be present. Although ichnodiversity may be high, it results

to recognize, local bathymetric zonation can

from minor variations within a few general and basic behavioral patterns. Surface trails are predominant in Paleozoic associations

be detected.

but the Mermia ichnofacies shows abundant infaunal organism structures during the Mesozoic.


Mixture of invertebrate, vertebrate, and plant structures. Nests of

floodplains, abandoned fluvial bars, crevasse splays, levees and vegetated eolian

Scoyenia

288

TABLE 17.1 Summarized Characteristics, Ichnotaxonomic Composition and Environmental Implications of Archetypal Continental Ichnofacies. The Skolithos Ichnofacies may Occur in High Energy Continental Deposits

289


when the channel is still active, while others reflect emplacement within the substrate after channel diversion (‘abandonment’) or during periods of low discharge virtually characterized by nondeposition (‘inactive’). The ichnofauna from active channels is characterized by low-diversity, typically monospecific, suites of simple vertical burrows and escape traces (e.g., Bradshaw, 1981; Zawiskie et al., 1983; Fitzgerald and Barrett, 1986; Woolfe, 1990; Sarkar and Chaudhuri, 1992). Moderately deep to deep Skolithos, commonly forming dense assemblages, and escape trace fossils are common components in pebble conglomerate and trough cross-bedded, planar cross-bedded, or parallel

ichnofacies seems to prevail in floodplain deposits of meandering systems. In any case, with respect to trace fossil distribution, the most useful distinction is that between channel and overbank deposits (Buatois and Mańgano, 2004). Fluvial channels are characterized by high to relatively high energy, rapid fluctuations in rates of sedimentation and erosion, and coarser grain sizes than those typically deposited in adjacent environments. Accordingly, channels represent stressful environments for benthic organisms and, therefore, production and/or preservation of biogenic structures is commonly inhibited. Some fluvial channel ichnofaunas seem to record substrate colonization Scoyenia Ichnofacies

Coprinisphaera Ichnofacies 2

1

8

2

6

4 3

7

9

3

8 1

8

5 4 1- Taenidium 2- Beaconites 3- Scoyenia 4- Rusophycus 5- Camborygma 6- Diplichnites 7- Mirandaichnium 8- Umfolozia 9- Cruziana

5

7 6

1- Palmiraichnus 2- Uruguay 3- Attaichnus 4- Coprinisphaera 5- Rosellichnus 6- Eatonichnus 7- Tacuruichnus 8- Celliforma

FIGURE 17.4 Schematic reconstruction of the Coprinisphaera ichnofacies. Based on Buatois et al. (2002).

FIGURE 17.2 Schematic reconstruction of the Scoyenia ichnofacies. Based on Buatois et al. (2002).

Mermia Ichnofacies

3

9

5

8

4 6

2

1- Mermia 2- Cochlichnus 3- Gordia 4- Helminthoidichnites 5- Helminthopsis 6- Planolites 7- Treptichnus 8- Tuberculichnus 9- Palaeophycus 10- Circulichnus 11- Vagorichnus 12- Undichna

FIGURE 17.3 Schematic Buatois et al. (2002).

12 10

1

7

11

reconstruction

of

the

Mermia

ichnofacies.

Based

on

Stratigraphic Unit & Location

Silurian

Clam Bank Formation

?Late Silurian

Tumblagooda Sandstone

Ichnotaxonomic Composition Diplichnites isp.

Sheet flood & abandoned

?Planolites isp.,

Abandoned channels

(Newfoundland, Canada) (Australia)

Depositional Subenvironment

Type of Fluvial System

References

Ephemeral

Wright et al. (1995)

Braided

Trewin & McNamara

channel Didymauliponomos cf.ro-

(1995)

wei, Selenichnites langridgei, Rusophycus rex ?Late Silurian

Tumblagooda Sandstone (Australia)

Diplichnites gouldi,

Ponds

Braided

?Paleohelcura antarcti-

Trewin & McNamara (1995)

cum, ?Protichnites isp., ?Diplopodichnus biformis, Beaconites cf.antarcticus, Skolithos isp. ?Late SilurianDevonian

Mt Daubeny Formation (Australia)

Cruziana isp., Didymaulichnus lyelli,

Distal alluvial fans & ponds

Ephemeral

Neef (2004a)

Diplichnites gouldi, Diplopodichnus biformis, Merostomichnites strandi, Palmichnium antarticum, Planolites isp., Rusophycus isp. Devonian

Ravendale Formation (Australia)

Diplichnites gouldi, ?Stiaria quadripedia

Sheet flood

Ephemeral

Neef (2004b)

Devonian

Wood Bay Formation (NW

Svalbardichnus trilobus,

Point bar & levee

Meandering

Wisshak et al. (2004b)

Spitsbergen, Svalbard)

Cruziana polaris,

Flooplain Abandoned channel &

Meandering Meandering

Carroll & Trewin (1995) Allen & Williams (1981);

Merostomichnites isp., Siskemia cf. elegans, Taenidium barretti, Planolites isp. Devonian Devonian

Upper Eday Sandstone (Scotland) Red Marl Group (Wales)

Cornulatichnus edayensis Beaconites antarcticus, Taenidium barretti, cf.

point bar

Morrissey &

Striatichnium

Braddy (2004)

Devonian

Red Marl Group (Wales)

Diplichnites gouldi

Sand bar

Braided

Smith et al. (2003)

Devonian

Milford Haven Group (Wales)

Taenidium barretti

Abandoned channel &

Meandering

Morrissey & Braddy (2004)

Meandering

Morrissey & Braddy (2004)

point bar Devonian

Milford Haven Group (Wales)


Age

290

TABLE 17.2 Selected Occurrences of Fluvial ichnofaunas. Only Papers that Combined Ichnotaxonomic Descriptions and Sedimentologic Data are Included. Ichnotaxonomic Assignments Were Revised Where Necessary. Occurrences Include Individual Ichnocoenosis, Trace Fossil Assemblages and Trace Fossil Associations (i.e., Recurring Assemblages)

Taenidium barretti, Cochlichnus anguineus,

Point bar & floodplain pool

cf. Cruziana, Diplichnites gouldi, Diplopodichnus biformis, Paleohelcura tridactyla, Palaeophycus isp., Tumblagoodichnus cf. hockingi, Selenichnites isp. Devonian

Maam Formation (Ireland)

Beaconites antarcticus

Abandoned channel

Ephemeral

Graham & Pollard (1982)

Devonian

Harrylock Formation (Ireland)


Ephemeral channel

Ephemeral

Bamford et al. (1986)

(distal alluvial fan) Devonian

Taylor Group (Southern Victoria Land, Antarctica)

Beaconites antarcticus, Taenidium barretti,

Braided

Bradshaw (1981); Woolfe (1990)


Floodplain

Braided

Bruck et al. (1985)

Kouphichnium aff. variabilis,

Floodplain pond

Meandering ?

Pollard & Hardy (1991)

Sheet flood & abandoned

---------------

Pearson (1992)

Skolithos linearis, Diplichnites gouldi Devonian

McAras Brook Formation (Canada)

Carboniferous

Westpahlian D (England)

Cochlichnus isp.,Lockeia isp., coprolites, vertebrate trackways Carboniferous

Strathclyde Group (Scotland)

Diplichnites cuithensis, Beaconites isp.

channel

Carboniferous

Coal pit at Mostyn (Wales)

Palmichnium pottsae

Channel margin

---------------

Carboniferous

Tupe Formation (Western

Archaeonassa fossulata,

Floodplain pond

Distal braided

Braddy & Anderson (1996) Buatois and Mańgano (2002)

Crevasse splay, levee,

Meandering

uszek (1995) Gl

Meandering

uszek (1995) Gl

Argentina)


Abandoned & active channels

Didymaulichnus lyelli, Helminthoidichnites tenuis, Palaeophycus tubularis, Planolites isp., root traces

Carboniferous

Upper Silesia Sandstone,

Cochlichnus anguineus,

Mudstone & Cracow

Planolites montanus,

Sandstone series (Poland)

Lockeia siliquaria, Lockeia

pond, and oxbow lake

avalonensis, Acripes isp., Sagittichnus lincki, Carboniferous

Jejkowice beds & Mudstone series (Poland)

Torrowangea rosei Cochlichnus anguineus,

Stagnant floodplain pond


291

Lockeia siliquaria, Lockeia avalonensis (continued)


Ichnotaxonomic Composition

Carboniferous

Stull Shale Member (Kansas)

Diplichnites cuithensis

Carboniferous

Cutler Group (New Mexico)


Carboniferous

Tynemouth Creek Formation


Carboniferous

(New Brunswick, Canada) Gaspe´ Sandstone Group (Quebec,

(Continued) Depositional Subenvironment


References

Abandoned channel

---------------

Mańgano et al. (2002)

Floodplain

Braided

Lucas et al. (2005a)

Sheet flood

Distal alluvial

Briggs et al. (1984)

fan Palmichnium antarcticum

Channel margin

---------------

Braddy & Milner (1998)

Rusophycus carbonarius,

Abandoned channel

Braided

Pickerill (1992)

Floodplain

Ephemeral

Keighley & Pickerill (1997, 1998,

Canada) Carboniferous

Albert Formation (New Brunswick, Canada)

Cruziana problematica, Skolithos isp.,Diplichnites triassicus, Monomorphichnus bilinearis, Diplichnites cf.incertipes, cf. Spongeliomorpha isp.

Carboniferous

Mabou & Cumberland groups (Nova Scotia, Canada)

Diplichnites cf. logananus, Diplichnites isp.,

2003)

Protichnites cf. carbonarius, Protichnites cf. kennedica, Protichnites cf. scoticus, Protichnites cf. variabilis, Protichnites isp., Stiallia cf.pilosa, Rusophycus carbonarius, Rusophycus isp., Selenichnites isp., Cruziana problematica Carboniferous


Carboniferous


Taenidium barretti,

Floodplain

Ephemeral


Ephemeral sheetflood

Ephemeral

Keighley & Pickerill (1997, 1998, 2003)

Floodplain pond

Ephemeral


cf. Taenidium barretti Hexapodichnus horrrens, Monomorphichnus cf.

2003)

lineatus, Protichnites cf. carbonarius, Protichnites isp. Carboniferous


Diplopodichnus biformis, Circulichnus montanus, cf. Circulichnus montanus, Gordia marina,

2003)


Age

292

TABLE 17.2

Gluckstadella cooperi, Protichnites isp. Carboniferous


Cruziana problematica, cf.

Ephemeral channel

Ephemeral

Cruziana problematica,


Rusophycus carbonarius, cf. Rusophycus carbonarius Carboniferous


Didymaulichnus cf. lyelli,

Perennial channel

Braided

Helminthopsis hierogly-


phica, Palaeophycus striatus, cf. Palaeophycus Carboniferous


Planolites beverleyensis, cf.

Levee

Meandering

Planolites beverleyensis,



cf.Planolites, Taenidium barretti, Treptichnus pedum, vertebrate trackways CarboniferousPermian Carboniferous-

Cumberland Group (Nova Scotia,


Braided

Ryan (1986)


Ephemeral

Voigt et al. (2005)


Ephemeral

Lucas et al. (2005b)


Ephemeral

Lucas et al. (2005c)

Skolithos linearis

Active channel

Braided

Fitzgerald & Barrett (1986)

Skolithos linearis

Active channel

Braided

Zawiskie et al. (1983)

Canada) Maroon Formation (Colorado)

Sand bar & abandoned channel

Paleohelcura isp., Striatichnium bromacker-

Permian

ense, Taenidium isp., vertebrate trackways Permian

Abo Formation (New Mexico)

Arborichnus isp., Monomorphichnus lineatus, Stiaria isp., cf. Tonganoxichnus robledoensis, vertebrate trackways

Permian

Abo Formation (New Mexico)

Permichnium isp., Stiaria intermedia, cf. Tonganoxichnus robledoensis, vertebrate trackways

Permian

Feather Conglomerate (Southern Victoria Land, Antarctica)

Permian

Takrouna Formation (Northern Victoria Land, Antarctica)

(continued)

293

294

TABLE 17.2 (Continued) Age


Permian

La Golondrina Formation (Patagonia, Argentina)

Ichnotaxonomic Composition Cochlichnus anguineus,



References

Pond

Braided

Buatois et al. (1997a)

Floodplain

Meandering

Acenõlaza & Buatois (1993)

Abandonned channel

Braided

MacNaughton & Pickerill (1995)

Floodplain

---------------

Biron & Dutuit (1981)

Ctenopholeus kutscheri, tenuis, Helminthopsis abeli, Palaeophycus striatus

Permian

La Colina Formation (Western Argentina)

Beaconites coronus, Didymaulichnus lyelli, Palaeophycus striatus,

Triassic

Lepreau Formation (Canada)

Palaeophycus tubularis Beaconites coronus, Archaeonassa isp., Fuersichnus isp., Gordia marina, Palaeophycus striatus, Palaeophycus isp., Planolites isp., Rusophycus isp., Skolithos linearis, Taenidium isp.

Triassic

Argana and Ourika formations (Morrocco)

Scoyenia isp., Umfolozia isp., vertebrate

Triassic

Molteno Formation (Lesotho)

trackways Archaeonassa isp.

Sand bar

Braided

Turner (1978)

Triassic

Beaufort Group (South Africa)

Cruziana isp.

Overbank floodbasin

Meandering

Shone (1978)

Triassic

Beaufort Group (South Africa)

Skolithos isp., Planolites isp.

Crevasse splay

Meandering

Shone (1978)

Triassic

Fleming Fjord Formation (East

Rusophycus eutendorfensis,

Overbank

---------------

Bromley and Asgaard (1979,

Greenland)

Cruziana problematica,

1991)

Cruziana isp., Diplichnites triassicus, Spongeliomorpha carlsbergi Triassic

Keuper Sandstone (England)

Cruziana isp., Rusophycus

Floodplain

Distal braided

Pollard (1981)

Abandoned channel

---------------

Schlirf et al. (2001)

isp., Merostomichnites isp., Planolites isp., verTriassic

Hassberge & Lo¨wenstein formations (Germany)

tebrate trackways Skolithos isp., Polykladichnus isp.


Helminthoidichnites

Triassic Triassic


Cruziana problematica

Bhimaram Sandstone (India)

Skolithos isp., escape trace

Abandoned channel &

---------------


Ephemeral

Sarkar & Chaudhuri (1992)

floodplain Active channel

fossils Triassic


Taenidium isp.

Inactive channel

Ephemeral


Triassic


Skolithos isp., Taenidium

Floodplain

Ephemeral


Triassic

Maleri Formation (India)

Skolithos isp., Palaeophycus

Channel & floodplain

Ephemeral


isp., Palaeophycus isp. isp. Triassic Jurassic

Dharamaram formation (India)

Skolithos isp., Palaeophycus

Floodplain

Ephemeral


Zagaje, Otrowiec & Przysucha

isp. Planolites isp., Cruziana

Levee & crevasse splay

Meandering

Pien´kowski (1985)

Formations (Poland)

isp., vertebrate trackways

Alcobaça beds (Portugal)

Taenidium isp.

Floodplain

Meandering

Fu¨rsich (1981)

Jurassic

East Berlin Formation (New



Ephemeral

Gierlowski-Kordesch (1991)

Floodplain

Meandering

Metz (1992)

England)

Scoyenia gracilis, Skolithos isp., Fuersichnus isp.

Jurassic

Towaco Formation (New Jersey)

Planolites montanus, Cochlichnus anguineus, Helminthopsis isp., Scoyenia gracilis, Treptichnus bifurcus

Jurassic

La Matilde Formation (Argentina)

Hexapodichnus casamiquelai, vertebrate trackways

Floodplain pond

Meandering?

de Valais et al. (2003)

Cretaceous

Wessex formation (England)

Beaconites antarcticus,

Floodplain, point bars &

Meandering

Goldring et al. (2005)

Sand bar & overbank

Braided

Fernandes & Carvalho (2001)

Floodplain ponds

Meandering

Aramayo & Bocanegra (2003)

Floodplain pond

Meandering

Kim & Paik (1997)

Taenidium barretti,


Jurassic

channel plugs

Cochlichnus anguineus, Cretaceous

Antenor Navarro Formation (NE

vertebrate trackways Taenidium isp.

Brazil) Cretaceous

Candeleros Formation (Argentina)

Scoyenia gracilis, Skolithos isp., Taenidium isp., Helminthopsis hieroglyphica, vertebrate trackways

Cretaceous

Hasandong Formation (Korea)

Taenidium isp., Planolites isp., Diplocraterion luniforme, Skolithos isp.

295

(continued)

Age


Cretaceous

Hasandong & Jinju formations (Korea)

Ichnotaxonomic Composition Chondrites isp., Circulichnus

296

TABLE 17.2

(Continued) Depositional Subenvironment


References

Levee

Meandering

Kim et al. (2002)

Crevasse splay

Meandering

Kim et al. (2002)

Floodplain

Meandering

Kim et al. (2002)

Abandoned channel

Meandering

Kim et al. (2002)

Overbank

---------------

Fordyce (1980)

Channel & floodplain

Braided

Bracken & Picard (1984)

Abandoned channel

Transitional

D’Alessandro et al. (1987)

montanus, Cochlichnus anguineus, Helminthopsis abeli, H. hieroglyphica,

montanus, Skolithos magnus, S. verticalis, Skolithos isp., Spirodesmos isp., Taenidium barretti, Thalassinoides suevicus Cretaceous


Beaconites coronus, Skolithos magnus, vertebrates trackways

Cretaceous


Beaconites coronus, Skolithos magnus, Palaeophycus tubularis, Thalassinoides paradoxicus

Cretaceous


Planolites annularius, P. montanus, Skolithos magnus

Cretaceous

Ohika Formation (New Zealand)

Cochlichnus anguineus, Helminthopsis isp., Helminthoidichnites

Cretaceous-

North Horn Formation (Utah)

Tertiary Eocene

tenuis Skolithos isp., Taenidium isp., root traces

Duchesne River Formation (Utah)

?Palaeophycus isp.

between braided and meandering Eocene

Duchesne River Formation (Utah)

Beaconites coronus,

Floodplain pond

Transitional

Taenidium isp., ?Palaeophycus isp.,

between braided and

Scoyenia isp., Skolithos

meandering


isp., root traces Oligocene

Floodplain

Braided

Uchman et al. (2004)


Laevicyclus isp., Planolites beverleyensis, P.

Lower freshwater molasse (Switzerland)

Cochlichnus anguineus, Steinsfjordichnus brutoni, Helminthoidichnites isp., ?Planolites isp., Treptichnus pollardi, brate trackways

Miocene

Gering & Monroe formations

Beaconites coronus,

Sand bar & abandoned

Braided

Stanley & Fagerstrom (1974)

Miocene

(Nebraska) Diligencia Formation (California)

?Skolithos isp. Taenidium isp.

channel Overbank

Braided

Squires & Advocate (1984)

Miocene

Tariquia Formation (Bolivia)

Taenidium barretti

Abandoned channel &

Anastomosing

Buatois et al. (in press a)

overbank Miocene-

Ridge Route Formation

Palaeophycus tubularis

Sand bar

---------------

Smith et al. (1982)


Palaeophycus tubularis,

Overbank

---------------

Smith et al. (1982)

Pliocene Miocene-

Scoyenia gracilis

Pliocene Pleistocene

Marine terraces along the Ionian coast (Italy)

Taenidium isp., root traces

Floodplain pond & abandoned channel

---------------


Pleistocene

Pehuen-Co (Argentina)

Taenidium barretti

Floodplain

Meandering ?

Aramayo et al. (2003)


Treptichnus isp., verte-

297

298


stratified, fine- to very coarse-grained sandstone channel deposits. Unfortunately, the identity of the tracemaker and the functional significance of the vertical burrows in fluvial channel facies are poorly understood, although interpretation as domiciles of suspension feeders seems reasonable. These low diversity (commonly monospecific) ichnofaunas dominated by simple vertical burrows are regarded as freshwater examples of the Skolithos ichnofacies (Buatois and Mańgano, 1998, 2004). In contrast, the ichnofauna of abandoned or inactive channel deposits is characterized by meniscate trace fossils (Beaconites, Taenidium), vertical to inclined burrows (Skolithos, Cylindricum) and simple horizontal burrows (Palaeophycus) (e.g., Allen and Williams, 1981; Graham and Pollard, 1982; Bamford et al., 1986; Sarkar and Chaudhuri, 1992; Miller and Collinson, 1994; Miller, 2000; Keighley and Pickerill, 2003; Morrissey and Braddy, 2004; Buatois et al., in press a). Ichnodiversity is almost invariably low. Trace fossils commonly occur in trough cross-bedded, planar cross-bedded, parallel stratified or current ripple cross-laminated fine- to coarse-grained sandstone. This ichnofauna reflects colonization of sandstone deposits after channel diversion (‘abandonment’) or during periods of low discharge virtually characterized by nondeposition (‘inactive’) (Buatois and Mańgano, 2004). Meniscate burrows most likely reflect the activity of vagile organisms moving into the substrate in search for food, revealing a combination of bypassing and ingestion. Vertical to inclined burrows have several functions, including permanent domiciles, semi-permanent shelters, nests, and passageways (Stanley and Fagerstrom, 1974). Insect nesting trace fossils may also occur, reflecting their ability to colonize different substrate types (Genise et al., 2000). Tracemakers are inferred to be behavioral generalists recording an opportunistic strategy (Miller and Collinson, 1994). Ichnofaunas of abandoned or inactive channel deposits are remarkably similar to those from overbank deposits, because abandoned channels lead to the formation of ponded areas (Buatois and Mańgano, 2002, 2004). These ichnofaunas can be confidently assigned to the Scoyenia ichnofacies. The most diverse and abundant trace fossil assemblages in fluvial depositional systems commonly occur in overbank deposits (e.g., Fordyce, 1980; D’Alessandro et al., 1987; Buatois et al., 1997a; Buatois and Mańgano, 2002, 2004; Keighley and Pickerill, 2003). Overbank settings include a wide variety of deposits, such as floodplains, crevasse splays and levees. In some cases, although no increase in ichnodiversity is apparent, overbank deposits are more intensely bioturbated than their equivalent

channel deposits (Buatois et al., in press a). It is relatively common that the only trace fossils in a fluvial succession correspond to fine-grained overbank horizons interbedded within unbioturbated, coarser-grained stacked channel deposits. The occurrence of distinct ichnofossil-bearing pond deposits within an otherwise unfossiliferous fluvial succession may be regarded as recording taphonomic and colonization windows (Buatois et al., 1997a). Ratcliffe and Fagerstrom (1980) noticed a disparity between the abundance of biogenic structures in Holocene overbank deposits and the relatively poor record of their ancient counterparts, underscoring the importance of taphonomic factors. In addition, Maples and Archer (1989) outlined a number of conditions that improved preservation potential of biogenic structures in overbank environments, namely deposition of fine-grained heterogeneous sediment, little or no reworking, and enough time between depositional events to allow colonization, but not so much time that plant colonization obliterates animal traces. These conditions allow preservation in protected ponded areas not only of tiny invertebrate traces, but also of delicate fish trails (e.g., Morrissey et al., 2004; Wisshak et al., 2004a). Some overbank ichnofaunas reflect emplacement of biogenic structures in water bodies that have been subjected to progressive desiccation (desiccated overbank) while others were emplaced subaqueously in water bodies filled by overbank vertical accretion without experiencing desiccation (overfilled overbank) (Buatois and Mańgano, 2004). Ichnofaunas from desiccated overbank deposits consist of arthropod trackways (e.g., Diplichnites, Protichnites, Hexapodichnus, Trachomatichnus), vertebrate trackways (e.g., Limnopus, Hyloidichnus), backfilled meniscate traces (e.g., Scoyenia, Taenidum), ornamented burrows (e.g., Spongelliomorpha, Tambia), and bilobate traces with scratch marks (e.g., Cruziana, Rusophycus). Vertical burrows (e.g., Skolithos, Cylindricum) are accessory components. Insect and arachnid nesting structures may also be present. Invertebrate ichnodiversity is low to rarely moderate, but vertebrate traces may be relatively diverse. Trace fossils typically occur in trough cross-bedded, planar cross-bedded, parallel stratified, climbing ripple cross-laminated, or current ripple cross-laminated, very fine- to medium-grained sandstone and mudstone. Associated physical structures are indicative of periodic subaerial exposure, such as desiccation cracks and raindrop imprints. Examples of desiccated overbank ichnofaunas have been extensively documented in the literature (Bromley and Asgaard, 1979; Biron and Dutuit, 1981;

ICHNOLOGY OF LACUSTRINE SYSTEMS

Bracken and Picard, 1984; Squires and Advocate, 1984; D’Alessandro et al., 1987; Debriette and Gand, 1990; Sarkar and Chaudhuri, 1992; Smith, 1993; Acenõlaza and Buatois, 1993; Buatois et al., 1996a; Kim and Paik, 1997; Gand et al., 1997; Eberth et al., 2000; Savrda et al., 2000; Aramayo and Bocanegra, 2003; Buatois et al., in press). Desiccated overbank ichnofaunas almost invariably belong to the Scoyenia ichnofacies (Buatois and Mańgano, 2002, 2004). Analysis of trace fossil morphology commonly reveals features indicative of firm substrates, such as striated walls in Scoyenia and Spongelliomorpha, sharp scratch marks in Tambia, Cruziana, and Rusophycus, and well-defined appendage imprints in arthropod trackways. In some cases, two distinct suites can be recognized: one ‘pre-desiccation suite’ characterized by meniscate, backfilled structures without ornamentation (e.g., Taenidium, Beaconites) developed in a soft substrate, and the second or ‘desiccation suite’ typified by striated traces (e.g., Scoyenia, Spongelliomorpha), cross-cutting the former and developed in a firm substrate (Buatois et al., 1996a; Savrda et al., 2000; Buatois and Mańgano, 2002, 2004). The resulting palimpsest surfaces record taphonomic pathways due to progressive desiccation of floodplain sediments. Desiccated overbank ichnofaunas tend to dominate in distal overbank settings and/ or arid to semiarid settings (Buatois and Mańgano, 2004). Ichnofaunas from overfilled overbank deposits consist of simple grazing trails (e.g., Helminthopsis, Helminthoidichnites), locomotion trails (e.g., Cochlichnus), horizontal dwelling burrows (e.g., Ctenopholeus, Palaeophycus), and resting traces (e.g., Lockeia). Tetrapod trace fossils, arthropod trackways, backfilled trace fossils, and bilobated traces with scratch marks either are subordinate elements or are directly absent. Most of the trace fossils are oriented parallel to the bedding plane and reflect very shallow tier emplacement. Ichnodiversity is low to rarely moderate. Examples of these ichnofaunas are also well documented in the literature (Turner, 1978; Fordyce, 1980; Miller, 1986; Pollard and Hardy, 1991; Gluszek, 1995; Buatois et al., 1997a; Buatois and Mańgano, 2002; Keighley and Pickerill, 2003; Uchman et al., 2004). Trace fossils typically occur in parallel stratified, climbing ripple cross-laminated or current ripple cross-laminated very fine- to mediumgrained sandstone and mudstone. Physical structures indicative of subaerial exposure are absent, reflecting overbank vertical accretion rather than desiccation of the water body. Morphologic details of the trace fossils are very poorly preserved, suggesting that they were formed in a water-saturated substrate (e.g., Buatois

299

et al., 1997a). Overall features of these ichnofaunas reflect the subaqueous nature of the associated environment. Poorly preserved traces may be crosscut by better defined softground trace fossils reflecting improving taphonomic conditions due to increasing firmness of the substrate. Although formed in floodplains, these ichnofaunas lack most of the diagnostic features of the Scoyenia ichnofacies and are regarded as examples of a depauperate Mermia ichnofacies (Buatois and Mańgano, 2002, 2004). The lower ichnodiversity of the Mermia ichnofacies in these floodplain deposits in comparison with their equivalents from lacustrine basins is probably an expression of the less stable conditions and temporary nature of overbank environments. Overfilled overbank ichnofaunas tend to dominate in proximal overbank settings of meandering systems and/or temperate and humid settings (Buatois and Mańgano, 2004).

ICHNOLOGY OF LACUSTRINE SYSTEMS Information on the ichnology of lacustrine deposits is summarized in Table 17.3 based on 70 data entries. Biogenic structures formed in lacustrine sediments probably have the highest preservation potential of all continental trace fossils. Preservation of biogenic structures is particularly favored in low-energy areas of lacustrine systems. For example, alternation of very fine sand and mud deposited from underflow or turbidity currents is conducive to preservation of tiny surface to very shallow traces (Buatois and Mańgano, 1995a, 1998). In low-energy coastal areas of lakes, preservation of biogenic structures is commonly linked to rapid influx of sand via non-erosive sheet floods (e.g., Zhang et al., 1998). Although monospecific trace fossil assemblages are present, moderately diverse ichnofaunas are common in lacustrine deposits (Table 17.3). Lacustrine systems can be divided into hydrologically open (i.e., with an outlet) and hydrologically closed (i.e., without an outlet) (Gore, 1989). Closed lakes are very stressful ecosystems, characterized by high salinity and rapidly fluctuating shorelines (Gore, 1989). Due to harsh conditions, faunal diversity is very low and biogenic structures emplaced under permanent subaqueous conditions are scarce or absent (e.g., Price and McCann, 1990; Uchman and Alvaro, 2000). However, moderately diverse ichnofaunas may occur at the lake margins, recording the activity of terrestrial rather than aquatic faunas (e.g., Zhang et al., 1998; Scott et al., in press). Overall, closed lake ichnofaunas consist of plant

Age

Stratigraphic Unit & Location Borrowdale Volcanic

Devonian

Old Red Sandstone

Group (England) (Scotland)

Diplichnites gouldi, Diplopodichnus


Type of Lake

References

Lake margin

Ephemeral

Johnson et al. (1994)

Lake margin

---------------

Pollard & Walker (1984),

biformis Siskemia elegans, Siskemia bipediculus, Siskemia lata-via, Stiaria quadripedia,

Walker (1985)

Stiaria intermedia, Danstairia vagusa, Danstairia congesta, Keircalia multipedia, Mitchelichnus farrydenensis, Mermia carickensis, Stiallia pilosa, Stiallia berriana, Rusophycus problematicus, Diplopodichnus biformis, cf. Merostomichnites Devonian

Hornelen Basin (Norway)

Siskemia elegans, Siskemia bipediculus, Diplopodichnus biformis,

Lake margin

Perennial

Pollard et al. (1982)

Shallow lake

Perennial

Tyler (1988), Higgs (1988)

Shallow lake (below wave

Perennial

Turek (1989)

Lacustrine shoreface

Perennial

Pickerill (1992)

cf. Taenidium isp., ?escape trace fossils

Wave-influenced shallow lake

Perennial


Planolites beverleyensis, Rusophycus

Offshore lacustrine

Perennial

Keighley & Pickerill (1997,

Merostomichnites isp., Cruziana problematica Carboniferous

Bude Formation (England)

Kouphichnium isp., Undichna bina, Undichna britańica, Undichna consulca,

Carboniferous

Radnice Member of the

Undichna radnicensis, amphibian

Undichna simplicitas Kladno Formation (Czech

swimming trails

base)

Republic) Carboniferous

Albert Formation (New Brunswick, Canada)

Cochlichnus anguineus, Planolites isp.,Palaeophycus tubularis, Helminthopsis tenuis, Gordia marina, Palaeophycus striatus, escape trace fossils

Carboniferous

Mabou & Cumberland groups (Nova Scotia,

Carboniferous

Emery brook Formation of

Canada) the Mabou Group (Nova Scotia, Canada)

carbonarius

1998, 2003)


Ordovician

Ichnotaxonomic Composition

300

TABLE 17.3 Selected Occurrences of Lacustrine Ichnofaunas. Only Papers that Combined Ichnotaxonomic Descriptions and Sedimentologic Data are Included. Ichnotaxonomic Assignments Were Revised Where Necessary. However, Taxonomy of Arthropod Trackways is in Need of Further Revisions and a Significant Reduction in Valid Names is Expected with Further Evaluation. Occurrences Include Individual Ichnocoenosis, Trace Fossil Assemblages and Trace Fossil Associations (i.e., Recurring Assemblages)

Carboniferous

Carboniferous

Mabou & Cumberland

carbonarius, cf. Rusophycus carbonarius,

Canada)

Helminthopsis hieroglyphica

Jericho Formation (Queensland, Australia)

Carboniferous

Cruziana problematica, Rusophycus

groups (Nova Scotia,

Agua Colorada Formation (Argentina)

Carboniferous

Agua Colorada Formation

Carboniferous

Agua Colorada Formation

(Argentina) (Argentina)

Lake margin

Perennial


Rusophycus devisi, Tasmanadia glaessneri,

Shallow lacustrine

Perennial

Cook & Bann (2000)

Alphaichnus alphaensis, Wadeichnus maryae, Cruziana isp. Palaeophycus tubularis, Planolites

Shoreline sand flats

Perennial

Buatois & Mańgano

Turbidite system (coloni-

Perennial

(1993b) Buatois & Mańgano

Perennial

(1993b) Buatois & Mańgano

beverleyensis Gordia marina, Helminthoidichnites tenuis, Mermia carickensis Gordia marina, Helminthoidichnites tenuis,

zation suite) Underflow deposits

Mermia carickensis, Archaeonassa fossu-

(1993b)

lata, Gordia indianaensis, Rusophycus isp., tia, Helminthopsis tenuis, Orchesteropus atavus, Treptichnus pollardi Carboniferous

Agua Colorada Formation (Argentina)

Gordia marina, Helminthoidichnites tenuis,

Deep lake

Perennial

Mermia carickensis, Helminthopsis

Buatois & Mańgano (1993b)

tenuis, Orchesteropus atavus, Treptichnus pollardi, Circulichnis montanus, Cochlichnus anguineus Permian

Oberho¨fer Schichten (Germany)

Megapodichnus spittergrundi

Lake margin

Ephemeral

Walter (1982)

Permian

Patquia Formation

Cruziana problematica, Diplocraterion isp.,

Lake margin

Ephemeral

Acenõlaza & Buatois

(Patagonia, Argentina)

cf. Diplopodichnus biformis, Kouphichnium? isp., Merostomichnites aicunãi, Mirandaichnium famatinense,


Undichna britannica, Undichna insolen-

(1993); Zhang et al. (1998)

Monomorphichnus lineatus, Palaeophycus tubularis, Umfolozia sinuosa, Umfolozia cf. U. longula Permian

Fitzroy Tillite Formation (Falkland Islands)

Umfolozia isp.

Glacial lake?

Perennial

Trewin et al. (2002)

Permian

Cantera Member, Brenton

Planolites isp., Diplocraterion isp.,

Turbiditic prodelta

Perennial


Loch Formation

Undichna cf. insolentia, Undichna bina

301

(Falkland Islands) (continued)

302

TABLE 17.3 (Continued) Age Permian

Stratigraphic Unit & Location Cantera Member, Brenton

Ichnotaxonomic Composition Umfolozia longula, Kouphichnium isp.,

Loch Formation

Cochlichnus isp.,Gordia indianaensis,

(Falkland Islands)

Helminthoidichnites tenuis, Spirodesmos


Type of Lake

References

Turbiditic deep lake

Perennial


Turbidite system

Perennial

Miller et al. (1991);

isp.,Planolites isp., Undichna isp. Mackellar Formation

Mermia carickensis?, Cruziana isp.

(Antarctica)

Miller & Collinson (1994)

Permian

Pagoda Formation (Antarctica)

Palaeophycus tubularis, Cruziana isp.

Glacial lake delta

Perennial

Isbell et al. (2001)

Triassic

Chinle Formation (New

Spongeliomorpha milfordensis, Planolites

Lake margin

---------------

Gillette et al. (2003)

Lake margin

Perennial

Hester & Lucas (2001)

Mexico)

montanus, Palaeophycus tubularis, Taenidium serpentinum, ?Arenicolites, Skolithos isp.

Triassic

Redonda Formation (New Mexico)

Scoyenia isp., Diplichnites isp., Cruziana isp., Lockeia isp., vertebrate trackways

Triassic

Passaic Formation (Pennsylvania)

Scoyenia gracilis, Spongeliomorpha milfordensis

Lake margin

Closed

Metz (1996)

Triassic

Passaic Formation

Cochlichnus anguineus, Didymaulichnus

Shallow lake

Closed

Metz (1996)

Lake margin

Closed

Metz (1995)

Lake margin

Ephemeral


(Pennsylvania)

lyelli, Helminthopsis isp., Mermia carickensis, Palaeophycus alternatus, Palaeophycus tubularis, Planolites annularis, Planolites beverleyensis, Treptichnus bifurcus, Treptichnus

Triassic

Lockatong Formation (Pennsylvania)

pollardi Cochlichnus anguineus, Lockeia siliquaria, Planolites montanus, Scoyenia gracilis, Spongeliomorpha milfordensis, Treptichnus pollardi


Skolithos isp., Rusophycus versans,

Triassic


Cruziana problematica

Lake margin

Ephemeral


Triassic

Fleming Fjord Formation

Arenicolites isp., Skolithos isp.,

Lacustrine tempestites

Ephemeral

Bromley and Asgaard

Triassic

(east Greenland)

Taenidium barretti, Scoyenia gracilis

Polykladichnus isp.

(1979, 1991); Dam & Stemmerik (1994)

Triassic

Fleming Fjord Formation (east Greenland)

Fuersichnus communis, Lockeia siliquaria

Lacustrine fairweather deposits

Ephemeral


Permian

Bromley and Asgaard (1979, 1991); Dam & Stemmerik (1994) Triassic

Fleming Fjord Formation

Scoyenia gracilis, Skolithos isp.

Lake margin

Ephemeral

(east Greenland)

Bromley and Asgaard (1979, 1991); Dam & Stemmerik (1994)

Triassic

Los Rastros Formation (Argentina)

Palaeophycus tubularis, Cochlichnus

Middle delta front

Perennial

Melchor et al. (2003)

Upper delta front to lower

Perennial


Perennial


Upper delta plain

Perennial


Lower delta front

Perennial

Melchor (2003)

Cochlichnus anguineus

Lake margin

Perennial

Melchor (2003)

Cochlichnus anguineus, Archaeonassa

Upper delta front

Perennial

Melchor (2003)

anguineus, Helminthoidichnites tenuis, Archaeonassa fossulata, Gordia indianaensis, Undichna britannica, Helminthopsis abeli

Triassic


Triassic

Los Rastros Formation

Palaeophycus tubularis, Cochlichnus anguineus Palaeophycus tubularis, Skolithos isp.

Triassic


Triassic

Ischichuca Formation (Argentina)

Upper delta front & distributary mouth bars

Palaeophycus tubularis, Palaeophycus striatus, vertebrate trackways Cruziana problematica, Cochlichnus anguineus, Diplichnites isp., Stiaria isp., Undichna britannica, Rusophycus stromnessi

Triassic

Ischichuca Formation (Argentina)

Triassic

Lomas Blancas Formation (Argentina)

fossulata

Jurassic

Towaco Formation (New Jersey)

Planolites beverleyensis, Planolites montanus

Shallow lacustrine

Jurassic

East Berlin Formation

Planolites montanus

Shallow lacustrine

Perennial

Gierlowski-Kordesch

Planolites montanus, Skolithos isp.

Playa mud flat

Ephemeral

Gierlowski-Kordesch

Cochlichnus anguineus,

Turbidite lobe fringe

Perennial

Wu (1985); Buatois et al.

Metz (1992)

(New England) Jurassic

East Berlin Formation

Jurassic

Anyao Formation (Central

(1991)

(New England) China)


(Argentina)

delta plain

(1991) Helminthoidichnites tenuis,

(1996b)

Helminthopsis abeli, Helminthopsis hieroglyphica, Monomorphichnus lineatus, Paracanthorhaphe togwunia, Tuberculichnus vagans, Vagorichnus anyao

303

(continued)

304

TABLE 17.3 (Continued) Age Cretaceous

Stratigraphic Unit & Location Wadhurst Clay &

Ichnotaxonomic Composition Cochlichnus anguineus, Diplichnites

Grinstead Clay

triassicus, ?Lockeia siliquaria,

formations

Palaeophycus striatus, Planolites monta-

(England)

nus, Unisulcus


Type of Lake

References

Ephemeral


Lake margin

Ephemeral


Lake delta

Ephemeral


Shallow to relatively deep

Open

de Gibert et al. (2000)

Open

Buatois et al. (2000)

Lake margin

---------------

Kim et al. (2002)

Lake margin

---------------

Kim et al. (2005)

minutus, vertebrate trackways Cretaceous

Wessex & Vectis formations (England)

Cochlichnus anguineus, Beaconites antarcticum, Lockeia serialis, Scoyenia cf. gracilis, Protovirgularia rugosa, vertebrate trackways

Cretaceous

Ashdown Formation (England)

Cretaceous

La Pedrera de Rubies Lithographic

Cretaceous

Limestones (Spain) La Hue´rguina Limestone Formation (Spain)

Taenidium barretti, Planolites montanus, vertebrate trackways Hamipes didactylus, Undichna britannica, Steinsfjordichnus brutoni, Gordia arcua-

lake (below wave base)

ta, Cochlichnus anguineus Cruziana problematica, Helminthoidichnites tenuis, Lockeia isp., Palaeophycus

Shallow to relatively deep lake (below wave base)

tubularis, Treptichnus pollardi Cretaceous


Chondrites isp., Beaconites antarcticus, Helminthopsis hieroglyphica, Palaeophycus tubularis, Skolithos magnus, Taenidium barretti, Torrowangea rosei

Cretaceous

Jinju Formation (Korea)

Beaconites antarcticus, Beaconites coronus, Taenidium barretti

Cretaceous


Diplichnites isp.

Lake margin

---------------

Kim et al. (2005)

Cretaceous


Beaconites coronus, Cochlichnus anguineus,

Lake margin

---------------

Kim et al. (2005)

Helminthopsis hieroglyphica, vertebrate trackways Cretaceous


Planolites isp., Palaeophycus isp., Skolithos magnus, vertebrate trackways

Lake margin

---------------

Kim et al. (2005)

Cretaceous


Beaconites antarcticus, Beaconites coronus,

Lake margin

---------------

Kim et al. (2005)

Shallow lake

Perennial

Perea et al. (2001)

Lacustrine delta

Perennial

Moussa (1968, 1970)

Planolites isp., Taenidium barretti, Cochlichnus anguineus, Helminthopsis Eocene

Fossil Hill Formation

hieroglyphica, Diplichnites isp. Cochlichnus isp., Helminthopsis isp.

(Antarctica) Eocene


Lake margin

Green River Formation (Wyoming)

Cochlichnus anguineus, Helminthoidichnites tenuis

Miocene

(Shandong, China)

Shanwangichnus diatomus

Diatomaceous shales

---------------

Yang (1996)

Miocene

Calatayud-Teruel Basin

Beaconites filiformis

Lake margin to shallow

Ephemeral

´ lvaro (2000) Uchman and A

Miocene

(Spain) Calatayud-Teruel Basin

Taenidium barreti, Labyrintichnus

lake Lake margin

Ephemeral

´ lvaro (2000) Uchman and A

(Spain)

terrerensis, Spongeliomorpha isp.,Polykladichnus aragonensis


Palaeophycus tubularis

Lake margin

Perennial

Smith et al. (1982)

Peace Valley Formation

Palaeophycus tubularis, Scoyenia gracilis

Lake margin

Perennial

Smith et al. (1982)

Miocene– Pliocene


Archaeonassa fossulata, ?Chondrites isp.

Delta front

Perennial

Smith et al. (1982)

Miocene–


Archaeonassa fossulata

Lake margin

Perennial

Smith et al. (1982)

Peace Valley Formation

?Chondrites isp.

Prodelta & deep lake

Perennial

Smith et al. (1982)

Burdur Formation

Arenicolites isp.

Deep lake

Closed

Price & McCann (1990)

Proglacial lake

Perennial

Gibbard & Stuart (1974)

Miocene– Pliocene Miocene– Pliocene

Miocene– Pliocene Pliocene

(Turkey) Pleistocene

Vale of St. Albans, Hertfordshire (England)

Dendroidichnites irregulare, Helminthoidichnites tenuis, Treptichnus

Pleistocene

Harassilta (Finland)

bifurcus, Cochlichnus anguineus Cochlichnus anguineus

Glacial varves

Perennial

Gibbard (1977)

Pleistocene

Near Liebegast, SW of

Warvichnium ulbrichi, Glaciichnium liebe-

Glacial lake (Shallow)

Perennial

Walter (1985, 1986); Walter

Hoyerswerda

gastensis, Lusatichnium slavensis


Pliocene

& Suhr (1998)

(Germany) Pleistocene

Near Liebegast, SW of

Cochlichnus anguineus

Glacial lake (Deep)

Perennial

Hoyerswerda (Germany) Pleistocene

Several sites near Union,

Walter (1985, 1986); Walter & Suhr (1998)

Dendroidichnites irregulare,

Iona and St. Mary’s

Helminthoidichnites tenuis, Treptichnus

(Ontario, Canada)

bifurcus, Cochlichnus anguineus, Gordia

Proglacial lake

Perennial

Gibbard & Dreimanis (1978)

marina, Diplopodichnus biformis Pleistocene

Lake Turkana (Kenya)

Trypanites weisei, Sertaterebrites nachukui

Lake margin

Perennial

Ekdale et al. (1989)

305

306


traces, arthropod trackways, chironomid, coleopteran, and annelid dwelling and feeding traces, and vertebrate traces (e.g., Rodriguez-Aranda and Calvo, 1998; Zhang et al., 1998; Uchman and Alvaro, 2000; Melchor and Sarjeant, 2004). Trace fossils commonly occur in parallel laminated and ripple cross-laminated, fine- to very fine-grained sandstone and mudstone and, to a lesser extent, evaporites. Associated physical structures indicate subaerial exposure (e.g., desiccation cracks, raindrop imprints). Lake-margin trace fossil assemblages of closed lakes are typical examples of the Scoyenia ichnofacies. Examples of these ichnofaunas in playa lake settings have been reported in a number of studies (e.g., Bromley and Asgaard, 1979; Gierlowski-Kordesch, 1991; Dam and Stemmerik, 1994; Kozur and Lemone, 1995; Rodriguez-Aranda and Calvo, 1998; Clemmensen et al., 1998; Zhang et al., 1998; Uchman and Alvaro, 2000; Schlirf et al., 2001). No examples of the Mermia ichnofacies are known from closed lakes. Open lakes are less stressful ecosystems, characterized by low salinity and relatively stable shorelines (Gore, 1989). Lake-margin ichnofaunas of open lake systems are dominated by meniscate, backfilled trace fossils, arthropod trackways and bilobate trails (e.g., Daley, 1968; Pollard et al., 1982; Smith et al., 1982; Pollard and Walker, 1984; Walker, 1985; Cook and Bann, 2000; Hester and Lucas, 2001; Kim et al., 2005). Vertebrate trace fossils are also extremely common in marginal lake facies (e.g., Olsen et al., 1978; Lockley et al., 1986; Prince and Lockley, 1989; Lim et al., 1989). Trace fossils commonly occur in parallel laminated and ripple cross-laminated, fine- to very fine-grained sandstone and mudstone containing evidence of subaerial exposure. These trace fossil assemblages represent examples of the Scoyenia ichnofacies, which is typically present in low-energy, lake-margin areas. Because the Scoyenia ichnofacies records the activity of a benthos adapted to low energy conditions in either very slightly submerged sediments that are periodically desiccated or in waterside subaerial substrates that are periodically submerged (Frey and Pemberton, 1987), it is particularly useful to delineate marginal lacustrine facies in sedimentologic studies. Substratecontrolled ichnofaunas are common in this setting due to desiccation of marginal lacustrine deposits. Firmground ichnofaunas, dominated by striated meniscate trace fossils, such as Scoyenia, and burrow galleries, such as Spongeliomorpha, are relatively common (e.g., Metz, 1993). Bioerosion in stromatolites has also been documented, but it seems to be relatively rare (Ekdale et al., 1989). In contrast to low-energy shorelines, moderate to high-energy lacustrine environments, such as wave-dominated

shorelines and delta mouth bars, contain simple vertical burrows (Skolithos), U-shaped vertical burrows (Arenicolites), and escape structures (e.g., Mańgano et al., 1994; Buatois and Mańgano, 2004). These are commonly preserved in planar to trough cross-stratified medium- to fine-grained sandstone or wave and current rippled fine-grained sandstone. These trace fossil assemblages can be assigned to the Skolithos ichnofacies (Buatois and Mańgano, 1998, 2004; Melchor et al., 2003). Ichnofaunas dominated by vertical burrows are less common than the typical lake-margin Scoyenia assemblages. In the permanent subaqueous zone of open lakes, under conditions of low energy and a high degree of environmental stability, feeding and grazing traces of detritus and deposit feeders are dominant. Arthropod trackways may be present, but are less common. Vertebrate traces are represented by the fish trail Undichna (Anderson, 1976; Higgs, 1988; Turek, 1989; Buatois and Mańgano, 1994; de Gibert et al., 1999; Trewin, 2000) and the amphibian trackways Lunichnium and Gracilichnium (Turek, 1989). Oxygen content, energy, food supply, and substrate are among the most important controls on trace fossil distribution in lakes. Oxygenation is a first order limiting factor; in lakes with thermal stratification the hypolimnion becomes anoxic/dysoxic and bioturbation is inhibited. Turbidity and underflow currents may provide oxygen to lake bottoms, allowing the establishment of benthic communities. Trace fossil preservation is also precluded in soupy substrates. Ichnologic analysis also helps to distinguish between deposits from sustained density underflows and episodic turbidity currents and between marine and lacustrine turbidites (see Buatois and Mańgano, 2004 for a discussion). Also, in turbidite and storm-influenced lacustrine basins pre- vs. post-depositional suites may be recognized. In such cases, the pre-event ichnocoenosis records the activity of the resident benthic fauna, while the post-event suite represents an impoverished opportunistic ichnocoenosis, reflecting colonization of the newly produced substrate. Examples of permanently subaqueous freshwater ichnofaunas have been reported in various studies, mostly in clastic deposits (e.g., Gibbard and Stuart, 1974; Gibbard, 1977; Gibbard and Dreimanis, 1978; Walter, 1985; Miller et al., 1991; Pickerill, 1992; Buatois and Mańgano, 1993b; Buatois et al., 1996b; Walter and Suhr, 1998; Melchor et al., 2003; Melchor, 2004) and, more rarely, in carbonate deposits (e.g., Buatois et al., 2000; de Gibert et al., 2000;). The Mermia ichnofacies is the archetypal association that characterizes permanent subaqueous lacustrine zones of open lakes. This ichnofacies extends from shallow to deep bathymetric

THE ICHNOFABRIC APPROACH TO FRESHWATER ICHNOFAUNAS

lacustrine areas. Available information suggests that there are no archetypal trace fossil associations that clearly distinguish shallow and deep lacustrine settings (Table 17.3). For example, the Palaeophycus ichnocoenosis documented by Pickerill (1992) from Carboniferous shoreface lacustrine successions of the Albert formation in New Brunswick consists of horizontal shallow burrows and trails produced by mobile predators and deposit feeders (e.g., Helminthopsis tenuis, Gordia marina, Cochlichnus anguineus). It is extremely similar to ichnofaunas recorded in deeper lacustrine settings affected by turbidity currents and other density flows (e.g., Buatois and Mańgano, 1993b; Buatois et al., 1996b). Both examples should be allocated to the same ichnofacies. Variation in trace fossil content from one lacustrine basin to the other most likely reflects the wide variability of lacustrine systems. However, in large, deep lakes, depth-related trace fossil zones can be established. Walter and Suhr (1998) documented a bathymetric zonation in Pleistocene glacial lakes of Germany. In these lakes, shallow-lacustrine trace fossil assemblages are dominated by arthropod trackways (e.g., Warvichnium, Glaciichnium, Lusatichnium), while grazing trails are abundant in deeper zones (e.g., Cochlichnus, Gordia, Helminthoidichnites). Metz (1996) noted that in Triassic lacustrine deposits of the Newark Basin, elements of the Mermia ichnofacies are replaced by typical representatives of the Scoyenia ichnofacies during shoreline regression. Similarly, Melchor et al. (2003) and Melchor (2004) documented the replacement of the Mermia ichnofacies by the Scoyenia ichnofacies due to progradation of lacustrine deltas in different Triassic redbed units from Western Argentina. Although there are no archetypal, recurrent ichnofacies that clearly distinguish shallow- vs deep-lacustrine settings, zonations prove to be useful at the scale of individual lacustrine basins.

THE ICHNOFABRIC APPROACH TO FRESHWATER ICHNOFAUNAS Ichnofabric comprises all aspects of the texture and internal structure of a substrate that result from bioturbation and bioerosion at all scales (Ekdale and Bromley, 1983; Bromley and Ekdale, 1986; Taylor et al., 2003, this volume). The ichnofabric approach became very popular during the last two decades, but still little is known about the nature and genesis of continental ichnofabrics, and review chapters are almost exclusively based on marine examples (e.g., Taylor et al., 2003). Notably, a conceptual and

307

methodological framework for the analysis of paleosol ichnofabrics has been advanced by Genise et al. (2004a) recently. These authors noted that soil features that disrupt the primary fabric of terrestrial deposits may be formed without the intervention of bioturbation (pedofabric). In addition, soil processes may also disrupt ichnofabrics. Genise et al. (2004a) noted that ichnofabric analysis in paleosols require modifications to the standard methodology developed from marine examples. They suggested construction of tiering diagrams, evaluation of the pedofabric independent of the ichnofabric, and construction of ternary diagrams showing percentages of bioturbation, pedofabric, and original bedding. These authors illustrated their methodology with examples from Mesozoic and Cenozoic paleosols from Argentina, Uruguay, and Egypt. The rest of our discussion in this chapter deals with freshwater ichnofabrics that are commonly much simpler than paleosol and marine ichnofabrics. Buatois and Mańgano (1998) addressed some of the potential and limitations of the ichnofabric approach in continental successions. These authors noted that evolutionary innovations of the terrestrial and freshwater biotas constrained the development of continental ichnofabrics. Paleozoic ichnofaunas are dominated by bedding-plane, very shallow trace fossils, mostly grazing trails and arthropod trackways (Miller, 1984; Maples and Archer, 1989; Buatois and Mańgano, 1993a, 1998; Buatois et al., 1998a). The dominance of epifaunal and shallow infaunal trace fossils result in little or no bedding disruption and, therefore, most Paleozoic continental deposits tend to be unbioturbated. Grazing trails, such as Mermia, Gordia or Helminthopsis, and arthropod trackways, such as Diplichnites or Umfolozia, which are very common in freshwater deposits, do not produce ichnofabrics. Accordingly, trail- and trackway-bearing deposits are commonly seen in cores as unbioturbated, fine-grained, thinly laminated rocks (Buatois et al., 1998b). This is particularly true for Paleozoic lacustrine deposits. However, Paleozoic fluvial deposits may contain distinct ichnofabrics characterized by monospecific assemblages of meniscate trace fossils that have been variably assigned to Beaconites or Taenidium (Fig. 17.5A) (e.g., Allen and Williams, 1981; Graham and Pollard, 1982; Morrissey and Braddy, 2004). Notably, large specimens (up to 250 mm wide) seem to be typical of Silurian-Carboniferous rocks (Keighley and Pickerill, 1994) and bioturbation depth may reach 1.44 m in examples from the Devonian Old Red Sandstone (Lance Morrissey, written communication, 2004). Based on their recurrent association with large

308


Beaconites Taenidium Ichnofabric

Composite Beaconites Taenidium + Scoyenia Ichnofabric

Scoyenia Ichnofabric

A

C

B

Emplacement in abandoned channels, overbank areas and lake margins (Softground)

Emplacement in desiccated ponds and lake margins (Firmground)

Suite replacement due to progressive dessication of water body (Softground to Firmground)

Skolithos Ichnofabric D

Colonization in lacustrine delta mouth bars and distributary channels

Colonization of active fluvial channels

Camborygma Ichnofabric G

Emplacement in areas of high water table

F

E

H

Emplacement in areas of low and/or fluctuation water table

Colonization in lacustrine tempestites

Fuersichnus Ichnofabric I

Establishment of a deposit feeding infauna in ephemeral fluvial and lacustrine environment

Planolites Ichnofabric J

Establishment of a deposit feeding infauna in ponds and lakes

FIGURE 17.5 Icons of most common continental freshwater ichnofabrics and their environmental implications. (A) Beaconites–Taenidium ichnofabric. (B) Scoyenia ichnofabric. (C) Composite Beaconites–Taenidium/Scoyenia ichnofabric. (D–F) Variants of Skolithos ichnofabric, reflecting colonization in different freshwater settings. (G–H) Variants of Camborygma ichnofabric, reflecting different positions of the water table. (I) Fuersichnus ichnofabric. (J) Planolites ichnofabric. See text for explanation.

THE ICHNOFABRIC APPROACH TO FRESHWATER ICHNOFAUNAS

Diplichnites and their similar size range, Morrissey and Braddy (2004) convincingly argued for a myriapod (e.g., arthropleurid) producer for these large meniscate trace fossils. Variants of the Beaconites–Taenidium ichnofabric seem to be common in abandoned channel and overbank deposits and represent probably the earliest continental ichnofabrics. Detailed analysis by Morrisey and Braddy (2004) suggests that the Beaconites–Taenidium ichnofabric records colonization of subaerially exposed sediment in response to seasonal desiccation with animals excavating into the substrate to aestivate or mould at water table level. This ichnofabric represents en masse colonization during a single bioturbation event and is, therefore, a simple ichnofabric. Since then Triassic meniscate ichnofabrics became common not only in fluvial environments but also in lake margin deposits (e.g., Johnson and Graham, 2004). In desiccated floodplain and lake margin deposits, meniscate ichnofabrics are commonly associated with desiccated substrates (Fig. 17.5B) and composite ichnofabrics, including both softground (Beaconites–Taenidium) and firmground (Scoyenia) suites, are common (Fig. 17.5C) (Buatois et al., 1996a). The ornamented burrow system Spongeliomorpha is also present in this environmental situation (Metz, 1993, 1995), but the associated ichnofabrics are still unknown. An ichnofabric dominated by vertical burrows seems to be present in freshwater deposits, representing an analogue to the marine Skolithos and Arenicolites ichnofabrics (Fig. 17.5D–F). Commonly, these ichnofabrics contain only one ichnotaxa. However, slightly more diverse examples are known from the Triassic of Greenland, where Skolithos and Arenicolites commonly coexist with Polykladichnus (Bromley and Asgaard, 1979, 1991; Bromley, 1996). Escape trace fossils may also be present (Sarkar and Chaudhuri, 1992). Recorded examples are present in moderate to high energy settings, such as active channels, wavedominated lacustrine shorelines, lacustrine delta mouth bars and storm deposits (Bromley and Asgaard, 1979, 1991; Bradshaw, 1981; Zawiskie et al., 1983; Fitzgerald and Barrett, 1986; Woolfe, 1990; Sarkar and Chaudhuri, 1992; Mańgano et al., 1994; Bromley, 1996; Melchor et al., 2003). This ichnofabric reflects the emplacement of moderately deep to deep burrows, which may form dense assemblages in the case of Skolithos pipe-rocks (Fitzgerald and Barrett, 1986). This ichnofabric most likely records opportunistic colonization of rapidly emplaced sands (Bromley, 1996). Another distinctive ichnofabric in abandoned channel, overbank, and lake margin deposits, particularly in Mesozoic and Cenozoic strata, is

309

dominated by the crayfish burrow Camborygma (Hasiotis and Mitchell, 1993; Hasiotis et al., 1993, 1998). Camborygma is commonly the only ichnogenus present in this ichnofabric, but several of its ichnospecies may occur. Burrow architecture is related to the position of the water table; complex architectures with many branches and chambers are constructed by primary burrowers in areas of high water table (Fig. 17.5G), while deep simple burrows are dominant in areas of low and/or highly fluctuating water table (Fig. 17.5H) (Hobbs, 1981; Hasiotis and Mitchell, 1993). Burrowing depth of 1 m seems to be fairly common (Hasiotis et al., 1998). The establishment of deep burrows in freshwater deposits led to considerable disruption of the sedimentary fabric (e.g., Hasiotis, 2002, p. 91). The Fuersichnus ichnofabric represents intense bioturbation in ephemeral lacustrine and fluvial deposits (Fig. 17.5I) (Bromley and Asgaard, 1979, 1991; Gierlowski-Kordesch, 1991; Bromley, 1996). Fuersichnus is commonly the only ichnotaxa present in the ichnofabric, but under low bioturbation intensities, Lockeia may be present as a subordinate element (Bromley and Asgaard, 1979, 1991; Bromley, 1996). The Fuersichnus ichnofabric is locally characterized by very high degrees of bioturbation, as illustrated by dense occurrences of Fuersichnus communis from Triassic successions of East Greenland (Bromley and Asgaard, 1979, 1991; Bromley, 1996). According to these authors, the Fuersichnus ichnocoenosis records the activity of shallow tier deposit feeders leading to common obliteration of all physical structures and, in most cases, of all other biogenic structures. It is most likely a rapidly produced structure reflecting the activity of opportunistic colonizers (Bromley, 1996). This is consistent with sedimentologic data, which suggest stressful environments subject to episodic flows and recurrent desiccation in ephemeral fluvial systems and playa lake complexes (Gierlowski-Kordesch, 1991; Dam and Stemmerik, 1994; Clemmensen et al., 1998). Mesozoic and Cenozoic permanent subaqueous lacustrine deposits may be moderately to intensely bioturbated and commonly contain a mottled texture that may be referred to as Planolites ichnofabric (Fig. 17.5J). Examples of bioturbated lacustrine deposits reflecting the activity of a middle-tier, depositfeeder infauna are particularly common since the Cretaceous (e.g., Whateley and Jordan, 1989; Flint et al., 1989; Buatois and Mańgano, 1998). This ichnofabric apparently reflects the activity of the fairweather lacustrine infauna, although ichnodiversity is commonly low, comprising monospecific ichnocoenoses. Burrowing by the Planolites producer

310


may have inhibited preservation of shallow-tier structures, such as grazing trails. Although most known ichnofabrics from continental environments are of low diversity and, more commonly, even monospecific, their analysis reveals subtle variations and may help to refine facies analysis. The notion of taphonomic pathways is particularly useful to understand the shaping of ichnofabrics in response to changes in substrate character and depositional dynamics (Buatois and Mańgano, 2004; Buatois et al., in press a). Additionally, taphonomic pathways help to understand the role of substrate and rapid environmental fluctuations as main controlling factors in ichnofacies development and replacement (Buatois and Mańgano, 2002, 2004). For example, in fluvial systems a variety of taphonomic pathways results from channel abandonment, overbank deposition, and establishment of ponded areas that may desiccate or be filled by overbank vertical accretion without experiencing desiccation (Fig. 17.6). In lakes, taphonomic pathways commonly reflect shoreline fluctuations and associated changes in substrate consolidation (Fig. 17.7).

APPLICATIONS OF ICHNOLOGY IN SEQUENCE STRATIGRAPHY OF CONTINENTAL SUCCESSIONS In comparison with their marine counterparts, continental trace fossils have not been extensively used in sequence stratigraphy. Buatois and Mańgano (2004) noted that application of trace fossils in continental sequence stratigraphy cannot be simply based on the extrapolation of marine sequence stratigraphy. Of most importance, substrate-controlled ichnofacies, in particular the firmground Glossifungites ichnofacies, develop in stable and cohesive substrates, reflecting erosive exhumation of the sediment (MacEachern et al., 1992). However, in continental successions, substrate-controlled trace fossils only rarely indicate erosional exhumation because they are commonly related to desiccation of water bodies which in turn is usually linked to autocyclic processes (e.g., Buatois et al., 1996a). Moreover, Fu¨rsich and Mayr (1981) documented continental firmgrounds rapidly developed under subaerial exposure, without implying a significant hiatus. Additional problems are related with the application of some sequence stratigraphic concepts in continental environments (Van Wagoner et al., 1990; Posamentier and Allen, 1999). In a seminal paper, Bohacs et al. (2000) noted some of the peculiarities of lacustrine sequence

stratigraphy and provided a valuable framework for analysis. These authors suggested that lakes differ from oceans in several ways, including the smaller volumes of sediment and water included in lacustrine systems, the direct link between lake level and sediment supply, and the fact that lake shoreline migration may be due not only to progradation but also to withdrawal of water. Bohacs et al. (2000) recognized three different types of lake basins: overfilled, balanced-fill, and underfilled (see also Bohacs et al., 2003). Recently, Buatois and Mańgano (2004) integrated ichnologic data within this classification framework in an attempt to evaluate the potential of trace fossils in lacustrine sequence stratigraphy (Fig. 17.8). In the same vein, Gierlowski-Kordesch and Park (2004) placed changes in species diversity in modern and ancient lakes within this framework. Overfilled lake basins occur when rate of sediment/water input exceeds potential accommodation. Overfilled lakes are commonly hydrologically open, contain fluvio-lacustrine siliciclastic deposits and display parasequences driven mainly by shoreline progradation and delta-channel avulsion. Overfilled lake basins contain well-developed softground trace fossils that are useful to delineate parasequences and parasequence sets (e.g., Buatois and Mańgano, 1995b; Melchor et al., 2003; Melchor, 2004). Fluvial discharge into overfilled lakes usually generates density currents that oxygenate lake bottoms, allowing the establishment of epifaunal and infaunal communities, as illustrated by Triassic examples in the Ischigualasto-Villa Unioń Basin of Argentina (Melchor, 2004). Additionally, these are freshwater lakes where no stress due to hypersalinity occurs, leading to the development of a relatively diverse benthos. Upward shallowing successions due to delta and shoreline progradation are typical. Distal facies commonly consist of underflow current and background fallout deposits hosting the Mermia ichnofacies. Intermediate facies may contain wave-dominated delta-front and nearshore deposits, including stormemplaced hummocky cross-stratified sandstone and fair-weather wave- and combined-flow ripple crosslaminated sandstone. Grazing trails of the Mermia ichnofacies may form colonization suites at the top of storm beds in such settings. However, assemblages are usually impoverished with respect to those of the more distal facies (Buatois and Mańgano, 1998). Under conditions of moderate to high energy due to continuous wave agitation, the Skolithos ichnofacies may be present. Proximal facies include distributary channel, trough and tabular cross-bedded sandstones that are commonly unbioturbated. Locally, these deposits may contain escape traces and vertical

Re-establishment of the active channel association

TAPHONOMIC PATHWAYS FLUVIAL ICHNOFAUNAS

AN

NE

PO

IO SIT

Striated burrows in subaerally exposed firmgrounds

N

Meniscate burrows CHANNEL REACTIVATION

Vertical burrows and escape traces

SUBSTRATE DEWATERING

SUBSTRATE DESICCATION

Obliteration of animal traces by root traces

ACTIVE CHANNEL

LOW DISCHARGE TO ABANDONED CHANNEL

Poorly defined traces in water-saturated substrates

Well defined traces in submerged softground

Skolithos ichnofacies

ESTABLISHMENT OF FLOODPLAIN WATER BODIES

INCIPIENT DEWATERING

COLONISATION BY PLANTS

Mermia ichnofacies OVERBANK DEPOSITION

311

FIGURE 17.6 Taphonomic pathways of fluvial ichnofaunas showing transitions between different channel and overbank trace fossil suites. Substrate consolidation plays a major role in controlling ichnofacies occurrence. Vertical burrows and escape traces are dominant in active channels (Skolithos ichnofacies). During channel abandonment or periods of low discharge, meniscate burrows are emplaced in channel deposits (Scoyenia ichnofacies) commonly crosscutting the previous suite. If channel reactivation is produced, the Skolithos ichnofacies is re-established. If a water body is formed in the floodplain, poorly defined grazing and feeding traces are emplaced in these water-saturated substrates. Poorly preserved traces may be crosscut by better defined trace fossils reflecting improving taphonomic conditions due to increasing firmness of the submerged substrate in the floodplain pond. Both suites are examples of a depauperate Mermia ichnofacies. Filling of the water body by overbank vertical accretion (overfilled overbank) led to preservation of the trace fossils. If colonization of the substrate by plants occur, animal trace fossils may be obliterated by root traces. Alternatively, floodplain water bodies may be subject to progressive desiccation (desiccated overbank). In this case two distinct suites of the Scoyenia ichnofacies are commonly recognized: one ‘pre-desiccation suite’ characterized by meniscate, backfilled structures without ornamentation developed in a soft substrate, and the second or ‘desiccation suite’ typified by striated trace fossils, cross-cutting the former and developed in a firmground. Arthropod trackways are commonly a significant component of floodplain deposits subject to desiccation.

APPLICATIONS OF ICHNOLOGY IN SEQUENCE STRATIGRAPHY OF CONTINENTAL SUCCESSIONS

CH

E LD

Scoyenia ichnofacies Meniscate burrows in emergent softgrounds

312


TAPHONOMIC PATHWAYS LACUSTRINE ICHNOFAUNAS OPEN LAKES

Meniscate traces and arthropod trackways

Vertical burrows and escape traces Dominance of horizontal grazing and feeding traces LAKE REGRESSION

SUBAQUEOUS DEPOSITION Mermia ichnofacies PROGRADATION OF CLASTIC WEDGES AND DEVELOPMENT OF HIGH-ENEGRY SHORE LINES

DEVELOPMENT OF PROTECTED LAKE MARGIN AREAS

Skolithos ichnofacies

Scoyenia ichnofacies

CLOSED LAKES Scoyenia ichnofacies

LAKE DESICCATION

TRACKWAY EMPLACEMENT IN DEWATERED SUBSTRATES

LAKE CONTRACTION

DEVELOPMENT OF TRACKED OMISSION SURFACE

TRACKWAY EMPLACEMENT IN WATER-SATURATED SUBSTRATES

TRACKWAY OVERLAP IN DEWATERED SUBSTRATES

FIGURE 17.7 Taphonomic pathways of lacustrine ichnofaunas. Hydrologically open lakes contain more varied softground ichnofacies. Vertical ichnofacies changes reflect lake regression. Typically, permanent subaqueous sediments of open lakes contain a moderately diverse assemblage of nonspecialized horizontal grazing and feeding traces (Mermia ichnofacies). During regression, vertical burrows and escape traces (Skolithos ichnofacies) can be established in high energy shoreline and nearshore sandstones (e.g., lacustrine delta front). On the other hand, meniscate traces and arthropod trackways (Scoyenia ichnofacies) are prevalent in low energy lake margin sites. Hydrologically closed lakes display limited softground ichnofacies, but abundant firmground suites in lake-margin deposits. Arthropod trackways are commonly formed in dewatered substrates of lacustrine margins during lake desiccation. If trackways are emplaced in substrates that still have a significant water content, morphology of appendage imprints is poorly preserved. Morphologic details and trackway overlap increase with progressive desiccation. Density of arthropod trackways may be very high, forming tracked omission surfaces reflecting significant time available for colonization of a single stratal surface. After Buatois and Mańgano (2004).

APPLICATIONS OF ICHNOLOGY IN SEQUENCE STRATIGRAPHY OF CONTINENTAL SUCCESSIONS

OVERFILLED LAKES Archetypal Mermia ichnofacies in underflow current deposits, thin- bedden turbidites or fine- grained suspension fallout deposits

Scoyenia ichnofacies (dominantly softground suites) in interdistributary bay deposits

Depauperate Mermia ichnofacies as colonization suites in tempestites or turbidites Skolithos ichnofacies in high energy shoreline deposits

+ + + +

+

+

+

+

+

+

+

+

+

+

Abundant softground ichnofaunas (freshwater condition) Scarce firmground ichnofaunas (no associated desiccation)

BALANCED - FILL LAKES

Skolithos ichnofacies in deltaic mouthbar sandstones

Depauperate Mermia ichnofacies in transgressive and highstand carbonates Scoyenia ichnofacies (dominantly firmground suites) in lowstand lake margin deposits

+ + +

+ +

+

+

+

+ +

+

+

+

+

+

+

+

+

+

Scarce softground ichnofaunas (hypersalinity during lowstands and oxygen depletion during transgressions and highstands Widespread firmground ichnofaunas (lowstand desiccation)

UNDERFILLED LAKES

Salinity- tolerant suites

Depauperate Mermia ichnofacies above flooding surfaces Scoyenia ichnofacies (firmground suites) in lowstand desiccated substrates and sequence boundaries

+ + + + + +

+ + +

+ +

+ +

+

+

+

+ Common supression of softground ichnofaunas (hypersalinity) Widespread firmground ichnofaunas (lowstand desiccation)

FIGURE 17.8 Trace fossil assemblages and lacustrine sequence stratigraphy. See text for explanations of Overfilled lakes, Balanced-fill lakes, and Underfilled lakes. After Buatois and Mańgano (2004) with stratal patterns illustrated after Bohacs et al. (2000).

313

314


domiciles of suspension feeders, representing the Skolithos ichnofacies (e.g., Melchor et al., 2003). In the case of deep overfilled lakes, relatively large basin floor turbidite systems can develop. The Mermia ichnofacies is commonly present in the middle to distal regions of turbidite lobe successions, comprising both pre- and post-depositional suites in thinbedded turbidite sandstones (e.g., Buatois et al., 1996b; Buatois and Mańgano, 1998). Integration of ichnologic and sedimentologic data may help to delineate environmental zonations in aggradational and progradational turbidite lobes (e.g., Buatois and Mańgano, 1995b; Buatois et al., 1996b). Land-plant derived organic matter is the prime source of nutrients, favoring the development of a depositfeeding benthic fauna in permanently subaqueous, low-energy zones. Firmground suites are rare because such large lakes usually do not experience desiccation. Balanced-fill lake basins are characterized by rates of sediment/water supply in balance with potential accommodation. Carbonate and siliciclastic facies can accumulate in lakes that are alternatively hydrologically open and closed. Successions record not only progradational parasequences, but also aggradation of chemical sediments due to desiccation. Abundant firmground trace fossil suites occur in balanced-fill lakes, but softground assemblages are usually depauperate. During lowstands, shallow balanced-fill lakes are characterized by relatively thin aggradational parasequences due to desiccation (Bohacs et al., 2000). Lowstand deposits contain abundant and widespread ichnofaunas of the Scoyenia ichnofacies. In particular, the firmground suite of this ichnofacies, containing striated trace fossils, such as Scoyenia and Spongeliomorpha, shows widespread development due to lake desiccation (e.g., Bromley and Asgaard, 1979; Gierlowski-Kordesch, 1991; Metz, 1995; Clemensen et al., 1998). Biogenic structures are usually preserved during subsequent flooding by rapid influx of sand. Relatively thick aggradational parasequence sets form in lake-floor turbidite systems in deep balanced-fill lakes during lowstands (Bohacs et al., 2000). Under these conditions, firmground trace fossils are absent. Lake hydrology is closed during lowstands and salinity usually increases (Bohacs et al., 2000), imposing a stress factor on the lake biota and, therefore, softground ichnofaunas are depauperate. Ichnofaunas from turbidite systems in balanced-fill lakes are less abundant and diverse than those from overfilled lake turbidites. For example, trace fossils are notably absent in the thin-bedded turbidites of the balancedfill Cretaceous Candeias formation (Recoˆncavo basin of Brazil), but abundant and diverse in identical facies

of the overfilled Jurassic Anyao formation (JiyuanYima basin of China) (Buatois et al., 1996b). During transgression, parasequences are relatively thick—displaying retrogradational stacking patterns—while highstand parasequences are variable in thickness and are either aggradational or progradational (Bohacs et al., 2000). Freshwater conditions are common during transgression, but dysaerobic conditions may prevail, imparting a stress factor on the benthic biota. Trace fossils may occur locally in transgressive and highstand carbonates. However, ichnodiversity is low and trace fossils are produced by epifaunal organisms. Presence of very shallow structures and paucity of infaunal traces are associated with brief periods of oxygenated bottom waters, but permanently anoxic interstitial waters, as illustrated by the Cretaceous Las Hoyas ichnofauna (e.g., Buatois et al., 2000). A depauperate Mermia ichnofacies is present in these deposits. Additionally, the preservation potential of trace fossils in carbonates is low due to diagenetic alteration. Scarcity or even absence of biogenic structures due to oxygen depletion was also noted in transgressive and highstand siliciclastic deposits of balanced-fill lakes (e.g., Olsen, 1989; Mańgano et al., 1994, 2000; Metz, 1995). Additionally, elements of the Skolithos ichnofacies may occur in delta mouth bars during highstand progradation of deltaic systems (Bromley and Asgaard, 1979; Mańgano et al., 1994, 2000). Gierlowski-Kordesch and Park (2004) noted that species diversity in balanced-fill lakes is also markedly affected by changes from hydrologically open to closed systems. In particular, the freshwater fish fauna decrease in diversity under closed hydrology due to a salinity stress, retreating via streams to freshwater sanctuaries. Species diversity increase with the return to freshwater conditions during times of open hydrology. Interestingly, Gierlowski-Kordesch and Park (2004) noted that overall species diversity in balanced-fill lakes is even higher than in overfilled lakes. Underfilled-lake basins occur when rates of accommodation exceed rate of supply of sediment/water. In hydrologically closed lakes, deposition of evaporites dominates, and parasequences record vertical aggradation. The Scoyenia ichnofacies is widespread in underfilled lake basins, but the Mermia ichnofacies is commonly absent. Lowstand deposition is characterized by evaporite accumulation in remnant pools developed in the zones of maximum subsidence (Bohacs et al., 2000). Evaporite pools are very stressful environments and almost invariably lack biogenic structures. In the remaining zones, sediments that accumulated during the previous highstand,

315

MARINE VS. NONMARINE

experience extreme desiccation during lowstand (Bohacs et al., 2000). The Scoyenia ichnofacies is associated with lowstand desiccated substrates in underfilled lakes (e.g., Metz, 1996, 2000). Density of arthropod trackways may be high, forming tracked omission surfaces, as shown in Permian playa lake deposits of the Paganzo basin in Argentina (e.g., Zhang et al., 1998). Some of these omission surfaces may represent sequence boundaries expressed by coplanar surfaces of lowstand and subsequent flooding. During pluvial periods, underfilled lakes experience rapid expansion and flash floods reach the basin, leading to deposition of event sandstones. Trace fossil preservation is mostly linked to rapid influx of sand via sheet floods entering into the lake (Zhang et al., 1998). Hypersalinity usually prevents the establishment of a subaqueous Mermia ichnofacies during transgression and highstand. However, elements of the Mermia ichnofacies may occur, albeit in reduced numbers, in very shallow water thin deposits, immediately above flooding surfaces at the base of parasequences. This assemblage is abruptly replaced upward by the Scoyenia ichnofacies reflecting lake regression, as demonstrated by (Metz, 1996, 2000) based on observations in the Triassic Passaic formation of the Newark basin. Additionally, dwelling traces possibly produced by aquatic chironomid larvae may be present (Rodriguez-Aranda and Calvo, 1998; Uchman and Alvaro, 2000). Transgressive system tracts recorded by thin transgressive parasequences usually reflect drastic ichnofaunal changes, from terrestrial assemblages (Coprinisphaera ichnofacies) to transitional terrestrial–subaqueous assemblages (Scoyenia ichnofacies) and salinity-tolerant subaqueous monospecific assemblages of Beaconites filiformis attributed to chironomids (Uchman and Alvaro, 2000). Rapid changes in depositional conditions reflecting desiccation during vertical aggradation led to the formation of composite ichnofabrics reflecting successive bioturbation events. Buatois and Mańgano (2004) noted that in alluvial settings, the sparse distribution of trace fossils primarily reflects changes in depositional system which, in turn, may be linked to system tracts. Widespread erosion, high energy, and high sedimentation rates, leading to channel amalgamation and extensive reworking of fluvial deposits, prevent formation and/or preservation of biogenic structures in fluvial channels. Interfluve areas may be characterized by extensive development of paleosols and terrestrial trace fossils, reflecting that the work of social insects may be very common, particularly in Cretaceous and younger strata (Genise et al., 2000, 2004; Genise, 2004). In particular, the Coprinisphaera

ichnofacies (and other paleosol ichnofacies still unnamed) may delineate sequence boundaries. Due to higher accommodation during the late lowstand, increasingly isolated fluvial channels encased in overbank deposits may develop, promoting preservation of biogenic structures. Eventually transgressive lacustrine and marsh deposits accumulate when rate of accomodation exceeds sediment supply (Legarreta et al., 1993; Posamentier and Allen, 1999). A trend towards the progressive replacement of vertical dwelling burrows and escape traces of the Skolithos ichnofacies in active channels by low-diversity assemblages of meniscate traces in abandoned channels and both the softground and firmground suites of the Scoyenia ichnofacies and even the subaqueous Mermia ichnofacies in overbank deposits was noted by Buatois and Mańgano (2004). This trend is reversed under increased sediment supply and decreased fluvial accommodation leading to deltaic progradation and increased channelization during highstand.

MARINE VS. NONMARINE Most, if not all, of the ichnotaxa present in the Coprinisphaera ichnofacies are produced by insects and are restricted to terrestrial environments (e.g., Coprinisphaera, Termitichnus, Celliforma, Eatonichnus). However, this is not the case with the ichnogenera commonly recorded from the freshwater Mermia and Scoyenia ichnofacies. In fact, with the exception of Scoyenia, Camborygma, and some arthropod trackways (e.g., Stiaria, Stiallia, Hexapodichnus), the other components of these ichnofacies are facies-crossing ichnotaxa reported in both continental and marine environments (e.g., Taenidium, Palaeophycus, Planolites, Gordia, Helminthopsis, Helminthoidichnites, Cochlichnus, Treptichnus). We are unaware of any report of the ichnogenus Mermia itself in a marine deposit, but this is expected with further research. On the other hand, there is a large number of ichnotaxa that are exclusive of marine environments, including the typical elements of the Nereites and Zoophycos ichnofacies and most of the ichnotaxa of the Cruziana ichnofacies (e.g., Asterosoma, Asteriacites, Curvolithus, Psammichnites, Teichichnus). Some typical marine ichnogenera (e.g., Paleodictyon, Nereites, Scolicia, Chondrites) have occasionally been recorded in a nonmarine context. However, further examination has cast doubts on their affinities. Structures referred to as Paleodictyon in freshwater assemblages (e.g., Archer and Maples, 1984; Wu, 1985; Pickerill, 1990)

316


are remarkably simpler than those from marine turbidites and commonly reveals post-event colonization. A feeding trace referred to as Nereites in lacustrine turbidites (Hu et al., 1998) lacks the internal structure of this ichnogenus and only superficially resembles this marine form. Trace fossils referred to as Scolicia in fluvial deposits (Hasiotis, 2002, 2004) are simple epirelief furrows lacking the complex meniscate backfill, double ventral cord or drain, and mucuslined vertical shafts that characterize this ichnogenus. Feeding traces assigned, sometimes with doubts, to Chondrites in lacustrine deposits (Smith et al., 1982; Kim et al., 2005) superficially resemble this ichnogenus. However, the possibility that they record branched or overlapped Planolites cannot be disregarded. Finally, some ichnotaxa that are more common in marine environments have occasionally been recorded in freshwater settings. These include common elements of the Skolithos ichnofacies, such as Arenicolites and Diplocraterion (e.g., Bromley and Asgaard, 1979; Price and McCann, 1990; Mańgano et al., 1994; Kim and Paik, 1997; Buatois and Mańgano, 2004). The ichnogenus Rhizocorallium, a common marine ichnotaxa, has been documented in a continental firmground (Fu¨rsich and Mayr, 1981).

FRESHWATER ICHNOFAUNAS IN MARGINAL MARINE ENVIRONMENTS It has been commonly assumed that freshwater ichnofaunas can only be present in continental environments. However, this is not always the case. There are at least two environmental scenarios where freshwater ichnofaunas may occur in marginal marine settings: fluvio-estuarine transitions of tide-dominated systems and glacially-influenced coasts and shallow seas. In estuaries tidal influence commonly extends further landward than the saltwater intrusion, particularly in macrotidal systems and, to a lesser extent, mesotidal estuaries (Fairbridge, 1980; Allen, 1991; Dalrymple et al., 1992; Buatois et al., 1997b). Accordingly, tidal deposits may occur in the uppermost zone of an estuary, under freshwater conditions. Ichnofaunas from these deposits have been recorded from several late Paleozoic units in the North American Midcontinent (e.g., Buatois et al., 1997b, 1998b, c; Mańgano and Buatois, 2004a) and from recent estuaries (e.g., Gingras et al., 1999). Arthropods are the dominant tracemakers in this region and the fluvioestuarine ichnofaunas seem to display a mixture of elements of the continental Scoyenia and Mermia

ichnofacies. The assemblages commonly occur in tidal rhythmites, and record the activity of typical freshwater/terrestrial biotas inhabiting tidal flats developed in the most proximal zone of the inner estuary under freshwater conditions. The presence of these mixed freshwater/terrestrial ichnofaunas in tidal rhythmites delineates a zone situated between the maximum landward limit of tidal action and the seaward salinity limit. The freshwater benthos inhabiting this zone does not have the special adaptations necessary to survive in the brackish environment. Freshwater ichnofaunas are common in glaciallyinfluenced coastal environments. Ichnofaunas from these environments can be referred to the Mermia and, to a lesser extent, the Scoyenia ichnofacies. Examples of these ichnofaunas have been mostly recorded from late Paleozoic units of Gondwana (e.g., Pazos, 2000, 2002; Buatois and Mańgano, 2003). Coastal regions with large fjords were apparently characteristic of periGondwanic landscapes (Buatois and Mańgano, 1992; Limarino et al., 2002; Kneller et al., 2004). Freshwater conditions were prevalent during most of the time because these areas were affected by a strong discharge of freshwater due to melting of the ice masses during deglaciation. Buatois et al. (in press b) noted that in contrast to coastal settings not influenced by glaciation, where fully marine ichnofaunas commonly occur in the transgressive, maximum, late transgressive deposits in these Gondwanic basins are characterized by freshwater ichnofaunas, reflecting the release of significant amounts of freshwater during melting. Although some of these settings have been referred to as ‘brackish seas,’ they may be called ‘freshwater seas’ because of the dominance of freshwater conditions during a large part of their history.

ACKNOWLEDGEMENTS Financial support for this study was provided by the University of Saskatchewan Start-up funds and a Natural Sciences and Engineering Research Council (NSERC) Discovery Grant 311726-05 awarded to Buatois. Robert Metz, Richard Bromley, and Dave Keighley provided useful information on several case studies. We thank Elizabeth Gierlowski-Kordesch and Robert Metz for reviewing this chapter.

References Acenõlaza, F.G. and Buatois, L.A. (1993). Nonmarine perigondwanic trace fossils from the late Paleozoic of Argentina. Ichnos, 2, 201.

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18 Traces of Gastropod Predation on Molluscan Prey in Tropical Reef Environments Sally E. Walker

are the first stage in the evolution of morphological change, and then ultimately, speciation (Winberger, 1994; Swanson et al., 2003). The aim of this chapter is to show that trophic polymorphisms in predatory gastropod groups that prey upon molluscs are common and, as a result, the taphonomic signature of their predatory behaviors is more diverse than previously recognized. Predator–prey dynamics are important in structuring paleocommunities, paleocommunity evolution, and for discerning morphological escalation (e.g., Harper, 2003; Kelley et al., 2003; Grey et al., 2006). Many invertebrate and vertebrate predators prey on molluscs (reviewed by Carter, 1968; Vermeij, 1987; Walker and Brett, 2002), but the full scope of these predators will not be discussed. Rather, this chapter focuses on tropical reef molluscs and their molluscan prey. Molluscs are the most diverse phylum in reef systems (Bouchet et al., 2002) and they have an excellent fossil record (e.g., Taylor et al., 1980). Predatory gastropods play an important evolutionary and ecological role in marine communities in temperate systems (e.g., Paine, 1962; Navarette et al., 2000) but their importance in tropical systems remains little studied (Taylor, 1978, 1989; Taylor et al., 1980). Most predatory gastropod families living today first evolved at higher latitudes; several genera originated 55–56 mybp (million years before present) when the tropics were latitudinally twice as broad as today (Taylor et al., 1980). Modern predatory gastropods, with few exceptions, exhibit a strong latitudinal gradient of increasing diversity toward the equator (Taylor and Taylor, 1977) and this biodiversity pattern

SUMMARY : To fully understand the evolution of tropical predator–prey systems, a trace fossil approach that examines the full range of predatory forensic evidence recorded on skeletal hardparts, is warranted. A review and synthesis of ecological research on modern predatory gastropods feeding upon tropical molluscs indicates that (1) trophic polymorphism (i.e., eating multiple prey types that require variations in capturing behavior) is wide spread, and (2) the potential trace fossil record as a result of trophic polymorphism is much more diverse than previously recognized. Predatory gastropods were ranked into three groups, those that exhibit extensive polymorphism (rank 3) to those that exhibit the least (rank 1). Predators of rank 3 were species-rich clades, and were predicted to leave a diverse trace fossil record of their feeding styles.

INTRODUCTION Trophic polymorphisms (also called resource polymorphisms, or diet polymorphisms) are well known within vertebrate groups, such as fishes (Swanson et al., 2003). Trophic polymorphisms enhance niche partitioning and speciation, and are characterized by several factors, including eating more than one prey type that may require more than one prey-capture method (Winberger, 1994). Polymorphisms need not have slight morphologic differences within species, rather they can have behavioral differences in capturing, killing, and eating prey (McLaughlin et al., 1999; Swanson et al., 2003). Differences in feeding behavior


324


SHELL-DRILLING AND SHELL-RASPING FAMILIES AND THEIR POTENTIAL TRACE FOSSIL RECORD

appeared first in the Miocene (Taylor et al., 1980). The tropics have received less attention in marine biodiversity studies when compared to the middle-and high-latitudes (Bouchet et al., 2002). However, this review and synthesis of the available literature indicates that tropical predatory gastropods leave a diverse potential trace fossil record.

OVERVIEW OF POTENTIAL TRACE FOSSILS ATTRIBUTED TO PREDATORY REEF GASTROPODS New and important groups of tropical gastropod predators either originated or diversified within the Cenozoic that may impact the fossil record of marine reef molluscs (Table 18.1): Five groups of shell-or-opercular drilling predators (Marginellidae, Muricidae, Naticidae, Nassariidae, and Ranellidae), two groups of shell raspers (Cassinae, Ranellidae) and several groups of shell-chipping, wedging, and shellbreaking predators (Buccinidae, Fasciolariidae, Melongenidae, and Muricidae). There are predatory gastropods that also use acids and toxins to subdue their prey; still others may elicit shell blisters by their predatory activities (Table 18.1). A number of these families exhibit trophic polymorphism, and may leave more than one type of predation-related trace on the shell of their prey. For example, muricids not only drill their prey, they also may wedge and chip the shells of prey, or use acidic secretions. In this manner, muricids may leave at least three different kinds of predatory traces on shells of their prey. Shell-drillers are well-known predators, and in particular, the naticids have been intensely studied (e.g., Kabat, 1990; Kowalewski and Kelley, 2002; Kelley et al., 2003). A number of other shell-drilling families are overlooked in paleoecological studies, such as the Buccinidae, Cassidae, Marginellidae, Nassariidae, and Ranellidae. These groups all have the potential to leave a drill hole or rasped hole on their molluscan prey. While the shelled prey has been the focus of much paleoecological work, calcareous operculae can be drilled as well. Least studied from a fossil perspective are gastropods that attack prey by wedging, chipping, and breaking the shell (i.e., Buccinidae, Melongenidae, and Muricidae). The potential trace fossil record from these predators is great, and has only recently been examined for buccinids (Deitl, 2004). Gastropods that use toxins or acidic secretions to subdue and kill their prey (i.e., Costellariidae, Conidae, Muricidae,

325

and possibly Olividae and Volutidae) also potentially leave a trace fossil record.

NOTE ON CLASSIFICATION, RANKING TREATMENT OF THE GASTROPOD GROUPS, AND OICHNUS Classification for the gastropod groups follows Bouchet and Rocroi (2005). Gastropod groups were ranked as follows: rank 1, if gastropods occurred in only one trophic type (e.g., always drill their prey), they had a ranking of one; rank 2, if gastropods exhibited two different predatory behaviors (e.g., drilling and shell chipping); and rank 3, if gastropods exhibited more than two types of predatory behavior (e.g., drilling, chipping, and sulfuric-acid etching). Drill holes, and other small round-to-elliptical holes in shells have an ichnological name, Oichnus (e.g., Bromley, 1981). Oichnus was once connoted to indicate predatory organisms. Just recently, however, Oichnus was emended to include a wide variety of penetrative holes and shallow pit-like impressions in shells (Nielsen et al., 2003), some of which include incomplete borings by sponges. Rasped holes from cassid predation are also attributed to Oichnus (e.g., Donovan and Jagt, 2002), although these holes are vastly different from muricid and naticid drilled holes. If meaningful predatory information is to be gleaned, the ichnogenus Oichnus needs to be reevaluated, and possibly split into different ichnogeneric terms to cover the non-predatory and predatory forms of ‘small round holes in shells.’ Therefore, Oichnus is not used in this paper because it can be confused with non-predatory behavior.

SHELL-DRILLING AND SHELL-RASPING FAMILIES AND THEIR POTENTIAL TRACE FOSSIL RECORD The best trace fossil evidence for predation are drill holes that are preserved in molluscan shells (e.g., Sohl, 1969; Bromley, 1981; Carriker, 1981; Kabat, 1990; Harper, 2003; Kelley et al., 2003). Two major gastropod groups (Muricidae and Naticidae) and four minor groups of shell drillers (Buccinidae, Margenellidae, Nassariidae, and Ranellidae) either evolved in the Late Cretaceous or Early-to-Middle Cenozoic. The evolutionary importance of shell drilling, especially in naticids, is discussed in Kowalewski and Kelley (2002) and Kelley et al. (2003), and will not be treated here

Clade and Gastropod Families

Fossil Record

Potential Trace Fossil Record

Trace Fossil Record

Prey

326

TABLE 18.1 Predatory Gastropods and Their Potential to Leave a Trace Fossil Record on Their Molluscan Prey.Systematics Follows Bouchet and Rocroi, 2005 Reference

Clade Superfamily Tonnoidea Family Tonnidae Subfamily Cassinae

Family Ranellidae

Late

Anecdotal reports of

Cretaceous to

rasped holes in prey:

Recent

secrete sulfuric acid

Early Cretaceous

Anecdotal reports of

Unknown

Mostly echinoids; can also drill gastropods

Hughes and Hughes, 1971, 1981; Hughes, 1986

Unknown

Gastropods, bivalves

Day, 1969;

drilling; toxins;

Littlewood, 1989;

sulfuric acid;

Morton, 1990; Taylor,

engulfment; shell wedging;

1998

shell blisters on bivalve prey; possible radula traces Clade Neogastropoda Superfamily Buccinoidea Family Buccinidae

late Eocene to Recent

Family Columbellidae

Shell wedging,

No trace fossils

breakage,

have been

edge-chipping,

named; record

and abrasion

of shell

of shell;

wedging in the

shell drilling

Cenozoic on

and rasping

bivalve prey

Eocene to

in a few groups ?Engulfment or

Recent

rasping of prey

Gastropods,bivalves; cannibalistic

Taylor and Reid, 1984; Titova, 1994; Dietl, 2004

Unknown

Gastropods

deMaintenon, 2005

Unknown

Gastropods, bivalves,

Stupakoff, 1986;

from shell; feeding behavior not well known Family Fasciolariidae

Early Cretaceous to Recent

Shell wedging, shell engulfment; rasping operculae; shell margin abrasion; shell chipping;

cannabalistic

Vermeij and Snyder, 2002

18. TRACES OF GASTROPOD PREDATION ON MOLLUSCAN PREY IN TROPICAL REEF ENVIRONMENTS

Littorinimorpha

spines broken and repaired on oyster prey Family Nassariidae Subfamily Nassarinae

Eocene to

Mostly scavengers;

Unknown

one driller

Moribund bivalves; driller of live bivalves

(Nassariinae)

Cernohorsky, 1984; Haasl, 2000; Morton and Chan, 1997

Family Melongenidae

Early

Drilling,

Cretaceous

shell chipping

to Recent

and breaking

Unknown

Bivalves, gastropods

Tan and Phuah, 1999; Tracey et al., 1993

Superfamily Naticoidea Family Naticidae

?Triassic,

Drilling, engulfment

Excellent

Cannibalistic,

Carriker, 1981;

Cretaceous

record:

gastropods,

Kelley et al., 2003;

to Recent

Cretaceous

bivalves

Kabat, 1990;

to Recent

Kowalewski et al.,

drill holes

1998; Sohl, 1969; Taylor et al., 1980

Superfamily Muricoidea Family Muricidae

?Late

Shell drilling,

Drill holes in

Gastropods,

Taylor and Reid,

Cretaceous;

calcareous operculae

shells known

Eocene to

drilling, edge drilling

from the late

Taylor and

Recent

and edge chipping,

Cretaceous;

Morton, 1996

shell engulfment,

other shell

shell wedging and

damage has not

chipping, toxins, acidic secretions, rasp

been reported from the fossil

operculae; shell

record

bivalves

1984;

abrasion of shell margins; decalcified areas on shell Family Costellariidae

Family Marginellidae

?Late

Toxins, little is

Unknown

Gastropods

Maes and Raeihle,

Cretaceous,

known about their

1975;

Paleocene to Recent

feeding habits

Cernohorsky, 1980

Miocene to Recent

Largely unknown, one reported genus

Unknown

Bivalves

Ponder and


Recent

Taylor 1992

that drills (continued)

327

328

Clade and Gastropod Families Family Volutidae

Fossil Record Late

Potential Trace Fossil Record Prey smothering;

(Continued)

Trace Fossil Record Unknown, but

Cretaceous

engulfment; feeding

a trace fossil

to Recent

behavior not well

record is

known

unlikely

Prey Gastropods, bivalves

Reference Morton, 1986; Tracey et al., 1993

Superfamily Olivoidea Family Olividae

Late

Engulfment; possible

Cretaceous

use of toxins; feeding

to Recent

behavior not well

Unknown

Gastropods,

Tracey et al., 1993

bivalves

known Superfamily Conoidea Family Conidae

Lower Eocene to Recent

Toxins, engulfment

Unlikely to leave a trace fossil record of predatory activities

Gastropods, bivalves

Kohn and Waters, 1966; Kohn, 1990


TABLE 18.1


in depth. Rather, a summary of tropical shell drillers and their potential trace fossil record will be presented with an emphasis on non-naticid gastropods.

Well-Known Shell-Drilling Family: Naticidae (Superfamily Naticoidea) The naticids leave an excellent trace fossil record (e.g., Kabat, 1990; Kowalewski et al., 1998; Kelley et al., 2003). Compared to muricids, naticids are much more specific in their dietary preferences, feeding only on molluscs (Carikker, 1981). They drill beveled holes in conspecifics, other gastropods and bivalves (Taylor, 1968). Drilling behavior in naticids originated in the Late Cretaceous (Sohl, 1969; Taylor et al., 1993), although drill holes are rare during that time, except in the Albian of England (see Kowalewski et al., 1998). When naticids diversified greatly in the Eocene, their drill holes became much more common (Kowalewski et al., 1998; Kase and Ishikawa, 2003). Potentially good news for trace fossil workers is the recent discovery that some species of naticids drill holes that are species specific (Grey et al., 2005). Their finding could revolutionize trace fossil recognition of paleoecological species-specific behavior in relation to naticid predation. Ratios of inner-to-outer drill-hole diameter were taken from temperate-zone naticids, and one species (Euspira heros) had a drill hole that was significantly different from drill holes produced by two other species (i.e., Euspira lewsii and Neverita duplicata). Using principal component analysis, however, all three naticid species had distinct drill holes (Grey et al., 2005). One issue that was not taken into account in their study was that drill-hole size may vary based on thickness and ornamentation of the shelled prey (e.g., Kowalewski, 2002). Grey et al. (2005) did not specifically account for these differences, but they did cogently argue that drill-hole diameter was distinct among the species. Their work needs to be extended to tropical naticids and for varying shell thickness of prey. In another paper, Grey et al. (2006) used multivariate selection techniques to show that naticids were not strong agents for evolutionary selection in bivalve prey morphology (i.e., shell length and shell thickness). These morphologic traits are thought to have adaptive value in relation to escalation between predator and prey (e.g., Kitchell et al., 1981; Kelley, 1988). Grey et al. (2006, p. 104) discussed several important findings for naticid predation: (1) that predation intensity is not necessarily correlated with selection (also see Leighton, 2002); (2) that shell length and thickness of the prey did not undergo any

329

selection-related trends induced by naticid predation from the Miocene to Recent; and (3) that selection of anti-predatory traits needs to be carefully measured. Future research needs to test temporal dynamics of predator–prey systems with multivariate selection techniques (i.e., Janzen and Stern, 1998). Not all naticids drill stereotypical drill holes: some drill the valve commissure, others drill randomly, and still others drill near the umbo region (Carter, 1968). For some prey, such as the temperate clam, Ensis, naticids will engulf the bivalve with their foot and pop open the valves (Turner, 1955). It would be important to know how often naticids may use nondrilling behavior, and also to examine their predatory behavior in reef systems.

Well-Known Modern Shell Drillers: Muricidae (Superfamily Muricoidea) Muricids, like naticids, are some of the best-known drillers in modern ecological studies (see Palmer, 1988, 1990; Rilov et al., 2004). Despite their diversification from the Eocene to Recent, they are rarely studied from a paleoecological perspective (but see Dietl et al., 2004). This is perplexing as they are globally distributed, abundant in most tropical and some temperate marine environments, and are voracious predators (Carriker, 1961; Taylor, 1978, 1998; Taylor et al., 1980; Vokes, 1990, 1996). Muricids chemically and mechanically drill into their prey. An accessory boring organ produces an acid that chemically dissolves the shelled prey and the radula provides mechanical abrasion to make a small drill hole (Carriker, 1961, 1981; Carriker and van Zandt, 1972). Muricid drill holes are usually cylindrical with straight edges (e.g., Carriker, 1981), but a recent finding suggests that their drill holes may be circular, cylindrical, and irregular in shape (Urrutia and Navarro, 2001; Harper and Peck, 2003). The shape of the drill-hole may vary depending on the prey species drilled (Gordillo and Amucha´stegui, 1998). Muricids then inject a toxin that paralyzes the prey through the drill hole (Carriker, 1981). Tropical muricids exhibit a variety of feeding strategies and habitat specializations (Taylor and Morton, 1996), characteristics that make them an excellent group in which to study trophic polymorphism. In general, muricid predatory behavior is quite variable because they can: (1) use a variety of toxins to subdue their prey and consume it without drilling (e.g., Menzel and Nichy, 1958; Carikker, 1981; Roseghini et al., 1996); (2) use different shell-drilling behavior depending on species

330


(Gordillo and Amucha´stegui, 1998); (3) change their drilling behavior during ontogeny (Gordillo and Amucha´stegui, 1998); or (4) resort to stealing prey from other predatory gastropods including conspecifics (kleptoparasitism; Morgan, 1972; Ishida, 2005). Molluscivorous muricids feed on sessile vermetids, limpets, mobile gastropods, and mussels (Taylor, 1976; Fairweather et al., 1984). Muricids may also drill empty bivalve shells (Carriker and Yochelson, 1968) or in one case, a muricid drills its own operculum (Prezant, 1983). Drilling empty gastropod or empty bivalve shells is a form of mistaken predation (after Walker and Yamada, 1993). If mistaken predation is common, it could lead to the over estimation of drilling predation in the fossil record. Non-drilling prey captured by muricids is discussed in the section ‘Gastropod predators that wedge chip-and-break, and abrade shells.’ Shell drilling in muricids is most likely a plesiomorphic behavioral trait (Vermeij and Carlson, 2000), although, not all muricid genera bore through hard exoskeletons (Castell and Sweatman, 1997). Why some groups of muricids have varied drilling and feeding mechanisms, while others have more stable drilling behavior is unknown. Drilled shells in a molluscan death or fossil assemblage would not give a reliable estimate of predation intensity or prey preference because a majority of the prey would be killed but not drilled. For example, the temperate zone Nucella lamellosa drills its prey (Mytilus trossulus) approximately 88% of the time (Kowalewski, 2004). Another muricid, Stramonita (formerly Thais) haemastoma may consume approximately one-third of their prey by not drilling (McGraw and Gunter, 1972; Gunter, 1979). In the Florida Keys, Morula nodulosa rarely drills its vermetid prey (Ingham and Zischke, 1977). Muricids studied in shallow waters off Hong Kong also exhibit variable drilling behavior: Thais clavigera drilled 21% of their prey, leaving 53% of the prey without damaged shells and 26% with shell margin damage (i.e., abraded margins); whereas, in the same habitat, Morula musiva drilled 79% of their prey, leaving 17% dead but undamaged shells, and 3% with shell margin damage (Taylor and Morton, 1996). Urrutia and Navarro (2001) reported that drill-hole size does not correlate with predator size: small drill holes were drilled by larger muricids, larger ones by smaller muricids (see also Taylor and Morton, 1996). In contrast, for temperate zone Nucella lamellosa preying on the mussel, Mytilus trossulus, drill-hole size did correlate with predator size (Kowalewski, 2004). Muricid behavior also may change over geologic time in relation to nutrients and competition for

those nutrients. Edge-drilling was more common in a species complex of Chicoreus and Phyllonotus during the Pliocene of Florida, when nutrients were abundant, and perhaps competition for resources was more fierce (Dietl et al., 2004). After the Plio-Pleistocene extinction, they found that edge drilling, a faster method for drilling prey, did not occur on any of the prey species (Chione); rather, the more time-consuming wall-drilling behavior became the main mode of predation. Their findings show that functional ecological roles of muricids can change en masse after an extinction, when the ecological structure of the environment changes. Additionally, Dietl et al. (2004) showed in laboratory experiments that modern muricids, Chicoreus dilectus and Phyllonotus pomum from Florida can edge drill when intraspecific interactions are common; when isolated, individual C. dilectus and P. pomum favor the more labor-and time-intensive shell-wall drilling behavior. The competition hypothesis of Dietl et al. (2004) can be further tested to examine whether biodiverse habitats in modern and fossil settings promote edge drilling in comparison to low-diversity habitats. Their work is an excellent example of trophic polymorphism that is induced by competition for resources. In other studies, predatory muricids that eat the same prey, may edge drill the prey in slightly different ways and with varying drilling frequencies. Rilov et al. (2004) showed that two species of muricids, Stramonita haemastoma and Hexaplex trunculus from the Israeli coast had vastly different prey handling times and edge-drilling frequencies: Stramonita occurs in food-rich high-wave energy habitats, and H. trunculus occurs below the intertidal, in relatively food-poor and low-energy habitats. Because of faster preyhandling times, Stramonita had a higher rate of predation on the mussel Brachidontes than Hexaplex. Despite the higher rate of predation, Stramonita drilled far less large-sized mussels than Hexaplex, drilling 30% of the prey that was killed, whereas, Hexaplex edge drilled 96% of its large mussel prey. The two species also differed in where they drilled the shell. Stramonita drilled valve margins leaving a small slit through which it possibly injected a toxin to incapacitate the prey. This relaxant may also seep through valves without drilling (McGraw and Gunter, 1972), perhaps accounting for the lack of drill holes. This slit (< 0.8 mm in narrowest diameter) is much smaller than those depicted for fossil edge-drilled shells (see Fig. 3 of Dietl et al., 2004). Hexaplex drilled on the valve margins like Stramonita, but the conical-shaped drill hole (approximately 3 mm in diameter) occurred on the thicker areas of the mussels. The drill holes of Hexaplex would be easier to see in the fossil record.


Morphological differences in edge-drilled holes could indicate habitat complexity and food availability in muricids, larger circular drillings may be indicative of low energy and low food availability habitats; whereas, slit-like edge-drilling may indicate high energy conditions and high food availability. Multiple factors affect where and how muricids drill into shelled prey (Kabat, 1990; Urrutia and Navarro, 2001), and therefore, stereotypy is not as common in muricids as it is in naticids. One of the reasons for this is that muricids may exhibit ontogenetic switching in drilling behavior (McGraw and Gunter, 1972; Gunter, 1979; Palmer, 1990). For example, the Chilean muricid, Chorus giganteus, will drill a large hole in the shell ligament area of their bivalved prey when young, while C. giganteus adults will drill smaller holes at the edge of the shell on the ventral side of their prey (Urrutia and Navarro, 2001). In temperate environments, muricids are known to attack small prey indiscriminately without preference for drill-hole location, while larger prey are drilled at specific locations on the shell (Hart and Palmer, 1987). In these temperate-zone muricids, stereotypy of drillhole siting varies with ontogenetic age, but once it is established, stabilizing selection may act to canalize drill-hole stereotypy in some adults (Hart and Palmer, 1987). Kowalewski (2004) did not find that temperate zone Nucella adults had stereotypic drill-hole siting, a further indication that muricid species are variable in their drilling behavior. In Florida, ontogenetic switching is more extreme: Muricanthus while young will drill prey, but as they get older and larger, they acquire shell-chipping or wedging behavior (Paine, 1967; Broom, 1982). This non-drilling behavior may be related to the functional loss of the accessory boring organ later in ontogeny (Urrutia and Navarro, 2001). The change in drilling behavior may be related to a number of factors that need further examination: ontogenetic switching could be attributed to learned behavior in prey handling; maturation of the foot for holding the prey; and, the ontogenetic development of toxins (see also Palmer, 1988). There is an extreme case of drilling stereotypy in tropical muricids. The muricid Haustrum baileyanum unwaveringly bores through the thickest part of its prey, the Australian reef abalone. Drilling through the thickest part of the shell increases prey-handling time, with the muricid taking seven days to drill and seven days to consume its prey (Thomas and Day, 1995). In an amazing show of canalized behavior, Haustrum’s drilling location does not change, even if the shell is experimentally thinned or the surface layer of the shell is removed from the prey (Thomas and Day, 1995). If the abalone survives the muricid attack, the

331

drill-hole area is repaired, forming blisters on the interior of the abalone shell; often, an abalone has several of these blisters (Thomas and Day, 1995). These blisters can be used in the fossil record to track muricid predation. Occasionally, two Haustrum individuals may drill over the same muscle tissue, leaving two complete drill holes (Thomas and Day, 1995). The work with Haustrum indicates that it is possible that more than one individual of the same species can drill the same prey, often at the same time. Aggregations of muricids drilling a single prey item were observed in other regions (e.g., Taylor and Morton, 1996). Multiple drill holes on a single prey could be used to examine the fossil record of aggregative drilling behavior in muricids and, from an evolutionary perspective, multiple drill holes may also indicate trophic-sharing of a large food-rich resource. Recent findings from the Pacific coast of North America indicate that muricids may vary their predation intensity spatially as a result of genetically-controlled behavioral differences. Sanford et al. (2003) found that Nucella canaliculata had greater predation intensity on its favored prey (Mytilus californianus) in the southern part of its range, and less predation in the northern part. This difference in predation had a strong genetic component and was mediated by direct development and evolution within habitats that had varying abundances of the favored prey, Mytilus. Their findings suggest that latitudinal differences in drilling frequencies need to be reinvestigated using localized and regional populations of muricids. Operculae may provide another skeletal element that can be used to examine behavioral traces of muricid predation. For example, the tropical muricid Dicanthais orbita drilled through the heavily calcified operculae of its thick-shelled gastropod prey, Ninella torquata (Taylor and Glover, 2000, see their Figs. 8–9). They found that 60% of Ninella shells were not drilled, but 40% were drilled between the operculum and the interior aperture, damaging both areas. Radular scrapings and acidic secretions contributed to the formation of an arc-shaped drill hole. Dicanthus also attacked other gastropod prey in a similar manner at additional localities in western Australia (Taylor and Glover, 2000). Elsewhere in western Australia, Dicanthus drilled patelloid and siphonarid limpets, or scavenged carrion (Taylor and Glover, 2000). Thus, Dicanthus, with its wide diet and flexibility in feeding modes, like almost all other muricids, exhibits trophic polymorphism. In summary, muricids are excellent candidates for studying trophic polymorphism. They exhibit a number of shell-drilling behaviors: drilling shells,

332


drilling operculae, and drilling in aggregations. Of these drilling behaviors, only drilled shells have received the most attention in modern studies and only limited study in the fossil record (Dietl et al., 2004). Drilling rates may also change, depending on the species of muricid and the type of prey. Drilling behavior may be common when the muricids are younger, but older muricids may not drill. Muricids do not exhibit stereotypic drilling behavior, nor does the size of the drill hole correlate with prey size. Drill holes are variable in morphology. Why all this variability? Perhaps trophic variability is related to the ability to live in more habitats than naticids, which have more stereotypic drilling behavior. Yet, even within similar habitats, localized selection can affect the drilling behavior of a muricid species (i.e., Sanford et al., 2003). Fortunately, because of their trophic polymorphisms, muricids may leave a more diverse and behaviorally more complex trace fossil record than any of the drillers. These behaviors have yet to be fully recognized in the fossil record.

Lesser-Known Shell-Drilling Family: Buccinidae (Superfamily Buccinoidea) Buccinids, such as Cominella, are known to bore through bivalve prey in western Australia (Peterson and Black, 1995). Cominella are the first buccinids known to drill into molluscan prey. Abundant in southwestern Australia lagoons, Cominella eburnea and Cominella tasmanica drill the first-year size class of venerid bivalves (Katelysia scalarina). Visually, their drill holes were indistinguishable from the drill holes of a muricid (Bedeva paivae) that feed on similar prey. Thus, it may be difficult to separate these predators based on their drill holes. Morphometrics of the drill hole may be necessary to statistically distinguish the drill holes among these species (see Grey et al., 2005 for naticids).

Lesser-Known Shell-Drilling Family: Marginellidae (Superfamily Muricoidea) In addition to parasitizing sleeping fish (Bouchet, 1989; Johnson et al., 1995; Bouchet and Perrine, 1996), some marginellids drill into small bivalves (Ponder and Taylor, 1992). The marginellids, Austroginella johnsoni and Austroginella muscaria from southeastern Australia drill irregularly-shaped holes in bivalve prey. An irregular interior drill-hole outline, however, distinguishes the marginellid drill holes from naticid drill holes. The outer drill-hole shape produced by the marginellids may not be distinguishable from

octopod borings. It is not known if the drill holes from marginellid differ from those produced by buccinids that prey upon Cominella spp. from southwestern Australia. Perhaps marginellid drilling behavior is parasitic or predatory in nature. Additional reports on marginellid feeding behavior are anecdotal (Winner, 1989). However, the forensic evidence in the form of irregular-shaped drill holes should exist in the fossil record if marginellids are common and abundant lagoonal species in many tropical localities.

Lesser-Known Shell-Drilling Family: Ranellidae (Superfamily Tonnoidea) The Ranellidae (including the former Cymatiidae) are ravenous carnivores that have deleterious effects on reef-associated gastropods and bivalves, especially oysters and giant tridacnid clams (Littlewood, 1989). They may have quite an impact on intertidal and subtidal molluscan prey, but further research on their predator–prey ecology is needed (Morton, 1990). The Ranellidae are known to be generalists, feeding on many organisms, usually molluscs, polychaetes, and ascidians (e.g., Taylor, 1998). Some ranellids may use toxins, such as tetramine to paralyze their prey (Shiomi et al., 1994). Some members within the subfamily Cymatiinae are known to drill their prey. The tropical cymatid, Monoplex australasiae, may drill into oysters and other bivalves such as Phaphirus largillierti and Anadara trapezia (Laxton, 1971), but this work may be based on anecdotal evidence. Cymatiinae from cooler waters in Europe are reported to drill into mussels, but further work needs to be done to see if this is a common behavior. Taylor (1998) observed that aquaria-bound ranellids dissolve small holes in Saccostrea oysters. If shell drilling by Cymatiinae can be substantiated, then this group would add to the growing pantheon of gastropod predators that could leave drill-hole traces on molluscan prey.

Lesser-Known Shell-Drilling Family: Tonnidae (Superfamily Tonnoidea) The superfamily Tonnoidea include several groups of tropical and subtropical predatory gastropods (e.g., Tonnidae, Cassinae, Ranellidae; Morton, 1990). Members of this group may use sulfuric acid to subdue, paralyze, kill, or digest their prey or they may use the acid as a defense mechanism (Morton, 1990). The Tonnidae subfamily Cassinae are tropical to warm-temperate predatory gastropods that prey on echinoderms (Hughes, 1986; Mortan, 1991).

GASTROPOD PREDATORS THAT WEDGE CHIP-AND-BREAK, AND ABRADE SHELLS

However, there are reports that Phalium labiatum and Phalium semigranosum may prey on bivalves (Day, 1969). The acid Phallium spp. secretes can etch the surface of Macoma shells (Day, 1969; but see Hughes and Hughes, 1971). If the Phalium group rasps holes into bivalve shells, they would add to the diversity of shell-drilling and rasping predators.

Lesser-Known Shell-Drilling Family: Nassariidae (Superfamily Buccinoidea) Nassariids are a diverse family with a Cenozoic record of approximately 300 extant and 600 extinct species (Cernohorsky, 1984). Originating in the Eocene, the mostly tropical subfamily, Nassarinae makes up 80% of nassariid diversity (Lozouet, 1999). Nassarinae are mostly scavengers (Cernohorsky, 1984), but one observation suggests that they drill molluscan prey. Morton and Chan (1997) showed in laboratory studies that the post-larvae of a nassarid, Nassarius festivus, drills into conspecific post-larval shells. This species drills holes of various shapes, ranging from elongate slits to countersunk spherical holes that indicate that both mechanical and chemical dissolution were used to penetrate the post-larval shells. Surprisingly, the adults of N. festivus are not known to drill, suggesting that drilling behavior is a juvenile trait that is lost in adulthood. In all, limited knowledge exists concerning nassariid drilling behavior.

GASTROPOD PREDATORS THAT WEDGE CHIP-AND-BREAK, AND ABRADE SHELLS Overview A suite of potential traces that are not studied in the fossil record, with some exceptions, including shell wedging that leads to shell chips or breakage; shell abrasion; and, shell dissolution (corrosion). Shell wedging refers to wedging open shelled prey using the shell margin of the predator (Wells, 1958a, b; Paine, 1962). In the wedging process, the shells from either the predator or the prey can be chipped or broken. Shell wedging may produce two types of potential traces left on the prey, but may be difficult to distinguish among families of predatory gastropods, as several groups employ this method in the tropics (i.e., buccinids, fasciolariids, melongenids, and muricids).

333

Shell breakage and subsequent repair by the prey may be difficult to discern from crab predation. However, temperate buccinids may leave more recognizable predation evidence, from fractured shell margins to different shell-chipping patterns (Dietl, 2003, 2004). Often, but not always, the predator will retain shell damage to the outer lip that is subsequently repaired. Repaired shell edges may or may not be directly attributable to predation. Shell damage can result from burrowing activities in bivalve species (Checa, 1993) or by breakage resulting from dislodgement within the rocky intertidal zone (e.g., Raffaelli, 1978; Cadeé, 1999). Human fishing activities also damage molluscan shells (e.g., Ramsay et al., 2000), adding to the difficulty in interpreting the precise cause of shell damage and subsequent repair (Ramsay et al., 2001). The labral spine (labral tooth) on some gastropod families may be used to wedge-and-chip the shells of prey, but other predatory gastropods may use the labral spine for stabilization in the predation process (Paine, 1967). Vermeij (2001, p. 469) suggests that the presence of a labral spine does not guarantee that it plays a direct role in predation. The labral spine evolved about 58 times in a number of different gastropod clades, from Ranellidae to Marginellidae and most of these groups occur in warm-temperate to tropical habitats (Vermeij, 2001). Shell abrasion is often associated with physical transport, but it also can occur when the predator uses its radula and/or shell to abrade the shelled prey. These abraded areas are figured by Carter (1968, his Plate I), and are quite distinctive traces from modern bivalves. Dietl (2003) has effectively used these traces to show buccinid wedge-and-chip behavior in the Cenozoic fossil record. A trace fossil needs to be named for this characteristic trace. Some predatory gastropods secrete acids to chemically dissolve the shelled prey. Shell wedging-and-chipping muricids may also leave a decalcified area on the interior of bivalve prey resulting from acidic secretions; whereas, buccinids and fasciolariids may not leave such a trace.

Wedge Chip-and-Breakage Behavior in Buccinidae (Superfamily Buccinoidea) Predatory buccinids may have a more diverse trace fossil record than previously recognized. Temperatezone buccinids are known to: (1) smash and crack bivalve shells to obtain food (Carter, 1968; Dietl, 2004); (2) abrade bivalve margins near the siphonal entrance such that the ornamentation is removed (Carter, 1968;

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Dietl, 2003); (3) edge-chip the valve openings (Colton, 1908; Carriker, 1951; Dietl, 2003); (4) shatter the umbo or shell margins in the process of forcing open valves of the prey (Menzel and Nichy, 1958); or, (5) no damage results when the predator applies force to the valves (Menzel and Nichy, 1958; Nielsen, 1975). The valve-edge chipping behavior has been examined in the fossil record (Dietl, 2003), but unlike the temperate zone, the effect of buccinid predation in tropical regions are not well known (Kohn et al., 1997). Temperate-zone buccinids are known to eat polyplacophorans, gastropods, and bivalves; they scavenge fish and other invertebrates (Magalhaes, 1948; Nielsen. 1975; Ingham and Zischke, 1977; Louda, 1979; Peterson and Black, 1995). For tropical buccinids, limited studies exist on their gourmet tendencies (Kantor and Harasewych, 1994; Kohn et al., 1997). Based on the few tropical species examined, it appears that large-sized buccinids are generalist predators, feeding on a wide variety of prey, while smaller buccinids eat polychates (Kohn et al., 1997). As an example, the large (> 20 mm) buccinid Cantharus undosus from the reefs located at the Houtman Abrolhos Islands, western Australia, eats polychaetes, fish, crustaceans, and other gastropods. While smaller buccinids (e.g., Caducifer) eat polychaetes (Kohn et al., 1997). Some buccinid genera are known to vary their dietary preferences depending on where they live. Pisania ignea from the Houtman Abrolhos Islands prey on gastropods (Kohn et al., 1997), while in the Mediterranean, Pisania striata prey on Cerithium gastropods, and to a lesser extent on polychaetes (Taylor, 1987). In Florida, Pisania tincta eat barnacles by mechanically breaking into their shell (Kantor and Harasewych, 1994). These species may also eat vermetid gastropods in other areas (Ingham and Zischke, 1977). Molluscivorous Pisania gain entry to vermetid shells by dislodging the operculum with their proboscis (Ingham and Zischke, 1977). For these examples, it is not known if a potential predatory trace is left on the shell of the prey. In general, buccinids use the edge of their shell to hammer away and eventually chip the valves of prey (Carriker, 1951; Paine, 1962; Nielsen, 1975). The distinctive shell-repair scars produced by the predator Sinistrofulgur on the bivalve prey (Mercenaria) are known from the Plio-Pleistocene of Florida (Dietl, 2003), but have not yet been recorded as a trace fossil. Except for the lack of shell damage, most of the buccinid shell-damage traces have the potential to be preserved in the fossil record.

Shell-Rasping and Wedge Chip-and-Breakage Behavior in Fasciolariidae (Superfamily Buccinoidea) Fasciolariidae originated in the Early Cretaceous and diversified in the Oligocene (Cernohorsky, 1980). They are known to eat benthic invertebrates including molluscs, polychaetes, and barnacles; they also scavenge carrion (Taylor et al., 1980). Larger Fasciolariidae are molluscivorous and are distributed in the tropics (i.e., Pleuroploca and Fasciolaria; Paine, 1967). Fasciolaria tulipa devours oyster drills, the gastropod Urosalpinx, and conspecifics (Wells, 1958b). Fasciolaria hunteria is known to chip valve margins of oyster prey, including the American oyster, Spondylus americanus in Jamaica (Faifarek, 1987). Other fasciolariid species, such as Leucozonia, may feed on small molluscs (Taylor and Lewis, 1995). In the Florida Keys, Leucozonia nassa rasps into and uses its shell margin to attack sessile vermetids (Ingham and Zischke, 1977). The fasciolariid, Latirolagena may be a specialist on vermetids, but they also eat cerithiid gastropods (Reichelt and Kohn, 1985; Taylor and Lewis, 1995). Vermetid shells have not been examined for predation marks resulting from fasciolariid attacks. Fasciolariids such as Peristernia, Latirolagena, and Latirus from Indo-Pacific reefs are predators on polychaetes; a few species consume gastropod prey, including vermetids (Taylor and Lewis, 1995). Fasciolariids either shell wedge (for bivalves and limpets) or rasp the operculum of gastropod prey (Wells, 1958b; Paine, 1963b; Paine, 1967). When attacking oysters, Fasciolaria hunteria may scrape off encrusting organisms and shell ornamentation with a combination of rasping (with the radula) and shell wedging (Wells, 1958b). Wells (1958b) showed that approximately 78% of the oysters he studied had a scraped-off surface (Wells, 1958b). Approximately 91% of the oysters will chip the dorso-posterior margin of their valves when closing them against the marauding proboscides of Fasciolaria. Once an oyster has been killed, conspecifics of Fasciolaria will share in the spoils. If more fasciolariids are attracted to the prey, the more the oyster shell may be chipped. Thus, shell abrasion along the margins of bivalve shells may be an excellent indicator of fasciolariid predation, but this has not been examined in the fossil record. Chipped areas do not always occur on the margins of the prey shells; repaired or broken spines may indicate fasciolariid attacks. For example, Fasciolaria tulipa feeds on the American spiny oyster, Spondylus americanus, and may leave chipped areas on the valve margin or they may break the spines, which can be

GASTROPOD PREDATORS THAT WEDGE CHIP-AND-BREAK, AND ABRADE SHELLS

repaired (Faifarek, 1987). Repaired Spondylus spines are reported from the Late Cretaceous (Carter, 1972). These repaired spines may be another potential trace fossil. Labral spines in fasciolariids are not used in opening shells of prey. The fasciolariid, Opeatostoma pseudodon has one of the longest labral spines of all gastropods, and it uses the spine to wedge itself into the sand while feeding (Paine, 1967). Thus, the presence of the labral spine in this species is not associated with predation. One of the largest predatory gastropods (approximately 60 mm in length) is the Florida Horse conch, Triplofusus giganteus (formerly Pleuroploca giganteus). This species, along with other members of this genus, use opercular rasping or insertion of the proboscis between the shell and the aperture of the gastropod prey. Triplofusus giganteus is cannibalistic toward its own members (e.g., Fasciolaria tulipa, Fasciolaria hunteria, Busycon contrarium, Busycon spiratum; Paine, 1963a). For gastropod prey, the proboscis of Triplofusus enters through the opercular opening, and in some cases, the operculum is rasped off and the meat consumed (Paine, 1963a). The radulae of Triplofusus is used to tear or rasp the soft tissue away from the shell (Gunter, 1936). This opercular-rasping behavior has also been described for Pleuroploca trapezium in the tropics (Taylor, 1968). For bivalve prey, they use shellwedging behavior. Oysters are wedged chipped and broken open by Triplofusus (Paine, 1963a). Pleuroploca princeps, a large predatory gastropod from the Gala´pagos Islands attacks gastropod prey with their large foot and then uses the proboscis to force entry into the aperture and then scrapes away the flesh using their radula (Stupakoff, 1986). This gastropod also excavates pen shells (Atrina) out of their sandy habitat and then wedges the shell open (Paine, 1963a). Little is known about whether fasciolariid species leave enough of a modern trace record of their feeding behavior on their shelled prey. For gastropod prey, fasciolariids may only leave a trace of their radular scraping. For bivalve prey, fasciolariids may make similar chip marks as buccinids and muricids when wedge-chipping bivalve prey.

Shell-Rasping and Shell-Breakage Behavior in Melongenidae (Superfamily Buccinoidea) Melongenids may have originated in the Early Cretaceous (Tracey et al., 1993) and most melongenids are tropical. They are predators on bivalves, gastropods, crustaceans, and ascidians, or are scavengers on dead crustaceans, fish, molluscs, and horseshoe crabs

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(Hathaway and Woodburn, 1961; Bowling, 1994; Tan and Phuah, 1999). In Florida, Melongena corona inserts its proboscis between the valves of bivalve prey and then rasps out the meat (Bowling, 1994). Sometimes, the prey will clamp down on the proboscis (Menzel and Nichy, 1958). The prey may be moribund from low tides during the summer months, making them more susceptible to melongenid predators (Menzel and Nichy, 1958). Other melongenids can use a variety of prey-attacking techniques, some of which may be preserved in the fossil record. The melongenid Hemifusus tuba from Hong Kong has a variety of methods to open their prey (Morton, 1985). For thinshelled bivalves (i.e., Sinovacula constricta), Hemifusus often breaks the shell along the mid-ventral margin in the process of pulling the valves apart (Morton, 1985). In contrast, larger and thicker bivalve prey had no visible evidence of predation because Hemifusus inverts its proboscis onto the siphons of the burrowed bivalves and kills them without shell damage (Morton, 1985). Overall, melongenids may leave a record of shell breakage, but it remains to be determined if the breakage is distinctive enough to be distinguished from other gastropod predators that produced similar shell damage.

Shell-Chipping, Edge-Chipping, and Abrasion Produced by Muricidae (Superfamily Muricoidea) Muricids that do not drill their prey occur in tropical reef settings (Castell and Sweatman, 1997). Thais tuberosa, a muricid from the Great Barrier Reef, feeds on gastropods by inserting its proboscis through the aperture while others (i.e., Morula fiscella and Morula biconica) may drill (Castell and Sweatman, 1997). Some muricids chip the shell edge, as some Dicathais are known to do in western Australia (Taylor and Glover, 2000). Other muricids may use a labral spine for opening of valved prey or puncturing holes in opercular plates of barnacles (Wells, 1958a; Perry, 1985; Vermeij and Carlson, 2000). Often muricids use their foot to apply the initial opening force, then either the shell edge or labral spine is inserted into the shell opening (Castilla et al., 1979). The first appearance of labral spines in the Muricidae occurred in the Late Oligocene, and may have evolved in response to increased primary productivity (Vermeij, 2001). In subtropical habitats, muricids with labral spines may have a variety of prey attacking techniques. For example, Acanthina (now called Acanthais, see Vermeij and Kool, 1994) may drill prey such as

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barnacles, rasp opercula of gastropods or edge-chip the shell of limpet prey. In temperate settings, Murex fluvescens attacks oysters by applying suction to the unattached valve and then inserts its proboscis into the valve interior and rasps the soft tissue (Wells, 1958a). During this process, the muricid may chip the upper valve or lower valve near the posterior margin (Wells, 1958a). In the tropics, muricids attack and abrade the posterior margin of thick-walled bivalve prey; the anterior and ventral margin of the prey shells can also be chipped (Wells, 1958a). When the interior of such shells are examined near the site of entry by the muricid, there is a ‘halo’ of decalcified shell material that is formed from the acidic secretions (Wells, 1958a). This decalcification has not been examined further in modern shells, but it appears to be a good candidate for a potential muricid predatory trace. In summary, muricids can damage the shell by abrasion and shell wedge-and-chip behavior. They can also dissolve the interior of the shell near the site of entry. In turn, the muricid retains shell damage on the outer lip that is repaired by the snail (Wells, 1958a). Muricid shell-chipping traces can be distinguished from buccinid chipping traces because the two groups of predatory snails hold the prey in different positions (Wells, 1958a); however, the shell damage was not depicted in Wells (1958a), and it is thus difficult to deduce if the gastropod families would leave characteristic distinctive trace fossils. Nor has the decalcified area produced by muricid acidic secretions been examined for its utility as a trace.

PREDATORY GASTROPODS THAT ENGULF PREY, PRODUCE TOXINS AND ACIDIC SECRETIONS, AND PROMOTE CORROSION OF THE SHELL OR SHELL BLISTERS Overview Engulfment without swallowing the shell is a very common form of predation by tropical gastropods. The prey is either subdued by a toxin or by saliva infused with sulfuric acid. Predatory gastropods that engulf their prey may provide yet another type of trace fossil resulting from corrosion of the prey’s shell, if the saliva is acidic; for those that use a non-acidic toxin, these groups may not leave a predatory trace fossil record. A radula trace may also be left because the meat is rasped from the shell. Shell blisters that result from larval gastropods that settle within living

bivalves can be potential trace fossils along with acidic secretions that may decalcify portions of the shelled prey.

Sulfuric Acid, Shell Blisters, and Rasping Traces of Ranellidae (Superfamily Tonnoidea) Molluscivorous Cymatiinae wedge their proboscis between the valves of their bivalve prey to secrete an anesthetizing toxin (Hughes and Hughes, 1971; Laxton, 1971). Some Cymatiinae produce a venom so powerful that 1 g of it could kill up to 51, 000 mice (Taylor, 1998, based on Shiomi et al., 1994). Cymatium pileare inserts its proboscis between oyster valves (e.g., Crassostrea, Isognomon, Ostrea), and releases a toxin. It then ingests the soft tissue, and proceeds to lay eggs within the oyster shell (Littlewood, 1989). The salivary glands of the shallow water cymatiinid, Linatella caudate, produces sulfuric acid that is injected into the mantle cavity of hard-substrate bivalve prey (Morton, 1990). While the bivalve shells are uninjured in this feeding process (Morton, 1990), the toxic fluid has a pH of 2.0 and may produce an etched surface where the predator has penetrated the shell. Cymatiinids most likely have a large impact on the gastropod record that would eventually be preserved in reef deposits. The Indo-Pacific triton, Cymatium nicobaricum, in laboratory conditions eats a variety of prey representing nineteen families of gastropods (Demond, 1957; Kohn, 1959) and is cannabilistic (i.e., Pago Bay, Guam; Yamaguchi, 1977). Cymatium nicobaricum is especially known to prey upon shallowwater cerithiid gastropods (Taylor, 1984). It grips the prey’s columella with its foot, and the proboscis is inserted into the prey’s mantle cavity where the toxin is released. The prey’s tissue from the aperture to the apex is then rasped away from the shell and ingested. The shell interior could potentially have radula traces that may indicate predation by cymatiid predators. In Guam, the cymatiinid Gutturnium (Cymatium) muricinum preys on the giant clam, Tridacna derasa, and the mussel, Modiolus auriculatus (Taylor, 1984; Perron et al., 1985). As a major predator of Tridacna (Taylor, 1998), Gutturnium appears to use an acidic secretion to subdue the prey. The acidic secretions could leave a potential trace on the prey’s shell, but have not been studied. Shell blisters are another potential trace fossil that indicates predation from Gutturnium. In Micronesia the larvae of G. muricinum settle and metamorphose between the shell and the mantle of tridacnids (Perron et al., 1985). This close association leads to shell blisters in response to the

PREDATORY GASTROPODS, TOXINS AND ACIDIC SECRETIONS

snail infestation. Within the tridacnid, the predatory Gutturnium will ingest the mantle tissue as it gets larger, until all the tissue is gone. It is not known if the shell blisters get larger as the predatory snail grows, or if the blisters occur in a particular pattern within the prey’s shell interior that can then be tracked in the fossil record. The Caribbean ranellid Charonia tritonis slathers its prey with sulfuric saliva while it feeds on molluscs, echinoderms, and crustaceans (Percharde, 1972). The prey is immediately paralyzed and wrapped within the predator’s foot. The proboscis of Charonia has strong radular teeth and two lateral chitinous jaws that may be used to open bivalve prey. However, the true function of the jaws has not been studied, nor whether the jaws leave any characteristic breakage pattern on the shells of the prey. Charonia tritonis in Trinidad and Tobago eat a wide variety of echinoderms (asteroids, holothuriods, echinoids), molluscs (gastropods and bivalves), and crustaceans (mainly lobsters; Percharde, 1972), but the shells of the molluscan prey have not been investigated to determine if the acidic saliva has left a specific pattern of shell dissolution.

Toxins and Stabbing in Conidae (Superfamily Conidea) Over 10,000 living species occur within the Superfamily Conidea, which include the Turridae, Conidae, Pervicaciidae, and Terebridae families (Taylor et al., 1993). Families within the Conoidea have a wide variety of radulae with variations on the harpoon-like tooth (Taylor, 1998; Kohn et al., 1999). Considering that this group has 350 genera and 4000 living species, the degree to which the radulae are modified for stabbing and attacking prey is staggering (Taylor, 1998). Within this superfamily, the Conidae are a very diverse group, with the genus Conus having approximately 500 species (Kohn, 2001), about half of which occur in tropical reef systems (Kohn, personal communication, 2006). The predatory Conidae are a monophyletic group of carnivorous predators that use a hypodermic radula to inject neurotoxins into a wide variety of prey, including fish, polychaetes, ascidians, and molluscs (Kohn, 1959, 1985, 1997; Kantor et al., 1997; Duda et al., 2001). The Conidae are known from the Lower Eocene and most likely arose from the polychaete-eating turrid gastropods (Kohn, 1990). Predation on polychaetes is considered to be the most ancient predatory mode starting in the Eocene, while molluscivorous species arose in the Upper Miocene (i.e., Conus textile, Conus canonicus;

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Duda et al., 2001). Conidae that consume gastropods use a modified, hollow radular tooth to inject neurotoxins (conotoxins, a complex of neuropeptides, see Olivera et al., 1990) into their prey (Kohn and Waters, 1966). The harpoon-like tooth is used only once to paralyze the prey (Nishi and Kohn, 1999), but more than one tooth may be used to kill the prey. Numerous Indo-Pacific Conus (e.g., Conus textile, C. episcopatus, C. marmoreus, C. omaria, and C. cononicus) attack live gastropods (Reichert and Kohn, 1985; Nishi and Kohn, 1999; Kohn, 2001). Some Indo-Pacific forms, such as C. canonicus, C. marmoreus and C. textile attack and consume congenera (Reichert and Kohn, 1985; Kohn, 2001). The soft tissue is extracted, but whether there is any evidence that Conidae leave a taphonomic signature on the shell is not known, as they do not have a rasping radula. Thus, although this group is abundant and diverse in reef systems, they may not leave a trace fossil record of their predatory habits.

Engulfment of Prey by Columbellidae (Superfamily Buccinoidea) The columbellids originated in the Eocene and include over 400 extant species (Radwin, 1977; Taylor et al., 1980; deMaintenon, 1999, 2005). They are very common in tropical shallow-water habitats (deMaintenon, 1999) and are mostly herbivorous, grazing on sea grasses (Nielsen and Lethbridge, 1989) and other plant or algal material (deMaintenon, 1999). Some species of columbellids, such as Mitrella, prey on molluscs (Kantor and Medinskaya, 1991; Medinskaya, 1992, 1993) presumably by engulfment and then radulation of the soft tissue from the shell. For example, the gut contents from Mitrella scripta from the Mediterranean off Tunisia contained radula and soft tissue from the herbivorous gastropod, Gibbula (Taylor, 1987). However, the molluscivorous habits of this group need to be explored.

Paralyzing Toxins from Costellariidae (Superfamily Muricoidea) The Costellariidae includes species that use toxins to subdue small gastropod prey (Maes and Raeihle, 1975). In Guam, Pusia amabile may paralyze its prey, Cerithium, with a toxin (Taylor, 1984). Thala floridana typically injects toxins into small gastropods (such as Planaxis) and then removes the soft parts (Maes and Raeihle, 1975). This species does not appear to leave a potential trace fossil on its prey. Other costellariids,

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such as Vexillum from Guam, may prey on opisthobranch molluscs (Taylor, 1986). Unfortunately, there is limited information concerning the diets of these abundant species in reef systems.

they could leave radula marks on molluscan prey similar to those left on foraminiferan tests by the predatory activities of another family, Olivellidae (see Hickman and Lipps, 1983).

Toxic Saliva of the Muricidae (Superfamily Muricoidea)

Shell Engulfment by Volutidae (Superfamily Muricoidea)

An alternative feeding strategy for muricids is to not drill their prey. Muricids may produce serotonin from the accessory salivary glands and choline esters from the hypobranchial gland that are effective in muscle relaxation and blocking neuromuscular activity, respectively (Roseghini et al., 1996; Taylor, 1998). Muricidae from reef settings, such as Drupa ricinus and Drupa clathrata, may eat chitons and vermetid gastropods by ejecting a toxic saliva into the prey (Taylor, 1968, 1983). In the Mediterranean (Tunisia), the muricid Phyllonotus also does not drill, rather, it attacks through the aperture of the gastropod prey (Taylor, 1987), but it is not known if it uses any toxins. In western Australia, Purpura rudolphi pulls limpets off of rocks without drilling them (Taylor, 1976). These genera have not been examined to determine if they leave potential traces of their predation behavior on their prey species, but it may be unlikely.

Limited information exists for feeding within the Volutidae (Morton, 1970, 1986). Some of the volutids may be similar to Olividae in that they have a foot pouch for storing prey (Taylor and Glover, 2000). Volutes may envelop the prey in their fleshy foot and thereby suffocate the victim (Taylor, 1981), or they may eat the victim so fast, suffocation is not an issue (Morton, 1986). Cymbium species appear to feed exclusively on gastropods and bivalves (Morton, 1986). The volute Melo amphora is known to eat other volutes, and Melo melo appears to be a specialist on predatory and herbivorous gastropods (Morton, 1986). Melo melo appear to attack their gastropod prey with ‘dramatic speed’ (for a snail) by enveloping the prey within the folds of the foot (Morton, 1986). Strangely, the Melo lies on its back while indulging in its gastropod prey, but unfortunately, no one has observed how the prey is consumed: is it rasped out of its shell? Do digestive enzymes loosen up the tissue to be ingested? Is venom extruded? All these methods may affect what is preserved on the shell. Until further study is done, it appears that the volutids may leave no discernable trace fossil record of their predatory behavior.

Possible Toxins in Olividae (Superfamily Olivoidea) Subtropical and tropical Olividae are suspension and deposit feeders; some are predators of foraminifera and mollusca (Taylor and Glover, 2000). Near Cairns, Australia, Taylor and Glover (2000) revealed that the predatory Oliva tigridella carried prey within a foot pouch. The snails then buried themselves within the sand and commenced to eat their captured prey, which consisted of the trochid gastropod, Isanda coronata, three species of bivalves (Cadella semen, Donax verninus, Mactra cf olorina), and assorted crustaceans, polychaetes, echiuroids, and echinoderms. Taylor and Glover (2000) observed that none of the shells of the molluscan prey were damaged after predation by Oliva. Carrying prey within foot pouches was also observed for Oliva sayana from Florida that preys upon bivalves, such as Donax and Laevicardium (Olsson and Crovo, 1968). The prey may be subdued by a chemical cocktail: choline esters that paralyze the prey and possibly, although not substantiated, a serotonin produced by the salivary glands that relax the prey (Taylor and Glover, 2000). This family ingests molluscan prey, but may not leave a predatory record of their activities. It is possible that

CONCLUSIONS The findings from this work indicate that (1) a predator may kill more prey than its fossil record indicates because of behavioral flexibility (see also Leighton, 2002, for an optimal foraging approach); (2) prey will exhibit a taphonomic signature of various predatory attacks because of behavioral plasticity; and (3) much of this behavioral flexibility is potentially recorded as trace fossils on the shells. Species of predatory gastropods that use a variety of feeding techniques and behavior to gain entry to a food resource exhibit trophic polymorphism. Predators were ranked into three groups, those that exhibit extensive polymorphism (rank 3) to those that exhibit little polymorphism (rank 1) (Fig. 18.1). Predators that ranked 3 were more likely to be species-rich tropical predatory clade that may leave a diverse trace fossil record of their feeding modes. To fully understand the

CONCLUSIONS

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RANK 1: GASTROPODS WITH ONE PREDATORY MODE Columbellidae Conidae Costellariidae Nassariidae Naticidae Marginellidae; Olividae Volutidae RANK 2: GASTROPOD FAMILES WITH TWO PREDATORY MODES Tonnidae

RANK 3: GASTROPODS FAMILIES WITH GREATER THAN TWO PREDATORY MODES Buccinidae Fasciolariidae Melongenidae Muricidae Ranellidae

FIGURE 18.1 Predatory gastropod families that leave a potential trace fossil record related to trophic polymorphism: the more feeding flexibility they have, the more likely they are to leave a multiple record of their feeding behavior.

importance of trophic polymorphisms in the evolution of tropical predator–prey systems, a trace fossil approach that examines all aspects of the forensic evidence left on the fossil shells of predators and prey is warranted. Therefore, the prey shells may contain more trace fossil information than has been previously considered; some shells may contain multiple traces of predation. Predatory feeding behavior may occur over ontogeny. For example, predatory behavior may change from drilling in juvenile stages to wedging as an adult, that is, not all drilling predators continue drilling through ontogeny. Intraspecific differences in prey selection occurs in that not all members of the same predator population select and feed on the same prey regardless of prey diversity or relative abundance. On a spatial scale, feeding techniques and prey selection vary geographically. Drilling differences along a geographic gradient may not be a function of predation intensity, but rather one of behavioral

differences in the predator population (i.e., Sanford et al., 2003). Time scales spanning months, years, and decades are also lacking to deduce the long-term effects of predatory gastropods in communities (after Paine, 1963b). Paine (1963b) found that the distribution and abundance of predatory gastropods in Florida fluctuated yearly. These fluctuations in predators may also contribute to episodic pulses of drilled, chipped, or rasped prey. This review shows that there are predation-related traces as yet undiscovered and that ecological/paleoecological studies need to be designed to fully understand the range of trophic interactions in the gastropod predatory guild especially in tropical habitats. The best trace fossil evidence of gastropod predatory activity are drill holes preserved in molluscan prey. Two major molluscan shell drillers (Naticidae and Muricidae) and four other groups of shell drillers (i.e., Buccinidae, Marginellidae, Nassariidae, and Ranellidae) occur in tropical reef

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and reef-associated environments. Naticids are the best and most studied from a fossil perspective, and muricid predatory behavior is just beginning to be studied. However, for the other groups, little is known about their modern record of predation, and consequently, nothing is known about their fossil record of predation. Ranellids originated in the Early Cretaceous, but there is as yet, no known fossil record of their drilling behavior, although, in some localities, these predatory gastropods are very common. Some ranellids also rasp shells, and how this predation trace differs from those made by other predatory genera is unknown. Nassariids and marginellids are also shell drillers, but limited information exists concerning their trophic ecology. Repaired shells that have been chipped is another type of potential trace fossil, but may be difficult to distinguish among predatory gastropods that employ similar methods of shell entry (i.e., fasciolariids, muricids, buccinids, and melongenids). Buccinids, especially, may leave potentially recognizable trace fossil evidence of predation, from fractured shell margins to varied predation chipping patterns, and their predatory traces on shells are a good candidate for a new trace fossil name. Some of these gastropods may use different behavior depending on the prey: muricids, for instance, may drill prey such as barnacles, rasp opercula of gastropods to gain entry, or edge-chip the shell of limpet prey. However, most work on shell-chipping and shell-wedging behavior in these groups is done on temperate-zone species. Shell abrasion can occur when the predator uses its radula and/or shell to abrade the shell of the prey. These abraded areas are not documented as yet from the fossil record. A diverse group of predatory gastropods produce acids to chemically dissolve the prey’s shell, sometimes in combination with other shell-damaging behavior. Shell wedging and chipping muricids, for instance, may leave a decalcified area on the interior of their prey’s valves resulting from acidic secretions. Predatory gastropods that engulf their prey may provide yet another type of trace fossil resulting from corrosion of the exterior and interior of the prey’s shell and then potentially rasping traces resulting from the radula extracting the soft tissue from the shell. Another potential trace that may be related to predation are shell blisters that are preserved on certain bivalve prey, such as giant tridacnid clams. These blisters are made in response to predatory gastropods that feed on the mantle tissue of these clams. Thus, there are more potential traces of predation than has been considered, and these traces can in turn be used to

examine the evolutionary importance of trophic polymorphism in the diversification of predatory gastropods.

ACKNOWLEDGEMENTS The author wishes to thank W. Miller III for inviting this contribution; J. Lintecume and M. deMaintenon for reference support; A. Kohn and J. Taylor for their expertise in molluscan diets and for their editorial expertise. Supported in part by NSF-SGER EAR0000894.

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Vermeij, G.J. and Snyder, M.A. (2002). Leucozonia and related genera of fasciolariid gastropods: Shell-based taxonomy and relationships. Proceedings of the Academy of Natural Sciences Philadelphia, 152, 23–44. Vokes, E.H. (1990). Cenozoic Muricidae of the western Atlantic region, Part VIII, Murex s.s., Haustellum, Chicoreus, and Hexaplex; additions and corrections. Tulane Studies in Geology and Paleontology, 23, 1–96. Vokes, E.H. (1996). Cenozoic Muricidae of the western Atlantic region, Part XI. The subfamily Ergalataxinae. Tulane Studies in Geology and Paleontology, 29, 27–44. Walker, S.E. and Brett, C.E. (2002). Post-Paleozoic patterns in marine predation: was there a Mesozoic and Cenozoic marine predatory revolution? In: Kowalewski, M. and Kelley, P. (Eds.), The Fossil Record of Predation, Special Publication of the Paleontological Society, pp. 119–193. Walker, S.E. and Yamada, S.B. (1993). Implications for the gastropod fossil record of mistaken crab predation on empty mollusk shells. Palaeontology, 36, 735–741. Winberger, P.H. (1994). Trophic polymorphisms, plasticity, and speciation in vertebrates. In: Stouder, D.J., Fresh, K.L. and Feller, R.J. (Eds.), Theory and Application in Fish Feeding Ecology, University of South Carolina Press, Columbia, South Carolina, pp. 19–43. Wells, H.W. (1958a). Feeding habits of Murex fulvescens. Ecology, 39, 556–558. Wells, H.W. (1958b). Predation of pelecypods and gastropods by Fasciolaria hunteria (Perry). Bulletin of Marine Science Gulf and Caribbean, 8, 152–166. Winner, B. (1989). Marginella (Prunum)apicina–eating and egg producing habits. Hawaiian Shell News, 37, 31. Yamaguchi, M. (1977). Shell growth and mortality rates in the coral reef gastropod Cerithium nodulosum in Pago Bay, Guam, Mariana Islands. Marine Biology, 44, 249–263.

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19 Early History of Symbiosis in Living Substrates: Trace-Fossil Evidence from the Marine Record Leif Tapanila and A.A. Ekdale

of their association is therefore highly sought after (Boucot, 1990). The term symbiosis is used herein to include relationships between two or more different species in which at least one of the species benefits from the association. Thus, the symbiosis may be mutualistic (both taxa benefit), commensal (one benefits while the other is unaffected), or parasitic (one benefits to the detriment of the other). In the fossil record, it may be impossible to determine whether both or either taxa benefit from the association (Fagerstrom, 1996), so clearly defined terminology is crucial (Table 19.1). Since spatial proximity and temporal resolution are both essential for preserving fossil associations, organisms with a sessile lifestyle are among the best targets to study symbiotic relationships. Sessile creatures use a variety of structural methods, including encrustation, boring and embedding, to procure a suitable place to live. The substrate on which or in which they inhabit may be the skeleton of another living organism. If it can be determined that the host skeletal substrate was alive while inhabited by another organism, a symbiotic relationship can be inferred. Bioclaustrations, which are formed by embedding animals, are an intriguing yet underexploited group of trace fossils that provide direct evidence of symbiosis. This chapter explores the fossil record of very specific symbioses in marine animals, and in particular, it highlights the potential of bioclaustration trace fossils in understanding the evolution of ancient ecosystems.

SUMMARY : The fossil record of animal symbiosis as a component of marine ecosystems dates back to at least the Early Cambrian. The embedment of animals inside the growing skeletons of other animals produces trace fossils known as bioclaustrations, which provide direct evidence of animal symbiosis. Bioclaustrations primarily record commensal relationships and demonstrate strong host preference among most symbiont–host pairings. Late Ordovician and Middle Devonian pulses in the diversity and abundance of bioclaustrations coincide with general increases in marine animal diversity, as well as other adaptive strategies that serve to partition habitats.

INTRODUCTION The intimate interactions and dependencies among animals during life are notoriously difficult to capture in the fossil record. Trace fossils of one taxon inhabiting the growing skeleton of another can provide a valuable view of symbiotic relationships in fossil situations. Symbiosis (literally ‘the living together’ of organisms in close proximity at the same time) is commonly recognized as an important ecological and evolutionary driving force in the modern biosphere, but its recognition in the fossil record is compromised by the vagaries of fossil preservation and biostratinomy. Direct fossil evidence for animals caught in the act


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19. EARLY HISTORY OF SYMBIOSIS IN LIVING SUBSTRATES: TRACE-FOSSIL EVIDENCE FROM THE MARINE RECORD

TABLE 19.1

Practical Definitions for Animal Associations and their Fossil Record in Skeletal Substrates

Term Association Attachment etchings

Definition Grouping of two or more organisms based on their spatial proximity; a time neutral term. Trace-fossil cavity produced by the shallow excavation of a holdfast structure into a hard substrate. If the hard substrate is skeletal, the etching may be an indirect indicator of symbiosis. Example: Podichnus (Bromley and Surlyk, 1973).

Bioclaustration

Trace-fossil cavity produced by the growth-interfering behavior of a symbiont that lives in the growing skeleton of the host. Provides direct trace-fossil evidence of symbiosis. Example: Helicosalpinx (Tapanila, 2004).

Bioimmuration

External mold (body fossil) of an organism that was passively overgrown by a skeleton-producing

Boring

organism. Example: ctenostome bryozoans overgrown by oysters (Taylor, 1990b) Trace-fossil cavity produced by the excavating behavior of an organism into a hard substrate. If the

Commensalism

Symbiosis where the symbiont materially benefits from the association, without material harm to

Host symbiont

The larger of two organisms involved in symbiosis, typically skeleton forming.

Intergrowth

Body-fossil record of two skeletonized organisms living in close proximity. May be reciprocal, where

hard substrate is skeletal, the boring may be an indirect indicator of symbiosis. Example: Trypanites. the host.

the margins of two adjacent organisms encrust each other, or full, where one skeleton is completely surrounded (but not completely overgrown) by another skeletonized organism. Example of full intergrowth: caunopores (Mistiaen, 1984). Mutualism

Symbiosis where both host and symbiont materially benefit from the association.

Parasitism

Symbiosis where the symbiont materially benefits from the association, while materially harming

Simple encrustation

Body-fossil record of one skeletonized organism that grew on the skeletonized surface of another

Settler symbiont

The smaller of two organisms involved in symbiosis, may be skeleton forming.

Symbiosis

Proximal association of two live organisms ‘living together’; at least one of the organisms benefits from the association, although the nature of the association is unspecified.

the host. organism, or other hard substrate. Examples: crinoid holdfasts and vermetid gastropods.

BIOCLAUSTRATIONS AS FOSSILIZED BEHAVIOR Bioclaustrations are cavities that are produced when one organism, a settler symbiont, takes residence on the skeletal surface of another live organism, the host symbiont. As the host grows, the activities of the living settler prevent it from being overgrown. Thereby a cavity is produced within the skeleton of the living host in which the embedded settler symbiont lives. The bottom-up construction of bioclaustration cavities is formationally different from the outside-in destructive process of bioerosion that results in borings (Fig. 19.1). Bioclaustrations can be recognized by the conformability of the cavity with parts of the skeletal host, and sometimes these parts may show deflection adjacent to the cavity. Borings in skeletal materials, on the other hand, can be seen to cross-cut and truncate the internal structure of the substrate (Table 19.2). Some cavities in skeletal materials may be produced by a combination of

embedment and bioerosion, and they may be occupied by one or multiple individuals. Although fossil bioclaustrations have been recognized since the late nineteenth century (Calvin, 1888; Clarke, 1908, 1921), Bromley (1970) was first to codify these cavities as a special class of trace fossil, which he called embedment structures in keeping with their constructional formation. The term bioclaustration was coined later by Palmer and Wilson (1988) and was differentiated from passively overgrown softbodied fossils, called bioimmurations (Voigt, 1979; Taylor, 1990a). The key to understanding bioclaustrations is that they can be formed only by the interaction of two organisms, which necessarily must be living in the same place at the same time, thereby preserving direct evidence of symbiosis. Previous descriptions of bioclaustrations as being ‘passive endoliths’, in contrast to the ‘active’ boring endoliths (e.g., Scoffin and Bradshaw, 2000), are misleading. Extension of the bioclaustration cavity requires not only that the host

CRITERIA FOR DISTINGUISHING BIOCLAUSTRATIONS

FIGURE 19.1 Formational contrast between boring and bioclaustration trace fossils. Destructive borings are excavated from the outside-in, whereas constructive bioclaustrations are grown from the bottom-up.

TABLE 19.2 Criteria Helpful in Recognizing Bioclaustrations. Modified after Lamond and Tapanila, 2003 Feature

Remarks

Margins

Substrate surface deflected at the cavity margin, either through increased or decreased host growth.

Path

Cavity usually elongate and unbranched.

Position in

Cavity oriented perpendicular to the outer

host

growth surface of the host skeleton, i.e., generally parallel to the host’s axis of skeletal growth.

Morphology

Cavity has regular shape. This feature is common to borings also, but it can help exclude irregular host growth in response to abiotic stimuli.

Distribution

Cavities in colonial hosts seldom occur solitarily (except for Hicetes) and rarely overlap.

skeleton continues to grow but also that the settler symbiont remains alive. Otherwise the cavity will cease to extend and will be overgrown. The resulting trace fossil therefore preserves dual activities on the part of the embedded settler : interference of host growth, and maintenance of a dwelling structure. Trace fossils produced in this way belong to the ethologic category, impedichnia (Tapanila, 2005). Most examples of bioclaustrations occur between two animals in marine environments. Exceptionally, bioclaustrations are described in lacustrine stromatolites and oncoids (Winsborough et al., 1994;

347

Lamond and Tapanila, 2003; Unal and Zinsmeister, 2005). Studies of the life habits of modern embedders have greatly helped our understanding of fossil bioclaustrations. Polychaetes, barnacles, and bivalves are one of the most diverse groups of settler symbionts in modern oceans, where they embed in the skeletons of a wide variety of hosts, including sponges, corals, gastropods, bivalves, and echinoderms. Nearly all the modern embedding symbionts are suspension feeders. Most are commensal; that is, they benefit from residing within their host’s skeleton, but they do not harm their host. Many barnacles and polychaetes are obligate commensals that show strong host preferences, because they are able to recognize characteristic chemical signatures of the host to ensure successful larval recruitment. Many other anatomical, physiological, and behavioral specializations are required for the symbiotic lifestyle (for examples, see Morton and Scott, 1980; Mokady and Brickner, 2001; Savazzi, 2001). Thus bioclaustrations may record significant adaptive strategies of typically soft-bodied animals that are otherwise unlikely to leave a fossil record.

CRITERIA FOR DISTINGUISHING BIOCLAUSTRATIONS Until recently, bioclaustrations have existed in a realm of taxonomic ambivalence. Prior to Bromley’s (1970) inclusion of embedment structures as trace fossils, bioclaustrations were described as body fossils and were classified most often as worms (e.g., Howell, 1962). Conventions for diagnosing ichnotaxa avoid the use of certain criteria as ichnotaxobases, such as one-dimensional size parameters, stratigraphic age, geographic location and identity of the host substrate (Magwood, 1992; Goldring et al., 1997). Several common characteristics of bioclaustrations may serve as a guide for distinguishing bioclaustrations from borings (also types of trace fossils) and encrustations (a life habit preserved by body fossils). These include deflected margins, open apertures, cavity linings, tabulae, cavity shape, and increased cavity size. Many of these characters could serve as valid ichnotaxobases in the naming of new bioclaustrations (Table 19.3). Deflected Margins Bioclaustrations often have margins that are marked by deflection of laminae of the host skeleton adjacent to the cavity. The deflection can be attributed

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TABLE 19.3 Examples of Valid Criteria (Ichnotaxobases) Used for Distinguishing Bioclaustrations Ichnotaxobasis

Character State

Orientation relative to host growth axis

Parallel Perpendicular

Chaetosalpinx ferganensis Catellocaula

Diameter with depth

Isodiametric

Chaetosalpinx ferganensis

Upward growth

Chaetosalpinx rex

Circular

Chaetosalpinx ferganensis

Diameter shape Aperture number

Example

Lenticular

Chaetosalpinx rex

One

Chaetosalpinx

Two

Hicetes

Pathway

Straight Spiral

Chaetosalpinx ferganensis Helicosalpinx

Wall lining

Absent

Chaetosalpinx

Present

Torquaysalpinx

Absent

Chaetosalpinx

Present

Phragmosalpinx

Transverse tabulae

to either an increased or a decreased growth rate of the host skeleton in response to the activity of the settler (Nishi and Nishihira, 1999; Wielgus et al., 2002). The observation of deflected skeletal margins excludes encrustation (overgrowth) and boring (truncation of skeletal elements) from the production of bioclaustrations. It should be noted that the process of boring can be used to enlarge cavities that were produced originally by embedment. Because deflected margins are a product of the live host substrate and not the cavity itself, they cannot be used as an ichnotaxobase. Aperture As long as a living organism occupies a bioclaustration, the aperture must be kept open. In fossil and modern examples, the aperture may be overgrown by the host following the death or departure of the embedded symbiont (Palmer and Wilson, 1988; Tapanila, 2002; Tapanila and Holmer, 2006). The absence of an aperture excludes the overgrowth of inactive grains in the formation of pearls (e.g., in molluscs) as being considered bioclaustrations. The presence of multiple apertures, for example, has been used as an ichnotaxobase for the bioclaustration Burrinjuckia (Chatterton, 1975). Linings and Tabulae Most bioclaustrations have a smooth internal surface produced by the skeleton-secreting host. In addition to the host-produced wall, the embedded symbiont may also secrete calcareous material within the cavity. A wall lining and floor-like tabulae are important diagnostic features of particular bioclaustrations, which indicate the ability of

the settler symbiont to precipitate its own calcareous material. Such features are therefore good ichnotaxobases. The tabulae may also constrain the maximum body length of the embedded settler. Comparison of the wall structure or mineralogy and other host skeletal elements can be used to determine if the cavity margins were precipitated by the host or the settler. Linings and tabulae produced by the embedded symbiont are considered part of the trace fossil (i.e., not part of a body fossil) only if they are found in association with a bioclaustration. This distinction separates simple encrustations and intergrowths (which are both body fossils) from bioclaustration trace fossils. Therefore, body fossils of organisms that are affixed to coral surfaces, such as Spirorbis, are not defined as bioclaustrations. In many situations, encrusting organisms can be overgrown passively by the skeleton of the host organism, but if the growth of the host skeleton is not inhibited or deformed in a characteristic way by the growth of the settler, then the resulting structure is not a bioclaustration. Overall Cavity Shape The course of the trace fossil through the host skeleton has been used as a primary criterion for distinguishing bioclaustrations. The shapes range from straight to sinuous to helical. The long axis of a trace most commonly is oriented perpendicular to the host skeletal growth surface. The shape may also indicate relative growth rates of the embedded organism compared to the host organism. A more tortuous helical pathway of the trace may suggest a faster growth rate of the settler compared to the vertical accretion of the host skeleton. The embedded

EARLY FOSSIL RECORD OF BIOCLAUSTRATIONS

symbiont of a straight trace (normal to the host growth surface) may have a growth rate that is roughly equal to that of the host, as is sometimes seen in the scallop bivalve Pedum (Nishi and Nishihira, 1999). Change in Cavity Size As the settled symbiont grows and increases in size, the cross section of the trace (or aperture) similarly may increase in size. Such a pattern of growth is observed in modern Spirobranchus tubes (Nishi and Nishihira, 1996), and it has been described in a few fossil examples (e.g., Streptindytes, Chaetosalpinx rex and Chaetosalpinx alamo: Calvin, 1888; Tapanila, 2002, 2006). Bioclaustrations that maintain a constant diameter throughout their length (referred to here as isodiametric) were likely made around embedded symbionts that grew longer but not wider.

BIOCLAUSTRATIONS IN CONTEXT WITH OTHER SESSILE ASSOCIATIONS A fixosessile lifestyle inherently facilitates the preservation of spatial relationships, as best exemplified in reef ecosystems. Among sessile animal associations, a skeletal body fossil serves as the substrate (or host), whereas the settling organism (or its behavior) may be preserved as either a body fossil or trace fossil. Encrusting animals, which produce simple encrustations, bioimmurations and intergrowths, are preserved as body fossils. Animals that bore into or embed within the substrate produce trace fossil cavities, such as attachment etchings, borings, and bioclaustrations (Fig. 19.2). Simple encrustations, bioimmurations, borings and etchings for dwelling or attachment may occur either while both animals are alive or while only one of the associated animals is alive. These are here considered facultative live associations. Any attempt to demonstrate a symbiotic relationship among these fossils during their lives requires circumstantial evidence. For example, encrusting auloporid corals aligned along the anterior commissure of a brachiopod have been suggested to represent a commensal relationship, where the auloporids are interpreted to have benefited from water currents generated by the hosting brachiopod (Fagerstrom, 1996). This interpretation seems logical, but the evidence is circumstantial, as there is no way of knowing whether or not the encrusting auloporids were alive at the same time as their brachiopod hosts. Similarly,

349

borings, attachment etchings and bioimmurations provide evidence only of the relative timing, as may be interpreted by cross-cutting or superposition relationships. At the opposite end of the structural spectrum are intergrowths and bioclaustrations, which are here considered obligate live associations. These necessarily form by the synchronous growth of two organisms, and therefore they record both the timing and spatial relationship faithfully. Intergrowths and bioclaustrations are differentiated by the presence or absence of an encrusted skeleton, respectively. Full intergrowths are exemplified by corals that grew within the laminae of larger stromatoporoid sponges during the Silurian and Devonian, e.g., ‘caunopores’ (Fig. 19.3; Mistiaen, 1984). Although most bioclaustrations are formed around a soft-bodied settler, many examples of skeletonized embedders are recognized. For example, the modern bivalve Pedum produces bioclaustrations in scleractinian corals (Savazzi, 2001). The growth interfering behavior of the settler prevents it from being encrusted onto by the host substrate. Inarticulate brachiopods that occupy cavities within host corals or stromatoporoids are analogous examples of skeletonized embedders from the Paleozoic (Tapanila and Holmer, 2006). Between the facultative and obligate live associations is the intermediate group, the intermittent live associations. These are exemplified by reciprocal intergrowths and compound boring–bioclaustrations. Such associations give direct evidence that multiple organisms interacted, but the timing of the interaction cannot be determined for at least part of the structure. In Ordovician and Silurian marine ecosystems, inarticulate brachiopods are known to have nestled in previously made borings inside living stromatoporoid and tabulate coral hosts (Newall, 1970; Richards and Dyson-Cobb, 1976; Tapanila and Holmer, 2006). As the host substrate grew, the nestling brachiopods inhibited being overgrown, creating a bioclaustration extension of the cavity (Fig. 19.4).

EARLY FOSSIL RECORD OF BIOCLAUSTRATIONS More than a century of literature exists on bioclaustrations (Calvin, 1888; Clarke, 1908, 1921), with the majority of accounts documented in the systematic descriptions of the host taxa (e.g., Sokolov, 1948; Flower, 1961). Tapanila (2005) compiled these sources to reveal major trends in the diversity of bioclaustrations for the Paleozoic. (While some

350


FIGURE 19.2 Structural types of fossil associations among sessile organisms that may indicate symbiosis. Body fossils act as substrates (or hosts) for different types of body or trace-fossil structures (highlighted in gray). Interpretations of symbiosis are circumstantial for structures that are facultative live associations, since they can form in either live or dead substrates. Obligate live associations include fossil structures that can be produced only through continuous live interactions (symbiosis). Intermittent live associations include structures that show discontinuous but direct evidence of symbiosis. Substrates are patterned after stromatoporoids, although any live skeletal substrate could be substituted. Downward deflecting laminae serve to diagrammatically indicate the concordance of substrate growth with bioclaustrations and intergrowths, although such deflections are not always present. See Table 19.1 and text for definitions and elaborations on the different fossil structures. For an alternative approach to organizing these fossil groups, see Darrel and Taylor, 1993.

bioclaustrations are known from the Mesozoic and Cenozoic Eras, their compilation is currently in progress, and they are not discussed here.) At least 12 ichnogenera and 21 ichnospecies of bioclaustrations are recognized from the Early to Middle Paleozoic, and these occur in a variety of hosts including calcareous sponges (stromatoporoids and chaetetids), corals (tabulates and rugosans), bryozoans, brachiopods, and crinoids (Table 19.4). Colonial Host Animals

FIGURE 19.3 Caunopore, the full intergrowth of a tubelike organism and a stromatoporoid sponge. Early Silurian, Manitoulin Island, Ontario. Scale bar = 1 cm.

The most well-known and diverse group of bioclaustrations occurs in corals and stromatoporoid sponges, which are hosts that possess a basal skeleton. Bioclaustration cavity morphologies range from straight to spiraled, and they may be concordant or

DIVERSITY TRENDS IN THE PALEOZOIC

351

skeletons of bryozoans similarly hosted bioclaustrations, although the current diversity of such trace fossils is limited to Catellocaula from the Late Ordovician of eastern North America and an unnamed trace fossil from the Devonian (Emsian) of Belgium (McKinney, F.K. personal communication, 2006). Brachiopods

FIGURE 19.4 Oblique longitudinal section of Klemmatoica, a compound boring-bioclaustration cavity in a host Clathrodictyon stromatoporoid. An inarticulate brachiopod resides in situ within the cavity. Note that the lower part of the cavity truncates the host laminae, while the upper part of the cavity is formed by the deflection of host laminae. Early Silurian, Anticosti Island, Quebec. GSC-10812 (Geologic Survey of Canada, Ottawa). Scale bar = 5 mm.

discordant with the main axis of skeletal growth of the host. Many of these bioclaustrations first appear during the Late Ordovician, including Chaetosalpinx and Helicosalpinx (Figs. 19.5 and 19.6). The sarcinulid tabulate corals, Columnopora and Calapoecia, are among the most common host taxa in the Ordovician. Studies suggest a strong association of specific bioclaustrations with these sarcinulid hosts, which may have synchronously evolved near the time of the Late Ordovician (Richmondian) biotic expansion on the Laurentian continent (Tapanila, 2002, 2004). With the decline of sarcinulid genera following the Late Ordovician mass extinctions, bioclaustrations dominantly occur in favositid tabulate corals during the Silurian and Devonian. Among these bioclaustrations, the contorted U-shaped Hicetes is perhaps the most widely recognized, occurring exclusively in Pleurodictyum corals from Devonian deposits on three continents (Fig. 19.7). The colonial basal

Three types of bioclaustrations are recognized in brachiopods. The earliest occurrence is described from the lingulate inarticulate brachiopod, Linnarssonia, which contains the bioclaustration Eodiorygma (originally described as a body fossil, Bassett et al., 2004). Only one specimen is known from the Cambrian, but several examples of the bioclaustrations Diorygma and Burrinjuckia are recognized in Devonian articulate brachiopods (Biernat, 1961; Chatterton, 1975). In both instances, the bioclaustration is a tubular projection of the inside surface of the brachiopod valve. The embedded symbiont is thought to have derived food directly from the incurrent feeding of the host brachiopod, and since that activity might have deprived the host of a portion of its food supply, this interpretation has led some researchers to regard this bioclaustration as evidence of parasitism (MacKinnon and Biernat, 1970; Basset et al., 2004). However, it is uncertain whether the presence of these embedders reduced the fitness of their host in a measurable way (e.g., by a reduced rate of growth). Crinoids Echinoderms have hosted symbionts since the Ordovician, and these relationships are especially common in crinoids. Several varieties and arrangements of parabolic pits, called Tremichnus, are described from the columnals and crowns of crinoids (Brett, 1985). Unlike bioclaustrations in most basal skeletons where growth decreases slightly near the cavity, the pits in echinodermal plates are often accompanied by increased and swollen skeletal growth. Similar bioclaustrations are found in echinoids from the Paleozoic and Mesozoic (e.g., Feldman and Brett, 1998; Neumann, C. personal communication, 2004), and they are currently being investigated.

DIVERSITY TRENDS IN THE PALEOZOIC Trends in the diversity of bioclaustrations appear to be consistent for the Paleozoic (Fig. 19.8). Pulses in generic diversification during the Late

352


TABLE 19.4 Paleozoic Marine Bioclaustrations (updated from Tapanila, 2005). Abbreviations: T, Tabulate Coral; R, Rugose Coral; S, Stromatoporoid Sponge; Ch, Chaetetid Sponge; Br, Brachiopod; By, Bryozoan; E, Echinoderm; Eu, Europe; NA, North America; Aus, Australia; Afr, Africa Ichnotaxon Burrinjuckia

Range Emsian

Chatterton (1975)

Remarks Cylindrical cavity with

Hosts

Place

Br

Aus

NA

Additional References

single, irregular shaped aperture. Found on internal dorsal valve of spiriferid brachiopods. One isp.

Catellocaula Palmer and Wilson (1988)

Caradoc

Radially disposed pits on surface of host. One isp.

By

Chaetosalpinx

Caradoc–

Circular to oval cylindrical

T, R

Sokolov (1948)

Givetian

Eu,

Stel (1976);

cavity oriented roughly

NA,

Tapanila (2002,

parallel to host growth axis.

Asia

2004, 2006)

Lacks distinct lining or tabulae. Five ispp. Diorygma Biernat

Givetian

(1961)

V-shaped cylindrical cavity

Br

Eu

with paired apertures. Found on internal ventral valve of

MacKinnon and Biernat (1970)

atrypid brachiopods. One isp. Eodiorygma

E. Cambrian

Bassett et al. (2004)

Cylindrical cavity with

Br

Asia

T, R, S

Aus, Eu,

single, circular aperture. Found on internal dorsal valve of an acrotretid brachiopod. One isp.

Helicosalpinx Oekentorp (1969)

Ashgill– Givetian

Elongate spiraled cylindrical cavity lacking both lining and tabulae. Two ispp.

NA,

Clarke (1908); Stel (1976); Tapanila (2004)

Asia Hicetes Clarke (1908)

Pragian– Givetian

U-shaped cavity with two

T

Eu,

Gerth (1952);

apertures that form tight

NA,

Schindewolf (1958);

spiral at base. One isp. only,

Afr

Plusquellec (1965)

known to occur in Klemmatoica Tapanila and

Llandovery– Ludlow

Pleurodictyum coral. Oval cylindrical

T, S

bioclaustration extending

NA, Eu

from boring. Inarticulate

Holmer (2006)

Newall (1970); Richards and Dyson-Cobb (1976)

brachiopod determined to be the embedding symbiont. One isp. Phragmosalpinx Sokolov (1948) Streptindytes Calvin (1888)

Early– Mid Devonian Mid Devon.– Carbonif.

Elongate spiraled cylindrical cavity having tabulae but lacking a lining. One isp. Inverted conical spiral

T

Aus,

Plusquellec (1968a)

Eu R, S,

NA,

Ch

Asia

T, S, Ch

Aus,

E

NA, Eu

having a wall lining. Three

Clarke (1908); Okulitch (1936)

ispp. Torquaysalpinx Plusquellec (1968b) Tremichnus Brett (1985)

Eifelian– Givetian Caradoc– Jurassic

Elongate spiraled cylindrical cavity with a lining and tabulae. One isp. Circular to parabolic pits in echinodermal plates. Four isp.

Stel (1976)

Eu Eckert (1988); Feldman and Brett (1998)

DIVERSITY TRENDS IN THE PALEOZOIC

FIGURE 19.5 The oldest known evidence of coral symbionts are Chaetosalpinx rex bioclaustrations, highlighted in this Columnopora tabulate coral. Inset shows the idealized morphology of the bioclaustration. Density banding in the host coral demonstrates occupation by individual symbionts for at least 5 years. Late Ordovician, Anticosti Island, Quebec. Scale bar = 2 cm.

353

FIGURE 19.7 Hicetes bioclaustration in Pleurodictyum tabulate coral. Inset shows the idealized morphology of Hicetes, with two surface apertures. Middle Devonian, New York. Scale bar = 5 mm.

FIGURE 19.8 Diversity of bioclaustration ichnogenera (gray) and ichnospecies (black) in Paleozoic marine environments. See Table 19.4 for valid ichnogenera. Updated from Tapanila (2005).

FIGURE 19.6 Two Helicosalpinx bioclaustrations in Calapoecia tabulate coral. Late Ordovician, Manitoulin Island, Ontario. Scale bar = 1 mm.

Ordovician and again during the Middle Devonian are reflected in a marked increase in bioclaustration morphologies and abundances. However, following the Givetian (late Middle Devonian), there is a decline in coral-settling symbionts preserved by bioclaustrations, long before the Late Devonian (Frasnian–Famennian) mass extinction events (Tapanila, 2005). This matches the great decline in coral diversity in the late Givetian (Copper, 2002). These increases in bioclaustration diversity are similar in timing to pulses in macroboring diversity during the Paleozoic (see Chapter 20), although the post-Givetian decline in bioclaustrations is not observed in the macroboring fossil record (Taylor and Wilson, 2003). Differences in the evolutionary patterns between embedders and borers may be linked to their substrate preferences, i.e., obligate versus facultative live associates. Future analysis of bioclaustrations during the Mesozoic and Cenozoic will help delineate patterns of symbiosis.

354


CONCLUSIONS A variety of fossil structures may indicate a direct association between two unrelated organisms, but only bioclaustrations and intergrowths give precise evidence of symbiosis. Bioclaustrations are trace fossils that result from a behavioral interaction between an embedding symbiont and its skeletonized host. The fossil record of bioclaustrations provides clear-cut evidence that symbioses have been common in marine ecosystems since at least the Ordovician, but they have often been overlooked. Further study of bioclaustrations will provide new data to aid in recognizing and understanding the evolutionary implications of symbioses.

ACKNOWLEDGEMENTS We thank reviewers M. Wilson and P. Copper for their constructive suggestions in refining the terminology and clarity of this chapter.

References Bassett, M.G., Popov, L.E. and Holmer, L.E. (2004). The oldestknown metazoan parasite? Journal of Paleontology, 78, 1214–1216. Biernat, G. (1961). Diorygma atrypophilia n. gen., n. sp. – a parasitic organism of Atrypa zonata Schnur. Acta Geologica Polonica, 6, 17–28. Boucot, A. (1990). Evolutionary Paleobiology of Behavior and Coevolution, Elsevier, New York, 725 pp. Brett, C.E. (1985). Tremichnus: a new ichnogenus of circularparabolic pits in fossil echinoderms. Journal of Paleontology, 59, 625–635. Bromley, R.G. (1970). Borings as trace fossils and Entobia cretacea Portlock, as an example. In: Crimes, T.P. and Harper, J.G. (Eds.), Trace Fossils, The Seel HousePress, Liverpool, pp. 49–90. Bromley, R.G. and Surlyk, F. (1973). Borings produced by brachiopod pedicles, fossil and Recent. Lethaia, 6, 349–365. Calvin, S. (1888). On a new genus and new species of tubicolar Annelida. American Geologist, 1, 24–28. Chatterton, B.D.E. (1975). A commensal relationship between a small filter feeding organism and Australian Devonian spiriferid brachiopods. Paleobiology, 1, 371–378. Clarke, J.M. (1908). The beginnings of dependent life. New York State Museum Bulletin, 121, 146–196. Clarke, J.M. (1921). Organic dependence and disease: their origin and significance. New York State Museum Bulletin, 221– 222, 1–113. Copper, P. (2002). Silurian and Devonian reefs: 80 million years of global greenhouse between two ice ages. In: Kiessling, W., Flu¨gel, E. and Golonka, J. (Eds.), Phanerozoic Reef Patterns, SEPM Special Publication, 72, pp. 181–238.

Darrell, J.G. and Taylor, P.D. (1993). Macrosymbiosis in corals: a review of fossil and potentially fossilizable examples. Courier Forschungsinstitut Senckenberg, 164, 185–198. Eckert, J.D. (1988). The ichnogenus Tremichnus in the Lower Silurian of western NewYork. Lethaia, 21, 281–283. Fagerstrom, J.A. (1996). Paleozoic brachiopod symbioses: testing the limits of modern analogues in paleoecology. GSA Bulletin, 108, 1393–1403. Feldman, H.R. and Brett, C.E. (1998). Epi- and endobiontic organisms on Late Jurassic crinoid columns from the Negev Desert, Israel: Implications for co-evolution. Lethaia, 31, 57–71. Flower, R.H. (1961). Montoya and related colonial corals. Memoir of the New Mexico State Bureau of Mines and Mineral Resources, 7, 1–97. Gerth, H. (1952). Die von Sipunculiden bewohnten lebenden und jungtertia¨ren Korallen und der wurmfo¨rmige Ko¨rper von Pleurodictyum. Palaöntologische Zeitschrift, 25, 119–126. Goldring, R., Pollard, J.E. and Taylor, A.M. (1997). Naming trace fossils. Geological Magazine, 134, 265–268. Howell, B.F. (1962). Worms. In: Moore, R.C. (Ed.), Treatise on Invertebrate paleontology, Part W Miscellanea: Conodonts, Conoidal Shells of Uncertain Affinities, Worms, Trace Fossils and Problematica, Geologic Society of America, Boulder, Colorado, and University of Kansas, Lawrence, Kansas, pp. F144–F177. Lamond, R.E. and Tapanila, L. (2003). Embedment cavities in lacustrine stromatolites : evidence of animal interactions from Cenozoic carbonates in U.S.A. and Kenya. PALAIOS, 18, 444–452. MacKinnon, D.I. and Biernat, G. (1970). The probable affinities of the trace fossil Diorygma atrypophilia. Lethaia, 3, 163–172. Magwood, J.P.A. (1992). Ichnotaxonomy: a burrow by any other name. In: Maples, C.G. and West, R.R. (Eds.), Trace Fossils, Short Course, No. 5, Paleontological Society, Knoxville, Tennessee, pp. 15–33. Mistiaen, B. (1984). Comments on the caunopore tubes: stratigraphic distribution and microstructure. Palaeontographica Americana, 54, 501–508. Mokady, O. and Brickner, I. (2001). Host-associated speciation in a coral-inhabiting barnacle. Molecular Biology and Evolution, 18, 975–981. Morton, B. (1990). Corals and their bivalve borers: the evolution of a symbiosis. In: Morton, B. (Ed.), The Bivalvia: Proceedings of a Memorial Symposium in Honour of Sir Charles Maurice Yonge, Hong Kong University Press, Hong Kong, pp. 11–46. Morton, B.S. and Scott, P.J.B. (1980). Morphological and functional specialization of the shell, musculature and pallial glands in the Lithopaginae (Mollusca: Bivalvia). Journal of Zoology (London), 192, 179–203. Newall, G. (1970). A symbiotic relationship between Lingula and the coral Heliolites in the Silurian. In: Crimes, T.P. and Harper, J.C. (Eds.), Trace Fossils, The Seel House Press, Liverpool, pp. 335–344. Nishi, E. and Nishihira, M. (1996). Age-estimation of the Christmas Tree worm Spirobranchus giganteus (Polychaeta, Serpulidae) living buried in the coral skeleton from the coral-growth band of the host coral. Fisheries Science, 62, 400–403. Nishi, E. and Nishihira, M. (1999). Use of annual density banding to estimate longevity of infauna of massive corals. Fisheries Science, 65, 48–56. Oekentorp, K. (1969). Kommensalismus bei Favositiden. Mu¨nstersche Forschungen zur Geologie und Palaöntologie, 12, 165–217.

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Tapanila, L. (2004). The earliest Helicosalpinx from Canada and the global expansion of commensalism in Late Ordovician sarcinulid corals (Tabulata). Palaeogeography, Palaeoclimatology, Palaeoecology, 215, 99–110. Tapanila, L. (2005). Palaeoecology and diversity of endosymbionts in Palaeozoic marine invertebrates: trace fossil evidence. Lethaia, 38, 89–99. Tapanila, L. (2006). Macroborings and bioclaustration in a Late Devonian reef above the Alamo Impact Breccia, Nevada, USA. Ichnos, 13, 129–134. Tapanila, L. and Holmer, L.E. (2006). Endosymbiosis in Ordovician– Silurian corals and stromatoporoids: a new lingulid and its trace from eastern Canada. Journal of Paleontology, 80, 750–759. Taylor, P.D. (1990a). Preservation of soft-bodied and other organisms by bioimmuration – a review. Palaeontology, 33, 1–17. Taylor, P.D. (1990b). Bioimmured ctenostomes from the Jurassic and the origin of the cheilostome bryozoa. Palaeontology, 33, 19–34. Taylor, P.D. and Wilson, M.A. (2003). Palaeoecology and evolution of marine hard substrate communities. Earth-Science Reviews, 62, 1–103. Unal, E. and Zinsmeister, W.J. (2005). Exotic biogenic structures from Early Cambrian of the Marble Mountains, California. Geological Society of America Annual Meeting. Abstracts with Programs, 37, 367. Voigt, E. (1979). The preservation of slightly or non-calcified fossil Bryozoa(Ctenostoma, & Cheilostoma) by bioimmuration. In: Larwood, G.P. and Abbott, M.B. (Eds.), Advances in Bryozoology, Academic Press, London, pp. 541–564. Wielgus, J., Glassom, D., Ben-Shaprut, O. and ChadwickFurman, N.E. (2002). An aberrant growth form of Red Sea corals caused by polychaete infestations. Coral Reefs, 21, 315–316. Winsborough, B.M., Seeler, J.-S., Golubic, S., Folk, R.L. and Maguire Jr, B. (1994). Recent fresh-water lacustrine stromatolites, stromatolitic mats and oncoids from northeastern Mexico. In: Bertrand-Sarfati, J. and Monty, C. (Eds.), Phanerozoic Stromatolites II, Kluwer Academic Publishers, Dordrecht, pp. 71–100.

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20 Macroborings and the Evolution of Marine Bioerosion Mark A. Wilson

macroborings are known from lacustrine algal structures (e.g., Ekdale et al., 1989) and vertebrate bones (e.g., Rogers, 1992; Paik, 2000), but they have not yet been systematically assessed. This chapter is confined to marine macroborings because they are very common, have a long evolutionary history, and are most valuable for paleoecological analyses. The emphasis here is also on trace fossils described outside the grey area of bites and shell breakage discussed by Bromley (2004). Sometimes holes in skeletons resemble borings but are instead the products of ‘passive endoliths’ (see Scoffin and Bradshaw, 2000) which produced various types of embedment structures or ‘pseudoborings’ (Palmer and Wilson, 1988) covered in Chapter 19 of this book. Borings are interesting from three primary perspectives. First, they are trace fossils and thus evidence of behavior not otherwise obtainable from body fossils. Second, as is typical with trace fossils, borings are often the only evidence found for entire groups of organisms that have left no other fossil record. Finally, borings are part of the geological process of bioerosion and thus evidence of the rates and intensities by which organisms reduce marine hard substrates. Since borings have a fossil record extending well back into the Precambrian, the evolution of boring communities and bioerosion can be documented over vast intervals of time. The mechanisms by which organisms bore into hard substrates are generally divided into two categories, although both can overlap in the same taxon. Some boring is done by chemical action such as lowering the pH on a carbonate substrate and thus

SUMMARY: Macroborings are macroscopic trace fossils in hard substrates. They received little attention from palaeontologists until a renaissance in their ichnotaxonomy and paleoecological interpretation was led by Richard Bromley in the 1970s. Since then we have amassed detailed records of their stratigraphic and palaeoenvironmental occurrences and have a better understanding of their diversity and classification. Macroborings have changed considerably in their types and abundances through the Phanerozoic as a function of various evolutionary events. They are thus important contributors to what we know about the ecological driving forces of evolution among marine organisms.

INTRODUCTION Borings are a type of trace fossil produced by organisms that grind, drill, dissolve, scratch, etch, or otherwise biologically excavate hard substrates (Fig. 20.1). The process of producing a boring is a form of bioerosion, the biological erosion of a substrate. This chapter covers macroborings which are here defined as any borings that can be detected with the naked eye (effectively meaning borings with long diameters no less than a millimeter or so). Microborings and the processes by which organisms produce them are the subject of Chapter 21 in this book. Most described macroborings are found in marine deposits even if some of the substrates, such as wood (e.g., Savdra, 1991), bones, and even coprolites (Tapanila et al., 2004), originated on dry land. Terrestrial


356


MOST COMMON MARINE MACROBORING TAXA

locally dissolving it (as some sponges do; see Pomponi, 1980) or by applying chelating agents to soften the carbonate substrate (used by some bivalves; see Lazar and Loya, 1991). Some boring is done mechanically with specialized portions of a shell, a technique especially prominent among rock- and wood-boring bivalves.

COMMONLY BORED HARD SUBSTRATES Many hard substrates are bored today in the oceans, most of which are made primarily of calcium carbonate. In fact, it is difficult to find a carbonate substrate in many marine environments that has not been bored, often to nearly complete destruction (see Fig. 20.1). These carbonate substrates include both aragonitic and calcitic shells, exposed outcrops of limestone and dolomite, beachrock, and carbonatecemented seafloor sediments known as hardgrounds. Other marine hard substrates bored today include wood, bones, and, rarely, igneous and metamorphic rocks (see, for example, Allouc et al., 1996). Numerous experiments have been done assessing the modern rates and patterns of bioerosion on various substrates (e.g., Powell et al., 2002). The types of hard substrates bored through geological time have, of course, changed dramatically. The earliest borings are microbial excavations in

357

Precambrian sedimentary grains such as ooids and pisoids (see Green et al., 1988). Archaeocyathid reefs were bored in the Early Cambrian (Kobluk and James, 1979), and the most commonly bored substrates in the Late Cambrian and Early Ordovician were carbonate hardgrounds (Wilson and Palmer, 1992). Starting in the Middle Ordovician, calcitic and aragonitic shells were often bored, their types varying with life’s history. Borings in the Palaeozoic, for example, were commonly excavated in the thick skeletons of trepostome bryozoans and rugose and tabulate corals; in the Mesozoic it was massive calcitic oysters that were often bored; and in the Cenozoic the scleractinian corals, host the greatest diversity of skeletal borings. There is even a global tectonic signal in the types of substrates bored since carbonate hardgrounds were most common during Calcite Sea intervals which were ultimately controlled by seafloor spreading rates (see Palmer and Wilson, 2004).

MOST COMMON MARINE MACROBORING TAXA Many marine taxa bore into hard substrates today, and many more have bored in the past. Summaries of marine bioeroders can be found in reviews by Radtke et al. (1997) and Taylor and Wilson (2003). For this chapter we will look at the most common boring groups. Their reasons for boring are as varied as their taxonomic diversity. The ichnotaxa mentioned below as examples are all listed in Table 20.1.

Worm-Like Animals There are many worm-like animals today that bore hard substrates. They include phoronids, polychaetes, turbellarians, sipunculids, and echiurids. Most construct domichnia for filter-feeding, so their borings tend to be cylindrical with at least one end open to the water (Fig. 20.2). The sabellarid polychaetes (‘feather duster worms’) with their elaborate filter-feeding apparatus and simple tubular holes are good examples of this behavior. Trypanites is a common boring by worm-like animals, as are Palaeosabella (Fig. 20.3), Caulostrepsis, and Maeandropolydora. FIGURE 20.1 Interior of the left valve of a modern marine bivalve (Mercenaria) riddled with sponge borings. Such intense bioerosion easily destroys carbonate substrates, especially calcitic and aragonitic shells. This shell is from the Atlantic coast of North Carolina. (Scale bar equals 10 mm.)

Sponges Some sponges today build elaborate sets of small tunnels and chambers in calcareous substrates (Figs. 20.1 and 20.4). Their excavations grow as they

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20. MACROBORINGS AND THE EVOLUTION OF MARINE BIOEROSION

TABLE 20.1 Phanerozoic Marine Macroborings (abridged and updated from Taylor and Wilson, 2003, Table 2. For additional details and discussion, see Bromley, 2004) Ichnogenus Caulostrepsis Clarke, 1908

Range Devonian– Recent

Remarks Pouch-shaped or ear-shaped borings or embedments

Additional References Bromley and D’Alessandro, 1983

produced by a gallery bent in a U-shape; single entrance. Modern spionid polydorid) polychaetes make incipient Caulostrepsis. Centrichnus Bromley and Martinell, 1991 Cicatricula Palmer and Palmer, 1977

Cretaceous– Recent Ordovician– Jurassic

Byssal etchings of anomiid

Bromley, 1999

bivalves. Radiating etched canals;

Fu¨rsich, 1979

canals subdivide and anastomose, producing a net-like pattern. Usually found on hardgrounds and possibly made by sponges.

Circolites Mikula´s, 1992 Clionoides Fenton

Jurassic– Recent

1908 Entobia Bronn, 1838

Fu¨rsich, 1979

echinoid boring.

Devonian

Tubular borings with irregular

Fagerstrom, 1996

Devonian–

branching; attributed to sponges. Rosette boring branched from

Plewes, 1996

and Fenton, 1932 Clionolithes Clarke,

Circular pits attributed to

Jurassic Devonian– Recent

elongate origin. Single or numerous chambers excavated in calcareous

Bromley and D’Alessandro, 1989

substrates; connected to surface by apertures. A senior synonym of Topsentopsis according to Tapanila, 2006. Filuroda Solle, 1938

Devonian– Jurassic

Gastrochaenolites Leymerie, 1842

Ordovician– Recent

Irregular tubes with rare

Plewes, 1996

branching and anastomosing. Clavate borings; aperture

Wilson and Palmer,

narrower than main chamber

1998; Ekdale and

and may be circular, oval, or

Bromley, 2001;

dumb-bell shaped; main

Benner et al., 2004

chamber may vary from subspherical to elongate. Usually made by bivalves which may be preserved in situ see Savazzi, 1999. Gnathichnus

Triassic–Recent

Bromley, 1975

Stellate, often pentameral scratches made by some

Fu¨rsich and Wendt, 1977

species of regular echinoids. Helicotaphrichnus Kern et al., 1974

Eocene–Recent

Helical borings made by spionid polydorid

Walker, 1992

polychaetes in the columella of gastropod shells occupied by hermit crabs. (continued)

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TABLE 20.1 Ichnogenus Lapispecus Voigt,

(Continued)

Range Pleistocene

1970

Remarks Cylindrical, curving boring with an occasional lateral

Additional References Bromley and D’Alessandro, 1987

vane. Leptichnus Taylor

Cretaceous–

et al., 1999

Recent

Groups of closely-spaced

De Gibert et al., 2004

small, shallow and typically elliptical pits excavated in calcareous substrates. Attributable examples are made by cheilostome bryozoans, each pit corresponding to a single zooid.

Maeandropolydora

Jurassic–

Voigt, 1965

Recent

Oichnus Bromley,

Cambrian–

1981

Recent

Long, sinuous to contorted galleries with pouches and two or more apertures. Circular or subcircular predatory borings in shells;

Bromley and D’Alessandro, 1987 Bengston and Zhao, 1992

made by gastropods, octopods or unknown predators. Palaeosabella Clarke, 1921

Ordovician– Recent

Unbranched, cylindro-clavate

Palmer et al., 1997

borings. Often confused with Trypanites and Vermiforichnus.

Petroxestes Wilson and Palmer, 1988

Ordovician– Miocene

Shallow to deep boring with

Pickerill et al., 2001

elongate outline and rounded base.

Phrixichnus Bromley and Asgaard, 1993

Miocene– Pliocene

Clavate boring with apparent

Dome`nech et al., 2001

growth lines. The producer of this boring remains unknown.

Podichnus Bromley and Surlyk, 1973

Silurian–Recent

Pedicle etchings of articulate brachiopods comprising a

Bundschuh, 2000

circular cluster of small holes increasing in size and obliqueness outwards. Radulichnus Voigt,

Jurassic–Recent

1977

Parallel sets of straight to

Kase et al., 1998

curved scrape marks forming scoop-like depressions. Incipient examples at the present day represent gnawing traces made by the radulae of chitons and gastropods.

Ramosulcichnus

Cretaceous

‘Worm’ borings in belemnites.

Pliocene–Recent

Etchings of the spiral

Hillmer and Schulz, 1973 Renichnus Mayoral, 1987

Taddei Ruggiero, 1999

attachments of vermetid gastropods. (continued)

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TABLE 20.1 (Continued) Ichnogenus Rogerella Saint-Seine, 1951

Range

Remarks

Devonian–

Pouch-shaped borings

Recent

Additional References Baird et al., 1990

produced at the present day by acrothoracican barnacles. Other names applied to acrothoracican borings are Brachyzapfes, Simonizapfes, and Zapfella.

Ropalonaria Ulrich, 1879

Ordovician– Cretaceous

Ramifying tunnels with

Pohowsky, 1978

periodic expansions and openings to the surface putatively made by ctenostome bryozoans. Various other ctenostome borings have been named, some as trace fossils but others as body fossils, including Iramena, Orbignyopora, Penetrantia, Pennatichnus, and Pinaceocladichnus. The total range of ctenostome borings is Ordovician–Recent.

Sanctum Erickson and Bouchard, 2003

Ordovician

Expanded and irregular chamber with single circular

Wyse Jackson et al., 2005

opening. Excavated in endozones of bryozoan skeletons. Spirichnus Fu¨rsich et al., 1994

Jurassic

Branching, spiraling tubes.

Bertling and Insalaco,

Talpina Hagenow,

Devonian–

Narrow curved branching

Plewes, 1996

1840

1998 Recent

tunnels connected to the surface by apertures. Attributed to phoronid worms. Conchotrema is a junior synonym.

Teredolites Leymerie,

Jurassic–Recent

1842

Tubular, clavate borings in

Savrda and Smith, 1996

wood, sometimes with calcareous linings. Some contain the shells of the trace-making bivalve.

Trypanites Ma¨gdefrau, 1932

Cambrian– Recent

Cylindrical, unbranched boring; length up to 50

Kobluk and Nemcsok 1982

times width. Vermiforichnus Cameron, 1969

Devonian–

Arcuate to sinuous cylindrical

Jurassic

borings with protuberances where direction changes; senior synonym of Cunctichnus.

Plewes, 1996


FIGURE 20.2 Polychaete borings in the exterior of a modern oyster from the eastern Florida coast. The outer shell layer has been removed by erosion, exposing the original bored tunnels as shallow ditches. (Scale bar equals 10 mm.)

361

FIGURE 20.4 Partially-eroded clionid sponge borings in the exterior of a modern oyster from southern Florida. The circular chambers were connected by tunnels seen here now as openings in the exposed pits. (Scale bar equals 5 mm.)

weakening it so that it may easily break apart when disturbed. Sponges have thus been important bioeroders since at least the Mesozoic.

Bryozoans

FIGURE 20.3 Natural casts of the worm-like boring Palaeosabella in a bimineralic bivalve (Caritodens) of the Upper Ordovician in northern Kentucky. The borings were excavated in the aragonitic inner shell layer of this bivalve. They are filled with calcite cement as the aragonitic substrate dissolved around them, exposing the borings as three-dimensional casts. Note the swollen distal ends of the boring which distinguish Palaeosabella from the similar Trypanites. (Scale bar equals 10 mm.)

do, always maintaining multiple connections to the outside water for filter-feeding. The effect is to produce a network of tiny holes on the surface of a shell, carbonate rock or hardground, each leading down into the chamber complex. The most common trace fossil made by sponges is Entobia, although some Entobia of the past, particularly the Palaeozoic, may have been made by other organisms. Much of the substrate is removed by these boring sponges,

Some cheilostome and ctenostome bryozoans etch into calcareous substrates to enclose their filterfeeding zooids. Since these bryozoans are sessile, these shallow borings in a sense mold the undersides of the colonies, showing the shapes of the zoaria and the directions in which they grew. The most common ctenostome borings in the fossil record are Ropalonaria; the cheilostome borings are Leptichnus.

Barnacles The shell-less acrothoracican barnacles can make domichnial macroborings known as Rogerella among fossils (Fig. 20.5). The borings are pouch-shaped with slit-like apertures so that these crustaceans can extrude their legs for filter-feeding.

Bivalves Marine bivalves of several types produce borings, including some of the largest and deepest excavations. These borings are usually strongly clavate with a large chamber which has increased in diameter with

362


FIGURE 20.5 Barnacle borings (Rogerella) in the interior surface of an Upper Cretaceous oyster from southern Israel. Minor abrasion and different angles of entry have produced this variety of cross-sectional outlines. (Scale bar equals 5 mm.)

FIGURE 20.6 Gastrochaenolites borings produced by bivalves in a Holocene limestone from an ancient rocky coast exposed in the southern Dominican Republic. The smaller holes around them are a combination of eroded barnacle and polychaete borings. (Scale bar equals 10 mm.)

the growth of the shell. At least one opening is maintained at the surface for filter-feeding currents or siphons. These bivalve borings are sometimes lined with a secreted fine-grained carbonate, especially those excavated in wood or other porous substrates. Gastrochaenolites is the most common bivalve boring trace fossil in rocks and shell (Figs. 20.6 and 20.7). Teredolites is the common bivalve boring in wood (Fig. 20.8). The earliest bivalve boring is the Ordovician Petroxestes, which was produced by Corallidomus, a facultative boring clam (Wilson and Palmer, 1988) (Fig. 20.9).

Gastropods The most prominent borings made by gastropods are predatory drillholes in the shells of various mollusks. This drilling is accomplished with the remarkable radula, essentially a moving ribbon of teeth. Many neogastropods use the radula to grind away at a shell on a narrow front, producing a circular hole which may or may not be beveled. The completed hole is known as the ichnogenus Oichnus when it is a fossil. The process is often not completed, leaving partial excavations on the outside of the shells of prey species. Grazing gastropods use their radulae to scrape hard substrates for microendoliths, producing distinct scratches on the surface. (These are known as Radulichnus in the rock record, which was also made by chitons and other radula-bearing grazers.) A few gastropods (such as some patellids) produce shallow ‘homing scars’ on

FIGURE 20.7 Gastrochaenolites anauchen in a limestone rockground from the Late Carboniferous of Arkansas, seen here in cross section. This is apparently the earliest bivalve-produced Gastrochaenolites. (Scale bar equals 10 mm.)

carbonate substrates. Attaching vermetid gastropods can leave a shallow etching on carbonate substrates known as Renichnus.

Echinoids Grazing regular echinoids make distinctive stellate scratches as they extract endoliths from carbonate substrates. The arms of these star-shaped excavations correspond with the teeth of the Aristotle’s Lantern jaw apparatus. In the fossil record these traces are known as Gnathichnus (Fig. 20.10).

HISTORY OF MACROBORING THROUGH THE PHANEROZOIC

363

FIGURE 20.9 Petroxestes pera, a bivalve boring in a hardground from the Upper Ordovician of southern Ohio. (Scale bar equals 10 mm.)

FIGURE 20.8 Teredinid bivalve borings in the wood of a modern wharf piling from the Gulf Coast of southern Texas. (Scale bar equals 10 mm.)

HISTORY OF MACROBORING THROUGH THE PHANEROZOIC Only recently have paleontologists begun to look at the history of macroborings through the Phanerozoic. Kobluk et al. (1978) published the first stratigraphic and evolutionary account of Early Palaeozoic borings. They showed a significant radiation of boring ichnogenera in the Ordovician, although the ichnotaxa they used include several forms we now know to be nonborings, and others as synonyms. Palmer (1982) published a compilation of taxa and ichnotaxa found on carbonate hardgrounds in the Palaeozoic and Mesozoic. He noted that the borings in hardgrounds had a dramatic increase in diversity and abundance in the Jurassic which he attributed to the corresponding infaunalization trends found in soft-sediment trace fossils. Wilson and Palmer (1992) confirmed this trend with additional data, noting, though, that more work was needed on the systematics of the borings before a more detailed stratigraphic pattern could be developed and interpreted. Two review articles appeared recently which opened a new era for work on the history of

FIGURE 20.10 Gnathichnus pentax in the interior of an oyster valve (Ilymatogyra) from the Upper Cretaceous of southern Israel. The stellate scratches match the Aristotle’s Lantern of an echinoid (Heterodiadema lybicum) found in the same unit. (Scale bar equals 10 mm.)

macroborings. They capitalized on the advances in ichnotaxonomy over the past two decades and the careful work on the systematics of boring organisms. Taylor and Wilson (2003) reviewed the paleoecology and evolution of hard substrate communities, including borings. Bromley (2004) independently assessed the stratigraphy of marine bioerosion. Together these works provide a detailed dataset for developing hypotheses about the changes in boring assemblages over geological time. Bromley (2004) cautions us that drawing from this record conclusions about the evolutionary history of the tracemakers themselves is still not possible, and that there are still many ‘grey areas’ in the ichnotaxonomy to be addressed (such as what to do with shells broken during predation, and how bioclaustrations and other embedment structures are assessed). Nevertheless, we now have an account, albeit imperfect, of the changes in macroboring styles and intensities

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25 Macroboring Ichnogenera Per Period 20

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FIGURE 20.11 Graph showing the numbers of ichnogenera found for each period of the Phanerozoic. The data are taken from Table 20.1. Note the diversification events in the Ordovician, Devonian, and Jurassic.

FIGURE 20.12 A rugose coral (Grewingkia) from the Upper Ordovician of southeastern Indiana showing numerous circular cross sections of borings. They are either Trypanites or Palaeosabella depending on the configuration of their distal ends. (Scale bar equals 10 mm.)

through the Phanerozoic. A period-by-period review of the record of borings has been compiled by Taylor and Wilson (2003), so it need not be repeated here. Bromley (2004) has also described the major boring taxa in stratigraphic detail, leaving us free to examine the larger changes. When we do that, three diversification events in the historical record of macroboring are clear (Fig. 20.11).

Ordovician Bioerosion Revolution There are only two macroborings in the Cambrian: the simple tubular Trypanites and the even simpler

FIGURE 20.13 Dense boring in the surface of a trepostome bryozoan from the Upper Ordovician of southeastern Indiana. (Scale bar equals 10 mm.)

circular hole Oichnus. By the end of the Ordovician, macroborings include at least eight ichnogenera, and just as important the intensity of macroboring has dramatically increased. Macroborings were rare in the Cambrian and Early Ordovician, but by the end of the Ordovician, shells and hardgrounds were not only thoroughly riddled with holes, most of them attributable to Trypanites and Palaeosabella (Figs. 20.3, 20.12 and 20.13), but also including bivalve borings (Petroxestes; Fig. 20.9), bryozoan etchings (Ropalonaria), sponge borings (Cicatricula), Sanctum (a cavernous domichnium excavated in bryozoan zoaria by an unknown borer) and a mysterious form of Gastrochaenolites which was bored by something other than a bivalve (Ekdale and Bromley, 2001; Benner et al., 2004). This increase in the diversity

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ACKNOWLEDGEMENTS

and abundance of borings has been termed the Ordovician Bioerosion Revolution by Wilson and Palmer (2006). It is the hard substrate equivalent of the Ordovician Radiation, corresponding with the soft-sediment ichnogeneric diversity increases noted by Mańgano and Droser (2004). The evolutionary importance of the Ordovician Bioerosion Revolution is that, with trace fossils we are seeing ecological and behavioral diversification as well as a taxonomic radiation. The increase in boring diversity and intensity in the Ordovician reflects niche differentiation among a variety of groups. Bioerosion also at this time becomes a measurable geological phenomenon.

Middle Paleozoic Marine Revolution The second diversification of macroborings takes place in the Devonian when the number of ichnogenera doubles. Many borings appear that are essentially modern in their form. New borings in the Devonian include several that had become prominent through the rest of the Phanerozoic: Entobia, Talpina, Caulostrepsis, and Rogerella. Soon afterwards, in the Carboniferous, the first Gastrochaenolites produced likely by a bivalve is found (Wilson and Palmer, 1998). This diversification of macroborings is again a reflection of a larger evolutionary event among marine invertebrates, in this case, the ‘mid-Paleozoic precursor to the Mesozoic Marine Revolution’ (Signor and Brett, 1984, p. 229). Beginning in the Middle Devonian, the number of shell-breaking and shelldrilling predators increased markedly (see for example Wilson and Taylor, 2006). Infaunalization was one of the responses of prey animals to this rise in predation, and this is apparently shown in the new boring types that appear.

Mesozoic Marine Revolution The rise in marine predators in the Mesozoic has been well documented as the Mesozoic Marine Revolution (Vermeij, 1977). The number of macroborings reaches its peak during the Jurassic. Many of these borings are also considerably larger in size than their precursors, especially Gastrochaenolites. As with the Ordovician Bioerosion Revolution, the Jurassic equivalent on hard substrates is notable not only for the diversity of borings but also for their abundance (Palmer, 1982; Wilson and Palmer, 1992). Like the Middle Palaeozoic Marine Revolution in bioerosion, the Jurassic version was in part an apparent infaunalization to escape predators.

CONCLUSIONS Macroborings are macroscopic trace fossils produced in hard substrates like rock, shells, and wood rather than in soft sediments. The biological reduction of these hard substrates is bioerosion, an important geological process, especially in carbonate - producing environments. Excavating hard substrates requires a significant energy investment, so the organisms that do it have a variety of specialized organs and behaviors. With increasingly sophisticated ichnological investigations of macroborings through the rock record, we are now able to see trends in these adaptations. The evolution of macroboring behavior has had three significant diversification events (in the Ordovician, Devonian, and the Jurassic), all tied to evolutionary radiations among marine organisms. Macroborings, because they record specific behaviors on hard substrates, are thus important for helping sort out the reasons behind evolutionary change.

ACKNOWLEDGEMENTS Richard G. Bromley and Frank K. McKinney provided very helpful reviews of the manuscript. Partial support for this work was received from the donors of the Petroleum Research Fund, administered by the American Chemical Society, as well as from the Luce Fund for Distinguished Scholarship at The College of Wooster.

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21 Microborings and Microbial Endoliths: Geological Implications Ingrid Glaub, Stjepko Golubic, Marcos Gektidis, Gudrun Radtke, and Klaus Vogel

identification of the microorganism together with its trace, as well as determination of the distribution of microboring organisms in relation to environmental and sedimentary conditions. Thus, the study of microboring traces has a geological application as paleoecological and paleobathymetric indicators (Golubic et al., 1975; Budd and Perkins, 1980; Vogel et al., 1987; Glaub, 1994; Vogel et al., 1995).

SUMMARY : The most important ichnotaxa (and some biotaxa) of microendolithic cyanobacteria, algae and fungi are presented. Their relations to environmental factors such as light, temperature, salinity, inorganic nutrients and their bioerosion potential are discussed. From the Silurian on, they form characteristic ichnocoenoses that are bathymetrically controlled and can be used for the reconstruction of water depths of fossil marine basins. Some ichnotaxa appeared as far back as the Ordovician, and some biotaxa in the Precambrian.

PREPARATION AND STUDY OF MICROBIAL ENDOLITHS AND MICROBORINGS

INTRODUCTION Fossil microborings are often filled with contrasting sediments or, more often, precipitates, which makes them visible in petrographic thin sections (Hessland, 1949; Campbell, 1982a). These microboring fills are often less soluble than the surrounding matrix (e.g., pyritized), so that they can be etched out with acids (Kobluk and Risk, 1977b). Natural casts on weathered rock surfaces from Ordovician (Calvet and Fontarnau, 1982), Jurassic (Gattrall and Golubic, 1970) and Pleistocene (Harris et al., 1979) were visualized in their three-dimensional display using a scanning electron microscope (SEM). However, a surprisingly high proportion of fossil microborings remained void or only partially filled. These have been cast in polymerizing resins, studied by SEM and compared with modern microborings. The samples of bored substrates are impregnated with polymerizing resins (epoxy, Araldite, SPURRS), as described by Golubic et al. (1970, 1983).

Microborings are traces of euendolithic microorganisms. Euendoliths actively penetrate mineralized substrates, whereas other microorganisms that are found in the interior of hard rocky substrates, called crypto- and chasmoendoliths, inhabit existing pores and fissures in the rock (Golubic et al., 1981). Microborings often conform tightly with the body outlines of the organisms that produced them, and may be characterized by species-specific morphological features. In such cases, modern and fossil microborings can be assigned to their trace makers with a reasonably high degree of precision. Microboring traces are abundantly preserved in fossil calcareous substrates such as limestone, carbonate sand grains and ooids, shells of mollusks and brachiopods, crinoid ossicles and coral skeletons (Glaub and Vogel, 2004). The interpretation of fossil microborings is aided by the study of modern counterparts, which permits


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DIVERSITY AND GEOLOGICAL SIGNIFICANCE OF MICROBIAL EUENDOLITHS

Embedded samples are suitable for preparation of oriented petrographic thin sections. Alternatively, the carbonate matrix can be partially or completely removed by acid (dilute HCl) and the borings exposed as casts for SEM observation. Fine microborings and structural pores down to submicron dimensions can be replicated using this method. Borings of modern and fossil endoliths are cast using minor modifications in sample preparations. Such modifications may include appropriate fixation, staining and dehydration of samples with resident endoliths, which can then be visualized light-microscopically in situ, using double-embedded preparations (Golubic et al., 1975). Partial etching is applied to evaluate the relations between the endolith and the bored substrate or to prevent the collapse and disruption of casts of finer boring structures, particularly when borings connect both sides of a shell (Hook and Golubic, 1993; Mao Che et al., 1996; Wisshak et al., 2005). Complementary application of these methods permits comparisons between fossil and modern microborings as well as comparisons and identification of borings and their makers among modern assemblages of microbial euendoliths.

DIVERSITY AND GEOLOGICAL SIGNIFICANCE OF MICROBIAL EUENDOLITHS Microbial euendoliths, defined by their microscopic size (< 100 mm tunnel diameter) are a diversified group, which includes prokaryotic and eukaryotic organisms: cyanobacteria and possibly other bacteria, algae (Chlorophyta and Rhodophyta), fungi and Foraminifera (Fig. 21.1). Cyanobacteria have produced characteristic traces in rocks and skeletal carbonates of different ages maintaining conservatively their shape and a close correspondence between the organism’s body and the boring they produced. Examples of traces and their trace makers are illustrated in Fig. 21.2. Borings of eukaryotic green and red algae form characteristic swellings and constrictions that correspond to positions of cells along algal filaments. Septate green algae grow long hairs from each cell, which is presumed to facilitate nutrient supply (Figs. 21.3.1 and 21.3.2). Siphonal green algae from fine reticulate borings (Fig. 21.3.3). Some macroscopic chlorophytes such as Acetabularia penetrate carbonate only with their rhizoids, where the nucleus rests and survives from season to season (Radtke et al., 1997a) (Fig. 21.3.4). Bangialean rhodophytes are macroalgae with a

369

complicated life cycle, in which only a part is spent inside a carbonate substrate. These endolithic forms have been described as a separate genus under the name Conchocelis before the life cycles of Porphyra and Bangia were completely understood. The name is now informally used to designate the endolithic stage (Figs. 21.3.5 and 21.3.6). Heterotrophic euendoliths are less well known. Several forms, described among lower fungi produce characteristic and easily recognizable traces. For example, Dodgella priscus produces club-shaped sporangial swellings interconnected by thin hyphae. Its trace, named Saccomorpha clava (Fig. 21.4.1), is common in modern shells at all depths and has been observed in geological strata throughout the Phanerozoic. In contrast, the endolithic trace Dendrina (Fig. 21.4.2) does not have a known modern counterpart. It is presumed to be made by a heterotrophic boring organism. The makers of tubular traces, e.g., Orthogonum lineare (Fig. 21.4.3), are also unknown, although they are quite common in modern environments, especially in the deep sea. Less common but of characteristic shape is Polyactina araneola, the trace of the lower fungus Conchyliastrum enderi (Fig. 21.4.4). Microbial euendoliths are known from terrestrial, freshwater and marine environments, where they are an integral part of various ecosystems. Symbiotically integrated as endolithic lichens, they are most successful on land on exposed limestone surfaces, where they are often the pioneer vegetation (Chen et al., 2000; Golubic and Schneider, 2003). Freshwater euendoliths contribute to limestone corrosion in lake littoral and participate in complex mobilization and reprecipitation of carbonate (Schneider et al., 1983; Schneider and Le Campion-Alsumard, 1999). Similar mechanisms have been proposed for microboring organisms in shallow marine environments to be contributing to consolidation of stromatolitic structures (Kobluk and Risk, 1977a; Macintyre et al., 2000; Reid and Macintyre, 2000). Modification of carbonate grains and formation of micritic envelopes by microbial endoliths in shallow marine environments of warm seas was recognized early (Bathurst, 1966), as was their contribution to fine-grain sediment production (Torunski, 1979). Most research was dedicated to marine microbial euendoliths, which is summarized in an extensive bibliography by Radtke et al. (1997b). Microborers are powerful geological agents involved in coastal bioerosion (Tudhope and Risk, 1985), particularly when interacting synergistically with grazing animals such as gastropods, echinoderms and fish (Schneider and Torunski, 1983; Bruggemann et al., 1994; Tribollet et al., 2002).

370

21. MICROBORINGS AND MICROBIAL ENDOLITHS: GEOLOGICAL IMPLICATIONS

FIGURE 21.1 The most important microendolithic bio- and ichnotaxa, some of them with simplified drawings, are given with their affiliation to organism groups.

In search for food, grazers remove a surface layer of the rock colonized by epiliths and endoliths, thereby stimulating phototrophic microborers to penetrate deeper into the rock. The bioerosion rates are variable, but values exceeding 0.5 kg m2 year1 have been reported in different shallow marine settings (e.g., Chazottes et al., 1995; Pari et al., 1998; Vogel et al., 2000), illustrating the importance of the process on a geological timescale. The combined action of endoliths, and grazers results in progressive erosion (Torunski, 1979) and is responsible for the formation

of a coastal bioerosional notch (Radtke et al., 1996, 1997c), a feature that marks sea level positions in the geological past (Neumann, 1966). Specialized euendolithic algae and fungi are ubiquitous inhabitants of coral skeletons worldwide (Le Campion-Alsumard et al., 1995a). Both permeate coral skeletons and keep up with coral growth and accretion. Damage by algae is mostly accidental, but fungiappeartoattackandparasitizebothalgaeandpolyps (Priess et al., 2000). The polyps respond by depositing dense repair carbonate to patch up fungal boreholes

DIVERSITY AND GEOLOGICAL SIGNIFICANCE OF MICROBIAL EUENDOLITHS

FIGURE 21.2 Euendolithic cyanobacteria and ichnotaxa of presumed cyanobacterial origin of different stratigraphic ages. (1) Fascichnus dactylus, resin-cast boring trace, presumably produced by the cyanobacterium Hyella caespitosa, in a bivalve shell. Kimmeridgian (Jurassic). Consolacao, Portugal. Glaub, 1994: pl.4, fig. 4. SEM. Scale bar 50 mm. (2) The cyanobacterium Hyella caespitosa, acid-extracted from a modern mollusk shell. Recent. Marseille, France. Glaub, 1994: pl.4, fig. 5. Light micrograph (LM). Scale bar 20 mm. (3) Fascichnus dactylus, in a brachiopod shell. Ordovician. Cut Blue Rock Road, Cincinnati OH, USA, Vogel and Glaub, 2004: fig. 13. SEM. Scale bar 100 mm. (4) Fascichnus isp. a boring with outline and dimensions that correspond closely to the Neoproterozoic fossil Eohyella dichotoma and the modern cyanobacterium Hyella stella, in a gastropod shell. Sarmatian (Neogene), Vienna basin, St. Margarethen, Austria. SEM. Scale bar 10 mm. (5) Eurygonum nodosum, a trace presumably produced by the filamentous heteroscystous cyanobacterium Mastigocoleus testarum, in a gastropod shell. Sarmatian (Neogene). Vienna basin, Nexing, Austria. SEM. Scale bar 30 mm. (6) Fascichnus acinosus, a trace presumably produced by Hyella balani, in a bivalve shell. Kimmeridgian (Jurassic). Consolacao, Portugal. SEM. Scale bar 20 mm. (7) Hyella balani (Cyanobacteria), in a shell fragment. Recent. Marseille, France. Glaub, 1994: pl.5, fig. 3. LM. Scale bar 10 mm.

371

372


FIGURE 21.3 Euendolithic eukaryotic phototrophs (green and red algae) and their traces. (1) Phaeophila dendroides (Chlorophyta), boring through a transparent calcite spar. Recent. Lee Stocking Island, Bahamas. Vogel et al., 2000: fig. 6B. LM. Scale bar 20 mm. (2) Rhopalia catenata, a trace produced by Phaeophila dendroides, cast from a bivalve shell. Recent. Lee Stocking Island, Bahamas. Vogel et al., 2000: fig. 6A. SEM. Scale bar 20 mm. (3) Ichnoreticulina elegans, a trace attributed to the siphonal green alga Ostreobium quekettii, in a bivalve shell. Stepovak Formation, Oligocene. Unga Island, Alaska. Vogel and Marincovich, 2004: fig. 3, 6. SEM. Scale bar 30 mm. (4) Fascichnus grandis, a trace attributed to euendolithic rhizoids of the green alga Acetabularia, in a bivalve shell. Eocene. Fercourt, France. Radtke, 1991: pl.11, fig. 4. SEM. Scale bar 100 mm. (5) Trace with series of swellings that correspond closely in shape and dimensions to monosporangial swellings of the Silurian fossil red alga Palaeoconchocelis starmachii, as well as to such swellings of modern endolithic Conchocelis stages of Porphyra nereocystis. In a brachiopod shell. Lower Cretaceous. Berrias, France. SEM. Scale bar 20 mm. (6) Trace corresponding to the Conchocelis stages of modern Bangialean red algae, in a gastropod shell. Sarmatian (Neogene). Vienna basin, Nexing, Austria. SEM. Scale bar 20 mm.

MICROBIAL ENDOLITHS AND MICROBORINGS IN THE FOSSIL RECORD

373

FIGURE 21.4 Ichnotaxa of presumed heterotrophs of different stratigraphic ages. (1) Saccomorpha clava, produced by lower fungus Dodgella priscus, in a brachiopod shell. Ordovician. Sharonville Industrial Park, Cincinnati OH, USA. SEM. Scale bar 30 mm. (2) Dendrina orbiculata, in a belemnite. Upper Cretaceous. Lu¨neburg, Germany, chalk quarry. Hofmann, 1996: pl. 7, fig. 1. SEM. Scale bar 500 mm. (3) Orthogonum lineare, a trace common in modern deep sea, thus presumed to be produced by a heterotroph, in a brachiopod shell. Lower Jurassic. Ko¨so¨sku´t, Hungary. Glaub, 1994: pl. 7, fig. 2. SEM. Scale bar 200 mm. (4) Polyactina araneola, produced by the lower fungus Conchyliastrum enderi, in a bivalve shell. Recent. Firth of Lorne, Scotland. SEM. Scale bar 30 mm.

forming pearl-like conical structures (Le CampionAlsumard et al., 1995b). Thus, healthy corals are able to cope and coexist with microbial endoliths, but their resilience is questioned when corals bleach and are otherwise stressexposed(Bentisetal.,2000).

MICROBIAL ENDOLITHS AND MICROBORINGS IN THE FOSSIL RECORD The endolithic mode of life among microorganisms evolved early (Table 21.1). The oldest fossil microbial

euendolithic cyanobacterium Eohyella campbellii was found to penetrate lithified surfaces of 1500–1700million-year-old ancient stromatolites (Zhang and Golubic, 1987), i.e., they are about three times the age of the skeletons of invertebrates that served later as hosts to euendoliths during the Phanerozoic Era. By the time of the Neoproterozoic, some 700–800 million years ago, entire assemblages of cyanobacterial euendoliths bored oolites and pisolite grains, which was later preserved by silicification (Knoll et al., 1986, 1989). They were preserved as body fossils in position, oriented toward the interior of the substrate. These fossil assemblages are quite similar

374


Quaternary

Carbonifer.

Ordovician

Stratigraphic Ranges of Fossil Microborers and Microboring (Body Fossils and Trace Fossils), Sorted by their First Occurrences

¨

#

#

# #

Orthogonum fusiferum

#

#

Ichnoreticulina elegans

#

#

Saccomorpha clava Scolecia filosa

#

Fascichnus rogus

#

#

#

#

#

#

#

#

#

#

#

# #

#

#

# #

#

Cyanobacteria

#

#

#

# #

#

#

#

#

fungi

#

#

#

#

#

#

#

Cyanobacteria

#

#

#

#

#

Cyanobacteria

#

#

#

#

#

#

#

#

fungi

#

Chlorophyta

¨

Rhodophyta

#

#

#

#

#

#

#

#

#

#

#

#

#

Polyactina araneola

#

#

#

#

#

#

Hyellomorpha microdendritica

#

# #

Planobola macrogota

Globodendrina monile -----------------Corresponding traces

Organism Group

Cyanobacteria

Fascichnus dactylus

Palaeoconchocelis starmachii -----------------Conchocelis traces

Neogene

Eohyella rectoclada -----------------Fascichnus frutex

Paleogene

Cyanobacteria

Cretaceous

¨

Jurassic

Cyanobacteria

Eohyella dichotoma -----------------Corresponding ichnotaxa

Triassic

¨

Permian

Cyanobacteria

Eohyella elongata

Devonian

¨

Silurian

Eohyella campbellii

Cambrian

Body Fossil ¨ Trace Fossil #

Proterozoic

TABLE 21.1

#

#

# #

?

#

fungi

#

Cyanobacteria

¨ #

#

Orthogonum lineare

#

#

Orthogonum spinosum

#

#

Orthogonum tripartitum

#

#

Foraminifera # #

#

#

#

#

#

? ? Rhodophyta ?

Eurygonum nodosum

#

#

#

#

Cyanobacteria

Fascichnus acinosus

#

#

#

#

Cyanobacteria

Cavernula pediculata

#

#

#

Chlorophyta

Cavernula zancobola

#

fungi

Planobola cebolla

#

?

Planobola microgota

#

Planobola radicatus

#

#

#

#

fungi #

Rhopalia catenata

#

#

Saccomorpha terminalis

#

#

Scolecia maeandria

#

#

fungi #

#

#

Chlorophyta

#

fungi

#

bacteria ?

Cavernula coccidia

#

?

Orthogonum appendiculatum

#

?

Orthogonum giganteum

#

Orthogonum tubulare

#

Dendrina orbiculata Fascichnus grandis

#

#

?

#

#

fungi ?

#

#

Chlorophyta

#

Cyanobacteria ?

#

#

fungi

#

#

#

?

Fascichnus parvus

#

Polyactina fastigata

#

Saccomorpha sphaerula

#

Scolecia botulifera

#

Scolecia serrata

#

? Rhodophyta ? bacteria ?

DISTRIBUTION AND ENVIRONMENTAL RANGES OF MICROBIAL ENDOLITHS

to modern assemblages active in ooids of the Bahamas and the Arabian/Persian Gulf (Green et al., 1988). Another organically preserved microbial euendolith could be extracted intact from ca. 420-million-yearsold ossicles of a Silurian crinoid (Kazmierczak and Golubic, 1976; Campbell, 1980). While the organically preserved microbial fossils are generally rare, microbial euendoliths leave abundant durable traces of their activity in hard substrates. These could be studied in petrographic thin sections or by SEM images of natural as well as artificial resin casts. Fossil microborings conducive to resin replication and SEM analyses are distributed throughout the Phanerozoic (Bromley, 2004; Glaub and Vogel, 2004) (Table 21.1). Work on fossil microborings in brachiopods of the Middle Devonian sea established the principles of description of fossil boring traces and tested their use as bathymetric indicators in correlation with general and sedimentary geological context (Vogel et al., 1987). The comparison was later expanded to older Silurian and younger Jurassic and Lower Cretaceous strata (Glaub, 1994; Glaub and Bundschuh, 1997; Bundschuh, 2000). Microborings in Devonian and Carboniferous conodonts were discovered by Glaub and Ko¨nigshof (1997). Study of microborings in Permian and Triassic reefs (Balog, 1996) followed earlier work on Triassic borings by Schmidt (1990, 1992). Microborings in selected sites of Jurassic and Lower Cretaceous age were analyzed by Glaub (1994) and those in the Upper Cretaceous by Hofmann and Vogel (1992) and Hofmann (1996). The microborings of the Paleogene and Neogene served for comparisons between different depositional basins and with modern forms (Radtke, 1991, 1998; Vogel and Marincovich, 2004). Examples are illustrated in Figs. 21.2–21.4.

DISTRIBUTION AND ENVIRONMENTAL RANGES OF MICROBIAL ENDOLITHS Microbial euendoliths are widely distributed in marine environments. They are encountered in various sedimentary settings from the supratidal to the deep sea. To our knowledge, microbial endoliths are a benthic phenomenon, most active at the sediment–water interface (Golubic et al., 1984), with few exceptions where their activity is inside sediment (May and Perkins, 1979). The environmental conditions that microbial endoliths can tolerate and under which they form competitive populations are important sources of information for the interpretation of

375

their fossil traces. Such tolerance refers to the range as well as timing of the environmental change within the scope of the lifetime of these organisms. Their success depends not only on conditions favorable for their growth, but also on their ability to persist in an inactive latent state. Along a depth profile, the range as well as the rates of change of environmental conditions is highest in the supratidal and intertidal ranges, and the conditions become more uniform with increasing depth. This is reflected in sharper zonal distribution of organisms, including microbial endoliths, which becomes less pronounced with depth. The temperature is low but fairly uniform globally throughout the deep ranges. It is, however, an important factor determining latitudinal distribution of marine organisms in shallow marine environments. Modern microborings were studied at higher latitudes in Scotland (Akpan and Farrow, 1985; Glaub et al., 2002); Tromsø, Norway (Glaub et al., 2002); and in Kosterfjord, Sweden (Wisshak et al., 2005). Microbial endoliths are well represented in different latitudes in tropical and nontropical environments, as well as in regions of upwelling, e.g., off Mauritania (Glaub, 2004). The distribution of microbial endoliths in different salinity ranges also indicates considerable tolerance. While stable low-salinity conditions in freshwater maintain a taxonomically different set of organisms (Schneider, 1977; Anagnostidis and Pantazidou, 1988; Seeler and Golubic, 1991; Schneider and Le CampionAlsumard, 1999), marine forms are highly tolerant to salinity fluctuations (Wisshak et al., 2005). Similar observations were made for the occurrence of microborings in fossil settings identified independently as brackish (Radtke, 1998). With respect to nutrients, microbial euendoliths fall into two distinct categories: phototrophs are largely autotrophic, requiring inorganic nutrients, whereas the heterotrophs depend on organic compounds mostly encountered within the substrate they bore. Distinction in boring pattern and exploration strategy within the bored substrate, including the ability and preference to target and penetrate organic matter in shells, has been observed (Golubic et al., 1975). Supply of inorganic nutrients to phototrophic microborers is facilitated by local recycling and increased nutrient level within the reef substrates (Risk and Mu¨ller, 1983; Ferrer and Szamant, 1988; Sansone et al., 1988). However, there is no evidence that these conditions influence either the growth or composition of microendolith communities. Experimental introduction of inorganic nutrients with concentrations 10–15 times higher than environmental P- and N-concentrations

376


on the Great Barrier Reef (Larkum and Steven, 1994) for 5 months had no detectable impact on the composition or bioerosion rates of the microendolith community (Kiene, 1997). Long-term effect of elevated nutrient supply on coasts polluted by petrochemical products reduced the diversity of euendoliths, but municipal sewage produced no such effect (Campbell, 1982b). In conjunction with nutrition, the substrate specificity may be important for distribution of organotrophic microendoliths, but appears to be less critical for the phototrophs. Certain substrate preferences in settlement by modern microendoliths could be observed by substrate exposure experiments at Lee Stocking Island, Bahamas (Vogel et al., 2000). The highest rate of colonization was recorded in micrites, compared to Strombus shells and clear calcite crystals. The abundance of heterotrophic microborers in shells of mollusks (Strombus, Tridacna) correlates with the high organic content of the crossed lamellar shell microstructure of these mollusks, which may serve as food for those organisms. Endolithic fungi are often observed to parasitize phototrophic endoliths (Schneider, 1976; Le Campion-Alsumard et al., 1995b), or participate in the formation of endolithic lichens (Le Campion-Alsumard and Golubic, 1985; Golubic et al., 2005). The study of microborings in fossil brachiopods, bivalves, ammonites and crinoids in Triassic sediments of Southwest Germany and in the Alps did not show any significant qualitative difference except in crinoids, which showed the lowest diversity (Schmidt, 1992). The implication of the known broad tolerances of microbial endoliths in relation to the environmental conditions just mentioned is that, for the fossil record, these parameters need to be established independently using other sedimentological and paleontological clues. These observations also support the focus on light as the most important environmental determinant of microbial euendolith distribution. Phototrophic microbial endoliths are light-dependent, and they populate the illuminated parts of the oceans, whereas the dark depths of the ocean are accessible to heterotrophs alone, provided there is availability of organic nutrients. However, different taxa of phototrophs have distinct requirements and preferences, which are reflected in a zonal depth distribution of their populations. The light in the sea attenuates with depth and shifts in its spectral composition toward the shorter wavelengths. In response, phototrophic organisms evolved efficient light harvesting systems and qualitative and quantitative chromatic adaptations. These responses also include the protection from excessive solar illumination. For geological

application, it is important to note that typical ichnocoenoses exist, which characterize different subzones along the gradient of attenuated light from the euphotic to the aphotic conditions (Fig. 21.5). The characterization of these ichnocoenoses was carried out first for the Upper Jurassic and the Lower Cretaceous by Glaub (1994) and has been confirmed by many paleobathymetric evaluations of fossil marine sedimentary basins, e.g., the Silurian (Bundschuh, 2000), Permian and Triassic (Schmidt, 1992; Balog, 1996), Upper Cretaceous (Hofmann, 1996), Paleogene and Neogene (Radtke, 1991; Vogel and Marincovich, 2004), as well as in the studies of modern microboring occurrences (Gektidis, 1997; Vogel et al., 1999, 2000; Glaub, 2004).

ICHNOLOGICAL TREATMENT OF MICROBORINGS Microborings are traces, and therefore need to be classified as ichnotaxa separately from their putative makers. As with other macro- and microscopic traces in hard and soft substrates, such treatment is a necessary precaution, because an organism is able to produce more than one trace type and, conversely, similar traces may be produced by different organisms (Bromley, 2004). Among microbial euendoliths, changes in boring behavior were observed in the course of the life cycle and thallus differentiation of a single organism, whereas other features reflected in boring morphology evolved convergently in different organisms, while adapting to the particular conditions of the endolithic mode of life. From the perspective of the organism, its boring behavior and the resulting borehole morphology is just another of many taxonomically relevant descriptors. From the perspective of the trace, its identity rests on its morphology, while the identity of its maker is hypothetic. Yet, the recognition of the microborer and its ecological requirements are relevant if microborings are used as environmental and paleoenvironmental indicators. There is a wide range in the degrees of certainty in identifying the makers of microboring traces; therefore, the nomenclature needs to be kept consistently separate, in spite of cumbersome double referencing to traces and their putative makers. Ichnotaxa were established for many important microborings by Vogel et al. (1987), Radtke (1991), Schmidt (1992), Tavernier et al. (1992), Glaub (1994) and Hofmann (1996). In addition, boring patterns were illustrated for many modern euendoliths (e.g., Golubic et al., 1975; Lukas, 1979; Lukas and Golubic, 1983;

ICHNOLOGICAL TREATMENT OF MICROBORINGS

377

FIGURE 21.5 Different photic zones determining bathymetric zonation and characterized by microendolithic ichnocoenoses, originally worked out for Upper Jurassic and Lower Cretaceous by Glaub (1994), since then confirmed by numerous studies for Silurian to modern sediments. ch – chlorophyta, cy – Cyanobacteria, rh – Rhodophyta, he – heterotrophs. (Palaeoconchocelis starmachii is a Silurian body fossil and should not be used anymore for trace fossils, as was done in earlier published versions of this diagram. A corresponding ichnotaxon has not been established. Therefore, we put the name into quotation marks.)

Al-Thukair and Golubic, 1991a,b; Radtke, 1993; Al-Thukair et al., 1994) and for some fossil euendoliths (Campbell, 1980), but these have not been formally described as ichnotaxa.

Two ichnogenera, erected by Radtke (1991) and since then cited in many publications, had to be renamed because of priority reasons (Radtke and Golubic, 2005). The name Ichnoreticulina (Fig. 21.3)

378


now substitutes for Reticulina and Fascichnus for Fasciculus. The name Palaeoconchocelis starmachii (Campbell et al., 1979) refers to a Silurian body fossil and should not be used to name fossil or modern traces attributed to endolithic rhodophytes. The established ichnotaxa are listed in Fig. 21.1 and Table 21.1, together with the corresponding biotaxa of their makers so far as these have been identified.

VERTICAL DISTRIBUTION OF PHOTOTROPHIC MICROBIAL EUENDOLITHS Supratidal and intertidal ranges are dominated by dense populations of cyanobacteria, which give the rock dark coloration. They inhabit coastal limestone and shells of barnacles (Schneider, 1976; Le CampionAlsumard, 1979; Le Campion-Alsumard and Golubic, 1985; Radtke et al., 1996). In the lower intertidal ranges in tropical settings, dominance occasionally shifts to Conchocelis developmental stages of bangialean red algae. The shifting sediment grains and ooids are the domain of coccoid euendolithic cyanobacteria, including different species of Hyella (Al-Thukair and Golubic, 1991a,b; Al-Thukair et al., 1994; Gektidis, 1997), which leave an array of traces classified as Fascichnus (Radtke and Golubic, 2005). These forms prevail throughout the shallow subtidal ranges, where they are joined by septate chlorophytes. Because of complex alternation of morphologically different generations, the systematic position of euendolithic green algae is not resolved. The most characteristic traces are classified as Rhopalia (Radtke, 1991). Shaded habitats in shallows and deeper ranges of the euphotic zone are dominated by the siphonal green alga Ostreobium quekettii. This extremely efficient phototroph dominates all carbonate substrates in a broad range of depths between 10 and 150 m in clear tropical seas. The record depths for this endolith was found on the steep slope of the Exuma Sound, Bahamas, at 300 m (Vogel et al., 1996). The maximum depth for any phototrophic endolith was reported for the cyanobacterium Plectonema terebrans at 370 m off the Florida coast (Lukas, 1979). Ostreobium quekettii is a regular inhabitant of skeletons of live and growing reef corals (Le Campion et al., 1995a), and both Ostreobium and Plectonema terebrans are significant contributors to primary production on degraded reefs and coral rubble (Tribollet et al., 2002). Only low-light specialists such as Ostreobium quekettii (trace: Ichnoreticulina elegans) and Plectonema terebrans (trace: Scolecia filosa)

occur in the dysphotic zone. In the aphotic zone, only heterotrophic microendoliths (e.g., fungi) occur (Glaub, 1994).

CONCLUSIONS The endolithic microbial niches provide sheltered and buffered microenvironments. They were occupied early by specialized microorganisms and have been maintained over the geological past. Microborings form characteristic, bathymetrically controlled ichnocoenoses from the Silurian on and can be used for the reconstruction of water depths in fossil marine basins. We consider that the essential factors that favored long stratigraphic ranges of fossil euendoliths are (1) the abundance of protected, buffered hard substrates since the early Earth history, (2) the mobility of endolithic reproductive cells, and (3) the ability of microborers to tolerate environmental fluctuations.

FUTURE RESEARCH The study of microbial euendoliths and microborings has been advanced by interdisciplinary ecological and geological approaches and the application of complementary research techniques, an effort that should be intensified in the future. The research to date has identified numerous problems and limitations in interpretation of fossil microborings, which need to be addressed and overcome. For example, some morphological features related to the substrate–water contact interface evolved convergently in phototrophic and organotrophic euendoliths, a distinction that is essential in paleobathymetric evaluations. Future studies will have to improve the precision in characterization of complex microborings and provide morphometric criteria for distinctions among them. Microboring activity is cumulative over time, resulting in multiple overprinting of otherwise specific signatures. Many eukaryotic microbial euendoliths have complex life histories, which include changes in boring patterns in the course of their development, seasonality and, possibly, alternation of morphologically different generations. These properties need to be identified and incorporated in the ichnological treatment. Pattern recognition and identification of entire assemblages of traces proved to be a reliable tool in paleoebathymetric correlations, and research should be encouraged in this direction.

ACKNOWLEDGEMENTS

In spite of considerable progress, the systematic position of many modern euendolithic phototrophs and organotrophs remain unresolved. Thus, future studies should further integrate the research on microborings with that of the organisms that produce them. The very mechanism of penetration into mineral substrate is still unknown, and models identifying constraints and the approaches have only started. Modern molecular tools are now available to approach the genotypic identity of euendolithic microorganisms, and this research should be started in specialized but widespread niches as, for example, the endoliths in corals. The geological, ecological and social importance of coral reefs requires that more attention be paid to the balance between constructive and destructive powers for their maintenance. Less attention has been paid to study microborers in phosphatic substrates such as conodonts, bones and fish teeth, which may extend their paleoenvironmental applications to sediments devoid of carbonate substrates. Geological applicability of the distribution of microendolithic ichnocoenoses should be expanded to sediments devoid of calcareous substrates.

ACKNOWLEDGEMENTS We acknowledge the competent reviews given by T. J. Palmer and J. Schneider. For technical assistance, we wish to thank many students, of whom Olga Sagert was the last one. This work was funded by the DFG grants Vo 90/21 and Vo 90/23. For the support of international and interdisciplinary cooperation, we thank the Alexander-von-Humboldt Foundation, Bad Godesberg and Hanse Institute for Advanced Studies, Delmenhorst, Germany.

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22 Stromatolites: A 3.5-Billion-Year Ichnologic Record Russell S. Shapiro

fossil occurrences contains an organic component and none are made by a singular colonial animal or individual plant (Monty, 1977). Stromatolites, and other microbialites, are primarily composed of mechanical sediments and cements produced through the activities of a microscopic consortium (Riding, 2000). Thus, they are analogous to other trace fossils as the resultant structure records ecologic interactions, not preservation of body fossils. The internal fabric and macroscale attributes of stromatolites have been used for biostratigraphic correlation and facies analysis, even though the taxonomic affinities of the microbial community are usually unknown. Indeed, it is quite probable that a particular microbial ecosystem may be responsible for more than one type of microbialite, and several different microbial consortia may construct a unique microbialite. The purpose of this chapter is to re-evaluate the construction of stromatolites and address their formation and utility in an ichnologic framework. By rethinking stromatolites as trace fossils, we may access the philosophic debates and successes of ichnologists and potentially gain new information from a 3500-million-year fossil record.

SUMMARY : Stromatolites are trace fossils that record the interaction between microbial communities and sediments. Microscopically, the details yield information on ecological gradients and pathways. Macroscopically, the shape of the stromatolite may represent stronger environmental controls. Study of the scalar attributes can yield insight into microbial ethology and foster biostratigraphic and facies analysis over the past 3500 million years.

WHY STROMATOLITES ARE TRACE FOSSILS Trace fossils record the interaction between animals and plants and their environment (Seilacher, 1967b). Recognizing that behavior is fossilized, ichnologists use trace fossils to deduce information on past ecosystems (Bromley, 1990). The trace itself is a disturbance or restructuring of the sediment or lithified interface. The sediments are typically seen as a passive component to be moved, burrowed, or digested and later altered in the subsurface (Bromley, 1990). Regardless of the nature of the activity, the unique shapes and sedimentary structures of trace fossils have proven amiable to taxonomic treatment and have biostratigraphic utility. Placing the trace maker in ethological context facilitates delineation of facies. In many cases, the biologic identity of the trace maker is unknown, but still the utility is realized. Heretofore, stromatolites have largely been treated as structures analogous to colonial organisms or eukaryotic algae, even though only a fraction of

THE COMPLEXITY OF FORM Most Phanerozoic marine stromatolites are relatively simple domes and columns with coarse though nondescript laminae (Awramik, 1992). This simplicity belies the various complex pathways of their formation. Each unique form or ‘morphotype’ of Copyright ß 2007, Elsevier B.V.


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carbonates—ideal environments for production of stromatolites (see recent review in Melezhik et al., 2005). Stromatolites of the Mesoproterozoic display a great variety of columnar, columnar-branching, domal, and stratiform shapes (Awramik and Sprinkle, 1999). In addition, many different types of microstructures comprise these largely micritic stromatolites (e.g., Knoll and Semikhatov, 1998 and others). This variation has proven most beneficial to stromatolite taxonomists (see review in Semikhatov and Raaben, 2000).

MODELS OF FORMATION

FIGURE 22.1 Diagram showing the variables that affect the composite form (= morphotype) of the stromatolite. Each variable can affect the morphotype directly, such as a change in biota. One or more variables can alter another variable (e.g., a change in the pH would alter the style of cementation, changing the morphotype). The result is that each morphotype reflects a complex interplay of various dynamic attributes. Superposed on this scheme are the effects of diagenesis.

stromatolite is the result of a complex interplay of organism–sediment–environment interactions (Fig. 22.1). The significance of each of these variables is difficult to predict and therefore hampers direct biological or ecological reconstruction. It is generally agreed that the gross form (= macrostructure) is largely controlled by environmental parameters such as current velocity or sediment accumulation rate, and that the microstructure more faithfully records the ecology of the microbial ecosystem (Fig. 22.2) (e.g., Horodyski, 1977). Based on analogy with modern, coarse-grained stromatolites forming in subtidal channels in the Exuma Islands, it is likely that streamlined columns record dominance of current flow, with the bulbous end pointing into the current (Dill et al., 1986; Shapiro et al., 1995). Extensive flat-laminated stromatolites are indicative of the high intertidal to supratidal zone. Columnar stromatolites are common features of high-energy environments. However, the record of Proterozoic stromatolites displays a broad variation of form and it is difficult to draw similar modern analogies (Awramik, 1992). The global period of intensive granitization in the late Archean through Paleoproterozoic led to development of extensive continental shelves and platform

There are currently four models developed for accretion of stromatolite laminae (Fig. 22.3) (Shapiro, 2005). The most commonly cited pathway for Phanerozoic marine stromatolites is the ‘trapping and binding’ model, first elucidated by Black (1933) for modern stromatolites formed around Andros Island, Bahamas, and later well described by Logan (1961) from Shark Bay, Western Australia. Recent work has demonstrated the importance of the ‘precipitating model’ in forming stromatolite laminae. Although cited as having largely occurred in the Neoarchean and Paleoproterozoic, precipitate stromatolites are found throughout the rock record (Hofmann and Jackson, 1987; Knoll and Semikhatov, 1998). Arguments exist as to whether the precipitation is driven by abiotic or biotic processes (Grotzinger and Knoll, 1999). A less commonly cited pathway is the ‘stabilizing model’ by which motile microbial ecosystems or expelled extracellular polymeric substances (EPSs) coat and stabilize loose sediment, resulting in upward accretion (Bartley et al., 2000). This leads to laminae that are thicker in the sediment layers, with more laterally extensive organic (if preserved) sealing layers. Also, the topography of the laminae becomes dampened in the growing direction. Finally, the ‘skeletal model’ encompasses microbialites that are composed of skeletal remains of the microbes, whether they were obligate calicifiers or merely served as an organic substrate for precipitation (Riding, 1977, 2000). Recognition of the dominant model is critical for understanding the ecology of the localized microbial ecosystem. Petrographic details record whether or not sediment (clay and coarser grains) was trapped by the microbial ecosystem. If trapped, the size and arrangement of the grains may yield clues as to the morphology and mechanics of the microbes (gliding, filamentous, producing EPS). Variations between or

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FIGURE 22.2 Comparison of different microstructures (A–C) and macrostructures (D–F). (A) Border between laminae of the ‘trapping and binding’-type stromatolite, Lower Permian, Kansas. Lower half of photo is largely micrite and upper half is coated grains. (B) ‘Precipitating’type stromatolite showing laminae of radiating crystal fans, Upper Carboniferous, Cape Breton Island. Cross-polarized light. (C) ‘Stabilizing’-type stromatolite showing remnants of dark organic layers and lighter muddy sediment, Paleoproterozoic, Minnesota. (D) Typical Phanerozoic elongated domical microbialites, Lower Cambrian, California. (E) Bacterial stromatolitic crust associated with methane seepage, Upper Cretaceous, Colorado. (F) Branching stromatolite growing off of concentric oncoid, Lower Carboniferous, Kansas. Scale for (A–C) is one millimeter, scale in (E, F) is one centimeter. Handheld rock hammer for scale in (D). Photo (E) courtesy of Julia Anderson (Gustavus Adolphus College).

HOW STROMATOLITES HAVE BEEN USED IN THE PAST AS TRACE FOSSILS

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FIGURE 22.3 Diagrams of the four models of stromatolite accretion. (A) Trapping and Binding. Successive generations of microbial filaments or extracellular polymeric substances (EPSs) trap grains or mud and bind the sediments via precipitated cements. (B) Precipitation. Cements are nucleated either directly upon decaying organic compounds or adjacent to the organics with little or no clastic sedimentary component. (C) Sealing. Mechanical sediment accumulates in depressions and microbial communities spread over the sediments, sealing the deposit. (D) Skeletal. The microbialite is composed of microbial body fossils (external or internal molds, casts, permineralized sheaths). Reprinted from Shapiro (2005).

within laminae can provide information on differentiation or tiering in the microbial community. Researchers have not yet established a clear relationship between particular cements and unique microbes (Buczynski and Chafetz, 1993), but the presence of precipitates can be used for reconstructing dispersion of organics and original geochemical parameters. Of course, all of the petrographic information must be interpreted with a clear understanding of later diagenetic alteration.

HOW STROMATOLITES HAVE BEEN USED IN THE PAST AS TRACE FOSSILS Taxonomy of Fossilized Entities Stromatolites had been recognized and recorded for hundreds of years prior to the coining of the term ‘stromatolith’ by Kalkowsky in 1908 (Monty, 1977). The first taxonomic treatment of a stromatolite was Cryptozoon proliferan (Hall, 1883) from the Saratoga Springs, New York area, and the first named

pre-Cambrian stromatolite was Archeozoon (Eozoon) acadiences (Matthew, 1890). During the middle of the twentieth century, there occurred a surge of articles on the systematic treatment of stromatolites, spearheaded by scientists of the USSR but also including researchers from Australia, Canada, China, the United States, France, and elsewhere (e.g., Maslov, 1937; Fenton and Fenton, 1939; Cloud, 1942). In many of these taxonomic descriptions, stromatolites were viewed as a type of calcareous algae and given genus and species names. One of the most accessible (to North American researchers) treatises on stromatolites was Johnson’s (1961) summary, which includes an extensive taxonomic base. Evidence of the influence of Johnson’s work is still seen as references to ‘algal limestone’ even though stromatolites are usually composed solely of sediment and the organic component was more likely (cyano) bacterial and not algal. The arguments for and against stromatolite taxonomy are lengthy and have existed for over a hundred years without resolution. This brief chapter is not the correct venue to discuss this tortured history; the

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reader is referred to Monty (1977) and Semikhatov and Raaben (2000). For a discussion of the systematics of thrombolites, see Shapiro (2000) and Shapiro and Awramik (2006). Although the taxonomy of ichnofossils is governed by the conventions of the International Code of Zoological Nomenclature, stromatolites have not been accepted by either botanists or zoologists, leading Stanley Awramik to remark that they are ‘nomenclatural orphans’ (written comm.). Among stromatolite workers there exists, at a minimum, an accepted binomial naming system that employs the Group (= ichnogenus equivalent) and Form (= ichnospecies equivalent) ranks (Maslov, 1953). Unfortunately, there is currently no accepted rule governing the defining criteria for Groups and Forms other than the hierarchical arrangement and usual formalities such as peer-reviewed publications and curation of type-specimens. Interestingly, like trace fossils, there are some Group names that are commonly applied by geologists, such as Cryptozoon, Collenia, and Conophyton (as well as the misused genus ‘Girvanella’), even if the greater scientific community is hesitant to accept stromatolite taxonomy. Pertinent to this discussion is a mention of the Russian taxonomic view (also shared by some researchers outside of Russia) that bases Group designation on macrostructural attributes and Form designation on microstructural fabrics. The latter is thought to represent ethology; therefore unique—and properly described—stromatolite Forms can be employed in reconstructing past behaviors in the same way that trace fossils are used.

Codifying Sedimentary Structures In the 1950s and 1960s, there was a fundamental shift from treating stromatolites as a type of macroalgae to viewing them as a sedimentary structure (Hofmann, 1973). One of the key articles in the sedimentary structure movement was by Logan et al. (1964). In this article the authors proposed a new, coded naming scheme using letters to represent attributes. For instance, ‘LLC’ represents ‘laterally linked columns.’ This scheme was not popular among stromatolite taxonomists because of the lack of detail, but it does demonstrate the view that stromatolites can be viewed as environmental indicators, and that their features might record environmental variations. Researchers in the former Soviet Union and Australia continued to treat stromatolites systematically with the hopes of developing interregional correlation and differentiation of the vastly long Proterozoic Eon

(Cloud and Semikhatov, 1969 for English discussions; Raaben, 1969). During this time, the discovery of preserved bacterial fossils in the Gunflint stromatolites (Paleoproterozoic, Ontario; Tyler and Barghoorn, 1954; Barghoorn and Tyler, 1965; Cloud, 1965) reinvigorated the theory that stromatolites were indeed constructed by unique biological communities, and the race was on for more and older microfossils. To date the oldest possible microfossils come from cherts interbedded with stromatolites in the 3.5-Ga Warrawoona Group of Western Australia (Hofmann et al., 1999) Currently, there are several schools of stromatolite studies. Taxonomic work continues, primarily for preCambrian stromatolites, with the goal of increased resolution in intra- and interbasinal correlation (Semikhatov and Raaben, 2000; Shapiro and Awramik, 2006). Stromatolites are also viewed as particular sedimentary structures that can be used with other sedimentological and stratigraphic information to deduce environmental parameters. Herein, I also stress that individual stromatolites should also be used as ichnofossils that record organism (chiefly bacterial)–sediment interactions and can yield information on the behavior and environmental constraints of the localized microbial ecosystems.

UTILITY AS TRACE FOSSILS With knowledge of the various models now recognized and an appreciation of variables implicated in stromatolite diversity, it is possible to use stromatolites in classic ichnologic studies. Specifically, stromatolites may record fine, microscale ethologic changes over the course of development. Also, it has already been demonstrated that some stromatolites can be used to create Seilacher-type ichnofacies, useful for basin reconstruction. Finally, taxonomic treatment of stromatolites does allow for some degree of both intra- and interbasinal biostratigraphic correlation.

Microscale Ethologic Changes As noted by Pickerill (1994), it is important to differentiate ethologic from physical sedimentary structures. The unique genesis of stromatolites makes distinguishing these end members problematic. However, as the microbial community is ecological and spatially integrated with these physical, chemical, and sedimentological parameters,

UTILITY AS TRACE FOSSILS

differentiation is not as critical as it is for invertebrate trace fossils. Following Pickerill’s (1994) lead, I propose the following list of criteria for identifying stromatolites that record the behavior of microbes: a. uniform thickness of individual laminae within a stromatolite (though the laminae may be heterogeneous); b. consistency of macrostructural form within a bed; c. the texture of the stromatolite can be differentiated from the enclosing sediments; d. presence of microbial body fossils or dispersed organics either at different concentrations or composed of different biomarkers than within the enclosing sediments. Most stromatolite researchers agree that evidence of microbial behavior would most likely be recorded in the microscopic and geochemical details of the laminae. As outlined earlier, it is important to distinguish between trapping and binding communities, reflected in coarse-grained laminae, and precipitating communities, preserved as original cements or as diagenetically altered products. There is always some cementation within a stromatolite because the biological activity induces alkalinity and drives precipitation. The fact that a stromatolite occurs in the rock record requires cementation. While there is no clear biological relationship between a particular fabric and the nature of the microbes responsible, it is clear that large, bound grains require either larger, more robust microbes or strongly adhesive substances. Based on analysis of both modern trapping stromatolites and well-preserved examples from the fossil record, these are likely produced by cyanobacteria. Similarly, micritic stromatolites, as a first approximation, are likely the result of bacterial or even archeal microbes. However, as with most trace fossils, the true identity of the responsible organism is rarely definitively known, even in ancient examples with preserved microfossils (Awramik and Grey, 2005).

Records of Tropism Stromatolites produced by photosynthesizing algae or cyanobacteria may show evidence of heliotropism. Heliotropism was first described by Vanyo and Awramik (1982, 1985) from 850-Ma sinusoidal stromatolite columns in the Bitter Springs Formation of central Australia. The authors argue that the inclination of the columns is a reflection of the average

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incident solar radiation. In extratropical zones, the change of seasons would lead to sinuosity, enabling researchers to record the number of days in the solar year in the past. Other types of tropism, including gravitropism, chemotropism, clastitropism, and aerotropism, are also expected from stromatolite-building communities. Dendrolitic microbialites have been used to argue for both negatively gravitropic, probably photosynthetic, microbial bushes and positively gravitropic microbial clusters in an open porosity framework of reefs (Shapiro, 2005). Evidence of chemotropism, specifically methanotropism, was cited for the occurrence of downwardly concave stromatolites in the Aleutian trench (Greinert et al., 2002). Similarly, there have been many examples from fossil and modern hot springs showing how the morphology, or macrostructure, of stromatolites is directly influenced by the geochemical gradients of effusing waters (Walter et al., 1972; Chafetz et al., 1991; Renaut and Jones, 2000). ‘Clastitropism’ refers to the growth of trapping and binding microbial communities toward the sediment source. In most cases, this is upward (negative geostrophism) as grains settle onto the surface. In high-velocity currents, the stromatolites may accrete into the current, resulting in a streamlined form in cross section with the long axis parallel to flow and the bulbous end upcurrent (Shapiro et al., 1995). As with many ichnologic studies, direct ecologic inference is hampered by a lack of definite correlation with the responsible organisms. Therefore, directed growth is only valuable in trophic studies if other clues (water depth, turbidity, grain size, geochemical parameters) to the possible microbial ecosystem are used in concert. As we learn more about the role of non-photosynthesizing bacteria in stromatolite formation, we will gain more tools for interpreting stromatolites from ‘extreme environments’ that were not formed by cyanobacteria.

Ichnofacies Several key articles have shown that microbialites can be used for inferring relative water depth at various spatial scales, similar to ichnofacies (Seilacher, 1964, 1967a). Like the subdivisions seen in Seilacher’s facies (e.g., Curvolithus ichnofacies of Lockley et al., 1987), stromatolitologists subdivide zones into more discrete facies. In most cases, the inference is necessarily supported by sedimentologic and stratigraphic data. In a recent article, Olivier et al. (2003) described macrostructural variation in different thrombolites

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within reef facies as a function of energy tolerance. The authors’ conclusions were supported by macrofossil evidence (phaceloid and ramose corals, sponges, oysters, thecideid brachiopods, serpulids, and others). The utility of microbialites as subfacies indicators is more strongly realized in pre-Phanerozoic successions. Kah and Knoll (1996) present one example from the Mesoproterozoic where the stromatolite microand mesostructures help to differentiate different subfacies in the tidal zone.

Biostratigraphy One of the most contentious approaches to stromatolite studies is their use as biostratigraphic markers. Here again the analogy to ichnology is instructive, and the same arguments apply. It is not necessary to know the taxonomic affinity of the trace maker, nor does the trace itself need to evolve in a Darwinian fashion. The only requirement for utility is that the trace is unique, recognizable, and temporally constrained. For several decades, stromatolite researchers have used unique stromatolite taxa for biostratigraphic correlation in the pre-Cambrian (Semikhatov and Raaben, 2000). Although the time scales are quite coarse by Phanerozoic standards, the important truth remains that predictable, interbasinal correlations have been achieved (Cloud and Semikhatov, 1969). That said, some researchers have argued against the use of stromatolites for biostratigraphy on the grounds that environmentally controlled morphotypes cannot be definitively constrained to the same degree as a lineage that evolves and goes extinct (Grotzinger and Knoll, 1999). But the data have borne out temporally constrained patterns, thereby validating biostratigraphic utility. To date, most of the effort has taken place in the Proterozoic. This is due to the combination of a wonderfully diverse suite of stromatolites (though the majority are not amenable to interbasinal correlation) and the lack of other suitable fossils for correlation (Awramik and Sprinkle, 1999). Similarly, invertebrate trace fossils are used for latest Proterozoic correlation in the absence of abundant invertebrates. Stromatolite taxonomists interested in interbasinal correlation primarily use microstructure (Cloud and Semikhatov, 1969; Raaben, 1969; Knoll and Semikhatov, 1998). Therefore, the ethological changes recorded show some temporal constraint. It is not known whether the shift was due to evolution or extinction of particular microbes or changes in the global environment. Regardless, the end product

recorded in the microstructural details is a reflection of changing ethology.

CONCLUSIONS Stromatolites extend the record of organism– sediment interactions back by 3500 million years. Most stromatolites do not preserve microbial body fossils; rather, they are trace fossils that record ecology on the macroscale and ethology on the microscale. The study of stromatolites and other microbial structures would benefit from an ichnologic view aimed at deducing behavioral evidence, facies dependency, and biostratigraphy. Stromatolitologists have long sought these goals, largely by studying the stromatolites as body fossils of either large calcareous algae or accumulations of (cyano) bacteria. By looking at the sediment and cement component as a reflection of microscale ethology, we can achieve a more accurate portrayal of the microbial ecosystems responsible for the formation of the stromatolites. This approach will also help to bridge the seemingly incompatible views of stromatolites as either sedimentary structures or biologic entities.

ACKNOWLEDGEMENTS Reviews by Ray Rogers and Steve Rowland were greatly appreciated.

References Awramik, S.M. (1992). The history and significance of stromatolites. In: Schidlowski, M., Golubic, S., Kimberley, M.M., McKirdy, D.M., and Trudinger, P.A. (Eds.), Early Organic Evolution: Implications for Mineral and Energy Resource, SpringerVerlag, Berlin, pp. 435–449. Awramik, S.M. and Grey, K. (2005). Stromatolites: biogenicity, biosignatures, and bioconfusion. Proceedings of SPIE, 5906, 59906P1–59906P19. Awramik, S.M. and Sprinkle, J. (1999). Proterozoic stromatolites: the first marine evolutionary biota. Historical Biology, 13, 241–253. Barghoorn, E.S. and Tyler, S.A. (1965). Microorganisms from the Gunflint Chert. Science, 147, 563–577. Bartley, J.K., Knoll, A.H., Grotzinger, J.P. and Sergeev, V.N. (2000). Lithification and fabric genesis in precipitated stromatolites and associated peritidal carbonates, Mesoproterozoic Billyakh Group, Siberia. In: Grotzinger, J.P. and James, N.P. (Eds.), Carbonate Sedimentation and Diagenesis in the Evolving Precambrian World, SEPM (Society for Sedimentary Geology), Special Publication, Tulsa, Oklahoma, 67, pp. 59–73.

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23 Trace Fossils in Evolutionary Paleoecology Marıá Gabriela Mańgano and Luis Alberto Buatois

SUMMARY : Ichnologic data provide insights into evolutionary paleoecology, including the nature of Ediacaran ecosystems, diversification events such as the Cambrian explosion and the Ordovician radiation, and the colonization of various habitats including brackish-water and continental environments. In many cases, trace fossil evidence demonstrates much greater evidence of ecologic change than that revealed by body fossils alone. Trace fossil distribution through geologic time reveals a process of colonization, resulting from the exploitation of empty or underutilized ecospace. Secular trends include increase in the diversity of biogenic structures, increase in the intensity of bioturbation, addition of new invaders, environmental expansion, and faunal turnovers.

the community level. This scheme provides a useful way to frame ichnologic data having implications in evolutionary paleoecology (e.g., Mańgano and Droser, 2004). Additionally, the concept of ‘ichnoguild’, introduced by Bromley (1990), is particularly useful to evaluate ecospace colonization in specific ecosystems through geologic time (e.g., Buatois et al., 1998). An ichnoguild reflects three parameters: (1) bauplan; (2) food source; and (3) use of space (Bromley, 1990, 1996). In terms of bauplan, trace fossils are categorized as permanent to semi-permanent burrows produced by stationary organisms or transitory structures made by vagile animals. Food source is reflected by trophic analysis of trace fossils, including categories such as detritus feeding, deposit feeding, suspension feeding, gardening and chemosymbiosis. Use of space is crudely equivalent to the vertical position within the tiering structure. Ichnoguilds are named after their dominant ichnotaxa (Bromley, 1996). A comprehensive review of all applications of trace fossils in evolutionary paleoecology is beyond the scope of this chapter. In contrast, we illustrate the usefulness of ichnology in selected topics within macroevolution. In particular, we review the potential of ichnology to provide insights into five major issues in evolutionary paleoecology: (1) Ediacaran ecosystems, (2) the Cambrian explosion, (3) the Ordovician radiation, (4) colonization of brackish water environments, and (5) colonization of continental environments. In many cases, trace fossil evidence demonstrates much greater evidence of ecologic change than that revealed by body fossils alone. The distribution of biogenic structures through geologic time reveals a process of colonization resulting from the exploitation of empty or under-utilized ecospace. Secular trends include increase in the diversity of

INTRODUCTION The use of trace fossils in evolutionary paleoecology represents a relatively new trend in ichnology that is providing valuable information to our understanding of patterns and processes in the history of life. The ichnologic record contributes significantly to our understanding of paleoecologic breakthroughs (e.g., Seilacher, 1956, 1977; Buatois and Mańgano, 1993; Crimes, 1994, 2001; Buatois et al., 1998, 2005a; Orr, 2001; Carmona et al., 2004; Mańgano and Droser, 2004; Uchman, 2004; Jensen et al., 2005; Seilacher et al., 2005). Droser et al. (1997) proposed a hierarchy of paleoecological levels that allow for the ranking of ecological changes through geologic time. First-level changes, the highest level, indicate colonization of a new ecosystem (e.g., life on land, in the sky), and fourthlevel changes, at the other end, indicate turnover at


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biogenic structures, increase in the intensity of bioturbation, addition of new invaders, environmental expansion, and faunal turnovers.

EDIACARAN ECOSYSTEMS Many recent studies have stressed the anactualistic character of the Ediacaran ecosystems by showing that they were dominated by benthic communities that developed in direct association with resistant microbial mats (Seilacher, 1999). The abundance of wrinkled surfaces, ripple patches, palimpsest ripples, elephant skin and other structures suggests that sediment stabilization by microbial binding was a major factor in Ediacaran ecosystems. Seilacher (1999) proposed that four major categories of interaction with the microbial mats were established during the Ediacaran: mat encrusters (encrusted into the microbial mats), mat scratchers (organisms grazing on the microbial mats), mat stickers (organisms growing inside of the mats) and undermat miners (those who constructed tunnels below the mat). While mat encrusters and mat stickers are essentially shown by body fossils, activity of mat scratchers and undermat miners are reflected in the ichnologic record. Trace fossils attributed to mat scratchers fall within two main groups: those reflecting the activity of worm-like metazoans and those recording the interaction of vendozoans with the matground (Fig. 23.1). By far the most abundant trace fossils in Ediacaran rocks belong to this first group and are represented by very simple feeding trace fossils and nonspecialized grazing trails, such as Helminthoidichnites, Helminthopsis and Gordia (Seilacher et al., 2005; Jensen et al., in press). These trails are preserved either as negative or positive hyporeliefs/epireliefs and are commonly associated with microbial mats, representing matground grazing (Gehling, 1999; Seilacher et al., 2005; Jensen et al., in press). These structures make up the Helminthopsis ichnoguild of Buatois and Mańgano (2003, 2004), which consists of transitory, near-surface to very shallow-tier, matgrazer structures produced by vagile vermiform animals. Grazing trails commonly crosscut corrugated surfaces resulting from microbial activity, without producing significant disruption. Seilacher (1999) noted that, contrary to the common assumption, these simple trails are not emplaced on the surface, but rather within the sediment. They reflect grazing of organic matter concentrated within microbial mats below a thin veneer of sediment, such as proposed in the Ediacaran death mask model of Gehling (1999).

Although noting the abundance of these simple trails in Ediacaran deposits, Jensen et al. (in press) suggested that occurrences should be evaluated on a caseby-case basis because filamentous body fossils can easily be confused with grazing trails. Segmented burrows reflecting peristaltic locomotion, although less common, are illustrated by the ichnogenera Nenoxites and Torrowangea (Seilacher et al., 2005). Because of the controversial nature of most of the Ediacaran body fossils, these trace fossils represent the clearest evidence of triploblastic organisms in the Neoproterozoic (Seilacher, 1989). Also, Ediacaran ichnofaunas may include trace fossils produced by vendobionts. Serially repeated resting traces of Dickinsonia and the related genus Yorgia have been recorded recently in Ediacaran shallow-marine deposits of the White Sea and South Australia (Ivantsov and Malakhovskaya, 2002; Fedonkin, 2003; Gehling et al., 2005). Notably, body fossils were found in direct association with the trace fossils, allowing identification of the producers, namely Yorgia waggoneri and Dickinsonia tenuis (Ivantsov and Malakhovskaya, 2002). Gehling et al. (2005) noted that the absence of preserved trails linking the resting traces suggests that the substrate did not record locomotion that did not disrupt the biomats. Another match between producer and trace fossil is illustrated by the ‘soft limpet’ Kimberella and the scratches produced on microbial mats by its paired radular teeth (Seilacher, 1997; Fedonkin, 2003; Gehling et al., 2005; Seilacher et al., 2005). Analysis of small specimens of Kimberella and the fan-like arrangement of scratch marks indicate that the animal used a proboscis to rasp on the microbial mat (Gehling et al., 2005). Undermat miners are also present in the Ediacaran ichnologic record. However, these seem to be more common in lowermost Cambrian deep-marine deposits than in Ediacaran rocks, being represented by the ichnogenus Oldhamia (Seilacher, 1999; Buatois and Mańgano, 2003). Accordingly, they will be addressed under our discussion of the Cambrian explosion. Other biogenic structures fall within the realm of bioerosion and reflect incipient predation during the Ediacaran. Predatory holes in the tubular shell Cloudina suggest that, although predation became more important during the Cambrian, shell-drilling predation was already present in the Precambrian (Bengtson and Yue, 1992; Hua et al., 2003). Although earlier studies (e.g., Runnegar, 1992a; Crimes, 1994) listed a large number of ichnotaxa for the Ediacaran period, the emerging view is that Neoproterozoic ichnofaunas are of very limited diversity and complexity (Jensen, 2003; Seilacher et al.,

393

EDIACARAN ECOSYSTEMS

13 10

14

12

19 17

16 15

1 11

21

18 20

22 9

Lower to Upper Cambrian Upper Cambrian to Lower Ordovician 10

9

2

8

1

7

8

1 11

2

9

Lowermost Cambrian (Nemakit-Daldynian) Lower to Middle Cambrian 5

4

2

3

1 6

1 2

1

Ediacaran Ediacaran

Shallow Marine Slop

e

Deep Marine

FIGURE 23.1 Ichnofaunal changes across the Ediacaran–Cambrian boundary. Microbial mats are widespread in Ediacaran shallow-marine environments and in Ediacaran–Middle Cambrian deep-marine environments. Increase in degree and depth of bioturbation occurred first in shallow-marine settings and later in the deep sea. (1) Helminthopsis, (2) Helminthoidichnites, (3) Gordia, (4) Radulichnus, (5) Dickinsonia trace fossils, (6) Yorgia trace fossils, (7) Treptichnus, (8) Oldhamia, (9) Diplichnites, (10) Planolites, (11) Cochlichnus, (12) Cruziana, (13) Rusophycus, (14) Skolithos, (15) Syringomorpha, (16) Diplocraterion, (17) Glockerichnus, (18) Megagrapton, (19) Saerichnites, (20) Dictyodora, (21) Lorenzinia, (22) Circulichnus. See text for further explanation.

2003, 2005; Mańgano and Buatois, 2004a; Jensen et al., 2005, in press; Droser et al., 2005, 2006). This in part reflects a reinterpretation of almost all the ichnogenera that were considered exclusive to the Ediacaran (e.g., Yelovichnus, Palaeopascichnus, Intrites, Harlaniella), which are no longer considered trace fossils (Gehling et al., 2000; Haines, 2000; Jensen, 2003; Seilacher et al., 2003, 2005; Jensen et al., in press). In particular, Jensen et al. (in press) provided a detailed table summarizing

current re-evaluations of Ediacaran ichnofossils. Problems also become evident with other ichnotaxa that occur through all or most of the Phanerozoic and whose supposed presence in the Neoproterozoic has been pointed out in several compilations. For example, unquestionable specimens of vertical burrows, such as Skolithos or Diplocraterion, have not been documented from Ediacaran strata (Seilacher et al., 2005; Jensen et al., in press). The presence of branched

394


burrow systems in Ediacaran rocks is controversial. Chondrites has been mentioned in Ediacaran strata (e.g., Jenkins, 1995). However, these structures commonly are preserved as furrows that lack the characteristic burrow fill. More recently, they have been reinterpreted as poorly preserved specimens of body fossils or as overlap of unbranched trace fossils (Seilacher et al., 2005; Jensen et al., in press). The radial structure Mawsonites is not longer considered a trace fossil (Runnegar, 1992b; Seilacher et al., 2005; Jensen et al., in press). However, very shallow, three-dimensional burrow systems (Treptichnus) occur in the uppermost Ediacaran, recording incipient exploitation of the infaunal ecospace and a slight increase in trace fossil complexity (Jensen et al., 2000; Jensen and Runnegar, 2005). Most of the recorded occurrences of trace fossils in Ediacaran strata (e.g., Flinders Ranges, White Sea, Namibia) come from shallow-marine clastic deposits and, accordingly, provide evidence on nearshore to, more rarely, shelf ecosystems. However, ichnologic information from a number of localities in North Carolina, the Mackenzie Mountains and Central Spain is based on deep-marine deposits and indicates that deep-sea bottoms were already colonized by benthic animals in Ediacaran times (Gibson, 1989; Narbonne and Aitken, 1990; Vidal et al., 1994; MacNaughton et al., 2000; Crimes, 2001; Orr, 2001; Seilacher et al., 2005), recording a first level ecological change sensu Droser et al. (1997). Ediacaran deep-marine ichnofaunas are not very diverse and are dominated by nonspecialized grazing trails (e.g., Helminthopsis, Helminthoidichnites) associated with structures indicative of microbial mats (Fig. 23.1). Colonization of deep-sea bottoms during the terminal Proterozoic is also supported by the body fossil record (Narbonne, 1998, 2005; Clapham et al., 2003; Narbonne and Gehling, 2003; Grazhdankin, 2004).

THE CAMBRIAN EXPLOSION The Ediacaran–Cambrian boundary (542 Ma +/ 1.0) represents a major divide in the history of life (Knoll et al., 2006). Ediacaran biotas were dominated by soft-bodied organisms that are considered at least in part to be unrelated to modern metazoan faunas (Seilacher, 1992a; Seilacher et al., 2003; Narbonne, 2004, 2005). On the other hand, the Cambrian witnessed the rapid development of almost all modern groups of animals, including the rise of skeletal faunas, a major evolutionary innovation known as the Cambrian explosion

(Conway Morris, 2000; Droser and Li, 2001; Erwin, 2001; Budd, 2003). As noted by Conway Morris (2000), our understanding of the Cambrian Explosion has implications for several key topics, including the origin of metazoan bodyplans, the role of developmental genetics, the validity of molecular clocks, and the influence of paleoenvironmental factors on macroevolution. Most evolutionary studies dealing with the Ediacaran–Cambrian transition have been based on the analysis of body fossils. However, the trace fossil record provides an independent line of evidence to calibrate and evaluate the Cambrian explosion. This is of great importance because there is still no consensus on whether the Cambrian explosion is a real evolutionary event or a preservational artifact related to an increase in fossilization potential (see Valentine, 2004, for review). As previously discussed, the diversity of Neoproterozoic ichnofaunas is generally low and behavioral complexity is also limited. This situation changed dramatically in the Nemakit–Daldynian (lowermost Cambrian) with the appearance of much more diverse and complex ichnofaunas, particularly in shallow-marine environments (Fig. 23.1). Relatively diverse ichnofaunas dominated by crawling traces (e.g., Diplichnites, Dimorphichnus) produced by arthropods and moderate to large shallow grazing and feeding traces (e.g., Psammichnites, Didymaulichnus) of deposit feeders are known worldwide in lowermost Cambrian strata (e.g., Banks, 1970; Young, 1972; Crimes and Anderson, 1985; Fritz and Crimes, 1985; Crimes and Jiang, 1986; Paczesńa, 1986, 1996; owski, 1989; Walter Hofmann and Patel, 1989; Orl et al., 1989; Bryant and Pickerill, 1990; Pickerill and Peel, 1990; Geyer and Uchman, 1995; Goldring and Jensen, 1996; Jensen, 1997; Li et al., 1997; Zhu, 1997; Jensen and Grant, 1998; MacNaughton and Narbonne, 1999; McIlroy and Logan, 1999; Droser et al., 2002; owski and Z_ ylin´ska, 2002; Jensen et al., 2002; Orl ´ Buatois and Mangano, 2004). Systematic guided meanders, such as those present in Psammichnites saltensis, reveal the onset of sophisticated grazing strategies that were notably absent in Ediacaran times (Seilacher et al., 2005). In contrast to the rather monotonous aspect of Ediacaran ichnofaunas, a wide variety of behavioral patterns is illustrated by Nemakit–Daldynian shallow-marine ichnofaunas. This fact undoubtedly reflects the appearance of a number of body plans of soft-bodied organisms which cannot be fully evaluated based on the analysis of the body fossil record alone. Lowermost Cambrian trace fossils are typically oriented parallel to the bedding plane and therefore they do not significantly disturb the primary

THE CAMBRIAN EXPLOSION

sedimentary fabric (McIlroy and Logan, 1999; Buatois and Mańgano, 2004; Mańgano and Buatois, 2004a). Bedding plane trace fossils mostly reflect shallow to very shallow infaunal feeding activities of mobile, bilaterian metazoans. Accordingly, the degree of bioturbation reveals only a very slight increase with respect to Ediacaran levels. As in the case of Ediacaran rocks, there is a conspicuous absence of Skolithos piperocks in Nemakit–Daldynian strata (Mańgano and Buatois, 2004a). Vertically oriented trace fossils are only represented by very shallow specimens of Gyrolithes (Droser et al., 2004). This limited extent and depth of bioturbation resulted in the widespread development of relatively firm substrates and the virtual absence of a mixed layer within the substrate (Dornbos et al., 2004, 2005; Droser et al., 2004; Jensen et al., 2005). In contrast to Nemakit–Daldynian assemblages, Tommotian–Atdabanian ichnofaunas are characterized by the appearance of vertical domiciles (Skolithos, Diplocraterion, Arenicolites) of suspension feeders and passive predators reflecting the onset of deep bioturbation (Fig. 23.1). This association records the establishment of the Skolithos ichnofacies that characterizes moderate- to high-energy settings, more typically in shallow-water environments. These vertical burrows may occur in prolific densities forming Skolithos pipe rocks (Droser, 1991). Additionally, the J-shaped spreite trace fossils Syringomorpha may occur in similar settings, forming distinct ichnofabrics (Mańgano and Buatois, 2004b). While Nemakit–Daldynian ichnofaunas were emplaced very close to the sediment–water interface, Tommotian–Atdabanian ichnofaunas reflect burrowing depths in the order of tens of centimeter, revealing an exponential increase in depth of bioturbation. Also, detailed ichnologic analysis reveals a more complex tiering structure with the development of multiple guilds (Mańgano and Buatois, 2004b). During the Tommotian–Atdabanian, matgrounds became rare due to the onset of vertical bioturbation and were replaced by mixgrounds in an event referred to as the ‘agronomic revolution’ (Seilacher and Pfluger, 1994; Seilacher, 1999). Also, archaeocyathid reefs containing high densities of Trypanites are present in Lower Cambrian hardgrounds, representing the onset of significant bioerosion by a macroboring biota (James et al., 1977). Additionally, increasing levels of predation were implicated in an arms race, spurring the development of complex predatory–prey interactions and spurring evolutionary innovations (Vermeij, 1987). Evidence of predation has been detected in some Lower Cambrian deep burrowing Rusophycus directly associated to worm burrows (Jensen, 1990).

395

The presence of multiple trophic guilds and a well established suspension feeding infauna represented by abundant pipe rocks in Tommotian–Atdabanian strata provides evidence of a significant change in complexity of shallow benthic communities, suggesting a coupling between plankton productivity and the benthos (Mańgano and Buatois, 2004b). As suggested by Butterfield (2001), the evolution of new key elements, such as filter-feeding mesozooplankton, were crucial in metazoan evolution. In fact, the addition of mesozooplankton to the trophic web may have acted as a triggering cause not only in the evolution of large metazoan, but also in the advent of the agronomic revolution. By repacking unicellular phytoplankton as nutrient-rich larger particles, zooplankton provided a more concentrated and exploitable resource for the benthos (Butterfield, 2001). This significant increase in the delivery of labile, nutrient-rich particles into the sediment may be behind the most significant change in the history of benthic ecology: the shift from matgrounds to mixgrounds. Mańgano and Buatois (2004a) noted that ichnologic evidence suggests that the presence of metazoa able to exploit the endobenthic environment preceded the establishment of a modern endobenthic ecologic structure (i.e., mixground ecology). Based on the ichnologic record, they proposed the decoupling hypothesis, which states that the Cambrian evolutionary event consists of two phases: diversification of body plans during the Nemakit–Daldynian and subsequent infaunalization during the Tommotian–Atdabanian. According to this scheme, the agronomic revolution is not coincident with the Ediacaran–Cambrian boundary. Because, according to the body fossil record, the appearance of most of the major clades occurred at the Tommotian–Atdabanian, the presence of rich ichnofaunas revealing diverse body plans during the Nemakit–Daldynian indicates the existence of a fuse-time previous to what is commonly referred to as the Cambrian explosion. Lower Cambrian ichnofaunas also display a remarkable segregation into two distinct environmentally related trace fossils associations: shallow- and deep-marine (e.g., Buatois and Mańgano, 2004) (Fig. 23.1). While shallow-marine ichnofaunas are relatively diverse and complex, deep-marine ichnofaunas consist of three main groups of trace fossils, simple grazing trails, arthropod trackways and different ichnospecies of the undermat miner feeding structure Oldhamia (Buatois and Mańgano, 2003). This association indicates that feeding strategies associated with microbial mats persisted in the deep sea during the Early Cambrian, representing a Proterozoic ‘hangover’ in the deep sea. This idea is consistent with the

396


notion of archaic relics taking refuge in the deep sea (e.g., Conway Morris, 1989). Oldhamia flourished in Early Cambrian deep-marine environments, experiencing a remarkable behavioral diversification as revealed by a great diversity of ichnospecies. Oldhamia-dominated assemblages in microbial mat ecosystems persisted in the deep sea after the rise of vertical bioturbation in shallow seas, suggesting a gradual closure of a taphonomic window during the Proterozoic–Cambrian transition (Buatois and Mańgano, 2004). This is consistent with the recognition of Ediacara-type body fossils in Cambrian strata (Gehling et al., 1998; Jensen et al., 1998; Crimes and McIlroy, 1999; Hagadorn et al., 2000; Shu et al., 2006). In addition to fully-marine environments, Lower Cambrian ichnofaunas have been documented from marginal-marine settings (e.g., Baldwin et al., 2004; Mańgano and Buatois, 2004b), revealing that representatives of the Cambrian evolutionary fauna were able to colonize brackish-water environments. Although the scarcity of land plants probably was a major limiting factor in colonization of marginalmarine systems, documentation of Cambrian cryptospores suggests the presence of plants with one or more life cycle phases on land (Strother, 2000; Strother and Beck, 2000). In contrast to complex modern estuarine food webs, Cambrian web chains in marginal-marine ecosystems were mostly marine-based, with acritarchs and algae being primary producers. However, a nascent terrestrial flora may have played a role in these ancient food webs (Mańgano and Buatois, 2004a).

THE ORDOVICIAN RADIATION Knowledge of the Ordovician radiation comes essentially from the body fossil record (e.g., Sepkoski, 1995; Sheehan, 2001; Droser and Finnegan, 2003). However, ichnologic information contributes significantly to an understanding of paleoecological breakthroughs associated with the Ordovician radiation (Mańgano and Droser, 2004). A significant amount of data comes from shallowmarine siliciclastic environments. Analysis of ichnodiversity changes through the Ordovician (Mańgano and Droser, 2004) does not support the widely accepted belief that shallow-water ichnofaunas were fully diversified by Cambrian times with no subsequent ichnodiversity increase (Seilacher, 1974, 1977; Crimes, 2001). Rather, continuous increase in ichnogeneric diversity is reflected throughout the Ordovician (Fig. 23.2). The number of shallowmarine ichnogenera doubled from the Tremadocian to the Ashgill (Mańgano and Droser, 2004). In addition, substantial changes in biofabrics (Kidwell and Brenchley, 1994; Li and Droser, 1999; Droser and Li, 2001) and compositional turnovers by the dominant bioturbators of shallow-water environments occurred through the Ordovician. Lower Ordovician shallow-marine siliciclastic deposits display abundant, trilobite-produced trace fossils. In periGondwanan settings, the most significant trace fossil turnover event is recorded by trilobite trace fossils, such as Cruziana and, to a lesser extent, Rusophycus

100 Total

N of ICHNOGENERA

Shallow marine 50 Deep marine

0 TREMADOC

ARENIG LLANVIRN CARADOC ASHGILL

FIGURE 23.2 Ichnodiversity changes through the Ordovician (after Mańgano and Droser, 2004). The ichnodiversity curves were compiled at the ichnogenus level because the taxonomy is more firmly established than for ichnospecies. The ichnogeneric compilation was plotted as ‘range-through’ data (lower and upper appearances were recorded for each ichnogenus, and its presence was extrapolated through any intervening gap). Total curve includes not only shallowand deep-marine ichnofossils but also continental trace fossils and boring ichnotaxa. The shallow-marine curve does not include borings.

THE ORDOVICIAN RADIATION

and possibly Dimorphichnus (Seilacher, 1970, 1992b, 1994). Elements of the Cruziana semiplicata group (Upper Cambrian–Tremadocian) are replaced by elements of the Cruziana rugosa group (Arenigian–Llanvirnian) (Crimes, 1975; Seilacher, 1992b) with representatives of both groups coexisting during the late Tremadocian (Mańgano and Buatois, 2003). Other common components of the Cruziana ichnofacies in Lower Ordovician strata are vermiform structures such as Planolites, Palaeophycus, Teichichnus and Phycodes. Middle to Late Ordovician shallowmarine ichnofaunas generally show more varied behavioral patterns. Trilobite trace fossils are rarely the dominant component in wave-dominated openmarine clastics, possibly reflecting the development of a deeper infauna (i.e., taphonomic bias). Mańgano and Droser (2004) noted that the dominant patterns include branched, spreiten burrow systems (e.g., Phycodes, Trichophycus), branched, constricted burrow systems (e.g., Arthrophycus), branched burrow mazes and boxworks (e.g., Thalassinoides), dumbbell-shaped traces (e.g., Arthraria), and chevronate trails (e.g., Protovirgularia). Most of these behavioral architectures were present in the Cambrian and Lower Ordovician sediments, but generally were subordinate in abundance and diversity to trilobite traces. In contrast to Cambrian faunas, shallow-marine Ordovician biotas display more complex community structures, as reflected by the tiering structure of infaunal resident communities. On the other hand, the postdepositional suite, which commonly reflects the work of opportunistic organisms, seems to be less sensitive to evolutionary events, being mostly recorded by vertical suspension feeder structures, such as Skolithos, Arenicolites and Diplocraterion (Mańgano and Buatois, 2003). In contrast to siliciclastic shallow-marine settings, softgrounds in carbonate environments do not show a significant increase in ichnodiversity through the Ordovician, but rather reveal increased ecospace utilization and tiering (Droser and Bottjer, 1989; Mańgano and Droser, 2004). Ichnofabric analyses of the inner shelf carbonate deposits of the Great Basin reveal two major increases in the extent and depth of bioturbation during the early Paleozoic: the first one between pre-trilobite and trilobite-bearing Cambrian rocks and the second between the Middle and Late Ordovician (Droser and Bottjer, 1989). The Ordovician increase of bioturbation results in part from an increase in the size of discrete structures (Droser and Bottjer, 1989). Although Thalassinoides is present in Cambrian and Lower Ordovician rocks, specimens typically are less than 10 mm in burrow diameter, architecturally simpler, and commonly

397

form two-dimensional networks (e.g., Myrow, 1995). In contrast, Upper Ordovician Thalassinoides burrow systems go up to 4 cm in diameter displaying classic ‘T’ and ‘Y’ branching and reach up to 1 m in depth (Sheehan and Schiefelbein, 1984). These Upper Ordovician Thalassinoides resemble modern structures produced by decapod crustaceans recording extensive reworking with severe obliteration of primary structures (Sheehan and Schiefelbein, 1984; Droser and Bottjer, 1989). Notably, Thalassinoides burrows reported by Canãs (1995) from Late Cambrian–Tremadocian lagoonal carbonates of Precordillera display unquestionable three-dimensional morphology, suggesting an earlier origin of boxwork architecture (Mańgano and Buatois, 2003). Furthermore, examples from Arenigian siliciclastic deposits of northwest Argentina also provide an early occurrence of Thalassinoides of modern aspect (Mańgano and Buatois, 2003). In any case, although these burrow systems have the typical boxwork architecture, assignment to the activity of decapod crustaceans is not possible because unquestioned malacostracan scratch marks have not been identified (Carmona et al., 2004). In addition, these occurrences largely predate the first occurrence of decapod crustacean body fossils, which are first recorded from the Devonian (Schram et al., 1978). Therefore, Carmona et al. (2004) concluded that these traces were likely not made by primitive burrowing decapods, and suggested other malacostracans (e.g., phyllocarids) or unrelated clades (e.g., enteropneusts) as potential producers, illustrating behavioral convergence in their burrowing activity. Ichnofabric evidence also indicates an onshore–offshore pattern because extensive bioturbation first developed in shallowwater settings and only later developed in more offshore environments (Droser and Bottjer, 1989). In addition, significant changes in the evolution of macroboring organisms occurred in shallow water during the Ordovician (Kobluk et al., 1978; Ekdale and Bromley, 2001; Wilson and Palmer, 2001, in press; Brenner et al., 2004). This significant rise in bioeroders probably occurred by the end of the Middle Ordovician and recently has been referred to as ‘the Ordovician Bioerosion Revolution’ by Wilson and Palmer (2001, in press). These authors noted that boring communities that appeared in the Ordovician do not significantly change until the Mesozoic Marine Revolution. At the end of the Cambrian, increased competition for ecospace and/or resources within shallow-marine ecosystems forced soft-bodied animals and shallowwater skeletal animals into deeper settings (Crimes et al., 1992; Crimes, 2001; Orr, 2001). During the Early

398


Ordovician, the main lineages of deep-marine trace fossils (i.e., rosette, meandering, patterned, spiral) were established in deep-sea environments. In contrast, Cambrian deep-marine ichnofaunas are composed mostly of ethologically simple, facies-crossing ichnogenera (e.g., Palaeophycus, Planolites, Helminthoidichnites), the undermat mining Oldhamia and shallow-water trace fossils (e.g., arthropod trackways). Lower to Middle Ordovician deep-marine ichnofaunas seem to be moderately diverse and fodinichnia commonly dominates (e.g., Orr, 2003). In contrast, Upper Ordovician–Lower Silurian ichnofaunas are considerably more diverse and both pascichnia and agrichnia are well represented (Orr, 1996, 2001). Ichnologic evidence records that the advent of a deep-marine ecosystem of modern aspect originated during the Ordovician, representing a second-level change sensu Droser et al. (1997); see also Orr (2001, 2003); Mańgano and Droser (2004). Compared with late Mesozoic to Cenozoic assemblages, however, Ordovician assemblages are significantly less diverse and display less complex ecologic structures. Finally, as will be discussed below, ichnologic data indicate an incipient colonization of continental and brackishwater environments during the Ordovician.

COLONIZATION OF BRACKISH WATER ENVIRONMENTS The colonization history of brackish-water environments has been explored in a recent study (Buatois et al., 2005a). Invasion of marginal-marine environments ranks as a first-level paleoecological event (sensu Droser et al., 1997) because it represents the appearance of an ecosystem. Secular trends experienced by brackish-water biotas through the Phanerozoic include increase in the diversity of biogenic structures, increase in the intensity of bioturbation, addition of new invaders, environmental expansion, and faunal replacements. Although the colonization of marginalmarine, brackish-water environments was a longterm process that spanned most of the Phanerozoic, this process of invasion of fully-marine organisms into restricted, marginal-marine habitats did not occur at a constant rate (Fig. 23.3). Five major phases were distinguished: Ediacaran–Ordovician, Silurian–Carboniferous, Permian–Triassic, Jurassic–Paleogene, and Neogene–Recent (Buatois et al., 2005a). The first phase (Ediacaran–Ordovician) represents a prelude to the major invasion that occurred during the remaining of the Paleozoic (Buatois et al., 2005a). An Ediacaran ichnofauna from southern Brazil reveals

one of the earliest attempts of metazoans to survive in an environmental setting subject to rapid changes in salinity, as well as in sedimentation rate and turbidity (Netto and Martini da Rosa, 2001). According to the sedimentologic framework, this biota apparently did not inhabit bays or estuaries, but was restricted to the lower reaches of distributary fluvio-deltaic systems. During the early Paleozoic, trilobites, eurypterids and trilobitomorphs were among the main tracemakers in brackish-water environments. Trilobite trace fossils (e.g., Cruziana, Rusophycus, Diplichnites) are relatively common in low-energy, fine-grained deposits, while high- to moderate-energy sandstones are characterized by vertical domiciles of suspension feeders or passive predators, such as Skolithos (e.g., Mańgano and Buatois, 2003). Almost all known Cambrian–Ordovician ichnofaunas come from tidedominated systems where salinity stress was probably attenuated by tidal mixing. Accordingly, euryhaline arthropods could have forayed from the open sea into estuaries and bays, most likely following salt wedges (Buatois et al., 2005a). While Cambrian trace fossil assemblages are apparently restricted to the outer regions of estuarine systems, Ordovician ichnofaunas show a limited degree of landward expansion (Mańgano and Droser, 2004). Intensity of bioturbation and ichnodiversity levels remained relatively low during this phase. The second phase (Silurian–Carboniferous) is characterized by the appearance of more varied morphologic patterns and behavioral strategies, leading to a slight increase in trace-fossil diversity (Buatois et al., 2005a). In contrast to Cambrian–Ordovician brackishwater ichnofaunas, which are dominated by arthropod trace fossils, Silurian–Carboniferous ichnofaunas also include structures produced by other benthic organisms, such as bivalves, ophiuroids and polychaetes. The replacement of trilobite ichnofaunas is most likely an effect of the end-Ordovician mass extinction, although an apparent decline in the abundance of trilobite-dominated ichnofaunas is detected by the Late Ordovician (Mańgano and Droser, 2004). The rapid appearance of new invaders is consistent with evolutionary rebound after the Late Ordovician mass extinction. Additionally, the Silurian–Carboniferous phase reveals a remarkable environmental expansion. While in early Paleozoic trace fossils are essentially present in outer estuarine deposits, later Paleozoic trace fossils occur in inner and middle estuarine deposits as well. Environmental expansion and complexity of estuarine food webs are most likely a result of widespread colonization of continental environments by land plants and animals. Still, brackish-water ichnofaunas seem to have been

399

COLONIZATION OF BRACKISH WATER ENVIRONMENTS

Middle Estuary 12 19 32 2

13 24

31

3

14

27 1

23

Neogene–Recent 13 2 2723

19

7

12 22

3 30

14 1 Jurassic–Paleogene

13 7

24 1

22

2

1 - Diplocraterion 2 - Teichichnus 3 - Skolithus 4 - Cruziana 5 - Rusophycus 6 - Dimorphichnus 7 - Palaeophycus 8 - Monocraterion 9 - Diplichnites 10 - Trichophycus 11 - Protovirgularia 12 - Asteriacites 13 - Planolites 14 - Chondrites 15 - Lockeia

16 - Lingulichnus 17 - Zoophycos 18 - Arenicolites 19 - Cylindrichnus 20 - Gyrochorte 21 - Psammichnites 22 - Thalassinoides 23 - Ophiomorpha 24 - Rhizocorallium 25 - Trichichnus 26 - Asterosoma 27 - Rosselia 28 - Scolicia 29 - Helminthopsis 30 - Gyrolithes 31 - Psilonichnus 32 - Gastrochaenolites

18 16

11

Permian–Triassic

13

7

12

17

19

2 14

1

16

Lower Estuary

Silurian–Carboniferous

7 9

7

10 19

1 32

24 26

3

7

19

Upper Estuary

Fluvial Vendian–Ordovician

Middle Estuary

Lower Estuary

2

31 1 18 22 23 14 15 27 Neogene–Recent

Cambrian–Ordovician

Upper Estuary

13 29

23

28 26

3

1

13 29

2

27 18 22

Jurassic–Paleogene 7 18

7 24

3

8

22

18


23

3

7

23 18

19

22 8

3

1

18


19

7

20

21

Permian–Triassic

23

1

Permian–Triassic

7 3

25

16

2

3 1

27

18 1

Jurassic–Paleogene

6 19

7 23

2

3 1

27

18

32

31

3

2 7

4

Cambrian–Ordovician

Neogene–Recent

FIGURE 23.3 Colonization of brackish-water estuarine environments through geologic time (after Buatois et al., 2005).

8 5

400


largely restricted to soft substrates, with representatives of substrate-controlled ichnofacies, such as the Glossifungites ichnofacies, only rarely preserved. Bioturbation intensity remains relatively low (Buatois et al., 2002). Carboniferous marginal-marine ichnofaunas were particularly abundant in tropical areas, reflecting suitable habitats and extensive development of coal–swamp ecosystems in low latitudes. The third phase (Permian–Triassic) is not very well understood, essentially due to the scarcity of data. However, available data seem to indicate that Permian brackish-water assemblages are more similar to Mesozoic ichnofaunas than to Paleozoic ones (Buatois et al., 2005a). In any case, Permian–Triassic brackish-water deposits remain less bioturbated and contain lower diversity trace fossil suites than their younger equivalents. Crustaceans were becoming important tracemakers in marginal-marine environments, reflecting the late Paleozoic crustacean radiation and the adaptation of some groups to brackish-water ecosystems (Briggs and Clarkson, 1990; Carmona et al., 2004). In contrast to older examples, Permian firmgrounds commonly are colonized by representatives of the Glossifungites ichnofacies, reflecting adaptations to compacted, dewatered muds (e.g., Buatois et al., 2001, 2005b; Mack et al., 2003; Tognoli and Netto, 2003; Bann et al., 2004). The fourth phase (Jurassic–Paleogene) is typified by a remarkable increase in ichnodiversity and intensity of bioturbation of estuarine facies. Relatively diverse assemblages have been recorded, particularly in Cretaceous brackish-water deposits of the Canadian Western Interior (e.g., Benyon et al., 1988; Benyon and Pemberton, 1992; MacEachern and Pemberton, 1994). Also, Jurassic–Paleogene estuarine deposits exhibit some intensely bioturbated zones (e.g., Benyon and Pemberton, 1992; Pemberton and Wightman, 1992; MacEachern and Pemberton, 1994), in marked contrast with older deposits. In any case, however, brackish-water ichnofaunas are impoverished with respect to that of the associated openmarine deposits. Colonization occurred not only in softgrounds and firmgrounds, but also in hardgrounds and xylic substrates (e.g., Bromley et al., 1984; Savrda et al., 1993; Gingras et al., 2004). Similarities between late Mesozoic and Paleogene estuarine ichnofaunas reveal continuity of behavioral strategies through the Cretaceous–Tertiary transition (Buatois et al., 2005a). The fifth phase (Neogene–Recent) records the onset of the modern brackish-water benthos. However, differences between ichnofaunas from the fourth and fifth phases are subtle. Although still impoverished with respect to their fully-marine counterparts,

brackish-water ichnofaunas may reach moderately high diversities, particularly in middle and outer estuarine regions. Additionally, the degree of bioturbation may be high in certain estuarine subenvironments, such as tidal flats (e.g., Gingras et al., 1999). During this phase, all types of substrates were colonized. Gingras et al. (2001) indicated that cemented surfaces, shells and clasts, though sporadically bored, represent a suitable substrate for colonization of various organisms (e.g., sponges, polychaetes, gastropods, bivalves), reflecting radiation of several groups of borers into brackish water. Buatois et al. (2005a) noted that of the five colonization phases, only the end of the first (Ediacaran–Ordovician) and the third (Permian– Triassic) are apparently coincident with mass extinctions (the Late Ordovician and Late Triassic mass extinctions, respectively). The remaining of the socalled ‘Big Five’, the Late Devonian, end-Permian and end-Cretaceous mass extinctions, do not seem to have affected estuarine communities. This is expected because brackish-water faunas typically consist of opportunistic organisms that flourish under extreme conditions and are able to rapidly colonize environments after a major disturbance (Ekdale, 1985; Bromley, 1996). These two features facilitate life in stressful brackish-water settings and rapid movement into vacated habitats after the extinction. Ichnologic data supports the notion that mass extinctions may have favored the persistence of intense bioturbators at the expense of epifaunal or shallow infaunal organisms (Vermeij, 1987). Although brackish-water ichnofaunas have changed through the Phanerozoic, allowing definition of the five phases analyzed, some ichnofaunas are remarkably persistent, reflecting the activity of conservative biotas. A typical example is that of Teichichnus assemblages forming monospecific suites or associated with Planolites, which are common in brackish-water, fine-grained, heterolithic facies having synaeresis cracks.

CONTINENTAL ICHNOFAUNAS THROUGH THE PHANEROZOIC The study of continental ichnofaunas provides valuable evidence of macroevolutionary events throughout the Phanerozoic, including the process of terrestrialization, evolutionary radiations and the exploitation of empty or under-utilized ecospace (Buatois and Mańgano, 1993; Buatois et al., 1998; Miller et al., 2002; Cohen, 2003; Miller and Labandeira, 2003; Braddy, 2004).

401

CONTINENTAL ICHNOFAUNAS THROUGH THE PHANEROZOIC

The earliest accepted records of land vegetation are from spores in Middle Ordovician rocks of Saudi Arabia (Strother et al., 1996) and spore-containing plant fragments in Upper Ordovician deposits of Oman (Wellman et al., 2003). However, terrestrial microorganisms are known since the late Archean (Watanabe et al., 2000) and were probably widespread by the late Mesoproterozoic to the early Neoproterozoic (Horodyski and Knauth, 1994; Prave, 2002). Additionally, spore-like microfossils, referred to as cryptospores, are known since the Middle Cambrian (Strother, 2000; Strother and Beck, 2000). Available information on lower Paleozoic cryptospores suggests the establishment of a nascent semi-aquatic to subaerial flora of bryophyte grade (Strother, 2000). In any case, ichnofossil occurrences predate data from the metazoan body fossil record (Rolfe, 1985). The onset of the terrestrial invasion by metazoans is indicated by the discovery of trackways produced by an amphibious animal in Late Cambrian to Early Ordovician coastal eolian dune deposits (MacNaughton et al., 2002). In addition, Retallack and Feakes (1987) and Retallack (2001) reported the presence of backfilled trace fossils attributed to millipedes and Johnson et al. (1994) documented arthropod trackways (Diplichnites, Diplopodichnus) undoubtedly produced by myriapodlike invertebrates in pond deposits that were desiccated periodically. As noted by Almond (1985), although myriapods are typically considered terrestrial, Early Ordovician to Late Silurian representatives are regarded as aquatic or possibly amphibious. Buatois et al. (1998) noted that the ichnologic record suggests a significant invasion of continental

environments close to the Silurian–Devonian transition. This is coincident with information derived from the analysis of the body fossil record (Cohen, 2003). By these times, a mobile arthropod epifauna (Diplichnites ichnoguild) was established in coastal marine to alluvial plain settings, as indicated by ichnofaunas from transitional marine to continental environments, mostly of peri-Gondwanic settings (Bradshaw, 1981; Woolfe, 1990; Trewin and McNamara, 1995; Draganits et al., 2001; Neef, 2004a,b; Davies et al., 2006). By the Devonian, arthropod-dominated ichnofaunas were well established in lake margin environments (Pollard et al., 1982; Walker, 1985) (Fig. 23.4). The presence of these ichnofaunas indicates that arthropod faunas colonized transitional alluvial–lacustrine settings, rather than fully subaqueous environments and this may be related with the concentration of land-derived plant debris along the lake shorelines, particularly near fluvial mouths (Buatois et al., 1998). Additionally, the presence of vertical burrows in Devonian high-energy fluvial deposits reflects the establishment of a stationary, deep suspensionfeeding infauna (Skolithos ichnoguild), although the role of marine influence in some of these deposits has been controversial (Bradshaw, 1981; Woolfe, 1990). Also by the Devonian, a relatively deep-tier depositfeeding infauna, represented by large meniscate trace fossils (Beaconites-Taenidium ichnoguild), was established in abandoned fluvial channel and overbank deposits (e.g., Gevers et al., 1971; Allen and Williams, 1981; Bradshaw, 1981; Gevers and Twomey, 1982; Graham and Pollard, 1982; Bruck et al., 1985; Bamford et al., 1986; Gordon, 1988;

A

B

C

Number of Ichnogenera

Ichnogenera My−1

Ichnogenera/106 Km3 Sediment

PERMIAN CARBONIFEROUS SILURIAN− DEVONIAN ORDOVICIAN

20 Ichnogenera

1 Ichnogenera My−1

1 Ichnogenera / 106 Km3 Sediment

FIGURE 23.4 Changes in diversity of continental invertebrate trace fossils through the Paleozoic (modified from Buatois et al., 1998). Evidence of plant–arthropod interaction and ichnofossils left in open nomenclature were not included. (A) Ichnogeneric diversity (plotted as number of ichnogenera). (B) Ichnogeneric diversity (plotted as ichnogenera per Ma-1) using time-averaged taxonomic diversities. (C) Ichnogeneric diversity (plotted as ichnogenera per volume of nonmarine sediment in 106 km3) normalized to correct for differences in outcrop volume. Because most of Silurian ichnotaxa come from sequences that apparently range into the Devonian, these two systems are not discriminated.

402


Keighley and Pickerill, 1997; Draganits et al., 2001; Morrissey and Braddy, 2004). While Ordovician–Devonian trace fossils are restricted to alluvial and transitional alluvial–lacustrine settings, Carboniferous ichnofaunas also occur in shallow and deep lacustrine deposits, indicating a significant expansion of the benthic fauna (Buatois and Mańgano, 1993a; Buatois et al., 1998) (Fig. 23.5). Permanent subaqueous lacustrine settings were colonized by a relatively diverse, mobile detritus-feeding epifauna of the Mermia ichnoguild. This expansion was probably linked to the rapid diversification and increase in abundance of land plants that, in turn, introduced abundant organic detritus into previously nutrient-poor, lacustrine habitats (Maples and Archer, 1989). An analogous situation was proposed for terrestrial environments based on the migration of plants from geographically marginal areas (upland areas peripheral to major basinal wetlands) to the Permanent Lacustrine 13 12

Floodplain to Lake margin

17

11 16

13

12 10

Cretaceous−Neogene 8

Triassic−Neogene 11

14

2

6 10

13

9

15

Triassic−Jurassic

12 4

3 7

Permian

1

3 2

8 9

Carboniferous−Permian

4 5

6

Ordovician−Carboniferous

FIGURE 23.5 Colonization trends in continental environments. Very shallow trace fossils are dominant in Paleozoic freshwater environments, while deeper structures tend to be common in the Mesozoic and Cenozoic. Increase in degree and depth of bioturbation occurred first in floodplain and lake margin settings and later in permanent subaqueous lacustrine environments. (1) Stiaria, (2) Rusophycus, (3) Mermia, (4) Diplichnites, (5) Siskemia, (6) Merostomichnites, (7) Gordia, (8) Helminthopsis, (9) Helminthoidichnites, (10) Taenidium, (11) Scoyenia, (12) Planolites, (13) Palaeophycus, (14) Tuberculichnus, (15) Vagorichnus, (16) Camborygma, (17) vertical burrows. See text for further explanation.

lowlands during the Carboniferous–Permian transition (DiMichele and Aronson, 1992). This pattern is consistent with environmental trends experienced by aquatic insects, which first originated in running water and later moved into lacustrine habitats (Wooton, 1988; Wiggins and Wichard, 1989). Ichnodiversity diagrams plotted as number of ichnogenera per Ma show a rapid diversification during the Silurian–Devonian and then a continuous increase in trace-fossil diversity during the late Paleozoic (Buatois et al., 1998). However, these authors indicated that when the data are normalized to correct for differences in volume of continental deposits, the major diversification event seems to have occurred during the Carboniferous (Fig. 23.5). This increase in ichnodiversity was accompanied by the diversification of freshwater organisms such as arthropods, annelids, fish, and mollusks (Maples and Archer, 1989). All continental sedimentary environments were colonized by the Carboniferous, and subsequent patterns indicate an increase of ecospace utilization within already colonized depositional settings (Fig. 23.5). For example, during the Permian, the presence of striated and back-filled trace fossils of the Scoyenia ichnoguild record the establishment of a mobile, intermediatedepth, deposit-feeding infauna that was able to colonize firm, desiccated substrates in floodplain environments. Cohen (2003) noted a decrease in diversity at familial level in lake environments during the Early Permian to the Middle Triassic, followed by a subsequent increase by the Late Triassic, in an evolutionary event referred to as the Lacustrine Mesozoic Revolution. Evolutionary innovations were ultimately conducive to the establishment of modern lacustrine ecosystems and food webs by the Late Cretaceous (Cohen, 2003). Ichnologic data (Hasiotis and Mitchell, 1993; Hasiotis et al., 1993) indicate that a stationary deep infauna, the Camborygma ichnoguild, was widespread in overbank and lake margin deposits by the Triassic (Fig. 23.5). Terrestrial environments experienced an increase in diversity of trace fossils, particularly in eolian deposits, where the ichnofauna displays more varied behavioral patterns than their Paleozoic counterparts (Gradzinski and Uchman, 1994). Also, a mobile, intermediate-depth, deposit-feeding infauna, the Vagorichnus ichnoguild, was established in deep-lake environments during the Jurassic (Buatois et al., 1996b, 1998). In contrast to Paleozoic permanent subaqueous assemblages typified by surface trails, Jurassic ichnocoenoses are dominated by infaunal burrows. High density of infaunal depositfeeding traces of the Planolites ichnoguild had caused

403

ACKNOWLEDGEMENTS

a major disruption of lacustrine sedimentary fabrics since the Cretaceous (Buatois and Mańgano, 1998; Buatois et al., 1998) (Fig. 23.5). Most insect mouthpart classes, functional feeding groups, and dietary guilds were established by the end of the Cretaceous (Labandeira, 2002). Diversification of modern insects is recorded by the abundance and complexity of structures produced by wasps, bees, dung-beetles, and termites in Cretaceous–Tertiary paleosols (Genise and Bown, 1994a,b; Genise, 2004; Genise et al., 2004). As noted by Genise and Bown (1994a) in a seminal paper, nests produced by these groups of insects have a greater preservation potential than other continental biogenic structures because they are constructed structures and not merely excavated ones. Interestingly, meniscate trace fossils of the BeaconitesTaenidium ichnoguild, which consist of large structures, occupying deeper tiers in the Paleozoic, are commonly smaller and occupied a middle-tier position during the Mesozoic and most of the Cenozoic (Buatois et al., in press). This pattern is consistent with the idea of Morrissey and Braddy (2004) that a myriapod (e.g., arthropleurid) produced these large meniscate trace fossils in the Silurian–Carboniferous. However, by the Miocene, large and deep backfilled burrows re-occupied deep tiers in similar overbank and abandoned channel deposits (Buatois et al., in press). Continental ichnofaunas display an overall increase in extent and depth of bioturbation through the Phanerozoic (Buatois et al., 1998; Miller et al., 2002; Miller and Labandeira, 2003). Comparative analysis of continental ichnofaunas in space and time suggests that increases in bioturbation depth and intensity took place progressively through time, from fluvial and lake-margin settings to permanent subaqueous lacustrine environments (Buatois et al., 1998) (Fig. 23.5). This increase in depth and intensity of bioturbation strongly influenced the nature of the stratigraphic record of continental environments, producing increasing disturbance of primary sedimentary fabrics.

CONCLUSIONS The potential of ichnology in evolutionary paleoecology is underscored and illustrated using a series of evolutionary events as examples, namely Ediacaran ecosystems, the Cambrian and Ordovician radiations, and the colonization of brackish-water and continental environments. Trace fossil evidence commonly reveals much greater evidence of ecologic change than

that inferred from body fossils alone. In contrast to the rather monotonous aspect of Ediacaran ichnofaunas, a wide variety of behavioral patterns is illustrated by Cambrian ichnofaunas, revealing that the Cambrian explosion is a real evolutionary event rather than a taphonomic artifact. However, because according to the body fossil record, the appearance of most of the major clades occurred at the Tommotian–Atdabanian, the presence of rich ichnofaunas revealing diverse body plans during the Nemakit–Daldynian (lowermost Cambrian) indicates the existence of a fuse-time previous to the Cambrian explosion. A continuous increase in ichnodiversity and compositional turnovers by the dominant bioturbators of shallow-water environments occurred through the Ordovician. Comparative analysis of brackish-water and freshwater environments through the Phanerozoic reveals a process of colonization, resulting from the exploitation of empty or under-utilized ecospace. Secular trends include increase in the diversity of biogenic structures, increase in the intensity of bioturbation, addition of new invaders, environmental expansion, and faunal turnovers.

ACKNOWLEDGEMENTS Some of the ideas exposed in this paper were originally presented in a Workshop on Trace Fossils in Evolutionary Paleoecology at the Annual Meeting of the Argentinean Paleontological Association in Santa Rosa. We thank So¨ren Jensen and Dolf Seilacher for valuable discussions on Precambrian–Cambrian ichnofaunas, and Mark Wilson and Chris Maples for reviewing the manuscript, and Patricio Desjardins for the drawings. Financial support was provided by the Antorchas Foundation (Buatois), the Research Council of the University of Tucuman (Mańgano), the University of Saskatchewan Start-up funds (Buatois) and NSERC Discovery Grants 311726-05 (Buatois) and 311727-05 (Mańgano).

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S E C T I O N III

ADVANCES, FRESH APPROACHES, AND NEW DIRECTIONS

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24 Importance and Usefulness of Trace Fossils and Bioturbation in Paleoceanography Ludvig Lo¨wemark

used in paleoenvironmental reconstructions. In paleoceanographical and paleoclimatological studies, however, trace fossils and bioturbation are usually a nuisance, causing a disturbance of the sedimentary layering that results in a smoothing of the proxy records used to reconstruct past environmental changes. However, trace fossil can also be helpful in a more technical way as recorders of sediment disturbances. In lithified sediments, the study of trace fossils is comparatively easy. The visibility of the trace fossils is often enhanced due to diagenetic processes or can be improved through wetting the surface by applying water or different oils. There are also ways to photographically or digitally enhance the trace fossils, and microscopic details of the trace fossils and surrounding sediment can be readily assessed by thin sections. In the unlithified deep-marine sediments used for paleoceanographic and paleoclimatic reconstructions, however, the fresh sediment is often rather homogeneous and other techniques are necessary. The most widely used method is to study the sedimentary structures through X-ray radiographs. The production of X-ray radiographs is quite simple and straight forward. About 1 cm thick plastic boxes are pushed into the sediment, cut out with a nylon string and placed in vacuum-sealed plastic pouches. The sediment slabs are then placed directly on the X-ray film bags and exposed to 20–50 kV for 5–20 minutes, depending on the sediment type and slab thickness

SUMMARY : The aim of this chapter is to look at the different aspects of bioturbation and trace fossils in unlithified piston and gravity cores from slope and deep-sea settings, which are the primary sources for Quaternary paleoceanographic records. The first part deals with the role of trace fossils in Quaternary high-resolution paleoceanography: what are the environmental changes that can be detected, and what is the resolution that can be expected. The second part addresses the adverse effects on highresolution time series by the homogenizing bioturbation in the mixed layer, and by deep-reaching discrete burrows. This kind of biogenic activity in the sediment may cause serious post-depositional shifts between different sediment parameters and age reversal of several thousands of years. Finally, the usefulness of trace fossils to estimate the stratigraphic completeness of the sedimentary record and the intactness of gravity and piston cores will be addressed.

INTRODUCTION Traces left in the sediment and preserved as trace fossils represent a record of animal behavior. The behavior of benthic animals is controlled by substrate consistency and composition as well as a number of environmental factors such as oxygenation and benthic food supply. Therefore, trace fossils are often


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(Fig. 24.1) (Bouma, 1964). By slightly tilting the slabs during exposure, stereo pairs can be obtained that better resolve the 3-dimensional structures of smaller details. In recent years, digital alternatives have been developed. The SCOPIX core scanner can scan whole and halved cores as well as slabs up to 150 cm long (Migeon et al., 1999), another example is the shipboard core scanner that scans whole core sections directly after core retrieval, before the core is opened and halved for sampling (Cato et al., 2000). Another core scanner that delivers an approximately 2 cm wide radiograph strip of up to 1.7 m long core halves is the Itrax core scanner. Its primary use is X-ray fluorescence measurements of major elements (Croudace, 2003). Computer tomography is another method that has found application in trace fossil research. It delivers 3D images of objects of contrasting density (Fu et al., 1994). This method, however, is rather cost- and labor-intensive and is more suitable for addressing specific morphological details than for down-core observation of changes in ichnofabric. However, Morris and Behl (1998) showed that variations in the type of bioturbation studied through X-ray tomography correlated to climatically induced environmental changes in a slope sequence from the California margin.

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TRACE FOSSILS Differences between Trace Fossils in Core and Outcrop Modern deep-sea trace fossils differ in several aspects from trace fossils usually encountered in outcrop. First, sedimentation rates on the slope and in the deep-sea are in an entirely different range compared to near-shore and shelf environments (Ekdale and Bromley, 1984). Second, substrate variability is typically small because the core locations are chosen to deliver records as complete and undisturbed as possible. Therefore, environments where large variations in flow regime, sediment input, or sediment movement can be anticipated are usually shunned. Third, one issue that has been central to ichnology is the bathymetric application of trace fossils, an issue seldom of interest in Quaternary material where water depth usually is known with a large degree of certainty. An important aspect of deepsea ichnology is that slope and deep-sea sediments are normally not preserved as outcropping exposures because these types of sediment are generally subducted at active margins, somewhat limiting their value as analogs.

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FIGURE 24.1 Radiograph production from unlithified sediment cores. After the core has been retrieved from the sea floor (A), the core is cut into short sections and split (B) into a working half used for sampling and an archive half. A shallow (1 cm) plastic box is pushed into the sediment and is separated from the core using a nylon string (C). The box with the sediment slab is put in a plastic bag and placed directly on the X-ray film before exposure in the X-ray machine (D). The radiograph film (E) can be studied either directly on a light table or as paper positive.

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There are also some inherent limitations to core material as compared to outcrop. Whereas the outcrop normally allows a 3D assessment of the trace fossils, this is only possible to a limited extent and involves considerable extra work. Because of the macroscopic size and the generally patchy distribution of the trace fossils, core material with its limited diameter only provides an incomplete portion of the ichnofauna, and does not necessarily represent the actual ichnofauna. In a core, bedding plane views of the sediment are rare and no ornaments or relief is seen in core sections of unlithified cores. Consequently, resting, locomotion, and grazing traces are difficult to impossible to detect. Furthermore, cores are usually chosen to provide as long and as complete vertical records as possible. In contrast, at outcrops, erosional events or other disturbances often provide the best exposure of the ichnofauna for taphonomic reasons.

Uniformitarian Approach Despite the abovementioned limitations, the traces left by organisms in sediments under known environmental conditions obviously can serve as useful analogs in the interpretation of trace fossils observed in fossil material. Recent examples include a study of Scolicia in cores from the northeast Atlantic that convincingly showed that the trace fossil Scolicia in the modern deep-sea is produced by irregular echinoids (Fu and Werner, 2000). That study also corroborates earlier studies that suggest a strong preference for coarse silts to fine sands by the producer (e.g., Wetzel and Werner, 1981; Wetzel, 1984, 1991). Another enigmatic trace fossil that has received attention is Zoophycos. Compilations of Zoophycos occurrences in Quaternary core material have given a rather clear picture of the environmental preferences of the producer. It seems Zoophycos is restricted to water depths deeper than 1000 m and generally is more abundant in sediments where the sedimentation rate is below 10 cm per ky and organic carbon content is between 0.5 and 1.5% (Wetzel and Werner, 1981; Lo¨wemark and Scha¨fer, 2003; Lo¨wemark et al., 2006). Detailed comparisons between material in the trace and surrounding material (Fu and Werner, 1995; Lo¨wemark and Scha¨fer, 2003) strongly suggest that the burrow is the result of a cache behavior, as speculated by Bromley (1991), and not deposit feeding as has been widely believed (e.g., Seilacher, 1967; Wetzel and Werner, 1981). However, considering the extreme variability in the trace fossils attributed to the ichnogenus Zoophycos, it is wise to apply the results from the modern deep-sea to fossil

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Zoophycos with caution. Other trace fossils that have been studied in some detail in modern material include Tasselia (Wetzel and Bromley, 1996) and Nereites (Wetzel, 2002). Studies of continental slope sediments off Norway (Romero-Wetzel, 1987) show that sipunculid worms are the producers of Trichichnus-like burrows. Box cores taken at locations with well-known modern environmental conditions and past sedimentation rates are especially suitable for ethological studies of the individual trace fossils.

Biology and Actuoichnology Recent interdisciplinary studies combining oceanography, sedimentology, and biology have investigated tiered benthic communities under different environmental conditions, for instance in the oxygen minimum zone in the Arabian Sea (Gage et al., 2000) and at the eastern North Atlantic margin (van Weering and McCave, 2002). The findings from studies of this kind are of fundamental importance to our understanding of the trace fossil record, and more studies are needed from a range of environments to improve our understanding of how different environmental conditions are reflected by the trace fossils. One limitation, however, is that biological studies of deep-sea benthos tend to focus on the relatively densely populated uppermost layer of the sediment, whereas the traces actually preserved in the fossil record belong to the much sparser fauna of deeply penetrating organisms. This chasm between deep-sea benthos biologists and ichnologists could be easily closed through cooperative, interdisciplinary sampling strategies of box cores and core top samples. In studies by Meadows et al. (2000) and Smith et al. (2000), benthic fauna and the type and intensity of bioturbation were studied in relation to changes in geochemistry and substrate parameters across the oxygen minimum zone in the Arabian Sea. Important results from their studies show that a decrease in bottom water oxygen levels corresponded with decreased mixed layer thickness and decreased burrow diameters, they also found a strong correlation between burrow diversity and species diversity, suggesting that trace fossil diversity could be used to estimate benthic faunal diversity. The most important observation, however, was that neither maximum burrow size nor maximum penetration depth of the burrows were correlated to bottom water oxygenation levels. Here ichnologists should take special notice, because the deeper and larger burrows have a considerably larger chance of being preserved in the fossil record, but these well-preserved burrows might


actually mask the ‘true’ response to oxygen variations and thus bias the environmental interpretation. Another example is a study comparing the benthic megafaunas of the Iberian and Celtic continental margins (Lavaleye et al., 2002). This study showed a relationship between high energy environments and the prevalence of filter feeders, and low energy environments and the occurrence of deposit feeders. Continued interdisciplinary studies are necessary to follow up on these important studies. One central aspect that deserves more attention is whether the benthic system observed is actually in steady state or not. As pointed out by Werner and Wetzel (1982, p. 280), with a penetration depth of up to more than 50 cm for the deepest tiers, the development of an ichnofabric reflecting steady state conditions would require steady conditions over more than 5000 years. A requirement seldom met, as can be deduced from the stable isotope record of climate change. It is therefore necessary to confirm whether the benthic fauna (and the related trace fossils) of the deeper tiers are associated with present conditions or if they represent responses to past conditions.

Environmental Reconstructions The style and intensity of bioturbation is controlled by substrate parameters such as consistency (shear strength), sedimentation rate, and grain size, and by environmental factors such as food flux and benthic food content, salinity, temperature, microbial activity, and bottom water oxygenation. There are also biological controls on the benthic fauna such as colonization, reproduction, and competition between species. Recent overviews of the different aspects of the factors controlling the style and intensity of bioturbation of marine sediments can be found in, for example, Wetzel (1991); Bromley (1996); Taylor et al. (2003). A high degree of correlation between trace fossils and variations in environmental parameters has been demonstrated in several studies. Fu and Werner (1994) showed a strong correlation between ichnofauna and current regime on the Iceland–Faeroe Ridge. On the northern slope, where bottom currents are sluggish and the sediment is generally characterized by poor sorting and relatively high organic carbon content, and by inference low pore-water oxygen levels, the ichnofauna is largely monospecific. The dominating trace, Chondrites, is considered a faithful indicator of low oxygen levels (e.g., Ekdale and Mason, 1988; Fu, 1991). In contrast, the southern slope, which is

characterized by stronger currents and well-sorted sediments and consequently lower organic carbon levels, displays a diverse ichnofauna with traces such as Scolicia, Zoophycos, Trichichnus, Planolites, and Teichichnus. In a more than 500 m long core from the New Jersey margin covering several glacial–interglacial cycles, Savrda et al. (2001) report two distinctively different ichnofabrics corresponding to glacial and interglacial intervals, respectively. While sea-level fall and lowstand phases are characterized by clay-rich sediments and a low diversity ichnofauna with diffuse mottling, the sand-rich sea-level rise and highstand phases exhibit a diverse ichnofauna with discrete burrows. The observed differences in ichnofauna were primarily attributed to differences in substrate, which in turn were controlled by sea-level induced variations in sedimentation patterns. Although short-term variations in the trace fossil composition were observed, the age control unfortunately does not allow a closer correlation of these events to environmental fluctuations. Higher resolution was obtained in cores from the pelagic platform off Tunisia in the eastern Mediterranean Sea, where Blanpied and Bellaiche (1981) observed a strong correspondence between glacial–interglacial environmental variations and the abundance and orientation of pyritized microburrows of the type Trichichnus and ‘Mycellia’ (Fig. 24.2).

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FIGURE 24.2 Trichichnus (T) typically are vertically oriented cylindrical, thread-like, and sometimes branched burrows, up to several tens of cm in length and with diameters normally less than 1 mm. In modern marine sediments, Trichichnus generally is pyritized below a sediment depth of 10–20 cm, and are, therefore, particularly discernible in radiographs. ‘Mycellia’ (M), not a formally named trace fossil, are small, randomly orientated filaments up to several centimeters in length and tenths of mm thick (Blanpied and Bellaiche, 1981). Inset shows SEM picture of pyritized burrow fragment.

Applications in Environmental Reconstructions In spite of these limitations, very high resolution records of environmental change can be obtained, under certain circumstances. In sediments of the Santa Barbara Basin, the variations in the bioturbation can be used to trace environmental changes on a, for trace fossils, unprecedented time scale (Behl and Kennett, 1996). The restricted circulation of the Santa Barbara Basin acts as an amplifier for variations in the oxygen content of the intermediate waters. Behl and Kennett (1996) used a bioturbation index consisting of four levels ranging from continuous lamination to completely bioturbated sediment to reconstruct fluctuations in bottom water conditions. As no

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Thomsen and Vorren (1984) noted similar variations in the abundance of pyritized microburrows that corresponded to variations in bottom water oxygen levels in a late Pleistocene sequence from the continental shelf off Norway. Comparable variations in burrow abundance were noted on the Iberian continental margin (Lo¨wemark, 2003; see below). However, the sometimes very deep penetration of these pyritized microburrows make them less useful for the high-resolution studies needed in Quaternary deposits. The different burrowing depths of the various trace makers is of major concern when trying to make highresolution environmental reconstructions using trace fossils as proxies for changing environmental conditions. Not only do the endobenthic animals burrow to different depths, the preferred depth may also depend on substrate as well as environmental conditions, which may vary on a seasonal scale (Wetzel, 2002). It is therefore crucial to determine the individual depth of each ichnospecies and also to determine whether the trace reflects the substrate at the level where it is found or the surface conditions at the time of construction (Fig. 24.3). Furthermore, the endobenthos often needs a long time to reach steady state in a deep marine habitat where sedimentation rates are low and the deepest tiers may reach as deep as 50 cm (Werner and Wetzel, 1982). Therefore, the ichnofabric observed is a palimpsest of different ichnocoenosis reworking the same sediment at different times. This is often the case with the producers of Zoophycos. Because of their sometimes extreme penetration depth (>1 m), they may overprint an ichnocoenosis that developed several thousands of years earlier in entirely different environmental conditions (Wetzel and Werner, 1981) (Fig. 24.4).

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FIGURE 24.3 Substrate control versus bottom water control. Scolicia (left) are produced by a deposit feeder and are usually regarded as indicating well-oxygenated conditions. As the producer burrows at a constant depth under the sediment surface, the trace fossil documents bottom water conditions at chronostratigraphic level B. Alternatively, the position of the trace fossil is controlled by substrate properties at lithostratigraphic level A. Chondrites (right), are usually considered as an indicator for dysoxic conditions. It may represent an opportunistic colonization of the sediment at chronostratigraphic level A, a deep tier developed in response to surface conditions at chronostratigraphic level B, or a response to anoxic pore waters at lithostratigraphic level A. Under non-steady state conditions when tiering sequences are poorly developed, these relationships can be tricky to determine, but for high-resolution reconstructions, the offset between lithostratigraphic position of the trace fossil and the chronostratigraphic position of the environmental conditions must be known with a high degree of certainty.

burrows penetrate deeper than 2 cm and as changes in bioturbation take place on 1 cm scale, anoxic events as short as 200 years were detected. They found 17 major anoxic events over the last 60 ky, which they were able to positively correlate to the major Dansgaard–Oeschger-events recorded in the Greenland ice core. This coincidence suggests that rapid climatic shifts were responsible for the observed variations in bottom water oxygenation in the Santa Barbara basin. Two further examples of trace fossil responses on millennial time scales come from the Iberian continental slope. There, benthic foraminifer communities, benthic 13 C, and trace fossil fauna all indicated an oxygen drawdown in connection with late Pleistocene Heinrich-events (Baas et al., 1998). During these events, ice-sheet surges released huge numbers of icebergs into the North Atlantic and large amounts of ice-rafted debris were deposited. A concomitantly increased freshwater input to the North Atlantic reduced or even halted the formation of deep-waters and led to dysoxic bottom water

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Z

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Z

Z

conditions along the Iberian continental slope. The ichnofauna just below the Heinrich-events, distinguished by large amounts of ice-rafted debris, is characterized by a strong increase in the numbers of Chondrites, indicative of decreased bottom water conditions (Fig. 24.5). In the second study, Lo¨wemark et al. (2004) used variations in the ichnofauna to trace variations in strength and bathymetry of the warm and saline contour current formed by the Mediterranean Outflow Water that flows out of the Mediterranean Sea through Gibraltar. Even millennial scale changes such as the Younger Dryas cold reversal were reflected by distinct changes in the ichnofabric. It is the nature of the trace fossils that decreasing bottom water oxygenation can be reconstructed at finer time scales than can increase. When the oxygen levels drop, burrowing depth decreases making the offset between the stratigraphic position of the trace fossils and the environmental event smaller. In contrast, when oxygen levels increase, burrowing depth increases, increasing the offset between trace fossils and environmental conditions and potentially also reworking older, dysoxic ichnofaunas, resulting in a palimpsest ichnofabric, consisting of trace fossils reflecting both oxic and dysoxic conditions. Thus, at the lower end of the oxygenation range, trace fossils have a strong potential to be used to reconstruct environmental fluctuation on millennial, or under certain conditions even centennial time scales.

Computerized Approaches T

10 cm

FIGURE 24.4 Example of a trace-fossil palimpsest. Zoophycos (Z) has overprinted and almost obliterated a previous ichnofauna consisting of Thalassinoides-like (T) trace fossils.

A number of studies have used computer modeling to explore how trace fossils are produced (nicely summarized by Hayes, 2003). These models can be very useful when interpreting the causative behavior of specific trace fossils, but are of limited practical use when dealing with the spatially limited records of deep-marine cores. There have been only a small number of attempts to apply digital image analysis methods to trace fossils from deep-sea cores despite the fact that X-ray radiographs offer close to ideal data for these kinds of approaches. Magwood and Ekdale (1994) demonstrated the usefulness of image enhancement techniques such as contrast enhancement, edge detection, sharpening, or smoothing in analyzing ichnofabrics from a deep-sea box core. They also described mathematical methods by which certain aspects of the ichnofabric in a picture can be represented as a single parameter. This allows an efficient and objective comparison of different

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BIOTURBATION

Z

IRD

Z

C

Z

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FIGURE 24.5 X-ray radiograph showing the interval surrounding Heinrich-event 1 in core PO200-10/28-2 from the Portuguese continental slope (water depth 2,155 m, core depth 84.5–109.5 cm). In the upper part of the radiograph ice-rafted debris (IRD) in the form of sand and numerous pebbles can be seen. In the lower part, large numbers of Chondrites (C) are visible. These Chondrites burrows were interpreted by Baas et al. (1998) as a response to dysoxic conditions caused by the slow deep water circulation following the large fresh water input to the northern North Atlantic during the ice berg surges. Note Zoophycos (Z) overprinted on the Chondrites ichnofauna.

ichnofabrics that may be diffuse and difficult to describe with conventional methods. This approach holds great promise, especially for the continuous X-ray radiograph records obtained from core scanners, where valuable information about changes in ichnofabric could be obtained semi-automatically through the scanning process. Another computer aided approach uses optical or backscattered electron micrographs of thin-sections to quantify the intensity of bioturbation in hemipelagic sediments (Francus, 2001). Although likely to be too work-intensive for continuous down-core applications, this method is especially well suited to detect microbioturbation at critical intervals. The strong contrast of long and thin pyritized microburrows such as Trichichnus and ‘Mycellia’ was used for automated detection of the burrow in digitized radiographs from cores from the Portuguese continental slope (Lo¨wemark, 2003). The pyritized burrows were detected, quantified and the average orientation relative to the horizon was determined using a computer program originally designed to analyze mineralogical thin sections. The results showed that variations in burrow abundance correspond to fluctuations in organic carbon content, grain size, and bottom water oxygenation. Burrow orientations, in contrast, did not correspond to environmental conditions. To automate parts of the ichnofabric analysis is actually possible, but the applications so far have been limited to simply showing that it works. If the trend towards continuous X-ray radiograph records of piston and gravity cores continues, however, automated analysis of key ichnological parameters has the potential to becoming a standard tool in paleoceanographical studies.

BIOTURBATION Mixing and Smoothing Trace fossils may represent a robust source of environmental information, but, the bioturbational activities of the benthic organisms also cause a distortion of other environmental proxy records in the sediment (e.g., Berger and Heath, 1968). Several workers have studied the vertical redistribution of sediment within the mixed layer using distinct tracers such as radioactive isotopes, tephra particles, microtectites, and natural and artificial chemical substances. Here only the basic principles of the mixing of environmental signals will be highlighted through two examples; the dispersion of a distinct tracer and

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the vertical signal shift caused by bioturbation in combination with a varying abundance of the signal carriers. When a distinct tracer such as a thin tephra, ice-rafted debris, or microtectite layer is deposited on the sea-floor, it becomes blended with the sediment (Fig. 24.6) until its concentration is homogeneous in the mixed layer (provided mixing is rapid relative to sedimentation rate). As sedimentation continues, the lowermost part of the mixed layer becomes incorporated into the historical layer and the new sediment added on top of the mixed layer leads to a successive dilution of the tracer concentration (Fig. 24.6). Consequently, the concentration of the tracer decreases upwards in the sediment column exponentially. It is important to notice that the maximum concentration is preserved at the base of the initial mixed layer, sometimes considerably lower than the initial stratigraphic position of the depositional event. In the case of continuous environmental proxies, such as the widely used stable isotopes and elemental ratios of foraminiferal calcite, the mixing obviously causes a smoothing and attenuation of the original signal, resulting in a considerably lower temporal

Sediment surface before event

Deposition of event layer (tracer)

resolution. Anderson (2001) showed by mathematical modeling of synthetic paleoenvironmental records that millennial-scale events were attenuated to half their original amplitude already by moderate bioturbation at sedimentation rates of 10–20 cm per ky. Of course, the degree of smoothing and attenuation is strongly dependent on bioturbation intensity and the thickness of the mixed layer, both of which can vary significantly depending on factors such as substrate properties, bottom water oxygenation, benthic food content, and flux. For example, in a study from the tropical North Atlantic (Legeleux et al., 1994), bioturbational mixing rates were unsurprisingly found to be highest at eutrophic sites and lowest at oligotrophic sites. On the other hand, De Master and Cochran (1982) found no correlation either between sedimentation rate and thickness of the mixed layer or the intensity of mixing. Apart from the smoothing and attenuation, the bioturbational mixing may also cause a vertical shift of the signal record when mixing affects a proxy carrier (usually foraminifer tests) that varies in abundance in the sediment. Basically, if the foraminifer abundance decreases upsection, older tests will tend to dominate the signal in the mixed

Homogenization of the tracer within the mixed layer

Tracer concentration preserved in historical layer

Continued sedimentation

Mixed layer

Transition into historical layer

Historical layer A

B

C Tracer concentration

D Tracer concentration

E Tracer concentration

Tracer concentration

FIGURE 24.6 An idealized conceptual box-model describing the reworking of a discrete event (After Berger and Heath, 1968; Ruddiman and Glover, 1972). (A) The sediment consists of a homogeneous mixed layer, with uniform mixing intensity, and the historical layer. (B) Instantaneous deposition of the tracer. Tracer concentration now is 100% in the event layer and 0% in the mixed layer. (C) If mixing is rapid relative to sedimentation rate the tracer will be homogeneously distributed through the sediment in the mixed layer. (D) As sedimentation continues, the lowermost part of the mixed layer will become a part of the historical layer, preserving the tracer concentration. The remaining mixed layer is mixed with freshly deposited sediment, resulting in slightly diluted tracer concentration. (E) As sedimentation continues, the mixed layer is shifted upwards and will successively become diluted by fresh sediment; the tracer concentration preserved in the historical layer consequently decreases asymptotically upwards. Maximum tracer concentration is preserved at a depth one mixed layer deeper than the original stratigraphic position of the event.

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BIOTURBATION

layer, shifting the signal curve upwards. Conversely, by an increase in foraminifer abundance, the signal of younger tests will dominate over older in the mixed layer because greater numbers will be mixed downward than upward, resulting in a downward shift of the curve (Fig. 24.7). These examples presume a homogeneous mixed layer of a specified thickness and with a discrete boundary toward the historical layer, neither of which is, of course, true. Even though the resulting mixing looks homogeneous, it is actually the result of an infinite number of extremely heterogeneous smallscale processes moving sediment particles randomly in various directions. It is even less realistic to assume that mixing is confined to the mixed layer and that its boundary to the historical layer is discrete. In reality the bioturbational mixing activity gradually decreases with depth, in addition, discrete deep-reaching burrows may pipe material up and down. Although this problem is well known and there is a large literature (see overview by Matisoff, 1982) dealing with the effect of bioturbation on environmental signals recorded in the sediments, these results have found little application in paleoceanographic research. Unfortunately, most Initial foraminifer abundance 0

25

50

75

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studies simply ignore the potential effects of bioturbation, or at best treat bioturbation as a homogeneously mixed layer that causes a reduction of the resolution that can be obtained. Thereby completely ignoring the adverse effects that can arise from the combination of complex and variable bioturbation and variations in abundance of the planktonic or benthic organisms in the sediment.

Discrete, Deep-Reaching Burrows Discrete, deep-reaching burrows, such as Zoophycos or Thalassinoides, pose a serious risk to high-resolution studies of deep-marine sediments. Such deep-reaching burrows may be actively or passively filled with material from the sediment surface or other stratigraphic levels. In spite of this, during core sampling these burrows, often filled with foraminifer-rich sediment, are sometimes erroneously referred to as ‘foraminifer nests’ (Hanebuth,T. personal communication.). Especially in intervals with low foraminifer abundance, they may represent a tempting but precarious source of sample material. The most treacherous trace fossil likely is Zoophycos (Fig. 24.8).

Initial isotope signal 1.0

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400

600

800

1000

A

B

C

D

FIGURE 24.7 A simple box-model using a mixed layer thickness of 100 mm was used to calculate the curve shift caused by bioturbation and foraminifer abundance variations in a hypothetical example. (A) and (B) show foraminifer abundance and stable isotope signal as they would be recorded in the sediment in the absence of bioturbation. The foraminiferal abundance rises step-like at 500 mm and the isotope signal displays a gradual decrease from 2 to 1% over an interval from 600 to 400 mm. (C) The resulting foraminifer abundance after mixing (black line) and the original abundance (gray line) for comparison. Because sediment with more foraminifers is mixed downward, the abundances below 500 mm are higher than initial values. Above 500 mm, in contrast, abundances are lower because the mixed layer still contains sediment from the level below 500 mm where abundances were low. (D) The resulting isotope curve (black line) has been shifted downward relative to the original curve (gray line) because large numbers of isotopically light foraminifers are mixed into smaller numbers of heavy.

2.0

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Open shaft

Open marginal tube of uppermost spreite

Spreite

Radiocarbon dating of the material in Holocene and late Pleistocene Zoophycos-spreiten showed that they contain large amounts of material transported downwards from a stratigraphically higher level, presumably the sea floor at the time of construction (Lo¨wemark and Werner, 2001; Leuschner et al., 2002; Lo¨wemark and Grootes, 2004), although examples of upwards transport are also known (Wetzel and Werner, 1981). Depending on sedimentation rate, the dating of spreiten material may give artificially young ages of up to several thousands of years. When looking at continuous proxy records, such as stable isotopes or foraminiferal faunal composition, single points affected by the foreign material piped down by these discrete burrows can often be identified as ‘outliers.’ In some settings though, certain core intervals may have such high abundances of Zoophycos that the chance of retrieving ‘uncontaminated’ samples is negligible. An example illustrating this is the gravity core GIK17925-4 from the northern South China Sea, in which more than 300 spreiten were counted in a core only 12 m long (Lo¨wemark et al., 2006). In this core, more than 30% of the data points were contaminated by Zoophycos material and the measured isotope signal was seriously biased. Zoophycos is most dangerous in slope and deep-sea settings; the trace fossil is usually found only at depths exceeding 1000 m (Lo¨wemark and Werner, 2001). In shelf environments, other deep-reaching trace fossils such as Thalassinoides or Gyrolithes may cause large-age errors when inadvertently sampled.

Outlook

10 cm

FIGURE 24.8 Zoophycos in X-ray radiograph showing the central part of the burrow with an open shaft connecting to the sea floor, the open marginal tube surrounding the trace, and a set of spreiten diverging from the central axis. The insets in the lower part show the outline of the burrow (left) and a conceptual model of Zoophycos (right).

Concerning the effect of deep-reaching burrows on high-resolution stratigraphy and radiocarbon dating, more information is needed on primarily two different aspects. First, why are there such large differences in the development of tiering sequence, ranging from no tiering to well-developed tiered sequences with five distinct tiers or more? Which factors determine the vertical penetration by the individual traces, and accordingly the thickness of the respective tiers? These questions could be addressed through actuo–ichnological studies on box cores from different regions with known environmental conditions. Second, to be able to estimate the potential influence of bioturbation on the proxy signals, it is necessary to understand how material is transported vertically by the different trace fossil producers. Infaunal deposit feeders such as the producers of Planolites or Scolicia likely shift relatively little material

TECHNICAL USES OF TRACE FOSSILS IN GRAVITY AND PISTON CORES

vertically, compared to the makers of trace fossils such as Zoophycos or Thalassinoides (Fig. 24.9). Attempts to quantify the amount of vertical transport caused by deep-reaching, discrete burrows have been made using artificial and natural tracers such as tephra, radiotracer profiles, and radiocarbon dating, but more research, especially on the Planolites/ Thalassinoides-like burrows commonly encountered

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in deep-sea cores is needed. If we knew which factors controlled the development of trace fossil tiers under different circumstances and the vertical transport of the trace fossils in the respective tier, a better understanding of how the proxy record has been altered could be obtained.

TECHNICAL USES OF TRACE FOSSILS IN GRAVITY AND PISTON CORES 7.5 cm

Stratigraphic Completeness P

S

Z

T

FIGURE 24.9 X-ray radiograph of a reworked tephra layer (white–gray) in core MD012388 from the Celebes Sea (water depth 3,302 m, core depth 1553–1568 cm). The lower part of the tephra layer has been reworked by an irregular sea urchin producing a Scolicia (S) seen here in longitudinal view. The meniscate backfill is seen as white arcs in the lower half of the trace. The ash particles have been shifted primarily horizontally. Below the ash layer two Zoophycos (Z) and a few small Thalassinoides (T) filled with ash particles are visible, suggesting significant vertical transport. In the upper part of the radiograph, a large number of pyritized Trichichnus and ‘Mycellia’ are visible.

Trace fossils can also be useful in a more technical way in the study of marine sediments. Erosional contacts are often easy to spot both in fresh core and in radiographs. To determine how much material was actually removed in each event, on the contrary, is usually difficult. Wetzel and Aigner (1986) devised a method by which the (minimum) amount of eroded sediment can be determined with a fair degree of certainty, at least in sediments with well-developed tiering of the trace fossils. The basic idea is rather straightforward. Because the traces in the uppermost sediment, the mixed and transitional layers, where active bioturbation takes place, are vertically stratified into different tiers (Fig. 24.10A), the sediment removed by erosion can be estimated by the number of tiers that have been removed from the top (Fig. 24.10B,C). The amount of removal that can be reconstructed is limited to the thickness of the actively bioturbated zone, when erosion reaches down into the historical layer, one can conclude that more than an amount equivalent to the entire tiered sequence has been removed, but not how much more (Fig. 24.10D). Further limitations of this technique lie in the fact that in the slope and deep-sea sequences used for paleoceanographic studies, the tiering is sometimes poorly developed and horizontal observations are inherently restricted in core studies. Nevertheless, this method has a great potential whenever flux calculations are performed.

Estimation of Sediment Deformation during Gravity and Piston Coring Since trace fossils have a higher resistance to dissolution and are less affected by diagenesis than most body fossils, trace fossils have a great potential as strain gauges (Seilacher, 1992). Trace fossils have found only minor tectonic applications probably because the persons able to identify the proper trace fossils rarely are the ones interested in the tectonic

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Turbidite

Sediment surface Mixed layer Erosional contact

Scolicia Planolites

Erosional contact

Thalassinoides Chondrites

Zoophycos Erosional contact

Historical layer

A

B

C

D

FIGURE 24.10 If the thickness of each tier can be determined either from observations in core or from analogies with similar environments, the thickness of the eroded sediment can be determined (Wetzel and Aigner, 1986). (A) Example of typical deep-marine tiering sequence. (B) Erosion has removed the mixed layer and parts of the Scolicia tier. (C) Erosion has removed the mixed layer, the Scolicia and Planolites tiers, as well as parts of the Thalassinoides tier. (D) Erosion has reached the historical layer and it is only possible to conclude that sediment equivalent to the tiered sequence or more has been removed.

B

10 cm

FIGURE 24.11 X-ray radiograph (positive) showing horizontally stretched burrows (B), presumably Thalassinoides, in core M39029-4 from the Portuguese margin.

evolution, and vice versa. In unlithified cores, trace fossils have found undeservedly little use although they are ideally suited to detect disturbances and sediment flow in otherwise more or less homogeneous sediment (Fig. 24.11). That the process of gravity coring can cause shortening of the sampled sediment

was initially noticed through the discrepancies observed between the sediment content in the core and the penetration depth indicated by mud smearing on the outside of the core barrel (Emery and Hu¨lsemann, 1964). This shortening or thinning of the sediment is sometimes erroneously referred to as ‘sediment compaction’. However, as showed by Skinner and McCave (2003), the time span of gravity coring is much too short for any significant compaction, which requires the outflow of pore water, to take place. Instead, the sediment thinning is due to lateral flow of the sediment in front of the coring device as it penetrates the sediment (Fig. 24.12A). Piston cores, on the other hand, often suffer from an uncertain amount of sediment stretching in the upper parts (Buckley et al., 1994; Skinner and McCave, 2003) (Fig. 24.12B). The thin and brittle trace fossil Trichichnus can offer a measuring stick for these kinds of sediment deformations. Trichichnus consists of threadlike thin burrows, often several tens of centimeter long but only fractions of a millimeter thick. These burrows are usually pyritized below the uppermost sediment and therefore particularly easy to recognize in radiographs due to their strong contrast to surrounding sediment. Although Trichichnus burrows are typically vertical, inclined or horizontal orientation is not uncommon. When the sediment in front of the penetrating gravitycore barrel is stretched, the fragile pyritized Trichichnus tubes break and the fragments are

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CONCLUSIONS

Piston core

Gravity core

Piston

TV

TH

10 cm

FIGURE 24.13 X-ray radiograph (core M39029-7, Portuguese margin) showing dashed line of Trichichnus fragments in stretched sediment (TH). In the upper left of the X-ray radiograph, two broken vertical Trichichnus (TV) that have been slightly stacked due to the sediment thinning are visible. A

B

FIGURE 24.12 Deformation of sediment during gravity and piston coring. (A) Sediment thinning or under-sampling. Near the sediment surface, shear strength is low and the corer enters the substrate with little deformation of the sediment (unplugged sediment entry). With depth, shear strength increases and together with increasing core length results in increased frictional drag between sampled sediment and coring device. The enhanced vertical stress deforms the sediment just below the penetrating tube (partially plugged sediment entry), resulting in sediment thinning of the lower strata sampled. The core might thereafter continue to penetrate into the substrate without sampling any sediment (fully plugged sediment entry) (terminology after Skinner and McCave, 2003). Before sampling, the sediment is undisturbed and horizontal, pyritized Trichichnus are still intact. After sampling, the sediment has been shortened vertically through horizontal flow of the sediment just in front of the coring device and the pyritized Trichichnus burrows consequently have been stretched into a string of burrow fragments. (B) During piston coring the sediment is sometimes stretched due to the suction caused by the retracting piston. If the stretched sediment contains segments of vertical Trichichnus, the amount of stretching can potentially be calculated by comparing the combined length of the burrow fragments with the distance between the uppermost and lowermost fragment. The feasibility of this method still needs to be tested.

separated from each other through the lateral flow of the substrate. Horizontal burrows thus end up as a dashed line of tube fragments (Fig. 24.13). The original length of the burrow can be calculated by summarizing the length of the fragments and the stretched length from the distance between the outer ends of the line of stretched fragments. Once a measure of the horizontal stretching has been obtained, the vertical thinning can be calculated. In piston cores, where the sediment may be stretched vertically, one could expect to find fragments of the fragile pyrite tubes stretched apart vertically by the flow of the sediment. By comparing the outer ends of the fragments belonging to one tube with the combined length of the fragments, a direct measure of the stretching should be obtainable. However, this idea needs to be tested on piston cores, ideally with corresponding gravity and box cores so that independent measures of the stretching can be acquired.

CONCLUSIONS Trace fossils can potentially record climatically induced changes in bottom water conditions on time-scales as short as hundreds of years under optimal conditions. However, there is a strong need for a better understanding of the factors controlling when and how tiered trace fossil sequences are developed. This is a problem that could be addressed

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by interdisciplinary biological, sedimentological, and ichnological studies of box cores from different settings where the environmental conditions are well known. Trace fossils and bioturbation may cause severe disruption to high-resolution stratigraphy in Quaternary gravity and piston cores. To better understand how the environmental signals have been distorted, a profound knowledge of how different types of bioturbation affect the sediment is needed. This could be achieved through more realistic computer models of how sediment particles are transported in combination with natural and artificial tracer studies on specific types of trace fossils. Trace fossils in unlithified gravity and piston cores can be useful as indicators of disturbances that may affect the sediment during coring. Trace fossils can also be used to estimate the stratigraphic completeness of the sedimentary sequence in turbiditic settings. The most urgent conclusion, however, is that it is necessary to promote the use of X-ray radiographs when working with unlithified sediment. X-ray radiographs are a comparatively inexpensive and simple method that offers a wealth of information about the sediment that is of crucial importance not only to ichnological studies but also to sedimentological, paleoceanographical, geochemical, and paleoclimatological studies as well. Information that can hardly be obtained with other methods.

ACKNOWLEDGEMENTS I thank Beate Bader and Chih-Chieh Su for their help with the SEM pictures and radiograph scanning, respectively. Konstantinos Konstantinou is cordially thanked for his help with the bioturbation modeling. My thanks are due to Andreas Wetzel and William Chaisson for their constructive criticism of an earlier version of this chapter.

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Berger, W.H. and Heath, G.R. (1968). Vertical mixing in pelagic sediments. Journal of Marine Research, 26, 134–143. Blanpied, C. and Bellaiche, G. (1981). Bioturbation on the pelagic platform: Ichnofacies variations as paleoclimatic indicator. Marine Geology, 43, M49–M57. Bouma, A.H. (1964). Notes on X-ray interpretation of marine sediments. Marine Geology, 2, 278–309. Bromley, R.G. (1991). Zoophycos: Strip mine, refuse dump, cache or sewage farm? Lethaia, 24, 460–462. Bromley, R.G. (1996). Trace Fossils: Biology, Taphonomy and Applications, Chapman and Hall, London, 361 pp. Buckley, D.E., MacKinnon, W.G., Cranston, R.E. and Christian, H.A. (1994). Problems with piston core sampling: Mechanical and geochemical diagnosis. Marine Geology, 117, 95–106. Cato, I., Rindby, A. and Rudolfsson, J. (2000). Unik sedimentscanner utvecklad. Geologiskt Forum, 25, 13–15. Croudace, I.W., Thomson, J. and Rothwell, G. (2003). Initial evaluation of the ITRAX micro-XRF sediment core scanner, New Ways of Looking at Sediment Cores and Core Data: an international conference and workshop at Southampton Oceanography Centre. Programme and Abstracts volume. SOC, Southampton, 14 pp. DeMaster, D.J. and Cochran, J.K. (1982). Particle mixing rates in deep-sea sediments determined from excess 210 Pb and 32Si profiles. Earth and Planetary Science Letters, 61, 257–271. Ekdale, A.A. and Bromley, R.G. (1984). Comparative ichnology of shelf-sea and deep-sea chalk. Journal of Paleontology, 45, 189–223. Ekdale, A.A. and Mason, T.R. (1988). Characteristic trace-fossil associations in oxygen-poor sedimentary environments. Geology, 16, 720–723. Emery, K.O. and Hu¨lsemann, J. (1964). Shortening of sediment cores collected in open-barrel gravity corers. Sedimentology, 3, 144–154. Francus, P. (2001). Quantification of bioturbation in hemipelagic sediments via thin-section image analysis. Journal of Sedimentary Research, 71, 501–507. Fu, S.(1991). Funktion, Verhalten und Einteilung fucoider und lophocteniider Lebenspuren, Courier Forschungsinstitut Senckenberg. Senckenbergische Naturforschende Gesellschaft Frankfurt a. M., pp. 1–79. Fu, S. and Werner, F. (1994). Distribution and composition of biogenic structures on the Iceland-Faeroe Ridge: Relation to different environments. Palaios, 9, 92–101. Fu, S. and Werner, F. (1995). Is Zoophycos a feeding trace? Neues Jahrbuch fu¨r Geologie und Palaëontologie, 195, 37–47. Fu, S. and Werner, F. (2000). Distribution, ecology and taphonomy of the organism trace, Scolicia, in northeast Atlantic deep-sea sediments. Palaeogeography, Palaeoclimatology, Palaeoecology, 156, 289–300. Fu, S., Werner, F. and Brossmann, J. (1994). Computed tomography: Application in studying biogenic structures in sediment cores. Palaios, 9, 116–119. Gage, J.D., Levin, L.A. and Wolff, G.A. (2000). Benthic processes in the deep Arabian Sea: introduction and overview. Deep-Sea Research II, 47, 1–8. Hayes, B. (2003). In search of the optimal scumsucking bottomfeeder. American Scientist, 91, 392–396. Lavaleye, M.S.S., Duineveld, G.C.A., Berghuis, E.M., Kok, A. and Witbaard, R. (2002). A comparison between the megafauna communities on the N.W. Iberian and Celtic continental margins - effects of coastal upwelling? Progress in Oceanography, 52, 459–476. Legeleux, F., Reyss, J.-L. and Schmidt, S. (1994). Particle mixing rates in sediments of the northeast tropical Atlantic: Evidence

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25 Theoretical and Experimental Ichnology of Mobile Foraging Karen Koy and Roy E. Plotnick

by intrinsic or extrinsic variables or obscured by preservational biases.’ They further stated that the main questions in ichnology include the kinds of behavior preserved and how that behavior has evolved over time.

SUMMARY : Trace fossils provide critical indications of the early evolution of sensory systems and of the evolution of behavioral responses to environmental heterogeneity. Foraging theory provides a useful conceptual framework for understanding the behaviors represented by foraging traces. We have developed a model for foraging trace formation that incorporates environmental heterogeneity, as well as contact and distance chemoreception. This model produces a wide range of trace morphologies from the same basic behavior. Changes in the occurrence of trace fossil types over time, in particular during the Precambrian–Cambrian transition, may be largely a consequence of the development of spatial heterogeneity on the ocean floor, rather than the development of new and more complex behaviors.

Given the clarity of this statement, therefore, it is surprising that studies of the behavior recorded in trace fossils, in particular those of marine traces, have generally paid little attention to the vast ecological literature concerning the nature and controls of animal activities. Ecologists have extensively studied the patterns and controls of organism movement in terrestrial environments and, to a much lesser extent, in marine environments. There are also closely related studies in foraging ecology and dispersal. The most notable exceptions again are the numerous studies on predation traces (e.g., Kitchell et al., 1981; Kelley, 1988; Leighton, 2002) as well as the studies of deep-sea traces by Kitchell and colleagues (Kitchell et al., 1978; Kitchell, 1979) which have incorporated ideas and concepts from foraging theory.

INTRODUCTION Trace fossils remain the major direct evidence we have of the behavior and biotic interactions of ancient organisms (Boucot, 1990). Studies of predation in the fossil record, for example, rely heavily on the preservation of bite marks, drill holes, and coprolites (Kowalewski, 2002). Consequently, the use of traces to reconstruct behavior has long been a major goal of ichnology (Frey and Seilacher, 1980; Ekdale et al., 1984, Bromley, 1996). Frey and Seilacher (1980, p. 183) made this point forcefully in stating that ‘uniformity in ichnology is mainly a function of the behavior of animals, no matter how that behavior may have been influenced

There have been numerous empirical studies of trace formation in modern environments, many of which are summarized in Bromley (1996). These include examinations of the geometry and distribution of modern burrows using X-radiography and, more recently, CAT scans (recent examples include Lo¨wemark, 2003; Mermillod-Blondin et al., 2003). There have also been many investigations of the effects of burrowing on the physical and chemical properties of sediments (e.g., Levin et al., 2003). Copyright ß 2007, Elsevier B.V.


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ICHNOFOSSILS: RECORDING BEHAVIOR

On the other hand, despite the long history of experimental neoichnology (at least as far back as Darwin (1881); see Pemberton and Frey (1990)) there have been few experimental studies regarding the formation of traces other than burrows. Previous reviews (Elders, 1975; Savazzi, 1994; Bromley, 1996) have focused on burrowing marine organisms and, in particular, on the functional morphology of burrowing. Important recent studies are Buck and Goldring (2003) and Dorgan et al. (2005). A notable exception is Seilacher-Drexler and Seilacher (1999). They experimentally studied undertraces produced by sea-pens and snails and noted the similarities to the traces Bergaueria and Psammichnites, respectively. At the same time, the extensive database on the history of behavior developed by ichnologists is little known among biologists. For example, the longestablished ethological classification for traces (Seilacher and Frey, 1980; Bromley, 1996) is, based on a survey of over one hundred publications from the late 1980s through 2005, unknown among ecologists, ethologists, and other students of animal behavior. The goal of this chapter is to examine the implications of modern theoretical and experimental studies of animal movement to ichnology. We will focus on current thinking about foraging behavior, in particular in heterogeneous environments. This will include an analysis of which of these activities are likely to be represented in the ichnological record. We will conclude with a discussion of the implications of these concepts for the early evolution of traces.

ICHNOFOSSILS: RECORDING BEHAVIOR Ichnofossils are known to represent behavior instead of specific organisms, but what is often overlooked is that they represent a suite or hierarchy of behaviors. This is readily recognized in more complex feeding–burrowing systems like Zoophycus (Miller, 1998), but even the simpler forms such as Nereites and Helminthoides also represent more than one behavior. The actual physical movements that result in locomotion could be considered one type of behavior. These movements are components of more complex, higher order behaviors. Higher order behaviors determine the way an animal moves: in which direction it moves, how fast, and why. These movements are used to achieve certain goals, which include foraging for food, migrating to new areas, and reproduction.

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FIGURE 25.1 Tracing of the grazing pattern left by a foraging fresh-water gastropod on a ceramic algae-covered tile.

As an example, in gastropods there are a set of physical behaviors involved in grazing: head movement, rasping and swallowing, forward motion, and turning of the body. The gastropod leaves behind a circular or meandering path with smaller internal meanders (Fig. 25.1). The smaller meanders represent the rasping, swallowing, and head-waving behaviors. The meandering course represents the movement of the gastropod’s entire body. The first set of behaviors simply depends on the presence of food in the location of the head. The whole-body movement depends on the size, shape, and palatability of the patch of food being consumed, as well as the metabolism and satiety of the grazing gastropod. The trace records the fact that the gastropod was moving, that it was eating, and that it was eating in a patch of a certain size and shape. A single, relatively simple ichnofossil such as Climactichnes (path with rasping marks) or Psammichnites (path with gastropod sole-wave marks) may thus record a suite of behaviors, controlled by the higher level behavior of grazing. Higher level behaviors, such as grazing, predation, or predation avoidance, are common to all animals. The implementation of these behaviors within a particular taxonomic group is far more specific to that group; e.g., rasping and head-waving in gastropods. In this context, although burrowing and surface locomotion are certainly very different locomotory behaviors, they nevertheless have other, higher order

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25. THEORETICAL AND EXPERIMENTAL ICHNOLOGY OF MOBILE FORAGING

behaviors in common, such as foraging, migration, mate searching, and predatory avoidance. Since many terrestrial organisms, such as birds and ground-living rodents, have been found to follow similar foraging rules, then there is little reason to suppose that infaunal and epifaunal benthic organisms would not also follow a similar set of rules.

WHAT IS FORAGING? Foraging behavior includes all the methods by which an organism acquires and utilizes sources of energy and nutrients. This includes the location and consumption of resources, as well as their retrieval and storage, within the context of the larger community. Foraging theory seeks to predict how an animal would choose to forage within its environment, based on the knowledge of resource availability, competition, and predation risk (Kramer, 2001). The purpose of foraging is to create a positive energy budget for the organism. In order to survive, an organism must balance out its energy spent with energy gained. In order to also grow and reproduce, there must be a net gain in energy. The major theoretical statement of this concept is Optimal Foraging Theory (Pyke et al., 1977; Stephens and Krebs, 1986; Brown, 2000), which assumes that an organism will optimize its energy budget by maximizing energy intake and minimizing energy expenditure. In other words, organisms with an ability to evaluate and selectively consume food will choose items with the greatest energy yield (E) per unit time (t); i.e., will maximize the ratio E/t. An alternative to Optimal Foraging Theory is an evolutionary stable strategy, or a strategy that is used by all members of a population and cannot be invaded or replaced by a newer strategy (Maynard Smith, 1982) so that an individual’s strategy is determined by that of its competitors and predators (Goldstein and Young, 1996). Energy is spent searching for resources, moving to the resource, and exploiting the resource. Energy is only gained during the exploitation phase of foraging. Under these assumptions, organisms will evolve to accurately assess the location and value of resources, to select among alternative resource locations, and to minimize the distance traveled to reach them (Pyke et al., 1977; Stephens and Krebs, 1986; Brown, 2000; Kramer, 2001).

FORAGING PHASES Kramer (2001) described ‘search,’ ‘assessment,’ and ‘exploitation’ as the three basic phases of foraging behavior. An important assumption is that an organism retains information gathered during these phases and uses this information in decision-making. These phases will be described below in the context of gastropod foraging. The search and assessment phases require the organism to obtain and utilize information about the relative quality and location of resources. The search phase includes the detection and location of resource patches that the organism is not in direct contact with (discussed later), and its travel to those patches. Once the resource patch or prey item has been physically located and directly encountered, the forager enters into the assessment phase. During this phase, the gastropod determines the potential net energy gain represented by this patch. The organism uses this information, along with information retained from previous foraging activity, to determine whether to utilize this patch or to continue searching. There are several key factors foragers take into account when making a patch assessment (Leighton, 2002). Patch encounter rate is the probability of encountering a resource patch per unit time. Higher values represent a greater density of patches, thus less travel distance between patches. Mean net energy gained from each encounter is the average net energy gain from all patches encountered. Search cost per unit time is the energy expended during the search phase; i.e., locating another patch other than the one the snail is in. Mean handling time per encounter is the total time from the first encounter with the prey until the prey is being actively eaten. This may include chasing, grasping, breaking through shells, and the tearing or cutting of food into ingestible portions (Stephens and Krebs, 1986). The greater the handling time, the lower the energy gain per unit time. The forager must use the information it has about the potential energy gain from a resource and the likelihood of finding another, richer patch during its assessment. It compares the net energy gain for the located patch to the chance that it will encounter a patch of greater resources. If the organism has experienced a high encounter rate of rich patches, or a low search cost, and the patch it is assessing has a low net energy gain, it may be more advantageous to keep searching. If the encounter rate is low, the average net energy of patches is low, or if the search cost is high, it will be more advantageous to exploit

CONTROLS ON FORAGING

the encountered patch, because the organism does not know whether it will encounter another patch of better quality before it loses too much energy in searching and traveling. If a decision is made to remain and exploit the patch, then the snail has entered the exploitation phase. The exploitation phase can include search and assessment within the individual patch. A heterogeneous patch would require continual assessment, and the forager would also have to detect patch boundaries in order to efficiently process the resource. Patch boundaries are not necessarily distinct, but often are some threshold level of resource. Exploitation also includes the preparation and ingestion of the food (Kramer, 2001). For a snail, this means radular scraping and swallowing of the algae. Foragers have to decide when it would be most efficient to leave a patch (Brown, 2000). These decisions are based on the quitting harvest rate (H), the rate of energy gain at the time the forager decides to leave a patch. The forager compares its quitting harvest rate to several factors. Metabolic cost (C), is the energy expended by an animal, including resting metabolic rate. Predation cost (P), includes the chance an organism will be killed or injured, and the cost of vigilance (time and energy spent watching for predators, which takes away from foraging and exploiting resources). Missed opportunity cost (MOC) assumes that searching for prey and exploiting prey are mutually exclusive activities—once a forager has decided to consume prey, it can no longer search for prey with a higher net energy gain (Stephens and Krebs, 1986). Patch exploitation should continue until the quitting harvest rate is equal to or less than the sum of its metabolic costs, predation costs, and missed opportunity cost: H C þ P þ MOC

ð1Þ

When the patch is no longer more resource-rich than the surrounding, non-exploitable area (average harvest rate), the snail will move on to find a new patch (Brown, 2000). Some organisms do not immediately consume the resources they obtain through foraging. Organisms as diverse as rodents and benthic invertebrates cache food as insurance for the future (e.g., Huntly et al., 1986; McIlroy and Logan, 1999).

CONTROLS ON FORAGING There are both intrinsic and extrinsic controls on foraging. Intrinsic factors include energy budget,

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morphology, and life stage. Extrinsic controls include resource availability, infection or disease, predation, competition, and the spatial distribution of resources. No one factor necessarily overrides the others, and which factor is most important can differ from one species to another, and even change over a single forager’s life (Taghon, 1982; Jubb et al., 1983; Juanes, 1992; Ritchie, 1998). Organisms must have energy available to cover the metabolic costs of foraging. Most organisms can function well below their optimal energy budget, but often modify foraging activities based on energy budget. A starved carnivorous snail will go from actively searching for prey, to lying in wait (Cheung and Wong, 2001). A negative energy budget may make a forager less picky when it comes to choosing whether to consume a resource or keep foraging. An organism that has very little available energy will take less energy-rich resources than an organism with a positive energy budget (Ollason and Ren, 2002). Morphology can determine the size of food ingested. Animals are limited by the size and morphology of their mouthparts. Many animals get around this limit by preparing their food—cutting, crushing, or ripping it into small enough pieces to be eaten. The mechanical and physiological constraints of morphology can also be restrictive. For example, decapod crustaceans choose smaller bivalve mollusks (thus not optimizing their net energy gain) in order to minimize wear and damage to their chelae (Juanes, 1992). The body size of a forager determines the scale at which it forages. The scale at which an organism perceives its environment effects how it perceives the geometry of the substrate and resource density. A smaller forager may detect a large, fractal landscape of many patches, while a much larger forager may perceive the same area as a single, homogenous patch. Foragers operating on different spatial scales would thus approach the same environment differently (Ritchie, 1998). Life stage affects all three previously described intrinsic controls. Non-reproducing juveniles and reproducing adults require more energy than non-reproducing adults. Breeding animals regularly experience a negative energy budget, because of the energy devoted to reproduction and the reduction in time available for foraging. Juveniles must devote a lot of energy to growth, and may be limited to consuming food containing essential nutrients. As an animal grows, the spatial range of its foraging often increases, as does the size of prey it can ingest. A juvenile, a nonreproducing adult, and an actively breeding adult of the same species would be expected to make very different foraging choices.

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Infection and disease affect foragers through altering intrinsic factors such as the energy budget and physical abilities of the forager. Infections and diseases increase the energy expenditure of a forager at all times, since the forager has to support an immune response and healing. Infections and disease may also alter the speed and mobility of a forager, restricting its ability to forage and forcing it to make different choices than it would if it were uninfected. The cost of predation (P in equation 1), also called the equation of fear (Brown, 2000), takes into account the probability of a forager being preyed upon at any given time, the forager’s fitness, and the foraging reward or expected harvest rate. Thus, the cost of predation can be increased by increasing the risk of predation, the fitness of the forager, or the value of foraging (Brown, 2000). An animal with a higher level of fitness has more to lose, and will leave a patch at a higher quitting harvest rate than a less-fit counterpart. Another cost of predation is the cost of vigilance. Time and energy spent keeping an eye out for predators is time and energy taken away from other activities, including foraging, resting, and breeding (Brown and Kotler, 2004). In deciding whether or not to be vigilant and to what extent, a forager must take into account how often it is likely to encounter a predator over time, how likely those predators are to be successful if the forager is not vigilant, the effectiveness of vigilance in lowering predator lethality, and the fraction of time the forager devotes to vigilance. A forager will want to increase its vigilance as the encounter rate or lethality of its predators increases (Brown, 1999). Competition can be from members of the same species, or from a different species which uses a common resource. Competitors often increase the availability of resources by partitioning their foraging strategies. They may do this by foraging at different times of day or night, foraging in different subenvironments or having different preferences for how they utilize resources (e.g., Kotler et al., 1991; Brown et al., 1997; Brown, 2000). Foragers may choose to utilize a resource in different ways. All foragers should preferentially choose the foods which offer the highest net energy gain. Some foraging communities partition themselves into ‘cream-skimmers’ and ‘crumb-pickers’ (Brown, 2000). Cream-skimmers consume the foods with the highest energy gain, and move quickly and efficiently from one patch to another. Cream-skimmers will concentrate on resource-rich or denser patches. Crumb-pickers will consume as much of the available energy in a patch as they can before moving on. They will harvest a patch to a lower abundance of

resources, and cannot move as quickly or efficiently between resource patches as the cream-skimmers (Brown, 2000; Chase et al., 2001).

RESOURCE DETECTION Nearly all mobile benthic organisms detect food chemically. Chemoreception can either be contact, in which the food is in direct physical contact with the organism, or distant, in which the detected molecules (odorants) are water borne. For distant chemoreception, the strength of the chemical signal detected should depend on the initial concentration of the resource at a particular location and on the distance of the organism from the resource; i.e., a close resource of low concentration may produce a stronger signal than a higher concentration resource at a greater distance. The ability of an organism to orient to a given resource signal should also be influenced by current directions and turbulence; e.g., the mixing of chemical signals in turbulent environments can reduce or increase an organism’s ability to orient toward a particular source (Ferner and Weissburg, 2005). Scale is also important (Moore and Crimaldi, 2004; Ache and Young, 2005). In general, microscopic organisms are in a physical realm where resource detection is controlled by diffusion. They react only to changes in concentration gradients over time and need to move their entire bodies to detect changes in concentrations. In contrast, larger organisms are in a physical realm where resource detection is controlled by turbulent flow. They react to changes in concentration over space using bilaterally located sensory organs, and generally move only those organs to detect changes in concentrations. In addition, as pointed out by Ache and Young (2005), contact chemoreception (‘taste’) and distant chemoreception (‘smell’) are combined in smaller and simpler organisms, but separate in larger and more complex organisms. Under unidirectional flow, organisms would be expected to orient upstream toward a chemical signal (rheotaxis; Croll, 1983). In still-water conditions, animals have been observed to orient themselves using chemical gradients (klinotaxis; Croll, 1983; Estebenet, 1995) or random search patterns (Teyke et al., 1992). Turbulent water creates a patchy chemical environment (Zimmer-Faust, 1996) in which neither klinotaxis nor rheotaxis would function well, suggesting that a random search would be the most effective strategy.

MOVEMENT RELATED TO FORAGING

Foragers should change their foraging strategies based on the perceived quality and quantity of food sources (Zimmer-Faust, 1987; Estebenet, 1995; Chevalier et al., 2003). For example, when faced with a choice, snails will choose algae with the greatest concentration of limiting nutrients (Chevalier et al., 2003). The need for limiting nutrients can cause an animal to forage sub-optimally in terms of energy gain (Simpson et al., 2004).

MOVEMENT RELATED TO FORAGING Resources on the modern seafloor are rarely, if ever, evenly distributed. Instead, their distribution is patchy on many scales (Levinton 2001). Numerous studies have examined the impact of patchiness on foraging (Brown, 2000; Chase et al., 2001), but these focused almost exclusively on terrestrial and freshwater environments. In general, the literature shows that animals foraging amongst patches have two distinct modes of movement: within-patch and between-patch movements. Within-patch movement occurs as a forager exploits the resources within a patch, and can take the form of complex spiraling or meandering movements (Heezen and Hollister, 1971; Gage, 2005). Betweenpatch movement represents the non-directed or directed movements as a forager travels from one patch to another, whether or not it has detected and oriented towards a new patch. Within-patch movements, which result in looping and meandering pathways, are the result of an animal responding to patch boundaries. These patterns of movement efficiently utilize the resource space while minimizing the total area traversed (Kitchell, 1979). The patch boundaries are marked by a drop in resource concentration or value detectable by the forager. This signals a change in resource value to a suboptimal level (Brown, 2000). Kitchell (1979) described how an organism’s response to patch shape may result in complex movement patterns. A forager may start at the edge or within a patch, then moves in a straight line, consuming resources as it goes. When it hits a patch boundary, the forager crosses a resource concentration threshold, and turns back to follow along its previous path (meander) or continues following the patch boundary, turning successively inward (spiral). An organism starting in the center may also begin as a spiral, then change to a meandering pattern as it encounters patch boundaries. When the entire patch

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has been consumed, the animal then leaves to find a new patch. Acorn worms in the deep sea have been photographed exhibiting these complex movements, then swimming off to a new location (Gage, 2005). There are many photographs of feces trails showing the spiraling and meandering patterns of movement (Heezen and Hollister, 1971). After a forager decides to leave a patch, it must locate and move to a new patch. The movements which take place when a forager leaves one patch and travels to another can be classified according to whether or not it has detected a food source. When a forager has not detected a new patch, straight or nearly straight movements seem to be most effective. A correlated random walk (which is similar to a random walk, but with turning angles not independent of previous turns, making the path nearly straight) model outperformed an exhaustive, spiraling search model except when the forager was capable of detecting patches at very large distances (Zollner and Lima, 1999). A nearly straight path avoids recrossing or returning to a previously searched area. If a forager has detected a new patch or food source, it must locate, orient, and navigate towards that source. This movement can be divided into nearfield and far-field search behavior. Marine animals and terrestrial arthropods rely heavily on chemosensory navigation to detect and locate resources during foraging. Foragers use far-field behaviors as they initially enter and move through an odor plume. Decapod crustaceans, mollusks, and fish exhibit odor-gated rheotactic behavior in this situation (Teyke et al., 1992; Zimmer-Faust et al., 1995; Weissburg and Dusenbery, 2002; Carton and Montgomery, 2003). In the presence of an odor, the animal moves directly upstream. In the absence of flow, animals wander around randomly (Teyke et al., 1992; Zimmer-Faust et al., 1996; Carton and Montgomery, 2003). If the animal begins to leave the odor plume, or has entered a large patch of unflavored water, it exhibits casting behaviors as it attempts to relocate the odor trail. This may include stopping or pausing, appendage or antennule waving, as well as vertical, horizontal, or spinning body movements (Teyke et al., 1992; Atema, 1996; Vickers, 2000; Weissburg and Dusenbery, 2002; Carton and Montgomery, 2003). The path to the odor source is thus straight to meandering, with pauses to reorient or correct path direction. When the forager has approached the odor source, it switches into a near-field search mode. Speed, heading angle, and body movement may all change. This distinct change in behavior as a source is

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approached has been observed in starfish (Moore and Lepper, 1997), nautiloids (Basil et al., 2000), crabs (Weissburg and Dusenbery, 2002), lobsters (Grasso and Basil, 2002), and crayfish (Wolf et al., 2004). This is most likely due to a change from reliance on chemo- and mechanoreceptors in the antennules to chemoreceptors in the appendages and visual or other stimuli (Basil et al., 2000; Vickers, 2000; Grasso and Basil, 2002; Keller et al., 2003). Far-field navigation seems to rely heavily on bilateral or multilateral comparison of environmental conditions. Bilateral or unilateral sensory arrays allow an organism to make an instantaneous comparison of the chemical environment on multiple sides of its body, providing navigational information. This works especially well if the sensor array is large relative to the odor plume (Webster et al., 2001). Lobsters and crayfish with one antennule removed or lesioned tended to wander more on their path to the odor source and were less successful in locating it (Atema, 1996; Beglane et al., 1997; KrausEpley and Moore, 2002). Nautiloids with one rhinophore blocked initiated far-field search behavior but were unable to locate the source (Basil et al., 2000). Starfish with the tips of their rays lesioned had more difficulty locating odor sources, and the non-lesioned rays became the leading rays (Dale, 1999).

A MODEL FOR MOBILE FORAGING The model described here is a major modification and elaboration of the one described in (Plotnick, 2003).

It incorporates: Spatial heterogeneity of the environment, such as resource distribution. The model thus allows representing different patterns of resource patchiness; Preference by the moving organism for a resource; Detection of this resource by the organism; Behavioral response to detection; and Alteration of the environment caused by the movement of the organism through it, such as ingestion of the resource. The model does not, at this time, provide for ‘memory;’ i.e., the simulated organism retains no knowledge of past foraging activities. Resources are distributed on 2D or 3D square lattices. Each cell in the lattices contains some level of resource, scaled from 0.0 to 1.0. Two-dimensional lattices represent distributions in a single layer, such as at the sediment–water interface. Three-dimensional lattices allow the modeling of changes in resource concentrations with depth. Movements in threedimensional lattices thus represent burrows. In the remainder of this chapter, we will focus solely on twodimensional movements. For two-dimensional simulations, the resource distributions can be: Even: resource distributions are the same at all locations; Random continuous: the level of a resource in a particular cell is randomly selected from an even distribution, but all nodes have at least some resource (Fig. 25.2); Random clumped: the level of a resource in a cell is again selected from an even distribution, but

FIGURE 25.2 Random 2-D map and associated movement trail; key used in all figures.

A MODEL FOR MOBILE FORAGING

values below a preset cutoff are set to zero. This produces a pattern of isolated resource patches of random size and shape; the greater the cutoff value, the greater the patchiness of the resource distribution (Fig. 25.3); Fractal: Fractal maps are produced using the midpoint displacement algorithm of Saupe (1988). Maps are characterized by a parameter H that ranges from zero to one (Plotnick and

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Gardner, 2002); low values of H (near zero) produce maps that are extremely fragmented, whereas H values near one produce highly aggregated maps. Fractal maps can be either continuous or clumped (Fig. 25.4); Map patterns can also be generated in advance and imported into the program. For example, an isolated patch with a linear gradient of resource is shown in Fig. 25.5. A similar patch, this time

FIGURE 25.3 Portion of random 2-D map (30% coverage) and associated movement trail; key as in Figure 2. Dot indicates starting position.

FIGURE 25.4 Clumped fractal 2-D map (H=0.7; 30% coverage) and associated movement trail ; as in Figure 2.

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FIGURE 25.5 Isolated patch with internal linear gradient (highest value to the right) and associated movement trail; key as in Figure 2.

FIGURE 25.6 Isolated patch with internal circular gradient (highest value to the middle) and associated spiral movement trail; key as in Figure 2. Reversals of direction probably result from the user of a square lattice.

with a decreasing radial gradient, is illustrated in Fig. 25.6. In both cases, resource values outside the patch are random and lower than inside the patch. The size of the lattices can be arbitrarily large, although very large lattices slow computation time, especially in the case of fractal maps. Lattices can be saved and reused. Organisms can be placed on the lattice at the location of the minimum or maximum resource values, at the middle, or at a specific location of the user’s choice. Each cell on the lattice releases a chemical signal s, with the strength of the signal released directly proportional to the amount of resource present in

that cell. The signal can either be detected by direct contact chemoreception (‘taste’) or by distant chemoreception (‘smell’). It is assumed that contact chemoreception has precedence over distant chemoreception. For contact chemoreception in two dimensions, the eight adjacent cells (next nearest neighbor) are examined and the ‘organism’ simply moves to the cell with the highest concentration of resource, i.e., to the cell with the maximum value of s. When an organism moves into a cell, the level of resource in it drops to a low ‘background’ level or zero, representing ingestion. If all of the adjacent cells are empty, then the model organism detects the chemical signal from

A MODEL FOR MOBILE FORAGING

more distant cells. This represents distant chemoreception. It does so by assuming that each of the eight empty adjacent cells receives a summed chemical signal from other, more distant cells within a given radius R of each. Only cells within this radius contribute to the summed signal in the neighboring cells. The higher the value of R, the more likely it is to detect distant resources. However, because, the number of cells N included increases proportional to R2, this number is usually set fairly low. For example, when R = 1 the signal comes from the four nearest neighbor sites and N = 4. When R = 12, the signal comes from a neighborhood of 440 sites. The summed signal S in each of the eight adjacent cells C is thus: X SðCÞ ¼ si aðdi Þ ð2Þ

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therefore, result only from differences in the spatial structure of the environment, rather than from behavioral differences. Therefore, this simulation can function as a ‘null model’ for the study of the evolution of behavior. Representative spatial patterns and corresponding movement pathways for two-dimensional paths are shown in Figs. 25.2–25.6. For all of these simulations: there is no bilateral bias in signal detection maximum; signal detection range for distance chemoreception is set to 2; signal attenuation is set to the square root of the distance; and all maps are 128 128 pixels (illustrated maps have been cropped).

N

where si is the signal from cell i within the radius R and a(di) is the attenuation of the signal as a function of its distance d from C. Again, the organism moves to the cell with the maximum value of S. If no chemical signal is detected in any of the adjacent cells, then the movement is random. A variety of functions are available to represent signal attenuation; they are designed to include a wide range of realistic representations of chemical dispersal. Signal attenuation functions include:

Uniform: no attenuation of distance; Inverse square root of distance; Exponential decline with distance; and Normal distribution.

Details of the functions are in Plotnick and Gardner (2002). At this time, it is assumed that signal dispersal is equal in all directions. The program can be adapted to allow biased signal dispersal. This would permit a more accurate representation of directional currents in simulations. For most runs, it is assumed that there is no directionality to signal detection; i.e., chemoreception is equally sensitive in all directions. One option, however, allows either or both contact and distant chemoreception to have biases; e.g., the organism is ‘bilateral,’ with the most sensitive detection in front and the least sensitive to the rear. In sum, the behavior described by this model is very simple: detect a chemical signal and move in the direction of its highest value, then ingest what is present. Any variations in movement pattern,

It can be clearly seen that the geometry of the movement trail is strongly controlled by the spatial distribution and density of the resources. ‘Loose’ or open meandering trails, in which successive loops are not in close contact, have been interpreted as being less advanced, in terms of behavioral optimality, than ‘tight’ trails in which the loops are in close contact (Seilacher, 1986). Similarly, Seilacher (1986, p. 69) described a trail with conspicuous kinks as representing a tracemaker with ‘problem in the execution of the meander program.’ As can be seen by comparing Figs. 25.2–25.6, this variability in features can be produced by biologically realistic variation in spatial heterogeneity, rather than requiring different behavioral patterns. Especially important are the implications of these results for the formation of meandering and spiral trails; in particular, the necessity for an organism to follow the rules underlying the model of Raup and Seilacher (1969) in order to produce these trails. Again, the only two behaviors explicit in the model are to move to the site of the greatest resource and ingest what is at that site, reducing that to a lower level. Phobotaxis, the avoidance of crossing a previous trail, thus results from the detection of low levels of resource in a previously exploited locality. Similarly, thigmotaxis, staying close to older parts of the trail, occurs if resources exhibit local concentrations larger than the ability of the organism to ingest in a single pass (see Figs. 25.4 and 25.5). Neither behavior needs to be ‘hardwired’ into the organism for the resulting paths to form. Hayes (2003, p. 394) expressed puzzlement over the third rule, that of strophotaxis, in which the organism periodically makes 908 turns, ‘something one would

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like to see emerge from simpler rules rather than being a built-in axiom.’ As can be seen from Figs. 25.4 and 25.5, the inferred behavior simply results from the encounter of an organism with a boundary; thus in agreement with the suggestion originally made by Kitchell (1979). The model results can be empirically tested using living organisms in controlled laboratory settings. Patches of different resource densities, gradients, size, and shape can be used to replicate the distribution and morphology of patches within the model. Observations of the movement patterns of foragers, or the physical traces left behind by foraging, can then be compared to the pathways created by the model, and to pathways preserved in the geologic record.

(Underwood, 2004). Thus, the presence of such safe havens should be associated with a locally high density of foraging trails. One would also expect a decrease in foraging trace number, size, and an increase in complexity, with distance from the refugia. Increasing distance from refugia coincides with an increase in the risk of predation, so foragers will choose denser or larger resource patches, spend less time foraging, and try to consume resources more efficiently by increasing the complexity of their movement pathways (Kitchell, 1979).

APPLICATIONS TO ICHNOLOGY

Both, lessons from foraging theory and the results of the model described above suggest that there is a close link between spatial heterogeneity of the environment and foraging movement patterns. Many of the morphological differences between different ichnotaxa may thus be related to differences in the spatial packaging of resources rather than to variations in the behavior of the tracemakers. This relationship has direct implications for the interpretation of the trace fossil record, especially during the Proterozoic–Phanerozoic transition. Numerous studies have suggested a rapid increase in trace fossil diversity in both shallow and deep water in the Cambrian (Crimes, 1992; Jensen, 2003; Jensen et al., 2005a,b). Jensen et al. (2005b) showed that many purported Ediacaran trace fossils are probably invalid, making the transition even more striking. In addition, nearly all of the valid traces are simple horizontal forms, formed at or near the sediment–water interface (Jensen, 2003; Jensen et al., 2005a). To a first approximation, this marked increase in diversity of trace fossils could reflect:

It can be assumed that extinct foragers and predators used the same basic rules and strategies for feeding as animals do today. The assumption of uniformitarianism in the ichnological record is based on the stability of the different morphologies and assemblages through time, the small number of behavioral patterns exhibited by invertebrates, and the decoupling of tracemaker from trace morphology (Frey and Seilacher, 1980). Since many groups of modern organisms use similar decision-making processes and foraging behaviors, the absence of a tracemaker’s identity is not a stumbling block in interpreting ichnofossils. Straight or wandering tracks like Cruziana may be interpreted as undirected or directed movement between resource patches. More complex traces, such as Helminthoides, Paleomeandron, and Nereites, may indicate the presence of a finite patch of resources. Difference in trace morphologies, therefore, may reflect differences in resource distribution rather than behavioral differences. Fear of predation can heavily influence an individual’s foraging choices. It is most likely that fossil organisms, like the modern biota, would have preferred to forage closer to hiding places from predators or refugia (Huntley, et al., 1986; Brown, 1999; Brown and Kotler, 2004). For example, although gastropods have shells and hard plates designed to protect them (traveling refugia), they also use preferred physical locations for refugia. Limpets produce home scars, to which they return at the end of every foraging bout; intertidal gastropods prefer to rest in crevices and on uneven surfaces

IMPLICATIONS FOR THE EARLY EVOLUTION OF TRACE FOSSILS

Taxonomic history of tracemaking organisms, such as the origin of trilobites and their association with Cruziana and Rusophycus. Macnaughton and Narbonne (1999) believed evolution to be the primary control of trace fossil distribution in a Neoproterozoic–Lower Cambrian succession in Canada; Evolution in the behavior of tracemakers, such as the suggested development of behavioral optimization in graphoglyptids suggested by Seilacher (1977, 1986), but questioned by Crimes and Fedonkin (1994); and

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ACKNOWLEDGEMENTS

Changes in the nature of the depositional environment, such as the nature of the substrate, density of food resources (Wetzel and Uchman, 1998), and oxygenation (McIlroy and Logan, 1999). Seilacher and Pflu¨ger (1994) and Seilacher (1999) described late Proterozoic soft-sediment substrates as being characterized by widespread microbial mats with little or no vertical bioturbation (matgrounds). These matgrounds are assumed to have been firm. In contrast, Phanerozoic sediments are characterized by extensive vertical bioturbation with microbial mats becoming scarce (mixgrounds); bioturbation results in a far softer and water-rich sediment surface. Seilacher and Pflu¨ger (1994) termed this transition ‘the agronomic revolution.’ Bottjer et al. (2000) and Dornbos et al. (2005) have extended this concept to include the evolutionary and ecological implications of this change in substrates, described as the ‘Cambrian substrate revolution.’ In particular, they considered the impact of this ‘revolution’ on organisms that utilized the matgrounds as a substrate. McIlroy and Logan (1999) suggested that the development of bioturbation in deeper waters was made possible by an increase in oxygen in the water column above the sediment–water interface and by a marked increase in the influx of the nutrient-rich particles to the seafloor. Both of these were driven, in turn, by the development of metazoan zooplankton, which produced carcasses, fecal pellets, and other high-quality organic debris that transferred organic matter from the photic zone to deeper waters. This transfer reduced the rate of oxygen consumption in surface waters, and allowed deeper waters to become oxygenated. A final factor may be the increase in the size of mobile organisms during this interval (NovackGottshall, 2005). As organisms became larger, the relevant flow properties of odorant movement changed from diffusion to advection (Moore and Crimaldi, 2004). The evolution of macroscopic organisms required the ability to navigate within spatially and temporally variable odor plumes. Taken together with the ideas discussed in this chapter, we can suggest a possible scenario for at least some of the increase in trace fossil diversity in the Cambrian. Neoproterozoic environments had relatively low spatial heterogeneity, at scales relevant to the earliest benthic bilaterians. The advent of zooplankton triggered the onset of infaunal burrowing, which is an energetically expensive mode of life (Hunter and Elder, 1989). These burrows greatly

increased the spatial complexity of the seafloor. Resource patchiness was also increased by the advent of macro- and microscopic organisms which produced spatially discrete carcasses, fecal pellets, and mucus-bound marine snow. Taken together, this suggests that the Cambrian was a period of rapid increase in the heterogeneity of the benthic environment. It became important for larger foraging organisms to develop mechanisms to detect patchy resources from a distance. This, in turn, could have led to morphologic innovations such as the antennae of trilobites and other arthropods. The development of trace fossil diversity, therefore, may be part of a larger feedback loop between the evolving biosphere and the physical world.

ACKNOWLEDGEMENTS This chapter is based upon work supported by the National Science Foundation under Grant No. EAR0207194 to R.P. Joel Brown is thanked for many useful discussions on foraging theory. Michal Kowalewski is thanked for his review and useful comments.

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26 Material Constraints on Infaunal Lifestyles: May the Persistent and Strong Forces be with You Peter A. Jumars, Kelly M. Dorgan, Lawrence M. Mayer, Bernard P. Boudreau, and Bruce D. Johnson

SUMMARY : Physics, materials sciences and mechanical engineering provide constraints that can be used to understand what infaunal animals do and did in the contexts of both making and destroying traces. As a primary example, on the temporal and spatial scales of burrow extension, many muds behave as linearly elastic solids that fail by cracking. These cracks are flattened, discoidal features that previously would not have been recognized as animal traces. Dominant guilds of deposit feeders in the oceans today are equipped with wedges, gills and feeding appendages to make, breathe in and feed in cracks. As a second example, feeding in different orientations with respect to gravity poses different problems in mixing and transport of digesta, and the varied solutions may leave different fossil signatures. Evolution of vertical bioturbation in mud required innovations in both crack making and digesta handling, suggesting that burrowing may have occurred first in sand, where burrowing at a shallow angle near the sediment–water interface is relatively easy and where detritus of high food value may have been easier to ingest and digest selectively.

between bioturbation and gaseous molecular diffusion. Large-scale consequences of gaseous molecular diffusion can be quantified in a diffusion coefficient, D [L2 T1] arising from two microscale features, a molecular velocity [LT1] and a mean free path [L]. (We use the physics convention of giving primary dimensions of length [L], time [T], and mass [M] in square brackets.) For bioturbation, Guinasso and Schink (1975) invoked a biological diffusion coefficient, DB, but did not draw explicit connection with microscale animal activities. The only explicit length scale that they introduced was Lb, the thickness of the bioturbated layer, which falls near 10 cm (cf. Boudreau, 1998). Wheatcroft et al. (1990) explicitly decomposed DB into a step length, Ls [L], and a rest interval, [T], between successive episodes of movement of particles, arguing that DB = L2s / and that large step lengths (of order 1 cm or more), resulting from ingestion and egestion by sediment-feeding animals, dominated. They also pointed out that DB should vary in magnitude with mixing direction as well as depth in the sediments—that DB is anisotropic (or in engineering terms transversely isotropic, i.e., symmetric about the vertical or z axis)—with horizontal mixing intensity generally and often greatly exceeding vertical. The fatal flaw in their approach, however, is the necessary assumption for macroscale–microscale connection that Ls Lb, which is clearly false for feeding displacements 1 cm (Meysman et al., 2003). The diffusive representation of bioturbation is thus comparable to diffusive models

INTRODUCTION Quantitative understanding of bioturbation has reached an impasse that requires fresh approaches. Implicit and explicit analogies have long been drawn


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INTRODUCTION

of turbulence, i.e., very good at fitting data, marginally successful at making predictions, but extremely limited in providing mechanistic understanding of the links between animal activities and sediment mixing. This final failure constitutes a major problem to further progress in this field and has led to automaton modeling, using explicit behavioral rules, as an alternative means to connect microscale processes with macroscale consequences (Boudreau et al., 2001; Choi et al., 2002). A primary difficulty in developing automaton rules further, however, is ignorance of the small-scale, short-term behaviors of infaunal species and thus of the rules needed to implement an automaton. How often, how far and how fast do they move, and how do sites of ingestion and egestion and forms of ingesta and excreta differ? Because ichnologists have formidable problems in making observations, they can easily appreciate that students of living deposit feeders share many of their difficulties in discovering what animals living in sediments do and where and when in the sediments they do it. The epithet ‘clear as mud’ aptly describes the opacity of granular, heterogeneous solids to electromagnetic radiation. Developing better observational tools is one obvious and important remedy being pursued, but progress in direct, in situ observation remains painfully slow. A less obvious and complementary approach is to identify constraints under which these gourmands of mud and sand operate, i.e., to narrow the possibilities to those that are physically, chemically and energetically feasible. In quantitative terms, a constraint provides another equation that helps in the struggle to match the number of equations with the number of unknowns. As an analogy, the broad field of biological fluid dynamics uses the properties of water (i.e., density and viscosity) and the principles of continuity and conservation of mass and momentum to reveal how, and how fast, organisms can swim (e.g., Ellington and Pedley, 1995). Recent characterization of muds as elastic solids provides a starting point for developing parallel constraints by sediments on infauna. Namely, explicit parameterization of material properties and forces should improve understanding of the process of moving through sediments and, in the case of deposit feeders, moving sediments to and through animals (Dorgan et al., 2006). It should also quantify the forces needed to make particular trace fossils. In this chapter, we attempt physical characterization of the medium and of location and orientation of animals within the medium as potential constraints on burrowing and feeding. For three intertwined reasons, we have come up short by comparison with biological

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fluid dynamics. One is simply that fewer minds over shorter intervals have worked on the mechanics of burrowing versus swimming. Second is the observational difficulty already noted. Third, sediments are inherently more complicated mechanically than is water. The time is ripe for new advances, however. Nanosciences and materials engineering are making tremendous strides in understanding of random, heterogeneous materials (e.g., Torquato, 2001), allowing transfer of useful information and approaches from this burgeoning literature. A primary goal of nanotechnology is to connect nano- and microscale structure of man-made materials with their bulk properties and mechanical behaviors and then to optimize the latter by manipulating the former. Animals have the potential, analogously, to modify sediment properties as well as to optimize their burrowing and ingestion behaviors in ways that account for the material behaviors that they encounter and in part produce. By ‘heterogeneous’ we mean that sediments contain at least two phases, one solid and one liquid. Moreover, organic particles may behave differently from quartz grains, and the medium outside grains may contain sufficient mucopolymers to greatly alter its mechanical behavior; many muds behave mechanically as though the intergranular material is a gel. By ‘random’ we mean that it is unnecessary to know the precise location of a particular grain to evaluate the bulk behavior of the medium, but how the grains are arranged with respect to each other and to the other phases typically has major influence on mechanics of the bulk. In a sediment column at steady state, grains are being relocated stochastically through bioturbation, but bulk mechanics remain the same, with strong vertical gradients superimposed on three-dimensional, more random structure. It is clear that many of the methods being used to devise novel composites and to better understand mechanics of traditional materials such as concrete will be transferred to terrestrial and marine soil mechanics. The effort has begun and can be expected to give insight into ichnology as well as benthic ecology. With some assumptions, likely based on mechanics of modern sediments, it may well become possible to recover mechanical properties of the native medium from a combination of rock structure and material models. More broadly, animal–sediment mechanics of burrowing and feeding are integral to the processes by which traces are both made and destroyed. One result of our initial animal–sediment mechanics studies and a major basis of our chapter is that some of these complex sedimentary composites—many marine muds that we have tested—show

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26. MATERIAL CONSTRAINTS ON INFAUNAL LIFESTYLES: MAY THE PERSISTENT AND STRONG FORCES BE WITH YOU

surprisingly simple and unanticipated mechanics on the spatio–temporal scales of organism burrowing. Namely, the bulk mud behaves as a simple, elastic solid, and bubbles and animals move through it by making cracks (Boudreau et al., 2005; Dorgan et al., 2006). Our arrival at this conclusion is very much an ichnologically relevant detective story that illustrates how much a search image can determine what one does not see: ‘I would not have seen it if I had not believed it’ (anonymous). Two of us Boudreau and Johnson were part of a team seeking to understand how methane bubbles grow in and move through sediments (Johnson et al., 2002). X-radiographs, however, failed to reveal them, even in sediments known to release methane bubbles. So the team decided to ‘blow’ bubbles in sediment through a thin tube and X-ray them. Bubbles in mud proved to be oblate spheroids (Fig. 26.1). The only forces involved in breaking and moving bubbles through mud are buoyancy and excess (over ambient) pressure controlled by gas transfer and surface tension. These forces for macrofauna-sized bubbles are modest and led us in turn to reason that burrowing cannot be as expensive as the biological literature had suggested (Hunter and Elder, 1989). Tellingly, prior work on burrowing did not explicitly characterize the burrowed medium, and by adding recently developed constraints (Johnson et al., 2002), we found by that animals exploit the same burrowing mechanism as do bubbles (Dorgan et al., 2005). Our results have led

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us to reinterpret much of the literature of burrowing (Dorgan et al., 2006). We do not reproduce our review here, but rather extract the most ichnologically relevant components and expand on them. We also examine the physical constraints on the fundamental deposit-feeding problem of moving sediments into and through animals and notice that there are correlations between postures and characteristics of digesta that can be understood in terms of needs to keep the deposit-feeder digestive disassembly line running at a high volumetric rate, to mix reactants and to extract products. Along these lines, we identify the numerically dominant guild of deposit feeders that live by making cracks and feeding from the new surfaces produced. They had for the most part been classified previously as ‘surface’ deposit feeders (e.g., Fauchald and Jumars, 1979) for the poor reason that those seen feeding were at the sediment surface and the only slightly better reason that similar feeding methods and morphologies may work on self-exposed surfaces below the primary sediment–water interface as on the primary sediment–water interface. Another message emerges from our analysis. It is that forces exerted on sediments by animals may vastly exceed those under typical conditions of simple static loading by sedimentation and burial or even by sediment transport. Cracks in particular, focus a great deal of energy at the crack tip. These forces are likely major destroyers of traces but have untested potential to produce structures as well. As the tentativeness of

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FIGURE 26.1 (A) X-radiograph of bubbles (white triangles as pointers) made within a natural mud. The arrow marks the tube used to make the bubble above and to its left, and the letter Z is a piece of lead 1 cm tall. (B) A bubble being blown in a gel made of double-strength gelatin in seawater. Mechanical properties of these two media are surprisingly similar and account for the oblate discoidal shapes of bubbles found in both (Johnson et al., 2002; with permission). Additional photographs, x-radiographs and CT scans of bubbles can be found in Boudreau et al. (2005).

THE MATERIALS

this last sentence suggests, those seeking definitive conclusions will be disappointed with our chapter. We hope that those seeking new questions will find greater satisfaction.

THE MATERIALS Mud of a broad range of grain sizes and sortings appears to behave in bulk, over short distances and times, as a solid and to fail by linear elastic fracture (Johnson et al., 2002). Failure in this materials-science sense is success for a burrower that must make an opening through which it can move or must break off a fragment of sediment for ingestion. We cannot take the space to develop these mechanics in any detail here, but many lucid engineering texts do (e.g., Anderson, 1995). Remarkably, two parameters suffice in many muds to determine both whether a crack will extend and what its initial shape will be. One is Young’s modulus, E, the ratio of stress to strain [M L1 T2], and the other is the critical stress intensity factor, KIc, an indicator of the stress at which failure occurs [M L1/2 T2]. For bubbles, the natural crack geometry is an oblate spheroid, and the source of stress is gas pressure (Fig. 26.2). Figure 26.2 is drawn for an isotropic pressure such as that within a gas bubble or liquid inclusion, but note that because of the bubble shape, the pressure exerts more force along the short axis than along the long axis of the bubble. In the case of a burrower, applied stress is typically concentrated even more strongly along the minor axis, b, by some structural ‘wedge,’ but the

p

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FIGURE 26.2 Diagrammatic cross section through an oblately spheroidal bubble defining the major a and minor b axes. Pressure, p, is the excess between the inside the bubble and the medium outside. Forces that lead to crack propagation are concentrated in the gray regions, to which the stress intensity factor, KI, applies. When pressure reaches a critical value (indicated by the subscript c), pc, so does stress intensity at KIc, and the crack extends, increasing a and decreasing p. Geometry in animal burrowing differs less from that in a bubble than one might expect because the wedging force producing tensile stresses in the sediment tends to be applied in a similar geometry, i.e., along axis b, and liquid under pressure is moved into the crack, leading to crack geometry similar to that of a bubble (Dorgan et al., 2006).

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crack geometry is similar. This shape may be maintained by injection of liquid during burrowing. Internal pressure of the bubble, liquid or dilating body part pushes, but the sediment experiences a tensile stress, just as it would if one grabbed this piece of effectively solid mud on both sides of the crack at their intersection with the short axis and tried to pull them apart. Somewhat intuitively, an existing crack, bubble or burrower is a place where the tensile stresses in the surrounding medium cannot travel, and so these stresses detour around it to concentrate at its edges. The non-intuitive dimensions of KIc result from the way that crack-tip stresses vary with the size of the crack, i.e., in proportion to a1/2. Thus cracktip stresses are most strongly dependent on crack radius when a is small, but they always increase with crack size. E and KIc together determine that geometry by controlling the aspect ratio (cf. Eq. (19) of Johnson et al., 2002), pffiffiffi bc KIc ð1Þ ¼ pffiffiffiffi E ac ac The subscript c for a and b indicates that the predicted geometry occurs just when the critical stress for fracture is reached. Observations on sediments fit that prediction well (Boudreau et al., 2005). A more thorough introduction, including derivation of the dependence on a1/2, can be found in a mechanics text under the term ‘linear elastic fracture mechanics’ (LEFM; e.g., Anderson, 1995). If a material behaves as a linearly elastic solid, these two parameters suffice to describe its behavior under the tensile stresses produced by a burrower. The resultant crack will be discoidal, with the cross-gap dimension decreasing away from the point at which maximal tensile stress is applied by the wedge. Events at the crack tip depend heavily on material properties and determine a great deal about the nature of bioturbation. If an animal simply makes a crack and then moves into it, relative sediment grain positions after the animal passes need not change at all. That is, an animal may move through without causing appreciable bioturbation. This result, however, is unlikely for four reasons. One is that some friction is required in burrowing, leading to some grain rearrangements. A more obvious reason is that deposit feeders also ingest and egest sediments. The third is that linear elastic fracture is an idealization that is good to first order for many sediments but may need correction to apply in some muds and may fail altogether in others. Animals exert larger, more focused forces over a wider range of temporal and spatial scales than do bubbles. These differences likely

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result in viscoelastic fracture or yield, with plastic rearrangement of grains at the tip of the crack as it propagates. Such plastic deformation as a burrow is opened is likely to be most prevalent in muds with the highest water and clay contents. At some time scale longer than that of crack opening, viscoelastic deformation (creep) will occur if the animal still occupies the crack. We refrain here from introducing parameterizations of viscoelastic properties and elastic–plastic fracture only because we have not yet succeeded in quantifying a sediment–organism case where they clearly apply. We have no doubt that such cases will be identified, and the needed parameterizations are readily available (Anderson, 1995). At the other end of the spectrum—in well sorted, coarse sands like those found on high-energy beaches—granular mechanics (not LEFM) are in effect, with forces transmitted along force arches.

Forces within granular media have been visualized by several clever means. One is through carbon paper put under a layer of sand. If a point force is exerted downward (z direction) on the upper sand surface, the underlying carbon paper reveals an array of widely separated points of transmission of that force to the x–y plane of carbon paper (Mueth et al., 1998); a few chains of grains carry the overwhelming bulk of the force. Use of birefringent particles in place of natural sands reveals the nature of the transmission path as force arches in the family of planes through the z axis (including the x–z and y–z planes; Fig. 26.3). Arches carry more and more weight as the thickness of overlying sediments increases. Although it is apparent that non-cohesive, high-energy beaches follow these granular mechanics, where in the grain size, sorting and gluing continua a transition occurs to elastic or viscoelastic fracture mechanics is unclear.

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FIGURE 26.3 Force arches in a simplified (two-dimensional) granular medium, visualized through photoelasticity. The ‘grains’ are pentagonal and roughly 1 cm in maximal dimension. (A) Force arches produced under weight of the pentagon plus hydrostatic head. (B) As in A, but with a point force added at the ‘sediment–water’ interface. (C) Arches due to the point force alone, obtained by subtracting the stresses in A from those in B. (D) Another realization like C, but with a different packing of ‘grains’ (Geng et al., 2001; with permission). It is easy to see why pounding sand is not a good idea.

THE PROCESSES

THE PROCESSES Making an Opening The cycle of movement through propagated cracks differs fundamentally from the classic dual-anchor description of burrowing. Across many phyla, burrowing has been described as the alternation of a ‘penetration anchor’ to resist a strong thrust that makes an opening through (largely implicit) compaction or plastic deformation with a ‘terminal anchor’ used to hold the anterior region in place while the rest of the body is pulled forward. Instead, both terminal and subterminal (near the functional anterior end but not at its tip) expansions function primarily as wedges and O-rings to drive a crack rather than as anchors. It takes little lateral or radial force to open a crack because the geometry of a crack focuses energy so effectively at the crack tip (Fig. 26.2). Once the crack propagates, low-force insertion of an anterior body portion can be made, during which the original subterminal wedge may serve as an anchor to resist backward motion of the body or of pore water pushed into the crack. The nature of the wedge and propulsion system differs among taxa. A bivalve shell is an obvious wedge, with foot as insertion device. The shell exerts stress, which is focused at the crack tip. Dilation of the foot against the crack wall exerts additional stress, resulting in crack propagation. Amphipods bear striking resemblance to the bubbles of Fig. 26.1. Moving the legs pushes the dorsal cuticular wedge through the sediments; like a bubble, the wedge itself is the insertion device. Polychaetes appear to show diversity in the extent to which a terminal (eversible pharynx) or subterminal (radial expansion of the body) expansion serves as a wedge. We focus here on a line-up of polychaete suspects previously thought to be surface deposit feeders in the sense of feeding more or less exclusively at the sediment–water interface. For decades, one of us (P. Jumars) has been doing the simple experiment of placing animals in monospecific batches in containers of mud in sea tables under conditions of ‘benign neglect’. Target species have been numerical dominants in the ocean, such as cirratulid polychaetes. In numerous experiments with bipalpate cirratulids (Aphelochaeta, Chaetozone and Tharyx), trichobranchids (Terebellides) and sternaspids (Sternaspis), no surface features were evident after these animals initially burrowed. High survival and little obvious internal structure within the sediments was found in the mud months later when the contents of the containers

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were sieved. At the time, however, we did not know about discoidal cracks and were therefore insensitive to their possible presence. We present a line-up of four taxa drawn by other authors, but chosen for suggested mechanical similarity to those in our experiments (Fig. 26.4) to demonstrate important similarities and differences among members of this burrowing guild that feeds from the surfaces of the cracks that it produces. Cossurids in cores are usually found several centimeters below the primary sediment–water interface. Published depictions of them as surface feeders (Fig. 26.4 of Tzetlin, 1994) are not based on direct observations (nor have we succeeded in any direct observations of their burrowing or feeding). Because of their striking resemblance in body plans to cirratulids, however, we conjecture that they also are primarily exploiters of cracks. In materials dominated by granular mechanics, it is a losing proposition to push one’s way downward against rigid and robust force arches (Fig. 26.3). They underlie the well-known futility of ‘pounding sand.’ Rather, an eraser-like motion that breaks individual arches or a liquid injection that liquefies the bed and separates arch ‘stones’ can more effectively allow progress (e.g., Trueman, 1970). The eraser rubbing may be made even more effective in knocking out arch grains if the eraser bears protuberances on a scale near that of the sand, likely explaining the rugose textures of soft-bodied burrowers in sands and their frequently papillated feeding appendages (Fig. 26.5). External shell sculpture in sand-dwelling molluscs may have similar function. Whether or not they are capable of selectively knocking out arch stones, protuberances in shear are likely effective at freeing grains from an adhesive matrix. Crustacean setae and urchin spines can achieve similar functions. Burrowing progress thus may be materially aided by rearranging a relatively small number of grains that bear a disproportionate fraction of the total load. Force arches also explain the observations that it is hardest to push a cone into sand vertically and that sand dwellers often initiate burrowing at a very shallow angle (e.g., Brown and Trueman, 1991). It is less widely known that liquefaction is used by some burrowing polychaetes that have erroneously been classified as surface deposit feeders (e.g., by Fauchald and Jumars, 1979). The burrowing terebellid polychaete Eupolymnia heterobranchia, for example, more or less continuously lays a horizontal tube as a pipe. It periodically breaks a hole from the top of the pipe to the sediment–water interface to ease flow production anteriorward in the segment of pipe that

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feeding tentacles

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ventral views

D top view

FIGURE 26.4 A rogues gallery of deposit-feeding polychaetes designed for fracturing and entering. Many of these species have been inaccurately described as exclusively surface deposit feeders (e.g., Fauchald and Jumars, 1979). They do feed from surfaces, but primarily from ones that they create by making cracks below the primary sediment–water interface. (A) Cirratulids (drawing from Hartman, 1958, p. 201) dominate benthic macrofaunas under most of the world’s oceans today. Resembling a train with a locomotive at each end (e.g., in Aphelochaeta), some bear muscularized burrowing expansions at both front and rear. (Pushing the long body backwards, like pushing a long train, is mechanically unsound.) (B) Cossurids (drawings from Fournier and Petersen, 1991, p. 72, with permission) often have a similar design. In shorter, stouter worms, burrowing expansions (wedges) can be even more prominent. (C) In some trichobranchids and some terebellids such as Artacama (drawings from Hartman, 1955, p. 59), the wedge for fracture can be immense and ornate. (D) Sternaspids (commonly known as sea owls, drawings from Fauchald, 1977, p. 113), consist of two bulbous, expandable portions that are flattened by the surrounding medium when burrowing. The anterior one is retractable. Rear-facing spines preclude backward burrowing, but the animal easily bends double within its fissure to reverse direction (Dorgan, unpublished). Besides expandable splitting wedges, these diverse fracturers share branchiae and tentacles (A–C) or spines (D) for freeing and collecting particles from the cracked matrix for ingestion.

THE PROCESSES

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Friction

everted pharynx

FIGURE 26.5 Characteristic rugosity of a sand-burrowing polychaete, the capitellid Notomastus magnus (Hartman, 1947, p. 465), with its papillated pharynx everted. We hypothesize and plan to test that the projections of scale comparable to the grain size are used to disrupt force arches and thereby facilitate burrowing and ingestion.

its body (as peristaltic pump) currently occupies. Flow through the pipe is used to liquefy the sediment, deploy the mop of feeding tentacles, supply oxygen and allow the animal to advance (Nowell et al., 1989). Whether in mud or sand, burrowing requires more work with increasing overburden. In mud in the field, Johnson and Boudreau (in preparation) have observed approximate doubling in KIc with increasing depth through the upper 10 cm. No measurements yet quantify the change in E over this same distance. Excavation of materials is one means to reduce this consequence of overburden but requires sediments that will neither creep nor fail (by cohesion will hold a steep angle of repose) or the construction of retaining (tube) walls (e.g., the lining of burrow segments through sand layers with mud by thalassinids). Differences in burrowing behavior in urchins at different depths in sand can be explained by increased overburden (Kanazawa, 1995). Echinocardium cordatum, which lives at 10 cm depth, lines the top of the burrow with mucus and moves sand grains posteriorly, depositing them directly behind the animal. Lovenia elongata burrows at a shallower depth (2–3 cm), and instead pushes grains to the side while the burrow collapses behind. Less mucus is present in traces left by Lovenia elongata, resulting in less lithification of traces. Aliquots of sediment may be removed from the matrix by either fracture or granular manipulation and carried to the surface (excavated) more or less intact as fragments of the matrix, entrained and emitted in water currents, or ingested and egested. Excavators are notable for sometimes reaching extreme burrowing depths; removing at least some of the forces of overburden apparently is a means of achieving these extremes.

How large a role friction plays in burrowing energetics is unclear. The only direct measures published to date were seminal in quantitative analysis of burrowing mechanics, but were made by literally putting a worm on a hook attached to a force transducer and measuring ‘tail-pulling force’ (Hunter and Elder, 1989). In a soft-bodied animal using peristalsis, it is not obvious that frictional shear of this kind needs to play any large role. While surrounding pressures of sediment overburden and elastic rebound are resisted by adjacent expansions of the body, coelomic fluids and integument within thinner sections may be able to move forward in successive waves without making strong, shearing contact with the medium. We have been using doublestrength gelatin in seawater as a sediment analog because it matches E and KIc of muds reasonably well (Johnson et al., 2002; Dorgan et al., 2005). Polychaetes do not appear to have difficulty moving into the cracks that they make in gelatin because their setae readily obtain frictional purchase. Further, our photoelastic stress analysis of burrowing in Nereis (Dorgan et al., 2005) revealed no large role of friction. We did visualize the small forces where setae and gelatin made contact, and the setae provided the little friction needed to move the body along into the opened crack. Crustaceans also likely generate their own friction with setae, which in burrowers are well designed to push the carapace in the opposing direction when the legs are moved (Nicolaisen and Kanneworf, 1969). In this case, we expect the stress exerted by the setae to be larger than for Nereis because this stress provides the driving force for the wedge. The often-observed hydrophobicity of benthic crustacean cuticles may help to prevent sediment from sticking on the body surface that opposes the moving setae and thus to reduce friction on that wedging surface. Most protobranch and tellinid bivalves, however, find gelatin lacking as a sediment mimic. They appear fully capable of making cracks but are entirely unable to pull the shell into them because the foot slips against the gelatin. The ‘sole’ exception that we have observed to date is the protobranch Yoldia, whose ability to splay its foot and press papillae on both sides of it against the crack wall allows it to pull the shell along. Acilla castrensis, another protobranch, has a similar foot, but we have not yet experimented with this species, and it is rarely found more than a body length below the primary sediment–water interface. The speed with which Yoldia moves is difficult to explain without benefit of burrow extension by crack propagation.

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Absence of sand or silt in clear gelatin thus presents a problem to most bivalves. Conversely, friction with sand and silt grains on the walls of cracks likely is a mechanism of short-distance, diffusive mixing of sediment grains. Considering grains as asperities, what else determines bulk friction of the organism with sediments as it moves through a crack? An elastic restoring force, likely proportional to the local Young’s modulus, plus any transmitted overburden, act on the short term to close the crack. If the net normal force on both valve surfaces is Fn and if k is a friction coefficient expressing the friction between the shell and crack walls, then the magnitude of the frictional force Ff resisting shell movement in the direction of burrowing is, to a first approximation, Ff = kFn, and the foot must obtain sufficient friction for the muscles to exert a tensile force greater than Ff in order to pull the shell along. Organic external coatings characteristic of protobranch and tellinid shells may help to reduce k. One wonders whether the animal through morphology and behavior might be able to unbalance the fore-aft symmetry of these forces to aid forward motion—much like one squeezes a watermelon seed to shoot it forward. Smooth shells with presumably low friction and particular shapes have often been associated with rapid burrowing in muds (e.g., Stanley, 1970). It is time to quantify the mechanisms. A little friction at the right time and in the right place and direction thus is a good thing in terms of allowing entry into a crack once it is made. It is not yet clear whether small or large numbers of particles are freed from the sedimentary matrix by crack propagation itself. If not, then friction with leading appendages during crack entry may also play a role in freeing particles from the matrix for subsequent ingestion. Sediment properties also change with distance from the sediment–water interface. In granular media, force arches deeper in the deposit support upper layers, making burrowing increasingly difficult with increasing depth in the sediments. Pressure on an object in a gel should also rise in proportion to the overlying thickness and excess density of gel. How well this pressure is transmitted to an animal in a crack in the gel is not clear. It is clear from first principles, however, that the greater the elastic restoring force or the greater the forces arising from the mass of overlying sediments, the greater will be the frictional resistance to motion. Feedback is also evident in an equilibrium profile of porosity controlled in part by burrowing; this feedback (especially near the sediment–water interface) reduces overburden by keeping sediment water content high (Mulsow et al., 1998). Subsurface tube building, as well as building and

shoring of a tunnel by excavators can be seen as means to reduce frictional costs of motion within the sediments. The question of friction leads naturally to the question of lubricants. Is mucus used to lubricate contacts with sediment? If so, is it applied widely or focused on particular locations and times of the burrowing cycle? One frequent observation made in coring is that worms extracted from sediments are remarkably cleaner of sediments than are one’s fingers in handling them. Perhaps lubricant secretions provide an explanation.

Ingestion, Transport through the Gut and Posture Frictional shear and (or) adhesive tensile stresses may operate via feeding appendages or a papillated pharynx for particle removal from the newly created surface, just as they do from the sediment–water interface (e.g., Guieb et al., 2004). Mechanics of selecting particles and getting material to the mouth clearly do depend on relative orientations of feeding appendages, the mouth and the gravity vector. Adhesive mechanisms of particle selection (Jumars et al., 1982) would appear to work poorly in selection among particles embedded in a gelatinous or mucous matrix and differently from a crack roof than from a crack floor unless the preferred particle types and sizes are easiest to pull out or stick best to the appendage, perhaps by hydrophobic means (Guieb et al., 2004). Burrowers do manage to accomplish particle selection with the aid of papillated pharynx eversion and retraction, e.g., in arenicolids and capitellids, and even with no obvious selective device at all, e.g., in sternaspids (Self and Jumars, 1998). Although there are kinematic descriptions of pharynx deployment and static descriptions of net selection achieved, there are no published quantitative, force-based, mechanical analyses of particle selection in subsurface deposit feeders. Through inclusion of abundant mineral grains, deposit-feeder digesta lie at the extreme of digesta density. Very little research has been done, however, on mechanisms and mechanical work of moving sediments through the gut. Taghon (1988) concluded, though, from a clever albeit indirect analysis of multiple unknowns through multiple equations, that the mechanical cost is relatively small even for arenicolids that ingest hundreds of times their own body weights of sediments per day and move them uphill. We reexamine the issue of digestive transport of sediments here not to imply that the direct

THE PROCESSES

mechanical costs are larger than previously thought, but to indicate that digestive styles differ with deposit-feeder posture and may provide some useful clues of past lifestyles of trace makers, which will be even more useful when quantitative constraints are identified. Gravity is the persistent (body) force to which we allude in our title. Even if mechanical costs are not large, in order to move digesta uphill, a mechanism is needed to feed in some postures (or in any posture with a long, coiled gut). Effects of posture relative to gravity on digestion have been documented extensively in ruminants and to some extent in other mammals (including humans) and birds (e.g., Place, 1992; Clauss, 2004; Hirota et al., 2004). The primary mechanism through which gravity has a documented effect in ruminants, other herbivores and seabirds is density separation. Although there is as yet little evidence that density separation plays a large role in most deposit feeders after ingestion, the physical and chemical functions of many and diverse digestive compartments in marine deposit feeders remain largely unknown (e.g., Penry and Jumars, 1990). One obvious case of density (and likely hydrophobicity) separation mechanisms is of Uca and other intertidal ‘bubbler’ crabs that use elution and ebullition to separate low-density particles (especially diatoms) for digestion. Although it depends on gravity and posture, this mechanism works only where animals have both air and water to bubble. Examination of characteristic postures and gut processing in deposit feeders that vary in lifestyles and relative gut lengths (to body length), however, does reveal some patterns. To understand them requires a very brief introduction to digestion in deposit feeders. They use a mixture of enzymes and surfactants, analogous to modern laundry detergents, to extract organic matter from sediments (Mayer et al., 2001). Such animals limit ingestion of associated seawater, but have various means to generate modest countercurrent (to the flow of particles) flows of water toward the absorptive midgut, protracting the time available for hydrolysis and absorption of the separated organics. In general, they feed at much higher rates and devote greater body volumes to digesta than do other feeding styles (Jumars, 1993). Mixing of digesta serves two functions. One is to bring and keep digestive enzymes and surfactants in contact with largely particulate foods. A second is to keep concentration profiles of dissolved digestive products steep near the gut wall at uptake sites to keep diffusion rates high and directed toward sites of product absorption. Effective mixing would appear to require movement of fluid through the granular

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digesta matrix or of particles through the fluid and thus to benefit from high permeability of digesta to pressure-driven flows, and thus from their loose packing and from large pressure differences that drive flows through digesta. Initially mixing a bolus of particles with hydrolytic enzymes and then coating that bolus with a membrane or mucus that is diffusively permeable to digestive enzymes is compatible with both functions, however. It sets up a situation where uptake of product at the gut wall always produces net outward radial diffusion of product from digesta and where flow or mixing between the coating and the gut lining can produce a very steep concentration gradient to speed that diffusion. It is not clear how early this innovation of a semi-permeable sleeve between digesta and gut wall was made in the evolution of benthic invertebrates. Mixing and transport of digesta are not accomplished in the manner that most people imagine. Peristalsis is the movement of wave-like contractions from anterior to posterior in the gut or its sections. Antiperistalsis is similar, but the contractions travel from back to front. Segmentation is the more random contraction of circular muscles. Unlike familiar peristaltic pumps in the laboratory, (anti)peristaltic contractions and segmentation in the gut do not typically close off the lumen. Depending on details of geometry, wave passage in a gut may be accompanied by little net transport (Yin and Fung, 1971), but mixing by such waves is typically effective over distances of about a gut diameter. Waves of (anti)peristalsis and episodes of segmentation thus serve primarily a mixing and not a transport function. Major transport events of solid digesta rearward from a gut compartment generally are accompanied by contraction of a sphincter in the anterior portion of that compartment, followed by contraction of longitudinal muscles in that gut section. Published observations on movement of digesta in deposit feeders are quite limited. Our largely unpublished observations are concentrated on two taxa, Pseudopolydora kempi japonica, a spionid polychaete, and Hobsonia florida, an ampharetid polychaete. Both are small enough to be reasonably transparent and will build their tubes against a glass wall convenient to observation. In spionids the gut is generally no longer than the animal, and in ampharetids it is typically not much longer, either. Hereafter, we term guts short when they are not much longer than the animal itself (a relative, non-dimensional length). Spionids appear to have a simple, gravity-aided digestive system. Particles are simply dropped from the ciliary transport stream into the foregut. At all but the highest ingestion rates, the foregut remains nearly empty. Material in the midgut is loosely packed,

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carries little overburden, and is mixed frequently by antiperistalsis. This mixing and accumulating overburden results in tighter packing toward the posterior midgut and hindgut, as well as net anterior motion of the fluid, which is displaced by settling and compaction. Defecation is accompanied by sphincter and then longitudinal muscle contraction. Hobsonia has a more complicated gut structure and is also optically less transparent. In its typical posture, the foregut and midgut are horizontal, and the hindgut is vertical with the anus downward. Midgut material is loosely packed, and the foregut and midgut are mixed more or less continuously by antiperistalsis. These observations make us appreciate how in an animal with a hydrostatic skeleton one set of muscular contractions potentially affects all others. Simultaneous contractions, coordinated among muscle groups, operate the heart (dorsal contractile vessel) and produce respiratory currents between the outer body wall and the inner tube wall as well as the gut mixing. Gravity again aids compaction of material in the animal’s hindgut, with defecation again employing a sphincter and longitudinal contraction. Polychaetes of the genus Capitella also have relatively short guts, but appear able to adopt a range of orientations and to be mobile while digesting. Immediately upon ingestion of a pharynx-load of particles, they mix digestive enzymes into prolate spheroidal pellets that become the units of backward transport and often are more or less evenly spaced along the gut. Again, the mechanics of their rearward transport are poorly known. Among the largest deposit feeders are epibenthic holothuroids. Their methods of processing gut contents bear some similarities to those of Capitella. Parastichopus californicus mixes particles only once, immediately after ingestion. It packages these batches of incoming sediment into mucus-wrapped, boudin-like structures, resembling a string of sausages (Penry, 1989), that are moved to produce a remarkably constant gut retention time that is likely set at the optimum for maximizing net absorption rate (Self et al., 1995). How these rows of beads (Capitella) or strings of sausages (Parastichopus) are moved rearward is unknown, but their periodic structure suggests that they might be relatively easily moved by peristaltic waves. The midgut of Parastichopus resembles an accordion, but the pleats show a slight bias toward pointing rearward. Contractions of this accordion could serve to mix the fluid between the gut plug and the uptake sites as well as to gently ratchet the sausages of sediment backward. Backward-pointing structures have been identified in several deposit feeders from diverse groups (Sampson, S. in manuscript), and

foregut spines in crustaceans are particularly obvious examples. Again a qualitative mechanism is suspected intuitively, but no explicit dynamic model with quantification of forces has been formulated. Contractions of a ratchet system of backward-pointing features of the gut lining on a periodic structure of boluses may be a basic mechanism for moving gut material when the gravity vector alone will not suffice. Capitellid and maldanid polychaetes are no longer considered to be closely related phylogenetically, but some maldanids (as well as some capitellids) feed head down and also contain serial, prolate pellets, suggesting convergence on a similar transport mechanism that is capable of moving material against the gravity vector. Interestingly, in no classic conveyor-belt species that move material against the gravity vector has the transport mechanism been described and analyzed. Doing so would seem a high priority in understanding these major disruptors of stratigraphy. It is not at all clear how animals with as little muscle as holothuroids in the genus Leptosynapta can move sand upward at such prodigious rates, but it is obvious from observing live specimens that the mechanics of the sand outside, the body wall and the sand inside all interact during the passage of waves of contraction (Powell, 1977). Moreover, it is important to distinguish mechanisms of more continuous upward motion from more obvious bouts of egestion. In Arenicola and Abarenicola, for example, a sphincter at the midgut–hindgut junction closes to permit longitudinal muscle contractions and rapid fecal ejections. These discontinuous ejections likely are adaptations that reduce risk of predation and do not reveal how material is transported up to this juncture. Among the deposit feeders, crustaceans, which in general have a relatively short gut, appear to have evolved relative freedom from particular orientations for digestion. This freedom is correlated with the use of a peritrophic membrane secreted at the foregut–midgut junction. It appears to provide both a kind of conveyor ‘tube’ for digesta, with diffusive (but not advective) permeability to digestive products, and a convenient space between the gut wall and the membrane for countercurrent flow of product-rich solutes toward absorptive sites. The mechanical means that move the tube with its contained sediments along the midgut, however, are not clearly known. Although questions of gravity and understanding of process point to upward- and downward-facing and omnidirectional animals with relatively short guts as worthwhile objects of study, most deposit-feeding taxa, as do humans, have guts considerably longer

DISCUSSION

than their bodies. Their guts thus must be coiled in some fashion and are usually held in a limited suite of postures relative to gravity. In animals with coiled guts (e.g., humans or the sternaspid of Fig. 26.4), no single orientation of the particle stream relative to gravity is possible. Because the ‘pipes’ in alimentary systems are flexible and often looped over one another, temporary bends and collapses in the pipe may serve as sphincters (Arun, 2004). Interaction of the transport process with gravity operates through mechanisms that remain to be clearly identified, but the fact of interaction has been verified experimentally; constipation is one of the unsung hazards of low-gravity space travel. A ratchet or passive valve system is suggested by the fact that exercise alleviates this problem, even in space (Arun, 2004). Comparable low-gravity experiments with deposit feeders have yet to be done.

DISCUSSION Material Properties The observation that animals extend burrows by propagating cracks raises many more questions about material properties than it answers. Why do diverse muds in terms of grain sizes seem to behave similarly and elastically? The answer is probably associated with mucopolymer secretions produced by sedimentary bacteria that populate interstices at remarkably high and uniform population densities of a billion per milliliter of pore water (Schmidt et al., 1998). Chain lengths of molecules and extent of cross linking both strongly influence mechanical behaviors of polymers but are unknown for the sedimentary composite. One of the things that these variables control is extent and rate of spontaneous annealing once a crack is made. Cracks follow paths of least resistance, but how long do previous cracks persist and present a preferred path for other cracks to enter? Bubbles appear to follow previously made bubble paths (Boudreau et al., 2005). Do animals passively or actively follow or avoid prior burrowers? Are recent crack paths exploited by predators? What methods can animals use to change a crack’s direction? To what extent do the mechanics of crack propagation change with depth in the sediments? Johnson and Boudreau (in preparation) have measured roughly a two-fold increase of KIc with depth over the top 10 cm of shallow-water sediments. Does this increase in fracture difficulty steer cracks back upward and ultimately control mixed-layer depth? How important is crack opening and propagation in solute exchange?

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Whereas we have growing confidence that a discoidal crack propagates in advance of many if not most burrowing animals in mud, we can offer only a little insight into how prevalent such features might be in the animal’s ‘wake.’ A critical issue determining true costs of burrowing as well as ichnological character and preservation potential is the timedependent strain response of sediment to stress. After the animal enters a crack, how long does it stay in one place, and how, and how much, do sediments deform around it? How much do they elastically rebound or creep back to refill the void when the animal does eventually move on? Very relevant to the issue of bioturbation is the question of whether any part of this process, including potential viscoelastic fracture (Anderson, 1995), results in rearrangement of sediment grains. The longer the animal stays in place and the larger it is, the more likely is creep to form a body-shaped opening in the sediments, one that fails to rebound back fully after the animal passes. Shull and Yasuda (2001) studied the extremely large (30 mg), burrowing cirratulid Cirriformia grandis in Boston Harbor. They (their Fig. 26.4, p. 464) presented a CT scan of a core that was extensively burrowed by this species. Burrows that remained open after the animal had passed were evident as dark, seemingly cylindrical channels roughly 0.5 cm in diameter, with a whiterthan-background halo of compacted mud forming a surrounding cylinder of 3 cm (outer) diameter. So some burrowers are large enough and slow enough to more or less cylindrically deform sediments inelastically in a manner relevant to trace-fossil production. Cirriformia is primarily a shallow-water genus noted for its physiological adaptations to low oxygen and is not one of the bipalpate genera of much smaller body sizes that dominate the deep sea. Because of the usual scaling of metabolic rate with animal size and its lowoxygen habitat, sluggish burrowing is expected and observed in Cirriformia. Do fast and small burrowers by contrast leave little trace? To what extent is trace reduction in smaller animals a function simply of size versus how long the burrower stays in one place? Whereas amphipods and burrowing bivalves have shapes that obviously utilize discoidal cracks, morphological adaptations of soft-bodied burrowers are more subtle. Cylindrical symmetry has appeared a more logical shape for burrowers than bilateral symmetry, but appearances can be deceiving, especially when based on animals removed from their native media. Scalibregma inflatum, a scalibregmid polychaete, is named for its balloon-like appearance when removed from sediments, a prolate spheroidal balloon followed by a cylindrical tail. In life position

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while actively burrowing, however, it is dorsoventrally compressed by the combination of discoidal crack shape and elastic rebound of the medium (Dorgan and Jumars, unpublished observations in seawater-gelatin). Like its confamilial species Polyphysia crassa (Hunter and Elder, 1989) it also shows a characteristic side-to-side wiggle of its prostomium; we reinterpret that motion to be a means of both enlarging the crack and scraping material for ingestion from the opened surfaces. If burrows opened radially, one would expect radial symmetry of entry devices. Instead, scalibregmids like many other taxa show bilateral symmetry anteriorly, grading to more radial symmetry posteriorly. Notable are positions of setae on anterior segments of most polychaete burrowers. Noto- and neurosetae are directed laterally, but slightly dorsal and ventral, respectively, where maximal frictional contact with a discoidal fracture would be achieved. The fact that in many burrowing polychaetes body cross sections and arrangements of friction-producing setae become more radial posteriorly in part reflects the reduction of the internal skeletal members (acicula) that support the parapodia. Without such internal support of a different geometry or an exoskeleton, maintenance of internal hydrostatic pressure plus external sediment creep will produce a cylindrical opening in sediments (and hence an advantage to more radial symmetry) over time. Very suggestively, Scalibregma under the previously described experiment of benign neglect in a sea table does maintain a cylindrical respiratory shaft up to the surface. This hypothesis further suggests that higher burrowing speeds will correlate with increasingly bilateral symmetry—and slower speeds with radial. It needs testing and may well have exceptions. Deepburrowing Aphrodite (the sea mouse), for example, may have more in common with urchins than with other polychaetes in terms of burrowing mechanisms. These new insights and hypotheses about burrowing mechanics and morphologies almost surely have implications for the microscale in bioturbation formulations. What is the characteristic step length (sensu Wheatcroft et al., 1989) of sediments ingested by crack-propagating, deposit-feeding burrowers? The lack of an answer emphasizes current ignorance about mechanisms by which particles are freed from the surrounding matrix for ingestion and about gut passage times in situ relative to burrowing times. It is possible that ingestion and egestion coupled with burrowing speed do typically result in step lengths much smaller than mixed-layer depths (Ls Lb), lending a diffusive character to sediment mixing.

An intriguing observation is that seemingly diffusive mixing occurs from macrofaunal burrowing in the absence of ingestion (Levin et al., 2003). This process occurs in very-low oxygen sediments, which are known for their ‘soupiness’ but remains to be quantitatively characterized rheologically. We suspect that sediments characterized as ‘soupy’ may be prime candidates for viscoelastic fracture of sediments, causing local relative motion of grains. Alternatively or in addition, friction used for moving in the burrow may displace grains. This new mechanical analysis of fracture, i.e., sediment failure, suggests new kinds of traces to look for, i.e., discoidal cracks. It also suggests revisiting specific means by which traces are destroyed. In two dimensions, where trace crossing is assured, and formation of a new trace destroys an old one, a maximum in short-term trace preservation is evident at intermediate producer abundance (Wheatcroft et al., 1989). Path crossing in a threedimensional random walk is not assured, and trace preservation may be reinforced if new burrower paths either follow or avoid old ones. Cracks may be channeled into previous cracks by following a path of least resistance. Deposit feeders seeking new resources, however, may use cues to avoid recently mined paths. An intriguing possibility suggested by Fig. 4 of Shull and Yasuda (2001) is that burrow-wall compaction arising from creep may sufficiently compress sediments to turn away new cracks by increasing KIc. Could staying long enough for creep to occur and produce this compaction be a passively operating mechanism to avoid feeding in the same place and steer away crack-propagating predators as well? Crack production may also be a way to make space for cached materials (Jumars et al., 1990). Whether or not these conjectures have merit, forces at a propagating crack tip are certainly among the largest that a buried trace would encounter. Crop-like grinding within specialized gut compartments (Penry and Jumars, 1990) is the other obvious means by which animals exert stronger mechanical forces than can geophysical fluid shears on sediments and are certainly important in destroying sediment features at ichnofabric scales small enough for ingestion. Friction with the burrow wall or tensile stress from an adhesive-coated feeding appendage by contrast would appear less severe, but a quantitative analysis of forces is lacking for any of these trace destruction mechanisms. Finally, this new look at material properties of sediments and where and how strong forces can be exerted in deposit feeding leads us to ask some questions about the beginnings of deposit feeding and

DISCUSSION

vertical bioturbation (Crimes and Droser, 1992). Early detritivores should have had a fairly rich diet. By definition the first ones had little interspecific competition, and if they fed through a mechanism similar to the one inferred for trilobites—by kicking up detritus and passing it forward endite to endite—they would have enriched the food further by losing the highdensity fractions. For two reasons, rich diets do not require large guts. First, a rich food can yield high rates of hydrolysis and absorption from a small volume. Second, by contrast with digesta dominated by indigestible materials, the volume of rich digesta decreases significantly during digestion. A short gut full of rich, low-density digesta held horizontally needs only a modest ratchet or valve system to move food along. Holding the body parallel to the gravity vector requires the least digestive innovation when the mouth is upward, and we speculate that Skolithos was an early innovator of this posture. A conveyorbelt posture with head downward requires more innovation for two reasons. Obviously, digestive processing must counter gravity. Less obviously, volumetric throughput rate must increase because the food on average is poorer; deposit feeding is the only option. Moreover, an individual that is stationary in this posture is fundamentally limited in selectivity (if areally averaged ingestion exceeds local deposition rate); otherwise, in the absence of sediment transport it will soon be surrounded primarily with material that it has rejected. Motility in a subsurface feeding mode allows greater selection. One caveat is that some modern worms that spend most of their time in a head-down mode (maldanids) have found it advantageous to enhance ingesta quality by pulling fresh deposits from the sediment–water interface for ingestion from the bottom of the tube or burrow (Levin et al., 1997); how early this innovation developed or how important it might be in producing characteristic ichnofossils is not clear. At first it would appear that horizontal burrowers might encounter little more difficulty than horizontal, epifaunal detritivores, but again this lifestyle requires adaptations to the processing of poorer foods. Operating a gut in a subsurface burrower presents additional challenges. For epifauna, external pressure stays more or less constant at the ambient hydrostatic value, and moving material in the gut for mixing or advection requires coordination only with the coelom surrounding the gut. For an animal with a hydrostatic skeleton, since internal pressures are quickly transmitted, operating a gut presents greater coordination problems when time-dependent forces

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are being applied to various body surfaces by the sedimentary medium in burrowing. Moreover, burrowing in mud itself requires innovations such as some sort of wedge. The bivalve shell or amphipod exoskeleton is a wonderful asset because it isolates the contents from these time-varying inward pressure forces and does so without muscle use. Many motile subsurface worms seem to have solved the dual problems of needing a large gut volume (relative to body volume) and coordinating gut movement with coelomic and burrowing pressures by being long, skinny and septate—through compartmentalization (e.g., the cirratulid and cossurid of Fig. 26.4). A further caveat is needed here. That an animal spends most of its time burrowing below the surface does not preclude its gaining an important fraction of its nutrition from surficial sediments. Cirratulids, scalibregmids and cossurids have been demonstrated by field experiments to have such access to fresh, isotopically labeled material (Blair et al., 1996; Fornes et al., 2001). How they get it, i.e., whether by reaching onto the sediment surface or by entraining surficial or near-surface material into upward- or downwardpropagating cracks, remains to be determined. Food quality on average decreases with depth in sediments, and animals in general selectively ingest higherquality foods. With animals that have both vertical and horizontal components to their burrowing, one can therefore expect the net transport of ingested material to be downward (e.g., Shull and Yasuda, 2001). Action on such a gradient in food quality makes problematic the dichotomous classification of animals as surface versus subsurface deposit feeders; animals will eat where and when risks are low and gains are high enough (e.g., Nichols et al., 1989). Various of these considerations lead us to speculate that some innovations needed for burrowing may have been easier in sand than in mud. Sand is no longer considered a desert by benthic oceanographers but instead a place of flow-intensified biogeochemical transformation and biological activity (e.g., Huettel and Rusch, 2000). Before the first burrowing deposit feeders, it was considerably richer in food content. Sand is easier than smaller particles to separate from organic flocs prior to ingestion. Sand is also easier physically and chemically to clear of its attached organic coatings after ingestion than is mud because pressure-driven flows in the gut will be driven through its interstices. Moreover, burrowing in sand does not require the innovation of a wedge and requires little force when done at a shallow angle near the primary sediment–water interface.

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CONCLUSIONS Whether this particular speculation about early burrowers is insight or folly, quantitative understanding of sedimentary biomechanics, i.e., of animals moving through sediments and sediments moving through animals, will enrich ichnology. New understanding of the behavior of muds and its quantification in terms of Young’s modulus and a critical stress intensity factor already provides insights into morphologies that drive cracks and provides both motivation and search image for new classes of traces and new modes of trace destruction. This success drives efforts to extend the approach of quantifying material properties of the medium in concert with forces produced by animals to more complex muds and to granular materials such as clean sands, as well as to the more complex process of moving liquid–solid mixtures through depositfeeder guts. One conjecture inspired by limited observation is that, in mud, persistent traces in the forms of crack-resisting pellets and burrow walls will be those that have been exposed to forces long and strong enough to elicit significant creep and compaction. That conjecture requires quantification to understand in detail how animal size and lifestyle combine to create bias toward or against high preservation potential, but it already leads to the prediction that fast burrowers and small burrowers yield few burrow traces. All these efforts at understanding trace production and degradation depend upon antecedent or parallel advances in the science of heterogeneous materials, which are being greatly accelerated by the drive toward novel nanotechnologies: ‘. . . in operational and practical fact, the medium is the message’ (McLuhan, 1964).

References Anderson, T.L. (1995). Fracture Mechanics: Fundamentals and Applications, 2nd edition. CRC Press, Boca Raton, FL, 688 pp. Arun, C.P. (2004). The importance of being asymmetric: The physiology of digesta propulsion on Earth and in space. Ann. N.Y. Acad. Sci., 1027, 74–84. Blair, N.E., Levin, L.A., DeMaster, D.J. and Plaia, G. (1996). The short-term fate of fresh algal carbon in continental slope sediments. Limnol. Oceanogr., 41, 1208–1219. Boudreau, B.P. (1998). Mean mixed depth of sediments: The wherefore and the why. Limnol. Oceanogr., 43, 524–526. Boudreau, B.P., Choi, J. and François-Carcaillet, F. (2001). Diffusion in a lattice-automaton model of biotorbation by small deposit feeders. J. Mar. Res., 59, 749–768.

Boudreau, B.P., Croudace, I., Algar, C., Reed, A., Johnson, B.D., Dorgan, K.M., Jumars, P.A., Gardiner, B.S. and Furukawa, Y. (2005). Bubble growth and rise in sediments. Geol., 33, 517–520. Brown, A.C. and Trueman, E.R. (1991). Burrowing of sandy beach molluscs in relation to penetrability of the substratum. J. Molluscan Stud, 57, 134–136. Choi, J., François-Carcaillet, F. and Boudreau, B.P. (2002). Latticeautomaton bioturbation simulator (LABS): Implementation for small deposit feeders. Comput. Geosci., 28, 213–222. Clauss, M. (2004). The potential interplay of posture, digestive anatomy, density of ingesta and gravity in mammalian herbivores: Why sloths do not rest upside down. Mammal Rev., 34, 241–245. Crimes, T.P. and Droser, M.L. (1992). Trace fossils and bioturbation: The other fossil record. Ann. Rev. Ecol. Syst., 23, 339–360. Dorgan, K.M., Jumars, P.A., Johnson, B.D., Boudreau, B.P. and Landis, E. (2005). Burrow extension by crack propagation. Nature, 433, 475. Dorgan, K.M., Jumars, P.A., Johnson, B.D. and Boudreau, B.P. (2006). Macrofaunal burrowing: The medium is the message. Oceanogr. Mar. Biol., Ann. Rev., 44, 85–121. Ellington, C.P. and Pedley, T.J. (Eds.) (1995). Biological Fluid Dynamics, Society for Experimental Biology, London. Fauchald, K. (1977). The polychaete worms. Definitions and keys to the orders, families and genera. Natural History Museum of Los Angeles County, Science Series, 28, 1–188. Fauchald, K. and Jumars, P.A. (1979). The diet of worms: An analysis of polychaete feeding guilds. Oceanogr. Mar. Biol., Ann. Rev., 17, 193–284. Fornes, W.L., DeMaster, D.J. and Smith, C.R. (2001). A particle introduction experiment in Santa Catalina Basin sediments: Testing the age-dependent mixing hypothesis. J. Mar. Res., 59, 97–112. Fournier, J.A. and Petersen, M.E. (1991). Cossura longocirrata: Redescription and distribution, with notes on reproductive biology and a comparison of described species of Cossura (Polychaeta: Cossuridae). Ophelia Suppl., 5, 63–80. Geng, J., Howell, D., Longhi, E., Behringer, R.P., Reydellet, G., Vannel, L., Cle´ment, E. and Luding, S. (2001). Footprints in sand: The response of a granular material to local perturbations. Phys. Rev. Lett., 87,035506, 4 pp. [DOI: 10.1103/PhysRevLett.87.035506]. Guieb, R.A., Jumars, P.A. and Self, R.F.L. (2004). Adhesive-based selection by a tentacle-feeding polychaete for particle size, shape and bacterial coating in silt and sand. J. Mar. Res., 62, 261–282. Guinasso, N. and Scink, D. (1975). Quantitative estimates of biological mixing rates in abyssal sediments. J. Geophys. Res., 80, 3032–3043. Hartman, O. (1947). Polychaetous annelids. Part VII. Capitellidae. Allan Hancock Pacific Expeditions, 10, 391–481. Hartman, O. (1955). Endemism in the North Pacific Ocean, with emphasis on the distribution of marine annelids, and descriptions of new or little known species. Essays in the Natural Sciences in Honor of Captain Allan Hancock, Univ. of Southern California Press, Los Angeles, pp. 39–60. Hartman, O. (1958). Systematic account of some marine invertebrate animals from the deep basins off southern California. Allan Hancock Pacific Expeditions, 22, 69–215. Hirota, N., Yoshiaki, S. and Hiromi, T. (2004). Effects of postprandial posture on orocecal transit time and digestion of milk lactose in humans. J. Physiol. Anthropol. Appl. Human Sci., 23, 75–80.

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27 Complex Trace Fossils William Miller, III

SUMMARY : Complex trace fossils include large, elaborate structures that appear to indicate long occupation and control of environmental factors; structures referred to as compound ichnotaxa, which represent different kinds of functions or behaviors within the same complex system; and certain forms of composite trace fossils that record intimate, recurrent ecologic associations of two or more trace-producing organisms. Their functional interpretation can be approached by teasing out evidence of construction, operation and maintenance, and portraying the results in a stylized paleoethologic blueprint showing behavioral subroutines arranged in spatiotemporal order. Complex trace fossils do not represent a fleeting, superficial interaction with the surrounding environment, but instead appear to record sophisticated ecologic roles and interactions, ability of the producers to actively construct a special habitat for themselves, and in some cases special behavior involved in controlling food supplies or other essential life functions. From this point of view, some of these intricate structures could be considered as phenotypic extensions or physiologic projections of the trace producers—in other words, parts of the bodies of the organisms that built and utilized them.

shapes: the former is a relatively small, more or less vertical, typically unlined burrow; and the latter is often a relatively large, ribbed, spiral structure. But they are also different in terms of complexity. Skolithos is a simple vertical tube: there isn’t much more to be said about its morphology; an adequate description of one of the large, helicoidal versions of Zoophycos, however, would require a fairly long, elaborate paragraph. In other words, some trace fossils are vastly more complex structures than are others, and this produces some challenging problems when it comes to applying ichnotaxonomy and proposing plausible ethologic interpretations. In this chapter, I will summarize the characteristics of complex trace fossils, and explore some of the problems involved in their classification and interpretation. Because ichnologists are just beginning to own up to the fact that complex trace fossils are different—in terms of biologic properties and implications—and because different specialists are bound to approach this issue in different ways, the following should be seen as an introduction based largely on my own perspective (Miller, 1996a,b, 1998, 2001, 2002, 2003a). Alternative approaches can be sampled in the special volume of Palaeogeography, Palaeoclimatology, Palaeoecology, ‘New Interpretations of Complex Trace Fossils,’ which was devoted entirely to description and interpretation of elaborate biogenic structures of all kinds (Miller, 2003b). To begin this discussion, I will define complex trace fossils as organism-produced artefacts that reflect underlying biologic complexity of some sort. This would cover large, intricate structures that appear to have been occupied for long intervals in many cases, and to involve habitat modification and possible control of resources by the producer; compound

INTRODUCTION: WHAT ARE COMPLEX TRACE FOSSILS? Even a beginning student, inexperienced in the special traditions and concepts of ichnology, would notice that the biogenic structures known as Skolithos and Zoophycos are strikingly different—and for more than one reason. They are clearly different in terms of


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structures featuring different morphologic subunits in different parts of the same structure, which appear to record varied functions or behaviors within the same system; and special cases of composite trace fossils reflecting a more or less contemporaneous, intimate and recurrent ecologic association of two or more trace-producing organisms. It should be noted that relatively simple trace fossils might not reflect the biologic complexity of trace producers: Skolithos burrows are produced by different kinds of organisms involved in different kinds of behavior, some of it demonstrably complex (Miller, M. personal communication). The structure in this case, however, does not record that complex behavior. I will only consider structures that actually reflect complex behavior, even if intermittent, of trace producers.

THE CONCEPT OF COMPLEXITY APPLIED TO BIOGENIC STRUCTURES There are several varieties of complexity associated with biologic processes and patterns. I will briefly review a list of these versions or concepts as they apply to trace fossils. At the outset, it is important to realize that being complicated and being complex are not always the same things. A very long, messy scribble on a piece of paper is certainly complicated, but a line from Virgil’s Aeneid is complex, even though it could be shorter and contain less variation. We perceive complexity when a structure has a stylized or repeated order, when patterns are contained within other patterns, or when an elaborate pattern denotes a message or reveals an underlying complex causation or control. In many but not all cases, complex programs write complex patterns. As an analogy, consider the list below with respect to the construction and utilization of an office building (Fig. 27.1).

Different Views of Complexity Applied to Trace Fossils Compositional complexity—Trace fossils could be complex owing mainly to the fact they contain many different structural elements. As in the introduction to this chapter, it is clear from a comparison of Zoophycos with Skolithos that the former contains many more parts that could be described or represented by symbols in some way. An inventory of the latter would be a

FIGURE 27.1 Office building under construction in downtown Denver, Colorado, in 1996. The construction, operation and maintenance of this human-produced structure can be compared to the structural and functional properties of complex trace fossils.

relatively short list or statement. (In the office building analogy, compositional complexity would be reflected in the long list of construction materials and fixtures used to erect and use the structure, compared to a simple makeshift shelter.) Organizational complexity—In some kinds of biogenic structures, the integration of parts, their spatial arrangement, and the number of repeated elements can be very regular and intricate. The structures referred to as graphoglyptids (e.g., Paleodictyon, Cosmorhaphe, Desmograpton) demonstrate this kind of complexity. Description of such structures would have to include characterizations of connections and repeated subunits.

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27. COMPLEX TRACE FOSSILS

(In the building analogy, this would be like the plans specifying how all the constructional elements fit together, and how they are repeated through the structure.) Developmental complexity—The construction, expansion, and modification of biogenic structures could involve a simple series of steps or a complex developmental sequence involving a main routine and many embedded subroutines. Complex trace fossils revealing an intricate developmental program are probably records of long occupation involving organism growth or expansion of activity, and the attendant changes in adaptive behavior through time. Early stages would be relatively simple structures; later stages (‘mature’ patterns) would be larger and more complex. Examples would be the large, intricate burrow systems produced by mud shrimp described by Ziebis et al. (1996) and the nests produced by social insects described by Hasiotis (2003). (In the analogy, this would be like combining the structural blueprints with a timeline for erecting the building.) Operational complexity—The behavioral programs needed to utilize certain kinds of biogenic structures for extended periods of time are complex compared to those for structures that represent a short-lived interaction of organism with environment. In other words (Miller, 2003a, p. 5), for certain kinds of complex trace fossils, ‘The algorithmic text describing [operation] would be significantly richer than the algorithm describing a simple animal artefact, like a footprint or escape structure.’ Models or flowcharts of intricate structures that were occupied for long intervals and served multiple functions would be complex in their own right and contain many symbols and pathways representing multiple processes. (This would be like an owner’s manual for using all of the building’s facilities.) Hierarchical complexity—Some trace fossils are best represented with models that feature modular organization, the various parts fitting inside other parts. This is like structural complexity except the organization consists of a system of nested, dynamic elements, processes, or behavioral routines. In this sense, the overall structure is the result of similarly scaled parts or subroutines interacting with each other or in sequence, and simultaneously deriving some of their characteristics (potentials, constraints) from internal working parts and from the enclosing system. (See Salthe (1993) for a comparison of this type of dynamic ‘scalar’ hierarchy with the kind

of complexity associated with development. In the analogy, functional parts of the office building can be viewed as consisting of smaller components, and at the same time making up larger elements, interacting in complex ways to produce the overall functional superstructure.) Complexity involving anatomic extensions or physiologic projections—Complexity can extend beyond the boundaries of trace-producing organisms and the structures they build and utilize. Some organisms may produce complex structures that are unique to that particular species, structures that the organisms must use in day-to-day survival and to ensure production of successful offspring (for examples see Dawkins, 1983; Butler, 1995; Turner, 2000). In such cases, it is difficult to draw the line, in terms of phenotypic traits, between the structure and the producer. Organisms may use intricate biogenic structures to ‘increase their physiologic reach’ in order to secure or maintain resources (Turner, 2000, 2003). (In terms of the office building, it is not farfetched to claim that construction and use of very elaborate shelters is one of the defining characteristics of Homo sapiens. In hostile locations or during inclement conditions, such structures permit our species to live and work in environments not otherwise available to humans.)

‘Incidental’ vs. ‘Deliberate’ Biogenic Structures Another way to visualize the difference between simple and very elaborate trace fossils is to draw the distinction between structures that record a fleeting and/or simple interaction of an organism with the surrounding environment, and complex structures that reflect habitat engineering, active control of resources, and possibly long intervals of occupation. I have referred to the former type of structure as incidental and the latter as deliberate (Miller, 1998, 2002, 2003a; Miller and Vokes, 1998). The distinction is easy to see in two very different kinds of insect-produced structures: a track recording movement of a termite over a muddy surface would be incidental; the large, elaborate nest from which the same individual emerged would obviously be a deliberate structure using my criteria (Table 27.1). The purpose in making the distinction was to suggest that deliberate structures deserve special attention as complex records of organism ecology, behavior, and evolution (Miller, 1998, 2003a).

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CLASSIFICATION

TABLE 27.1 The Differences between ‘Deliberate’ and ‘Incidental’ Trace Fossils (from Miller, 2003, table 1)

Characteristics

Examples

Significance

Deliberate Structures

Incidental Structures

Complex structure Multiple functions

Simple structure One main function

Rich in behavioral tokens

Record of simple behavior

Long occupation?

Fleeting interaction

Too complex for Seilacher’s classification

Fits one category in Seilacher’s scheme

Zoophycos

Skolithos

Graphoglyptids

Planolites

Compound ichnotaxa

Escape structures

Termite nests

Footprints

Failure of traditional methods and concepts Habitat re-engineering and control of food supplies

Snapshot of simple behavior or interaction No habitat, disturbance or resource controls

Extended phenotypes, projected physiologies (= characters

Not vital extensions of the organism’s body

of the trace producer, not independent structures)

CLASSIFICATION Most of what ichnologists do involves the description and naming of newly discovered trace fossils, redescriptions and ichnotaxonomic revisions, documentation of assemblages of trace fossils, and finding useful applications to sedimentary geology. For this reason, most ichnologists will be more concerned with potential taxonomic problems associated with complex trace fossils than with more purely biologic aspects. Categories of complex biogenic structures include the large, elaborate ichnogenera like Zoophycos, structures that consist of ‘more than one ichnogenus’ known as compound ichnotaxa, and superimposed or interpenetrating structures representing close ecologic association referred to as contemporaneous composites. Examples were illustrated in Miller (2003a, fig. 1). In the case of large, intricate structures, ichnogeneric names are applied based upon morphology, which is the generally accepted method of delineating categories and applying formal names to trace fossils of all kinds (see Ekdale et al., 1984; Pickerill, 1994; Bromley, 1996). ‘Morphology’ (really meaning inventory of parts, form, and size of organism-produced ethologic structures) is the fundamental criterion. But even with a well-known and distinctive example like Zoophycos, there are problems with nomenclature. This particular ichnogeneric name is applied to a variety of structures that superficially resemble each other, that were produced at different times by different kinds of animals in different kinds of marine environments, and probably reflect many ways of making a living at the seafloor. A careful

re-evaluation of morphologic features probably would justify delineation of several groups having ichnogeneric status within the ‘Zoophycos group’ (Uchman, 1995). I will leave it to others in this book to approach the practical problems of taxonomic overgeneralization and entrenched names (see the chapters by Bertling and Olivero, and references therein). From a biologic point of view, such structures can be seen as extensions or projections of the phenotypes of trace producers (Fig. 27.2), and in a very plausible sense not strictly independent structures (Miller, 2002). If organisms produce distinctive ‘tailor-made’ biogenic structures, on which their survival and fitness depend (even if they do so occasionally or under certain circumstances or with special environmental cues), the structures begin to seem more like body fossils than trace fossils. It is nonetheless useful to apply ichnotaxonomic labels, unless perhaps an exact match of producer and unique, indispensable biogenic (=ethologic) structure can be established. Pickerill (1994, p. 23) made the important distinction between compound and composite specimens. Compounds are typically specimens that ‘. . . comprise intergradational forms in which one ichnotaxon passes gradually or directly into another . . . in most situations probably reflecting different behavioral activity of the same producing organism.’ Composites, by comparison, result from interpenetrations, superpositions, and spatially intimate recurrent associations of different producing organisms. With compound specimens, Pickerill and Narbonne (1995) recommended applying names that reflect the major components, in order of predominance in the structure. Thus, I described complex Paleocene trace fossils

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structure, or using abandoned structures as domiciles), or an example of small-scale facilitation in the course of ecosystem succession.

INTERPRETATION FIGURE 27.2 Projection of the phenotype of organisms that produce complex structures such as Zoophycos. Each band represents a set of functions and adaptive structures at increasing distances from the genome: (a) realm of genes and chromosomes; (b) cellular processes and patterns; (c) cellular integration and tissue function; (d) integration of tissues into organs and organ systems; (e) whole-body organization and function; and (f) the outer reaches of the phenotype, including construction, operation and maintenance of complex, indispensable structures, such as intricate burrow systems, webs, and nests. A set of stretched, nested ellipses is used in the diagram, rather than nested circles, to emphasize structuring of the phenotype through reciprocal interaction with the environment, which includes other organisms. Long axis of the ellipses represents coordinated adaptation of the varied functions and structures of the trace-producing organism; the periphery—the complex structure inhabited and utilized by the organism—is indicated with a star. (Reproduced from Miller, 2003a, fig. 3.)

from pelagic limestone deposits of Italy, consisting mostly of a ‘core’ region of interconnecting, horizontal tunnels and having digit-like outer regions, as Thalassinoides-Phycodes burrow systems (Miller, 2001). A potential problem arises when attempting to label an extensive structure featuring many—not just a few—different subunits, which would be accorded many different names if exposed or preserved in isolation. And again, the biologic perspective needs to be considered: should such complex structures, representing adaptive extensions of the producer’s anatomy or physiology, be given a long string of ichnotaxonomic labels or regarded as body fossils? Contemporaneous composites, although it may be practically difficult to delineate the superimposed or interpenetrating ichnotaxa, are actually simpler as far as names are concerned. Each distinctive trace fossil only requires its own ichnogeneric or ichnospecific designation, once the different structures have been delineated. The biologic significance of more or less contemporaneous, recurrent spatial associations of biogenic structures, however, is much more important. Such patterns could record possibly obligate and contemporaneous ecologic interactions (predator–prey or parasite–host relationships, competitors, mutualistic partnerships), a penecontemporaneous association (scavenging or recycling organic material from a recently abandoned

The standard approach to interpretation of complex trace fossils has been to affix one of the paleoethologic category names of Seilacher (1953; expanded versions can be found in Ekdale et al. (1984) and Bromley (1996)). For example, the large, spiral versions of Zoophycos have been referred to traditionally as ‘fodinichnia,’ meaning endobenthic deposit-feeding structures. If complex structures record multiple functions or behaviors, especially ones not having official ethologic category names, this approach is bound to fail; and continuing to propose new categories (e.g., Hasiotis, 2003) may not help much. It is also clear to many ichnologists that the ethologic categories proposed in the 1950s were useful as a starting place, but that a half-century of behavioral ecologic observations has revealed that many kinds of trace-producing animal are involved in different kinds of behavior at different times. More significantly, the details of the natural history of most organisms—including many modern trace producers—are simply unknown, so that a strong element of dogma seems to be involved in the continued application of Seilacher’s categories. A more analytic approach involves documentation of complex structures in exacting detail and then identifying a modern trace producer capable of constructing at least some of the same features (a remarkable example has been illustrated by Bromley et al., 2003). Most studies that push beyond naming and describing specimens, and the documentation of distribution patterns, typically conclude with a static reconstruction, or an ‘action cartoon’ showing the producing organism building or utilizing the structure (e.g., Miller and Aalto, 1998, fig. 6). A standardized, comparative approach to interpretation has never been adopted.

Fabrication Analysis of Complex Trace Fossils As a way to approach the functional interpretation of complex trace fossils, I proposed a method in which components recording various activities of the producing organism are teased out and considered in the appropriate spatiotemporal order (Miller and Aalto, 1998; Miller and Vokes, 1998; Miller, 2003a). The results could be displayed in the form of

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CONCLUSIONS

a paleoethologic blueprint: a stylized diagram showing the embedded records of behavioral adaptations and interactions (behavioral tokens) preserved in the overall structure. A blueprint of this kind would contain information about the following activities, recognizing that some of them ordinarily overlap in terms of function and developmental order: Construction—The activities involved in establishment of the system fall in this category. This includes excavation, importing/exporting material, and positioning and fabrication of the various elements within the structure. In burrow systems, initial construction encompasses excavating tunnels and galleries, organizing runways and outlets, establishing the primary orientation and branching order of tunnels, and the earliest augmentation of special features including burrow linings and fillings. Operation—Activities involved in the moment-tomoment utilization of a complex structure belong to this category. Subroutines would include importing/exporting material, gradual elaboration of the structure to accommodate expanded utilization or growth of the producer(s), recycling or restocking contents, irrigation/ventilation and possible gardening activity, and in some cases brooding of young and communication functions. Maintenance—Repairs, renovations, and major expansions not part of the normal round of system operation would be included here. Damage control routines, repairs that sustain or reinitiate irrigation/ventilation, replacement of destroyed structural elements following minor disturbances, replenishment of food stores following an interval of dearth or a plundering event, seasonal re-establishment of brood chambers, and catching up on disposal of feces or spoil material are all subroutines of system maintenance. This method would seem to be an improvement over action cartoons. It forces the observer to recognize and compile an inventory of all behavioral tokens, to arrange them in the correct temporal and spatial order, and facilitates a point-for-point comparison with other complex structures, such as possible modern counterparts. Symbols for tokens, pathways, and routines could be standardized, and ichnologists with a flare for computer modeling might see the potential here for digital inventories, formalized systems analysis, and morphometric comparisons.

Additional Considerations Catastrophic encounter with another organism (including other trace producers), physical erosion, or changes in properties of the substrate could destroy or alter a structure, initiating abandonment or other special behavioral responses (Miller and Curran, 2001). Environmental stress (depressed O2 tension, dehydration, elevated temperature) and diminution of trophic supplies could also release special responses, not within the normal scope of the producing organism’s behavioral or physiologic responses (e.g., Miller and D’Alberto, 2001). If the structure is eliminated or rendered uninhabitable, however, the general fabrication routine is reinitiated by survivors or fresh recruits that begin construction of new structures based on the same complex behavioral program. The specific kinds of routines in these three categories obviously would be different for different kinds of structures, such as complex deep-marine burrow systems like Paleodictyon as opposed to elaborate terrestrial structures like termite nests. Nonetheless, the same kind of method could be used to illustrate the interrelated activities required to produce, use, and repair a complex system. An application of this method to Phymatoderma from the marine Pliocene of Ecuador is shown in Fig. 27.3. (For description and interpretation of this trace fossil, see Miller and Aalto, 1998; Miller and Vokes, 1998.) This is one possible approach to the study of complex trace fossils. Any standardized method that produces an inventory of features denoting behavioral or physiologic functions, that portrays the details of the dynamic architecture as it develops through time, and reveals properties of the behavioral ecology of producing organisms—in a way that would facilitate comparison with other structures—would be a step in the right direction.

CONCLUSIONS Complex trace fossils are not merely interesting taxonomic puzzles or preservational oddities, but rather a large class of objects that has been mostly neglected, until rather recently, by paleobiologists. Complex structures have certainly proven challenging to taxonomists and useful to sedimentary geologists, but their real significance is biologic: they are the records of elaborate behavioral adaptations by organisms that (in some cases) inhabited the structures for long intervals, appear to have controlled food supplies, and seem to have

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FIGURE 27.3 An example of a paleoethologic blueprint, in this case for a Phymatoderma burrow system in Pliocene bathyal mudstone, Esmeraldas Province, northwestern Ecuador. The blueprint is used to portray major features of the ethology of the trace-producing organism recorded in the structure: 1 represents burrow initiation, 2–7 represent tunnel construction and stocking with fecal pellets gathered at the seafloor, 8 and 9 are examples of revisiting the tunnels and recycling/restocking the contents, and 10 represents abandonment of the structure. Even though the blueprint is fairly complex, it summarizes only the most obvious features of this particular specimen. (Bar scale in photograph represents 4 cm; reproduced from Miller, 2003a, fig. 2.)

re-engineered their surroundings to new specifications. It is likely also that they controlled or influenced the survival and fitness of co-occurring organisms. These structures record complex ecologic roles and interactions of trace producers, reveal the ability of some producing organisms to actively construct a special habitat for themselves, and therefore can be viewed plausibly as phenotypic

extensions or physiologic projections of those producers (e.g., Dawkins, 1983; Jones et al., 1994; Butler, 1995; Lewontin, 2000; Turner, 2000, 2003; Miller, 2002, 2003a; Odling-Smee et al., 2003). As such, complex trace fossils deserve special attention, and bringing them to center stage could result in forging new and mutually productive connections to behavioral ecology and evolutionary theory.

ACKNOWLEDGEMENTS

ACKNOWLEDGEMENTS Humboldt State University Foundation, the California State University System, the National Geographic Society, Petroleum Research Fund, and the American Philosophical Society have supported at various times, my work on complex trace fossils. Al Curran and Molly Miller provided many thoughtful suggestions for the improvement of this chapter.

References Bromley, R.G. (1996). Trace Fossils: Biology, Taphonomy and Applications, 2nd edition. Chapman and Hall, London, 361 pp. Bromley, R.G., Uchman, A., Gregory, M.R. and Martin, A.J. (2003). Hillichnus lobosensis igen. et isp. nov., a complex trace fossil produced by tellinacean bivalves, Paleocene, Monterey, California, USA. Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 157–186. Butler, D. (1995). Zoogeomorphology: Animals as Geomorphic Agents, Cambridge University Press, Cambridge, 231 pp. Dawkins, R. (1983). The Extended Phenotype: The Long Reach of the Gene, Oxford University Press, Oxford, 307 pp. Ekdale, A.A., Bromley, R.G. and Pemberton, S.G. (1984). Ichnology: Trace Fossils in Sedimentology and Stratigraphy. Society of Economic Paleontologists and Mineralogists Short Course, 15, 317 pp. Hasiotis, S.T. (2003). Complex ichnofossils of solitary and social soil organisms: understanding their evolution and roles in terrestrial palaeoecosystems. Paleogeography, Palaeoclimatology, Palaeoecology, 192, 259–320. Jones, C.G., Lawton, J.H. and Shachak, M. (1994). Organisms as ecosystem engineers. Oikos, 69, 373–386. Lewontin, R. (2000). The Triple Helix: Gene, Organism, and Enviroment, Harvard University Press, Cambridge, MA, 136 pp. Miller, W., III. (1996a). Behavioral ecology of morphologically complex marine ichnogenera. Paleontological Society Special Publication, 8, 276. Miller, W., III. (1996b). Approaches to paleoethology of marine trace fossils: fabrication analysis and other descriptive methods. Geological Society of America Abstracts with Programs, 28, A-489. Miller, W., III. (1998). Complex marine trace fossils. Lethaia, 31, 29–32. Miller, W., III. (2001). Thalassinoides-Phycodes compound burrow systems in Paleocene deep-water limestone, Southern Alps of

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Italy. Palaeogeography, Palaeoclimatology, Palaeoecology, 170, 149–156. Miller, W., III. (2002). Complex trace fossils as extended organisms: a proposal. Neues Jahrbuch fu¨r Geologie und Palaöntologie Monatshefte, 2002, 147–158. Miller, W., III. (2003a). Paleobiology of complex trace fossils. Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 3–14. Miller, W., III. (Ed). (2003b). New Interpretations of Complex Trace Fossils. Special Issue, Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 1–346. Miller, W., III. and Aalto, K.R. (1998). Anatomy of a complex trace fossil: Phymatoderma from Pliocene bathyal mudstone, northwestern Ecuador. Paleontological Research, 2, 266–274. Miller, W., III. and Vokes, E.H. (1998). Large Phymatoderma in Pliocene slope deposits, northwestern Ecuador: associated ichnofauna, fabrication, and behavioral ecology. Ichnos, 6, 23–45. Miller, M.F. and Curran, H.A. (2001). Behavioral plasticity of modern and Cenozoic burrowing thalassinidean shrimp. Palaeogeography, Palaeoclimatology, Palaeoecology, 166, 219–236. Miller, W., III. and D’Alberto, L. (2001). Paleoethologic implications of Zoophycos from Late Cretaceous and Paleocene limestones of the Venetian Prealps, northeastern Italy. Palaeogeography, Palaeoclimatology, Palaeoecology, 166, 237–247. Odling-Smee, F.J., Laland, K.N. and Feldman, M.W. (2003). Niche Construction: The Neglected Process in Evolution, Princeton University Press, Princeton, NJ, 472 pp. Pickerill, R.K. (1994). Nomenclature and taxonomy of invertebrate trace fossils. In: Donovan, S.K. (Ed.), The Palaeobiology of Trace Fossils, John Wiley, Chichester, pp. 3–42. Pickerill, R.K. and Narbonne, G.M. (1995). Composite and compound ichnotaxa: a case example from the Ordovician of Que´bec, eastern Canada. Ichnos, 4, 53–69. Salthe, S.N. (1993). Development and Evolution: Complexity and Change in Biology, MIT Press, Cambridge, MA, 357 pp. ¨ ber die Seilacher, A. (1953). Studien zur Palichnologie. I, U Methoden der Palichnologie. Neues Jahrbuch fu¨r Geologie und Palaöntologie Abhandlungen, 96, 421–452. Turner, J.S. (2000). The Extended Organism: The Physiology of AnimalBuilt Structures, Harvard University Press, Cambridge, MA, 235 pp. Turner, J.S. (2003). Trace fossils and extended organisms: a physiological perspective. Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 15–31. Uchman, A. (1995). Taxonomy and palaeoecology of flysch trace fossils: the Marnoso-arenacea Formation and associated facies (Miocene, Northern Apennines, Italy). Beringeria, 15, 115 pp. Ziebis, W., Forster, S., Huettel, M. and Jørgensen, B.B. (1996). Complex burrows of the mud shrimp Callianassa truncata and their geochemical impact on the sea bed. Nature, 382, 619–622.

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28 A Constructional Model for Zoophycos Davide Olivero and Christian Gaillard

SUMMARY : Zoophycos is a complex trace fossil. Hundreds of these fossils, very similar to the type ichnospecies, have been observed in Devonian to Cretaceous deposits. The detailed analysis of the characteristics of the traces has resulted in a detailed constructional model. The specimens of Zoophycos that we have studied were constructed upwards into the sediment. They are the result of a very efficient mining programme, corresponding to the sediment feeding activity of a supposedly sipunculid worm. The formation of lobes may be linked to the evolution of the trace-maker or to its ethology.

to Cretaceous. The morphology, the constructional dynamics, and the ethology of the trace-maker are detailed.

MAIN CHARACTERISTICS Of all the trace fossils commonly related to the Zoophycos group, we have chosen to describe one very common type that shows a striking similarity with the specimens described by Massalongo in 1855 (see Olivero, Chapter 13), and at first named Zoophycos by that author. These ichnofossils have been abundantly observed by the authors in Palaeozoic and Mesozoic successions, particularly in the Devonian of Bolivia (Gaillard and Racheboeuf, in press), in the Carboniferous of Belgium (Gaillard et al., 1999), and in the Jurassic (Gaillard and Olivero, 1993; Olivero, 1994, 2003; Olivero and Gaillard, 1996) and Cretaceous of southeastern France (Olivero, 2003; Savary et al., 2004). The model presented here does not attempt to explain all the trace fossils classically considered as Zoophycos. For a greater convenience of language we will name these ichnofossils simply as ‘Zoophycos’, being aware of the fact that different forms are described today under the same name. The basal organisation of a Zoophycos, as first noted by Sarle (1906) is characterised by (Fig. 28.1):

INTRODUCTION Zoophycos is a trace fossil whose exact organisation and significance have been discussed for long. According to the modern interpretations, it is a complex spreiten structure with a tremendous morphological variability (Bromley, 1996). Numerous descriptions have appeared since its first description in 1855 by Massalongo (see Olivero, Chapter 13), and this has led to a general confusion concerning its taxonomic attribution and its interpretation. Numerous synonyms have been applied to trace fossils that are actually different. All these trace fossils may be included in the large ‘Zoophycos group’ (sensu Uchman, 1991). In recent years, the morphology of the ichnofossil and the taxonomy and ethology of the supposed trace-maker are subjects of a large disagreement among ichnologists. The aim of this chapter is to present one type of Zoophycos, very similar to the type specimen of Massalongo, that occurs in deposits ranging at least from Devonian

(1) A marginal tube. A tubular structure bordering an area of bioturbated sediment and considered as a tunnel produced by a worm-like organism within the sediment. (2) A lamina. It corresponds to the bioturbated sediment bordered by the marginal tube. Copyright ß 2007, Elsevier B.V.


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CONSTRUCTION OF THE LAMINA

FIGURE 28.1

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General morphological characteristics of a simple Zoophycos lamina.

(3) Primary lamellae. Arched grooves and ridges characterising the lamina and interpreted as the subsequent positions of the marginal tube during its lateral displacement into the sediment.

CONSTRUCTION OF THE LAMINA Following the previous characteristics and according to all descriptions, Zoophycos is typically a spreite resulting from the lateral shifting of a burrow. The last location of this burrow corresponds to the marginal tube. The marginal tube, which is empty or sometimes filled with pyritised material, is typically an unlined open burrow. The tube borders the lamina, which is characterised by the primary lamellae. Primary lamellae bend and become tangent in the proximity of the marginal tube. Their convexity indicates the direction of progression of the spreite. This is confirmed by observations of sections of the lamina (Fig. 28.2). The backfill aspect is the result of the alternation of arched structures of varying colour and/or composition. These ‘menisci’ are the sections of the primary lamellae and their concavity correspond to the direction of lateral shifting of the marginal tube inside the sediment (i.e., the direction of construction of the lamina). The lamina may be simple (planar) or complex (spirally coiled).

Simple Planar Forms (Figs. 28.3B and 28.4A) In these uncommon but very informative variants, the lamina is lunate shaped with a curved side and a straight side (Figs. 28.3B and 28.4A). The curved side is the current open marginal tube and the opposite straight side corresponds to the first position of the marginal tube. Between the two, the muscle-shaped lamina is made of regular primary lamellae indicating the different intermediate positions of the marginal tube. Two basic observations concern the marginal tube: the two extremities are quite distant; and one extremity is deeper than the other in the sediment. This suggests a tube with only one opening. These simple planar forms are associated with the following more complex forms and they clearly illustrate the initial growth stages of Zoophycos (Fig. 28.4B).

Complex Spirally Coiled Forms (Figs. 28.3, 28.4B, and 28.5) They are more common and can be considered as derived from the previous forms. The lamina is spirally coiled around a vertical central axis forming a well-marked cone-shaped trace (Figs. 28.3C–E). The upper conical extremity forms the apex that points upward. The marginal tube bounds the external border of the whole spreite, while no axial tube has been observed in the centre of the structure. As in simple forms, the marginal tube has two distant extremities: the upper one ends in the upper apex and

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28. A CONSTRUCTIONAL MODEL FOR ZOOPHYCOS

FIGURE 28.2 Left: A Zoophycos lamina in a polished section of a fine-grained limestone (Early Cretaceous, Arde`che, France). The backfill structure is represented by the alternation of black and grey menisci. Their concavity corresponds to the direction of the lateral shifting of the marginal tube, i.e., the direction of construction of the lamina inside the sediment (arrow). Scale bar = 1 cm. Right: Several Zoophycos laminas (arrows) in a polished section of a fine-grained limestone (Middle Jurassic, Alpes de Haute Provence, France). One of the laminae bypasses a bivalve shell (b).

FIGURE 28.3 Five stages of the growth of a Zoophycos structure. (A) At the beginning, the organism excavates a simple tube nearly vertical, with one opening at the seafloor. (B) The tube is shifted laterally, creating a muscle-shaped lamina. The curved side, where the tube is now ‘marginal’, corresponds to the activity zone of the animal. The straight side corresponds to the initial position of the tube. (C) The lamina begins to turn to the horizontal plane. (D) A whorl is created and the lamina turns around a central axis. The upper apex corresponds to the opening at the seafloor. (E) By the addition of a new whorl, a complex spirally coiled form is created. u.e.—upper extremity; l.e.—lower extremity; f.t.—first tube; m.t.—marginal tube; L—lamina; ipt—initial position of the tube; a.c.—axis of coiling; and u.a.—upper apex. Modified from Gaillard and Olivero (1993).

represents the opening of the burrow at the seafloor; the lower one is situated deeper in the sediment and forms the deeper part of the trace. Fundamentally, the Zoophycos structures that we have observed result

from the regular displacement (producing primary lamellae) of a simple tube (marginal tube) having only one opening on the seafloor (Gaillard and Olivero, 1993). This clearly differs from conceptual models

THE CONSTRUCTION OF LAMELLAE

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FIGURE 28.4 (A) Simple planar form. The lamina is lunate-shaped with a curved side and a straight side. The curved side is the open marginal tube (m.t.) and the opposite straight side corresponds to the first position of the marginal tube. The two extremities are quite distant: one of them is deeper (l.e.) that the other (u.a.). Middle Jurassic, Alpes de Haute Provence, France. Scale bar = 10 cm. (B) Complex spirally coiled form. The specimen clearly shows the initial stage of growth of the lamina, nearly vertical, with a deep lower extremity (l.e.) and a straight side (ipt). After, the lamina turns to the horizontal plane (h.p.). This example corresponds to Fig. 28.3D. Carboniferous of Mons, Belgium. Scale = 15 cm.

exhibiting two openings and indicating that Zoophycos is a U-burrow (Seilacher, 1967; Bromley and Ekdale, 1984). The curvature of the lamellae shows that the direction of construction of the spreite is usually upward (Figs. 28.3, 28.4B, 28.5, and 28.6A). In this case, the width of the lamina also increases upwards. Zoophycos is a spreite produced by a proximal movement (toward the aperture). In a few cases (Fig. 28.6A), the spreite may have a downward direction of coiling. The coil (Fig. 28.6B) may be both dextral or sinistral (Gaillard et al., 1999) and up to 5 superimposed whorls may be observed in a single specimen.

THE CONSTRUCTION OF LAMELLAE Secondary Lamellae The trace fossil Zoophycos has a more complex architecture than described in the previous section. The complexity is due to the presence of secondary lamellae that are oblique structures regularly arranged between primary lamellae (Fig. 28.7). These structures have already been described in other articles as ‘minor lamellae’ (Simpson, 1970; Bromley and Hanken, 2003), or ‘secondary lamellae’ (Gaillard and Olivero, 1993; Olivero, 1994, 2003;

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FIGURE 28.5 Four complex spiral forms of Zoophycos from different stratigraphic levels. All are similar and show an upward growth. (A) Devonian, Bolivia. Scale bar = 5 cm; (B) Carboniferous, Belgium. Scale bar = 5 cm; (C) Middle Jurassic, France. Scale bar = 10 cm; (D) Early Cretaceous, France. Three superimposed whorls are visible. Scale bar = 10 cm.

Olivero and Gaillard, 1996). Unfortunately, secondary lamellae are often poorly visible, but they strongly help to understand the way of construction of the primary lamellae. Secondary lamellae (Fig. 28.7) are sigmoidal structures, a few millimetres long, located obliquely between the primary lamellae. The angle between primary lamellae and secondary lamellae varies from a few degrees to nearly 40–458. This angle strongly influences the visibility of secondary lamellae. When this angle is low, secondary lamellae are not clearly visible (Fig. 28.8). Moreover, secondary lamellae may be poorly preserved. When well preserved, they are revealed by an alternation of raised and grooved sigmoidal structures (sometimes

having dark/light-coloured alternation). Each set of secondary lamellae draws a band that is parallel to the border of the lamina and the width of such band may reach 1 cm. The orientation of the lamellae is always the same in each band and in the whole lamina. The bands are separated by a thin and hollow furrow, which corresponds to the primary lamellae. This organisation has been previously illustrated by Simpson (1970). In a set of secondary lamellae, one lamella clearly corresponds to enclosing sediment because colour and resistance to erosion are similar. The other lamella is interpreted by us to be sediment previously ingested by the trace-maker. Faecal pellets have not been

THE CONSTRUCTION OF LAMELLAE

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FIGURE 28.7 Secondary and primary lamellae on a specimen from Middle Jurassic (France). Scale bar = 1 cm.

FIGURE 28.6 (A) Directions of construction of the spreiten. The upward direction is dominant, including nearly 95% of the observed specimens. (B) Directions of coiling; 50% sinistral and 50% dextral.

FIGURE 28.8 Zoophycos with indistinct secondary lamellae. Middle Jurassic, France. Scale bar = 5 cm.

observed in studied specimens but are usually present in more recent Zoophycos (Wetzel and Werner, 1981; Lo¨wemark and Scha¨fer, 2003). We propose to name these two kinds of secondary lamellae: ‘Sediment Lamellae 2’ and ‘Faecal Lamellae 2’ (see Fig. 28.9). In order to understand the way of construction of such structures, it is necessary to observe the border of the lamina with the marginal tube. Figure 28.9 should remind the reader of an illustration in Bromley and Hanken (2003, fig. 18), which clarifies this constructional model.

Figure 28.9A shows a specimen from the Middle Jurassic of France having the ending of a band of secondary lamellae. The marginal tube borders this band, turns parallel to the last secondary lamella, and continues to border the previous band. It appears as the lateraxl extension of a primary lamella. This clearly shows that the lamina is constructed by the adding of subsequent sets of secondary lamellae. The curvature of these last elements corresponds to the direction of progression of the developing trace, and this progression is the same in the whole lamina (Fig. 28.9B).

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FIGURE 28.9 (A) End of a band of secondary lamellae. Middle Jurassic (France). Scale bar = 1 cm. (B) Construction of the bands of secondary lamellae.

Mining Programme What is the trace-maker? We assume that it is a worm-like marine sediment-feeder. Following Wetzel and Werner (1981), a sipunculid worm is the most probable trace-maker. Several species are sedimentfeeders burrowing and eating with an extensible proboscis. These worms also have an important characteristic: their mouth and their anus are located at the same anterior extremity of their body (Cutler, 1994; Brusca and Brusca, 2002).

How are lamellae produced? We propose the following mechanism (Fig. 28.10). The animal lives and moves inside the marginal tube. The major part of the worm body always stays in the marginal tube while the anterior extensible proboscis, by which it feeds on the sediment, creates the secondary lamellae. The proboscis is extended in order to connect with the marginal tube bordering the previous band of secondary lamellae (A). Then, the proboscis withdraws in the newly produced oblique tunnel while expelling the faeces. Faeces partially fill

CONSTRUCTION OF LOBES

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this way and constructs a long band of secondary lamellae (Fig. 28.9), consisting of alternating unexploited sediment (Sediment Lamellae 2) and faeces (Faecal Lamellae 2). The whole spreite is thus the result of various bands of secondary lamellae, produced one after another. The whole mechanism allows a regular and efficient exploitation of the sediment and shows three major phases: (1) Locomotion phase: progression of the whole trace-maker at the extremity of the active part of the marginal tube. (2) Ingestion phase: proboscis extension with ingestion of sediment. Formation of a Sediment Lamella 2 by the collapse of enclosing sediment. (3) Excretion phase: proboscis withdraws with excretion of undigested sediment. Formation of a Faecal Lamella 2 by the deposition of faecal material.

FIGURE 28.10 Mechanism of construction of the secondary lamellae. See also Simpson (1970).

the gallery forming a Faecal Lamella 2 (B). After this excretion phase, the proboscis is invaginated (C). Then, a locomotion phase occurs and the whole animal moves slightly forward (D). When stopped, an ingestion phase begins. The proboscis is extended toward the previous marginal tube (E). By doing so, some unexploited enclosing sediment is crushed on the previously created oblique gallery, that quickly collapses and disappears. When the proboscis is fully extended and connects to the marginal tube (F), this mechanism has produced a Sediment Lamella 2. This new lamella is parallel to the previously formed Faecal Lamella 2. Then the proboscis withdraws in the gallery, expelling the faecal pellets, which, once again, fill the tube (G). Another Faecal Lamella 2 is produced (H). The animal continues in

What is the direction of construction of primary lamellae? In all the observed specimens, the curvature of the secondary lamellae shows that the feeding movement of the trace-maker in the marginal tube is directed towards the apex that is upward, toward the seafloor (Fig. 28.11A). This movement is slow as it corresponds to a complex feeding activity. When a new band of secondary lamellae reaches the surface, the organism goes back in the newly formed open marginal tube (Fig. 28.11B). This movement is rapid as it corresponds to a simple locomotion activity. Afterwards, the animal starts again to produce a new set of secondary lamellae, always produced in an upward direction of progression. As noted earlier, the direction of construction of the lamina is mainly upwards for the Zoophycos we have studied. This fundamentally upwardworking activity leads to a major ecological conclusion. The trace-maker feeds only slightly deep into the marginal tube (activity zone) near its opening at the seafloor, where oxygenation is easier (Fig. 28.12). This corresponds to the most efficient mining programme with respect to energy expenditure.

CONSTRUCTION OF LOBES The Zoophycos laminae may be characterised by lobes, more or less developed, that can complicate the outline of the structure. The morphology of lobes seems to be linked to different possible causes.

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FIGURE 28.11 Movement of the trace-maker in the marginal tube and direction of construction of the lamina.

FIGURE 28.12 Activity zone (black) in the marginal tube of a Zoophycos during the subsequent phases of construction. See Fig. 28.3 for comparison. Modified from Gaillard and Olivero (1993).

Evolution of the Trace-maker (Fig. 28.13A) Fundamentally, the oldest Zoophycos are usually unlobed while recent specimens commonly exhibit well developed lobes. For example, based on our observations, unlobed specimens are commonly recorded in Devonian (Gaillard and Racheboeuf, in press), and Carboniferous (Gaillard et al., 1999). In Early Jurassic deposits unlobed and fewer lobed specimens are recorded (Olivero and Gaillard, 1996; Olivero, 2003), while frequent lobed specimens occur in Middle Jurassic to Late Cretaceous successions (Olivero, 2003; Savary et al., 2004). Lobes become increasingly frequent but also increasingly developed. This increase in the morphological complexity is linked to an increase in the size of the whole trace with specimens reaching nearly 2 m of width during the Late Cretaceous (Olivero, 2003). Several authors have reported this change in Zoophycos morphology during geologic time (Seilacher, 1986; Bottjer et al., 1988). One of us has proposed Zoophycos as extended phenotype; as a consequence, the change in the morphology of the trace fossil may reflect a possible evolution of the supposed trace-maker (Olivero, 2003).

According to this hypothesis, the trace fossils we studied could represent one single clade of traceproducers. The presence of lobes might be related to a possible evolutionary trend of the trace-makers, that change their burrowing and feeding over millions of years. The very regularly lobed Zoophycos that appear in the Late Cretaceous and become common in Cenozoic deposits (Miller and d’Alberto, 2001; Bromley and Hanken, 2003) are possibly the result of this general evolutionary trend.

Environmental Conditions (Fig. 28.13B) Because lobed and unlobed Zoophycos can occur during the same periods, it could be assumed that lobes are produced under specific conditions revealing adaptative behaviour. We can imagine a behaviour corresponding to the formation of ‘active lobes.’ The trace-maker could form long and sometimes narrow lobes to quickly explore a part of the substrate locally/temporarily enriched with nutrients (Olivero and Gaillard, 1996) or an unusual deposit such as a turbidite (Fig. 28.14A)

CONSTRUCTION OF LOBES

FIGURE 28.13

The formation of the lobes.

FIGURE 28.14 (A) Active lobes. Several superimposed specimens on an upper surface of a calciturbidite bed (Early Cretaceous, France). Two lobes (L), bordered by a large marginal tube (m.t.), and the corresponding central part of the lamina (c.l.). Scale bar = 5 cm. (B) Passive lobes. Lobes produced by the contact (arrows) with contemporaneous Zoophycos (1, 2, 3). Carboniferous, Belgium. Scale = 15 cm.

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(Savary et al., 2004). If enough organic matter is available, the organism slows down its activity and begins to more regularly exploit the substrate, producing unlobed laminas. This behaviour suggests that highly lobed Zoophycos could indicate unstable environments and an opportunistic strategy, while simple unlobed Zoophycos could indicate stable environments and a more specialised strategy. Another important behaviour simply corresponds to avoiding obstacle with the formation of ‘passive lobes.’ Clearly, the occurrence of shells, like those from bivalves and ammonites, in the exploited sediment induces the formation of lobes as they are turned (Olivero and Gaillard, 1996). Sometimes, in highly bioturbated sediments, obstacles correspond to other contemporaneous Zoophycos (Fig. 28.14B). This illustrates a clear intraspecific competition for substrate exploitation, with complex relations between lobes (Olivero and Gaillard, 1996; Gaillard et al., 1999).

CONCLUSIONS The study of hundreds of well-preserved burrow systems, occurring in rocks from Devonian to Cretaceous in age and clearly similar to the type specimen of Zoophycos Massalongo, 1855, leads to the following main conclusions: (1) The Zoophycos we have studied correspond to a simple tubular unlined burrow with only one opening at the seafloor. They are not U-burrows. (2) The construction of the lamina and the construction of the primary lamellae are fundamentally upward. This allows the best oxygenation of the part of the tube where the trace-maker is working. (3) The construction of the burrow system illustrates an efficient mining programme corresponding to a feeding activity. We assume that Zoophycos is made by a sediment feeder, probably a sipunculid worm, exploiting nutrients deeply stored inside the sediment (see Cutler, 1994). The proposed model is probably not valid for all burrow systems described as Zoophycos because other descriptions and interpretations have been made, mainly for complex Cenozoic forms (Kotake, 1989; Ekdale and Lewis, 1991; Bromley and Hanken, 2003).

ACKNOWLEDGEMENTS The French CNRS (Centre National de la Recherche Scientifique) provided funds for the field missions. Sincere thanks to William Miller and Francisco Rodriguez-Tovar for the constructive reviews.

References Bottjer, D.J., Droser, M.L. and Jablonski, D. (1988). Palaeoenvironmental trends in the history of trace fossils. Nature, 333, 252–255. Bromley, R.G. (1996). Trace Fossils: Biology, Taphonomy and Application, 2nd edition. Chapman & Hall, London, 361 pp. Bromley, R.G. and Ekdale, A.A. (1984). Trace fossil preservation in flint in the European chalk. Journal of Palaeontology, 58(2), 298–311. Bromley, R.G. and Hanken, N.-M. (2003). Structure and function of large, lobed Zoophycos, Pliocene of Rhodes, Greece. Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 79–100. Brusca, C. and Brusca, G.J. (2002). Invertebrates, Sinauer associates, Sunderland, MA, USA, 880 pp. Cutler, E.B. (1994). The Sipuncula. Their systematics, Biology, and Evolution, Cornell University Press, Ithaca, NY, 480 pp. Ekdale, A.A. and Lewis, D.W. (1991). The New Zealand Zoophycos revisited: morphology, ethology and paleoecology. Ichnos, 1, 183–194. Gaillard, C. and Olivero, D. (1993). Interpre´tation palaeóećologique nouvelle de Zoophycos Massalongo, 1855. Comptes Rendus de ’Acade´mie des Sciences, Paris, t. 316, ser. II, pp. 823–830. Gaillard, C. and Racheboeuf, P. (2006). Trace fossils from nearshore to offshore environments: Lower Devonian of Bolivia. Journal of Palaeontology, 80, In press. Gaillard, C., Hennebert, M. and Olivero, D. (1999). Lower Carboniferous Zoophycos from the Tournai area (Belgium): environmental and ethologic significance. Geobios, 32, 513–524. Kotake, N. (1989). Palaeoecology of the Zoophycos producers. Lethaia, 22, 327–341. Lo¨wemark, L. and Scha¨fer, P. (2003). Ethological implications from a detailed X-ray radiograph and 14C study of the modern deep-sea Zoophycos. Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 101–121. Massalongo, A. (1855). Zoophycos, novum genus Plantarum fossilium, Typis Antonellianis, Veronae, pp. 45–52. Miller, W. III and d’Alberto, L. (2001). Palaeoethologic implications of Zoophycos from Late Cretaceous and Palaeocene limestones of the Venetian Prealps, northeastern Italy. Palaeogeography, Palaeoclimatology, Palaeoecology, 166, 237–247. Olivero, D. (1994). La trace fossile Zoophycos du Jurassique du Sud-Est de la France. Signification palaeóenvironnementale. Documents du Laboratoire de Geólogie de Lyon, 129, 329 pp. Olivero, D. (2003). Early Jurassic to Late Cretaceous evolution of Zoophycos in the French Subalpine Basin (southeastern France). Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 59–78. Olivero, D. and Gaillard, C. (1996). Palaeoecology of Jurassic Zoophycos from South-Eastern France. Ichnos, 4, 249–260. Sarle, C.J. (1906). Preliminary note on the nature of Taonurus Proceedings of Rochester Academy of Science, 4, 211 pp.

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Savary, B., Olivero, D. and Gaillard, C. (2004). Calciturbidite dynamics and endobenthic colonisation: example from a late Barremian (Early Cretaceous) succession in southeastern France. Palaeogeography, Palaeoclimatology, Palaeoecology, 211, 221–239. Seilacher, A. (1967). Bathymetry of trace fossils. Marine Geology, 5, 413–428. Seilacher, A. (1986). Evolution of behavior as expressed in marine trace fossils. In: Nitecki, M.H. and Nitecki, J.A. (Eds.), Evolution of Animal Behavior, Oxford University Press, New York, pp. 62–87.

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Simpson, S. (1970) Notes on Zoophycos and Spirophyton. In: Crimes, T.P. and Harper, J.C. (Eds.), Trace fossils. Geological Journal, (3), 505–514. Uchman, A. (1991). ‘Shallow water’ trace fossil in Palaeogene flysch of the southern part of the Magura Nappe, Polish Outer Carpathians. Annales Societatis Geologorum Poloniae, 61, 61–75. Wetzel, A. and Werner, F. (1981). Morphology and ecological significance of Zoophycos in deep-sea sediments off NW Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 32, 185–212.

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29 Arthropod Tracemakers of Nereites? Neoichnological Observations of Juvenile Limulids and their Paleoichnological Applications Anthony J. Martin and Andrew K. Rindsberg

with the Zoophycos and Nereites ichnofacies of Seilacher (1963), whose modern counterparts were predicted to occur in deep-sea environments before being found by means of cores and submersibleaided observations (Chamberlain, 1978; Ekdale, 1980; Wetzel, 1991), including the ichnogenus Nereites (Wetzel, 2002). Nevertheless, some well-known ichnogenera have yet to be consistently linked to extant traces and their tracemakers. For example, Wetzel (2002), who reported on modern Nereites from the deep sea, did not find or identify its tracemaker. Nereites is a commonly reported ichnogenus, yet its makers and manner of production remain obscure despite a consensus view that the tracemaker was a worm (Seilacher and Meischner, 1965; Chamberlain, 1971; Uchman, 1995). However, to our knowledge, no one has ever witnessed a worm making Nereites. It thus came as a surprise to find that one modern maker of a Nereites-like structure was an arthropod: juveniles of the horseshoe crab Limulus polyphemus (Xiphosura). In all probability, xiphosurans were not the only potential makers of trace fossils similar to Nereites, but one group among many kinds of short-bodied arthropods and perhaps other organisms that made such trace fossils. Other trail-like trace fossils with traits that overlap morphologically with Nereites, such as the ichnogenera Arthrophycus and Psammichnites, also invite comparison and inquiry about their

SUMMARY : To get the most out of the paleoichnological record, the behavior and resultant traces of extant animals must be studied carefully, even if this upsets long-established ideas about the makers of trace fossils. Observations of modern juvenile limulids (Limulus polyphemus) show that they make modern traces similar to the ichnogenus Nereites on sandy tidal flats of Sapelo Island (Georgia, USA)—with the understanding that ichnogenera are morphologically based groups of trace fossils with no implication as to the maker. Our results confirm earlier work that suggests various arthropod makers as the makers of some Paleozoic Nereites—while throwing into question the established interpretation of Nereites as a burrow of vermiform tracemakers. Accordingly, Nereites-like traces should be reinvestigated on a caseby-case basis with regard to their characteristic bioprint, i.e., the set of morphologic features that allows the identification of the maker of a trace.

INTRODUCTION The paleoichnologic record has provided numerous opportunities for a sort of ‘reverse uniformitarianism’ in that some trace fossils have prompted interest in finding their modern analogs and their tracemakers. This is particularly the case for trace fossils associated


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NEREITES AND ITS MAKERS: PREVIOUS HYPOTHESES

probable tracemakers. Following Seilacher (2004) and Bromley (2004), we submit that identification of key anatomical and behavioral characteristics in ichnogenera, or bioprint (Rindsberg and Kopaska-Merkel, 2005), helps to interpret their potential tracemakers. Because of their relatively large size and complex anatomy, arthropod tracemakers are especially well suited for this approach. Among the noteworthy aspects of our description of limulid-produced Nereites-like traces is better documentation of how different growth stages of single species of marine arthropod can produce a suite of traces. Such assemblages might have been regarded previously as the work of many species of substantially different anatomy and behavior. As a result, knowledge of ontogenetic influences on ichnodiversity can prevent overestimates of biodiversity represented in trace fossil assemblages.

NEREITES AND ITS MAKERS: PREVIOUS HYPOTHESES Reported examples of the ichnogenus Nereites include a broad range of structures and inferred behaviors (Uchman, 1995). This trace fossil is unbranched, subhorizontal, and indefinitely long. As generally understood, the trace fossil has a complex internal structure that looks very different depending

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on how it is preserved and sectioned (Seilacher and Meischner, 1965; Chamberlain, 1971, 1978, 1980; Uchman, 1995). Nereites includes a central zone or ‘ribbon’ having an apparently meniscate structure, surrounded by an outer zone with a lobate lower part and a relatively smooth upper part (Fig. 29.1A). In especially well-preserved material, the lobes display laminations. Ichnospecies of Nereites are differentiated partly on the basis of the course of the burrow (Uchman, 1995). For example, Nereites saltensis (Acenõlaza and Durand, 1973) has a meandering course in which successive meanders curve back to touch the previous turn before changing direction. Nereites imbricata (Mangańo et al., 2000) only shows moderate variations to its course, with broad bends along mostly straight pathways. Nereites missouriensis (Weller, 1899) has a relatively unprogrammed course (Conkin and Conkin, 1968; Rindsberg, 1994; Wetzel, 2002). Seilacher (1974, Fig. 2) and Chamberlain (1980) suggested that such differences in behavior might represent the evolution of a lineage of tracemakers. Unfortunately, the general course of the burrow, though significant, sheds scant light on the identity of its tracemaker, such as whether it were propelled by a muscular foot, jointed legs, tube feet, or other means of locomotion. Closer details of the course, such as three-dimensional construction, turns, and sculpture, contribute more readily to a trace’s bioprint.

FIGURE 29.1 Nereites as both a trace fossil and arthropod interpretation for formation of a similar trace (this article). (A) Nereites missouriensis of the Hartselle Sandstone (Lower Carboniferous) of Alabama, GSA 1052-134 (also figured in Rindsberg, 1994); scale in centimeters. (B) Composite of Nereites-like locomotion trace formed by modern juvenile limulid in transition from surface locomotion trace to shallow burrow.

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29. ARTHROPOD TRACEMAKERS OF NEREITES? NEOICHNOLOGICAL OBSERVATIONS

Clues to the maker of Nereites include its stratigraphic range and environmental distribution, as well as details of its morphology. Reported Nereites has a Phanerozoic range, and selected Cambrian, Carboniferous, and Tertiary specimens can have remarkably similar superficial morphology. The tracemakers lived in clay, silt, and sand. Paleozoic Nereites occurs in nearshore to deep-sea settings (Rindsberg, 1994; Mańgano et al., 2000), but post-Paleozoic Nereites is generally bathyal to abyssal (Uchman, 1995, 2003). Apparently, Nereites is largely confined to marine or marginal marine environments; a report from lacustrine facies (Hu et al., 1998) has been rejected as not belonging to the ichnogenus (Mańgano et al., 2002). The earliest researchers who encountered Nereites thought this trace fossil was actually a body fossil, such as a polychaete worm. This interpretation is reflected by its name, which means ‘related to Nereis’ (e.g., MacLeay, 1839; Emmons, 1844). Similarly, paleobotanists like Schimper and Schenck (1879–1890) considered Nereites to be a type of fossil seaweed. In contrast, the maverick paleobotanist Nathorst (1881, pp. 28, 86), impressed by actualistic comparisons with modern crustacean trails, stated forcefully, ‘The so-called Nereites are in large part the traces of crustaceans, and some perhaps the traces of worms and gastropods.’ In the past half-century, interpretations of the Nereites maker have focused on the indefinitely long character of the burrows. Evidently, the makers lived within the substrate, feeding as they traveled. Apparently, too, the animals could recognize previous paths, both theirs and others, because even the earliest and most irregular ichnospecies of Nereites are at least clumsily phobotactic, e.g., Nereites saltensis. From this point, however, two models diverge. In one model, the maker is long-bodied, such as a worm, perhaps an enteropneust (Seilacher and Meischner, 1965; Chamberlain, 1971; Seilacher, 1986). In the other, the maker is short-bodied, such as some arthropods or gastropods (Nathorst, 1881; this chapter). This problem is similar to that encountered for Arthrophycus: The ichnologic community is evaluating a polychaete model (Seilacher, 2000) and a trilobite model (Rindsberg and Martin, 2003) for this ichnogenus. The worm model for the Nereites maker has been standard for a long time. Based on bathyal Carboniferous material from Oklahoma, and following Seilacher and Meischner (1965), Chamberlain (1971, pp. 228–229, Figs. 5A–I) deduced that the tracemaker was a worm that fed successively within each lobe and then filled the medial ribbon and previous lobes with digested or transported sediment. This model has appeal, but does not explain why

adjacent lobes crosscut one another, which requires explanation, given that Nereites makers were consistently phobotactic. Nor does it explain how the worm maintained an open burrow while it was feeding elsewhere in sediments ranging from soft deep-sea clay to loose shallow-marine sand. Moreover, no modern tracemaker has been observed making burrows similar to Nereites in this manner. As a result of these inconsistencies and our observations of a modern arthropod tracemaker of Nereites-like traces, we favor the arthropod model pioneered by Nathorst (1881), in which the lateral lobes are pressure-release structures made by legs rather than excavated cavities that were later filled (Fig. 29.1B). In a classic neoichnologic work, Nathorst made plaster casts of trails made by modern invertebrates. Among other findings, he noted the similarity of Nereites and similar trace fossils to trails made by amphipods (Corophium longicorne) and decapods (the shrimp Crangon vulgaris). Dawson (1890, pp. 596–597) pointed out that Silurian Nereites and Arthrophycus can interconnect and therefore had the same makers, which he too interpreted as arthropods. Unfortunately, Dawson’s work was poorly documented, but we have since confirmed that Silurian trinucleine trilobites could have made both Nereites and Arthrophycus (Rindsberg and Martin, 2003). With this possibility in mind, a serendipitous discovery of modern traces similar to Nereites made by modern juvenile limulids provided a test of Nathorst’s (1881) and other subsequent ideas about this important ichnogenus.

TRACES OF JUVENILE LIMULUS POLYPHEMUS: A NEOICHNOLOGICAL ANALOG FOR NEREITES Natural History of Juvenile Limulids The horseshoe crab, Limulus polyphemus, is only one of four living species of limulids that lives in the Western Hemisphere; the other species—Tachypleus gigas, T. tridentatus, and Carcinoscorpius rotundicauda—occur in southeast Asia. All four species are similar ecologically, living in intertidal, estuarine, or shallow continental shelf environments (Shuster et al., 2003), although C. rotundicauda can breed in freshwater streams within the Ganges delta (Anderson and Shuster, 2003). The Carboniferous xiphosuran Euproops danae lived in brackish water to freshwater swamps in North America, and may even have extended into subaerial environments (Fisher, 1979), inviting caution

TRACES OF JUVENILE LIMULUS POLYPHEMUS: A NEOICHNOLOGICAL ANALOG FOR NEREITES

against applying the habits of modern organisms too literally to ancient animals. Limulus polyphemus ranges from Maine to Yucatań on the continental shelf of eastern North America (Shuster, 1982; Botton and Ropes, 1987; Shuster et al., 2003). The literature on L. polyphemus is extensive and has been summarized partially by Tanacredi (2001), Walls et al. (2002), and Shuster et al. (2003). However, far more of the literature is related to uses of limulids in biomedical research (e.g., Swan, 2001; Levin et al., 2003) than to natural history. Adult L. polyphemus live most of their lives, probably about 20 years, on the eastern continental shelf of North America in water as much as 30 m deep (Rudloe, 1981). One individual, however, was discovered at nearly 1100 m depth (Botton and Ropes, 1987). They are significant predators of bivalves, but gut contents show a wide range of invertebrate prey (Botton, 1984; Botton and Ropes, 1989). Although adults are largely epifaunal and vagile, in one study about 20% were found buried just below the seafloor (Carmichael et al., 2003). Relatively few studies of juvenile L. polyphemus have been published (Rudloe, 1981; Meury and Gibson, 1990; Gaines et al., 2002; Botton et al., 2003a), but their biological significance is becoming better understood as interest in the life history of this species increases (Shuster and Sekiguchi, 2003). At sexual maturity, L. polyphemus congregates in large numbers on beaches. Mating is most common during nighttime high tides associated with new and full moons in the spring to early summer (Rudloe, 1980a; Carmichael et al., 2003). Males, which make up the majority of the population, conjoin with or otherwise crowd the significantly larger females in the intertidal zone. Females crawl near the water’s edge and onto beaches (some with attached males), partially bury themselves, and excavate a shallow (10–20 cm deep) nest to lay eggs (Rudloe, 1981; Brockmann, 1990; Penn and Brockmann, 1994; Ehlinger and Tankersley, 2003). Nest selection and subsequent egg development are dependent on beach morphology, sand moisture level, interstitial oxygen concentration, redox potential, and, to a certain extent, temperature (Botton et al., 1988; Penn and Brockmann, 1994; Brockmann, 2003). Limulids are also repelled by H2S, and hence will avoid anaerobic sediments (Botton et al., 1988). Some males, using a combination of competition and close proximity to the female, fertilize eggs externally soon after they are laid by injecting sperm into the newly made nests (Brockmann, 1990; Penn and Brockmann, 1994; Brockmann, 2003). Interestingly, this is the only known example of external fertilization in arthropods;

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Limulus is also unusual in being an offshore species that comes ashore to breed. The horseshoe crab may thus lend insights to the evolutionary history of arthropod reproduction (Brockmann, 2003). Eggs are subjected to predation by several species of shorebirds that time their migrations with limulid mating cycles (Castro and Meyers, 1993; Walls et al., 2002; Botton et al., 2003b). The remaining eggs hatch typically in about two weeks, coincident with inundation caused by high tides of the next cycle of the new or full moon (Ehlinger and Tankersley, 2003). Egghatching times, however, can vary considerably, and both eggs and larvae are capable of overwintering (French, 1979; Botton et al., 1992). The limulid larvae are called trilobites by biologists because of their remarkable morphological similarity to their distant relatives from the geologic past. These trilobites may swim nocturnally for about six days until the molt to the first juvenile instar (Botton et al., 2003a), or remain dormant in the beach sand. After their first molt, they abruptly become benthic and diurnal (Rudloe, 1981; Shuster and Sekiguchi, 2003). Juvenile mortality is nearly 98% for hatchings before they become epibenthic, and only an estimated 3 out of 100,000 survive the first summer (Carmichael et al., 2003; Botton et al., 2003a). Part of this mortality is attributable to fish and shorebirds, the latter of which feast on the newly hatched limulids in the late spring and early summer (Botton et al., 2003b). This predation is made possible by the settling preferences of juvenile limulids, which are more common in benthic habitats close to the shore, such as intertidal zones (Loveland, 2001; Shuster and Sekiguchi, 2003; Botton et al., 2003b) For the next two years, the young horseshoe crabs crawl circuitously on intertidal surfaces when not resting within the sand (Rudloe, 1981). Some trilobites, however, become dormant and stay in the beach sands for months, even over the winter (Bolton et al., 1992). Feeding preferences of hatchlings in natural settings are still unknown, although second instars in aquaria eat a wide range of invertebrates and algae (French, 1979). More mature juveniles feed at first on meiofauna and organic detritus, and later on small polychaetes, bivalves, and other invertebrates (Rudloe, 1981; Gaines et al., 2002). Prey is dug from the substrate, grasped with the legs, moved to the gnathobases and crushed, then moved to the mouth for ingestion (Shuster, 1982; Botton et al., 2003b). Although juvenile horseshoe crabs have broad tolerances for salinity, temperature, pH, and dissolved oxygen (Shuster, 1982; Shuster and Sekiguchi, 2003), they show the greatest activity in warm months; the months then depend accordingly on latitude

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(Rudloe, 1981). Movement of adult Limulus is both circatidal and circadian, and experiments performed on their locomotor activities demonstrate increased movement of adults during nighttimes and high tides (Powers and Barlow, 1985; Chabot et al., 2004). Juveniles, in contrast, are most active during daytime low tides (Rudloe, 1981). Moreover, juveniles can orient themselves and avoid high-contrast objects by sight (Rudloe, 1980b; Errigo et al., 2001). Nevertheless, at least some of their behavior is apparently tactile, based on observations of their movement and traces reported in this study. Based on one population measured in Massachusetts, juvenile prosomal width is 16.6 ± 0.9 mm after the first year of growth (Carmichael et al., 2003), but the wide variation in sizes for different populations suggests that this metric is not universally applicable. For example, limulids in Georgia are the largest known, hence their populations should be distinctive from others (Riska, 1981). Nonetheless, locomotion traces of one-year-old juveniles on intertidal sandflats should approximate the prosomal size ranges attributed to this age group in each respective region. Older (and larger) individuals leave wider (>2 cm) locomotion traces than one-year-old juveniles, as well as distinctive trackways comparable to the ichnogenus Kouphichnium; such traces have been long attributed to xiphosuran makers (Packard, 1900; Caster, 1938; Barthel et al., 1990). As Caster (1938) summarized, these traces characteristically show the imprint of three anatomical attributes: (1) appendages (five pairs of walking legs); (2) edges of the carapace (prosomal and opisthosomal); and (3) telson. As we will explain later, differences in these characteristics imparted by ontogeny can result in distinctively different traces made by juvenile versus adult limulids. When submerged under calm-water conditions, juveniles move by either springing off sedimentary surfaces or burrowing shallowly, the latter causing partial burial of their prosomas (Meury and Gibson, 1990). Burrowing in limulids is caused by combined use of the walking legs and prosoma, as described by Eldredge (1970), Shuster and Anderson (2003), and observed by one of us (Martin). The first four pairs of walking legs push sand medially and posteriorly, forming a hollow under the prosoma. Sand is moved behind the body by the powerful pair of rear walking legs. Forward movement of the body is accomplished by: (1) upward arching at the hinge between prosoma and opisthosoma, which causes the prosoma to retract into the hollowed area and (2) simultaneous flattening of the body and pushing

by the legs, which propels the bladed prosoma into the sediment like a shovel. The telson plays a minor role in burrowing by sweeping sand behind the opisthosoma, and in juveniles dorsal spines stop the animal from sliding rearward. This series of actions can be repeated but is typically punctuated by long pauses to rest. These movements thus impart a discontinuous trail that may actually contain numerous (but subtle) resting traces. Depth of burial of a burrowing limulid is partially determined by mechanoreceptors on the carapace and legs (Eldredge, 1970). When both buried and submerged, a limulid can form currents underneath its body by a coordinated motion of its branchiae and operculum, effectively flushing water behind it on either side of the telson (Barthel, 1974; Shuster and Anderson, 2003). This action can form gas bubbles, but, more importantly from an ichnological perspective, it causes a depression underneath the limulid so that the sediment immediately surrounding it collapses. Juvenile limulids under laboratory conditions generate the same backward flow of water (Shuster and Anderson, 2003). A few probable traces that resulted from this behavior are described here from Sapelo Island.

Setting of Study Area: Sapelo Island, Georgia (USA) The study area, Sapelo Island (Georgia, USA: Fig. 29.2), is well known for providing the raw material for neoichnological models, along with other barrier islands of the Georgia coast (Weimer and Hoyt, 1964;

FIGURE 29.2 Study area: left, southeastern US, where GA = Georgia, SC = South Carolina, and FL = Florida, arrow indicating location of Sapelo Island; right, outline of Sapelo Island and locations of Nannygoat and Cabretta Beaches.


Pemberton and Frey, 1985; Frey and Pemberton, 1987). Beach and foreshore environments on the Georgia coast are affected by an ebb-dominated mesotidal regime, with an average tidal range of 2.4 m and average spring tide of nearly 3.4 m (Frey and Howard, 1988). The shoreface is composed mostly of finegrained quartz sand mixed with minor amounts of heavy minerals, some silt and clay, and shell debris (about 3–5% of the fraction), all of which is reworked by tides, waves, tropical storms, and bioturbation (Howard and Reineck, 1972; Howard and Frey, 1985; Frey and Howard, 1988). Beaches slope gently (28) and rarely have berms; ridge and runnel systems are prominent and form during ebb tides (Pilkey and Richter, 1964; Howard and Scott, 1983). Physical sedimentary structures include swash marks, antidunes, and oscillation, current, and rhomboid ripples, as well as flasers, which are caused by accumulation of clay fecal pellets (Frey and Howard, 1988). The two beaches examined in this study, Nannygoat and Cabretta (Fig. 29.2), are considerably broadened during low tides and are thus amenable for detailed observations of infauna and epifauna, some in the act of making traces. Cabretta Beach is particularly well suited for the study of traces, as it connects with expansive sandflats near the tidal inlet of Blackbeard Creek (Frey and Pemberton, 1987; Frey and Howard, 1988).

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FIGURE 29.3 Locomotion traces of juvenile Limulus polyphemus on exposed intertidal sandflat at Cabretta Beach, Sapelo Island, Georgia, July 2004. Scale in centimeters.

Locomotion Traces Made by Juvenile Limulids In July 2001, one of us (Martin), accompanied by other ichnologists, observed copious Nereites-like traces about 10 mm wide on rippled, intertidal sandflats on Cabretta Beach (Fig. 29.3). The tracemakers at first were presumed to be small gastropods, which were also crawling on the beach (Fig. 29.4), but exhumation of the actively burrowing tracemaker at the end of one trace revealed juvenile specimens of Limulus polyphemus. Repeated investigations of other similar traces resulted in identification of the same tracemaker. The intriguing relationship between this trace and tracemaker was duly noted and mentioned by Rindsberg and Martin (2003) as one piece of evidence supporting an arthropod maker for some Arthrophycus, Asterosoma, Cruziana, Phycodes, and Nereites. Interestingly, Frey and Pemberton (1987, Fig. 11) briefly mentioned and figured juvenile limulid traces from the Georgia barrier islands but did not describe their detailed morphology or compare them to Nereites. Return visits to Sapelo by Martin in June and July 2004 confirmed the same traces and

FIGURE 29.4 Trail of small gastropod on the same beach as Fig. 29.3. Scale in centimeters and millimeters.

tracemakers, but with more thorough documentation that included measurements, descriptions, and still and motion photography. These summer observations were augmented during early March 2005; the same traces and tracemakers were present, albeit less abundant. In the summer, juvenile limulids and their traces were abundant at both Cabretta and Nannygoat Beaches on sandflats exposed at low tide, as well as along edges of runnels that developed during ebb tides (Fig. 29.5). Juvenile limulids responsible for the formation of the traces are as small as 8 mm long (not including the telson) and 4 mm wide across the widest, ventral part of the prosoma; larger individuals (up to 2 cm

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wide) also made similar traces. These larger traces, however, also contain distinctive trackways absent in the smaller ones. The youngest juveniles have a nearly circular outline and short genal spines and telson (Fig. 29.6A). Older, larger juveniles have longer genal spines and telson as well as additional cephalic spines. As mentioned earlier, the latter are more prominently developed in juveniles than in adults, and assist in burrowing (Fig. 29.6B). These morphological additions and greater size help to distinguish locomotion traces made by limulids of different ages. The traces consist of indefinitely long (>1 m), straight to wandering, 8–16 mm wide, shallow (3–4 mm deep) furrows that frequently loop and intersect themselves as well as other furrows. Curving and looping portions of the trails are broad

to tight, but rarely double back as 1808 turns; even these are for short distances (2–3 cm) before resumption of a more linear course. In some cases, abrupt turns of nearly 908 are seen. Juveniles are so abundant, and crosscutting of their traces is so common, that individual traces merge in places and cannot be followed in their entirety. Although concentrated in ripple troughs and other depressions, traces may cross ripple crests, generally at close to a right angle (Fig. 29.7). Juvenile limulid locomotion traces have a diagnostic sculpture that helps to distinguish them from gastropod trails of similar size in the same tidal pools. The limulid trails are composed of a ribbon flanked by two raised ridges. The ribbon is 5–10 mm wide, about 50–75% the total width of trails, and is

FIGURE 29.5 Runnel bank developed during ebb tide, Cabretta Beach, Sapelo Island, Georgia. Juvenile limulid locomotion traces are most abundant at lower edges and emergent to very shallow areas of runnels. Scale (center foreground) 15 centimeters.

FIGURE 29.7 Abundant juvenile limulid locomotion traces in ripple troughs, but with some crossing ripple crests: Nannygoat Beach, Sapelo Island, Georgia. Note rightangle turns to some traces and juvenile limulids (indicated by arrows). Scale in centimeters.

FIGURE 29.6 Morphological comparison of juvenile limulids from Sapelo Island, Georgia. (A) Smaller (= younger) specimen with semi-circular outline, very short genal spines, and small telson. (B) Larger (= older) specimen with longer genal spines and telson, as well as cephalic spines. Scale in millimeters and centimeters.


FIGURE 29.8 Juvenile limulid (same individual pictured in Fig. 29.6b) burrowing into saturated, cohesive, very finegrained sand, Cabretta Beach, Sapelo Island, Georgia. The beadlike structures in the flanks of the trail were produced by the walking legs; note that their flatter halves slope in the direction of movement.

bilobate, with a structure composed of chevron-like lamellae that connect with a thin (1 mm) medial groove; ridges are about 2–3 mm tall. The medial groove is continuous in straight to slightly meandering trails, but is broken up into short, discrete, offset segments wherever trails turn at abrupt angles. Upraised ridges, which are commonly beaded or padded, delimit trail flanks. The bead-like structures are subspherical to asymmetrical with flatter surfaces sloping forward (Fig. 29.8). Wider ends of chevrons can be used as predictors for finding the tracemakers at the ends of trails, confirming the direction of locomotion. An upraised mound of sand or, conversely, a depression slightly larger than limulid body size indicates the tracemaker’s presence at the trail end (Fig. 29.9). Where a mound of sand is formed, the limulid is burrowing under a few millimeters to as much as a centimeter of sediment, but the resultant trace has the appearance of a ‘surface trail.’ Terminations of locomotion traces thus show the transition between an epibenthic locomotion trace (made like a trackway, but plowing through mobile, thixotropic sediment to produce a surface trail) and a shallow endobenthic burrow. Hence, our reference to the resulting structure is as a locomotion trace, rather than either a trail or burrow. A depression results from a buried limulid flushing water while at rest, which collapses the sand beneath its body. These depressions are further deepened by the absence of the formerly resting limulid.

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FIGURE 29.9 Juvenile limulid locomotion trace showing an initial concave resting trace (bottom) followed by multiple looping behavior and a terminal convex resting trace (top): Nannygoat Beach, Sapelo Island, Georgia. Note considerable changes in trace morphology throughout its course. Scale in centimeters.

FIGURE 29.10 Juvenile limulid locomotion trace showing transition between Nereites-like trail and trackways with distinct, individual tracks Cabretta Beach, Sapelo Island, Georgia. Offset of telson drag mark (arrow) indicates that tracemaker movement was left to right.

Differences in substrate consistency strongly affect morphologic details of the locomotion traces. Structure is muted in traces submerged in 1–2 cm deep water within ripple troughs, and clearest on exposed surfaces. The beaded flanks of traces made in areas with more cohesive (less saturated) sand, drained for a few hours during low tide, are noticeably better defined. Some of the traces

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FIGURE 29.11 Nereites-like juvenile-limulid locomotion trace, in which wet, cohesive, very fine-grained sand formed ridges and pads of sand, made by limulid prosoma and rear pair of walking legs (respectively); Cabretta Beach, Sapelo Island, Georgia.

show smooth, contiguous morphological transitions of furrows into trackways (Fig. 29.10), meaning that individual juvenile limulids were capable of making ‘trails’ (furrows), burrows, and trackways all along the same pathway. Clay content, however minor, also contributes to sand cohesiveness and helps to accentuate beads of sediment on the flanks of the locomotion traces. The morphology of these locomotion traces, like all traces, results from an interaction of substrates, tracemaker behavior, and tracemaker anatomy. The wet, cohesive, commonly slightly clayey, very fine- to fine-grained sand of Sapelo beaches provides substrates that hold the shape of the traces, including ridges and individual pads of sand made by the prosoma and the posterior pair of walking legs (respectively) on trail flanks (Fig. 29.11). The forward movement of the tracemakers, initiated and maintained by the anterior four pairs of walking legs, forms the structure of nested chevronlike lamellae. Dragging of the telson creates a medial groove, together with short, disconnected segments where the telson was lifted and set back down with each separate movement during turns. Turning or banking movements by limulids to change direction mound the sediment on the outer flanks, a pressure-release structure (sensu Brown, 1999; Martin, 2004) that reveals the direction of locomotion. In contrast, trails of small gastropods made at the same time and place are notably asymmetric in overall plan view. These gastropod trails only infrequently have beads or pads of sediment on trail flanks, and

lack medial grooves (Fig. 29.2). These circumstances seem logical, considering that the tracemakers are also asymmetric; hence, gastropod trails in which sand is shunted aside are likely to be asymmetric as well, as documented without comment by Scha¨fer (1972, p. 208), Frey and Howard (1972, Figs. 3, 4), Miller (1997), and others. With these search images in mind, it was possible to predict accurately which tracemaker was buried at the end of its trail. Possible interrelationships between trace preservation and behavior should be emphasized. Juvenile limulids are most active on sandflats during daytime low tides in late spring and summer. This coincidence of abundant traces with higher temperatures is conducive to dehydration of their traces, which presumably could enhance their preservation in the geologic record. Experiments using different mixes of sand and mud under prescribed temperature variations might test this hypothesis. Furthermore, burial of trails, trackways, and shallow burrows might cause difficulties in later distinctions of epibenthic vs. endobenthic components of locomotion traces. Indeed, such perceived differences may be moot, as a juvenile limulid traveling along a stiff sedimentary surface below a sediment-water or sediment-air interface would still produce a similar trace on the lower portion of a burrow.

NEREITES AND ITS MAKERS RECONSIDERED Given the dominance of arthropods in modern and ancient ecosystems, their subsurface traces should be common in the Paleozoic record. Yet only a few ichnogenera of such traces are accepted, generally as made by arthropods, especially Cruziana (Seilacher, 1970). As Bromley (2004) and Seilacher (2004) recently emphasized, the key to identification of tracemakers is the recognition not of generalized behaviors that many different groups of animals can make, but of a distinctive ‘signature’ or ‘fingerprints’ that ideally only a particular group can make. Such ‘fingerprints’ are better termed the traces’ bioprint in accordance with recent usage in biometrics, the technology of identifying individual humans (Garfinkel, 2002; Rindsberg and Kopaska-Merkel, 2005). The bioprint of ancient animals is most easily deciphered by reference to the behavior of modern animals (Scha¨fer, 1972). In practice, the bioprint of a trace is rarely so distinctive as to pinpoint only one clade of maker. Indeed, there can be a seamless

NEREITES AND ITS MAKERS RECONSIDERED

continuum from certainty to uncertainty of the maker (Bromley, 2004). In modern juvenile limulid traces, as in Silurian trilobite-made Arthrophycus brongniartii (Rindsberg and Martin, 2003), we see several features that are suggestive of short-bodied, stiff animals with paired appendages. These features, which together make up the juvenile limulids’ bioprint, include: Discrete, short, and regular segments occurring within a locomotion trace; Resting traces embedded within the locomotion trace, in some cases showing details of the anterior anatomy (including legs); Abrupt turns that show accompanying sediment deformation caused by a stiff body, rather than coelomic expansion and contraction; Lateral beads or pads of sediment joining with a more medial structure of nested lamellae; and Medial grooves imparted by a tail-like telson, which also may show offset segments associated with turns. Granted, not all of these traits may be preserved in any given trace made by a short-bodied arthropod, but the presence of any one of them should prompt an examination for evidence of the others. Nonetheless, the most critical limulid bioprint is the groove made by dragging of the stiff, tail-like telson. This bioprint is important to note because it overlaps on some of the most angular curves of trails. This unusual feature might recur in locomotion traces made by trilobites or other arthropods having a terminal pygidial spine. In most post-Paleozoic occurrences, this bioprint probably indicates a xiphosuran maker. In the Upper Jurassic Solnhofen Limestone of Bavaria, a much-photographed specimen of a limulid at the end of its trackway shows several such telson imprints (Barthel et al., 1990, Fig. 7.35)—not the staccato telson imprints of an animal in its death throes, but normal imprints made by the animal while turning before it dies. Modern juvenile limulid traces on Georgia beaches are admittedly imperfect analogs for ancient Nereites for several reasons: Limulids are shallow-marine, but Nereites is largely or exclusively found in deep-sea settings in post-Paleozoic strata (Seilacher, 1963, 1964). Nereites, however, is common in shallow-marine settings in Paleozoic strata (e.g., Rindsberg, 1994). Most (though not all!) ancient Nereites was probably made at a greater depth in the

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sediment than the observed modern traces (compare Rindsberg, 1994; Wetzel, 2002). This difference is perhaps less important than it seems, for juveniles of burrowing species commonly burrow more shallowly than adults, and the mechanics of digging are similar in ancient Nereites and modern limulid traces. It is clear that modern microcarnivorous limulids do not make fecal ribbons, which result from deposit-feeding. The consensus search image for Nereites includes an internal fecal ribbon (Seilacher and Meischner, 1965; Chamberlain, 1971; Uchman, 1995), which is replaced by a medial imbricate ribbon in modern limulid traces. Probably both structures are represented in the fossil record among specimens called Nereites, and type specimens of the various ichnospecies should be reinvestigated to determine which, a study that is beyond the scope of this chapter. Thus, unlike Wetzel (2002), we can only report modern examples of Nereites-like traces, not Nereites itself. However, we can state positively that we have documented modern traces that, in form, mode of construction, and function, are the most similar analogs yet known to ancient Nereites. What can we get from this? Some formerly puzzling features of Nereites can be explained given a short-bodied arthropod as a maker. The internal ribbon of nested lamellae and beads (or pads) of sediment occur in modern limulid trails as well as in Nereites. Yet Nereites from different paleoenvironmental settings can look remarkably similar. Additionally, because juvenile limulids also plow through sediment as they move along a surface, their pathways represent a transitional interface between epibenthic and endobenthic traces. Though some workers consider Nereites as a strictly endobenthic burrow, not a surface trail, our evidence indicates that trails and shallow burrows can be contiguous; the distinction is thus artificial. Closer attention to the bioprint of modern arthropods would likely make it clear that Phanerozoic Nereites was made by diverse arthropods of similar shape—and perhaps even allow tracking of individual lineages of tracemakers through time. Other ichnogenera should be reexamined with the same attention to tracemaker. In sum, short-bodied xiphosurans, trilobites (e.g., trinucleines) and other arthropods of similar form should be considered as possible tracemakers of Nereites or morphologically similar trace fossils in the geologic record. Our findings are in contrast to

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long-held views by some, that Nereites tracemakers must be worms, gastropods, or similar legless animals (Chamberlain, 1971; Seilacher, 1986) and are based on actualistic examples rather than conjecture. Until a neoichnological model for a legless tracemaker of Nereites-like traces is proposed, using a real (not speculative) animal, our model is the only standard for comparison.

ONTOGENY AND ICHNODIVERSITY As a final note, our observations of juvenile L. polyphemus traces indicate that ontogenetic changes in anatomy and behavior of a single species of tracemaker can produce a number of distinctively different trace forms. Locomotion by L. polyphemus would generate Nereites-like traces during the first (juvenile) year of life, then Kouphichnium after the second or third year; the full range of traces made at different ontogenetic stages is as yet only incompletely known. In principle, traces made by different instars should be distinguishable because the animal gains in mobility of the telson and other appendages, as well as size and complexity of behavior. Thus, modern traces of Limulus polyphemus provide further confirmation that ichnodiversity does not correspond to biodiversity (Seilacher, 1953; Rindsberg and Martin, 2003; Martin and Pyenson, 2005). A suite of trail-like trace fossils such as Nereites, Arthrophycus, and Cruziana, including those of different sizes, can be made by the same species of arthropod.

CONCLUSIONS Juvenile limulids in intertidal sandflats of Sapelo Island (Georgia, USA) provide a neoichnologically based argument for the formation of Nereites-like traces by short-bodied arthropods such as xiphosurans, trinucleine trilobites, and similar shaped arthropods. As a consequence, Phanerozoic examples of Nereites should be examined more closely to test the applicability of the arthropod-tracemaker model. Awareness that different growth stages can produce morphologically distinct traces can help to prevent overestimation of biodiversity based on trace fossil assemblages.

ACKNOWLEDGEMENTS This research was inspired during an informal field trip to Sapelo Island in July 2001, before the 6th International Ichnofabric Workshop organized by the late Nicola´s Munõz in Isla Margarita, Venezuela. Accordingly, we would like to dedicate this chapter to Nicola´s, whose tirelessness and good cheer are fondly remembered. Field trip participants Richard Bromley (University of Copenhagen), Murray Gregory (University of Auckland), and Alfred Uchman (Jagiellonian University) are appreciated for their valuable ichnological input, and Stephen Henderson (Oxford College of Emory University) for his assistance in the field. Jon Garbisch (University of Georgia Marine Institute) and Ruth Schowalter (Georgia Institute of Technology) helped with logistics for successive visits by Martin from 2001–2004. Murray Gingras (University of Alberta) and an anonymous zoologist reviewer enriched the experience of writing and rewriting the manuscript. Lastly, the juvenile limulids, which at the time managed to survive 98% mortality rates, are acknowledged for their tracemaking activities, which made this research possible.

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Rudloe, A. (1980a). The breeding behavior and patterns of movement of horseshoe crabs, Limulus polyphemus, in the vicinity of breeding beaches in Appalachee Bay, Florida. Estuaries, 3, 177–183. Rudloe, A. (1980b). Orientation by horseshoe crabs, Limulus polyphemus, in a wave tank. Marine Behavioral Physiology, 7, 199–211. Rudloe, A. (1981). Aspects of the biology of juvenile horseshoe crabs, Limulus polyphemus. Bulletin of Marine Science, 31(1), 125–133. Scha¨fer, W. (1972). Ecology and Palaeoecology of Marine Environments. Edinburgh, Oliver and Boyd, University of Chicago Press,Chicago, 39 pl., 568 pp. Schimper, W.P. and Schenck, A. (1879–1890). Palaeophytologie. In: Zittel, K.A.von (Ed.), Handbuch der Palaeontologie, 2, Mu¨nchen and Leipzig, Oldenbourg, 958 pp. ¨ ber die Seilacher, A. (1953). Studien zur Palichnologie, I. U Methoden der Palichnologie. Neues Jahrbuch fu¨r Geologie und Palaöntologie, Abhandlungen, 96(3), 421–452, 14 pl. Seilacher, A. (1963). Kaledonischer Unterbau der Irakiden. Neues Jahrbuch fu¨r Geologie und Palaöntologie, Abhandlungen, 10, 527–542. Seilacher, A. (1964). Biogenic sedimentary structures. In: Imbrie, J. and Newell, N.D. (Eds.), Approaches to Paleoecology, John Wiley and Sons, New York, pp. 296–316. Seilacher, A. (1970). Cruziana stratigraphy of ‘nonfossiliferous’ Palaeozoic sandstones. (Crimes, T.P. and Harper, J.C. Eds.), Trace Fossils, Geological Journal, Special Issue, 3, 1 pl., 447–476. Seilacher, A. (1974). Flysch trace fossils: evolution of behavioural diversity in the deep-sea. Neues Jahrbuch fu¨r Geologie und Palaöntologie, Monatshefte, 4, 233–251. Seilacher, A. (1986). Evolution of behavior as expressed in marine trace fossils. In: Nitecki, M.H. and Kitchell, J.A. (Eds.), Evolution of Animal Behavior, Oxford University Press, New York, pp. 67–87. Seilacher, A. (2000). Ordovician and Silurian arthrophycid ichnostratigraphy. In: Sola, M.A. and Worsley, D. (Eds.), Geological Exploration in Murzuq Basin, The Geological Conference on Exploration in the Murzuq Basin held in Sabha, September 20–22, 1998, organized by the National Oil Corporation and Sabha University, Amsterdam, Elsevier, pp. 237–258. Seilacher, A. (2004). Principles of ichnostratigraphy. In: Buatois, L.A. and Mańgano, M.G. (Eds.), Ichnia 2004, First International Congress on Ichnology, April 19–23, 2004, Museo Paleontolo´gico Egidio Feruglio, Trelew, Patagonia Argentina, Abstract book, pp. 9–10. Seilacher, A. and Meischner, D. (1965). Fazies-Analyse im Palaözoikum des Oslo-Gebeites. Geologische Rundschau, (for 1964), 54(2), 596–619. Shuster, Jr. C.N. (1982). A pictorial review of the natural history and ecology of the horseshoe crab Limulus polyphemus, with reference to other Limulidae. In: Bonaventura, J., Bonaventura, C. and Tesh, S. (Eds.), Physiology and Biology of Horseshoe Crabs: Studies on Normal and Physiologically Stressed Animals, Alan R. Liss, New York, pp. 1–52. Shuster, C.N. and Anderson, L.I. (2003). A history of skeletal structures: clues to relationships among species. In: Shuster, Jr. C.N., Barlow, R.B. and Brockmann, H.J. (Eds.), The American Horseshoe Crab, Harvard University Press, Cambridge, Massachusetts, pp. 154–188. Shuster, Jr. C.N. and Sekiguchi, K. (2003). Growing up takes about ten years and eighteen years. In: Shuster, Jr. C.N., Barlow, R.B. and Brockmann, H.J. (Eds.), The American Horseshoe Crab,

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30 Macaronichnus isp. Associated with Piscichnus waitemata in the Miocene of Yonaguni-jima Island, Southwest Japan Nobuhiro Kotake

Pickerill, 1994; Pickerill and Narbonne, 1995; Uchman and Wetzel, 1999; Miller, 2001). In many cases, composite ichnofossils represent a combination of a primary larger host structure and the subsequently produced smaller sized forms created by an infaunal deposit feeder. For example, Chondrites and associated host burrows, Gyrolithes, Planolites, and Thalassinoides, have been known to occur together as composite ichnofossils (e.g., Krejci-Graf, 1936; Ehrenberg, 1942; Kennedy, 1967; Bromley and Frey, 1974; Ekdale and Bromley, 1984; Miller, 2001). Piscichnus waitemata Gregory (1991) is a large, simple, pothole-like excavation structure occurring in sandy sediments deposited in shallow marine settings and is the result of the feeding behavior of rays (elasmobranchs) (Howard et al., 1977; Gregory et al., 1979; Gregory, 1991; Martinell et al., 2001; Kotake and Nara, 2002; Kotake et al., 2004). The fill in P. waitemata usually exhibits sedimentary structures related to the specialized feeding manner of the producer and subsequent re-sedimentation processes (Howard et al., 1977; Gregory et al., 1979; Gregory, 1991; Kotake et al., 2004). Many well-preserved specimens of P. waitemata occur in the uppermost stratigraphic interval of the Yonaguni Formation (early Middle Miocene) distributed on the Yonaguni-jima Island, Okinawa, southwest Japan. The P. waitemata-bearing interval consists of massive or weakly stratified, very fineto fine-grained sandstone or silty sandstone. Piscichnus waitemata occurring in the interval

SUMMARY : A composite ichnofossil is characterized by two or more discrete structures belonging to different ichnotaxa apparently making up a single structure. In this chapter, a peculiar specimen of a composite ichnofossil, which consists of separate elements assignable to Piscichnus waitemata and Macaronichnus isp., is described and interpreted. The fill in the host ichnofossil P. waitemata produced by feeding behavior of rays was completely emplaced by subsequently produced Macaronichnus isp. Producers of Macaronichnus isp. treated herein may have invaded the Piscichnus-fill in a very short period after the production of P. waitemata and completely reworked the sediment in the fill. The fill in Piscichnus was utilized by the Macaronichnus-producer as a new but temporary habitat. Such a deep penetration of Macaronichnus isp. has led to an unusually high potential of preservation for this ichnofossil, which typically represents the shallowest tier ichnofossil in the studied interval.

INTRODUCTION A composite ichnofossil is characterized by two or more discrete trace fossils belonging to different ichnotaxa seeming to be parts of a single burrow. Such specimens are recognized as a common mode of trace fossil occurrence (Seilacher, 1964; Bromley and Frey, 1974; Chamberlain, 1975; Fu, 1991; Wetzel, 1991;

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GEOLOGIC SETTING

examined is easily recognizable in terms of the difference in lithologic and fabric aspects between the fill and the surrounding host sediments. Some remarkable specimens of P. waitemata, of which fill is completely reworked by densely packed Macaronichnus isp., are found in the interval. The composite structure consisting of a combination of P. waitemata and Macaronichnus isp. must be treated as a co-occurrence of two completely different ichnofossils. However, little is known about such a combination. In this chapter, I intend to (1) describe the characteristics of morphology and mode of occurrence of this remarkable example of a composite ichnofossil occurring in the Middle Miocene shallow marine sediments, (2) consider ecologic and ethologic significance of the composite structure, and (3) discuss the relationships between the bioturbation induced by feeding behavior of rays and the significance of the preservation potential of Macaronichnus isp.

GEOLOGIC SETTING The early Middle Miocene Yonaguni Formation represents a basal rock unit of the sedimentary succession on Yonaguni-jima Island, Okinawa, southwest Japan (Fig. 30.1). Excellent exposures of the formation are restricted to the coastal cliffs, and elsewhere is covered by the thick limestone unit of the Lower to Middle Pleistocene Ryukyu Group (e.g., Nohara, 1971; Sakai et al., 1978; Yazaki, 1982; Iryu and Suzuki, 1990; Ota and Omura, 1992), or by subtropical forest. The Yonaguni Formation consists mainly of repetition of sandstone- and mudstonedominated lithologic units, both of which were deposited in shallow marine settings ranging from deltaic tidal flat to inner shelf environments (Sakai et al., 1978; Kotake and Nara, 1995). Piscichnus waitemata occurs abundantly in the Yonaguni Formation cropping out at Kubura-bari (Figs. 30.2 and 30.3). The Piscichnus-bearing interval

FIGURE 30.1 Index map showing the study area and simplified geologic map of the Yonagunijima Island. Geologic map is modified after Sakai et al. (1978). 1—Quaternary terrace deposit and alluvium, 2—Lower to middle Pleistocene Ryukyu Group, and 3—Middle Miocene Yonaguni Formation.

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30. MACARONICHNUS ISP. ASSOCIATED WITH PISCICHNUS WAITEMATA IN THE MIOCENE OF YONAGUNI-JIMA ISLAND

represents the uppermost part of the formation. The gentle dip (less than 108 southward) of the Piscichnus-bearing strata and excellent exposures of the interval permit detailed field observation of the trace fossils not only on bedding plane surfaces but also on vertical surfaces of the coastal cliffs (Fig. 30.3A). Lithologic and sedimentologic characteristics strongly suggest that the P. waitemata-bearing interval accumulated on the seafloor between the inner shelf and lower shoreface environments. The sediments deposited at the inner shelf environment consist of well-sorted, very fine- to fine-grained sandstone and silty sandstone without any sedimentary structures of hydraulic origin owing to intense bioturbation after deposition (Fig. 30.3B). By contrast, the sediments of the shoreface environments consist of very fine- to fine-grained, massive, weakly stratified sandstone, in which amalgamated hummocky cross-stratification and low-angle trough cross-stratification occur as the distinct sedimentary structures (Fig. 30.3C). The P. waitemata-bearing interval contains trace fossils such as Bichordites monastiriensis, Macaronichnus isp., Ophiomorpha nodosa, Palaeophycus isp., Rosselia isp., Schaubcylindrichnus coronus, Skolithos linearis, and Thalassinoides suevicus. The cross-cutting relationships among the trace fossils occurring in the host sediments show that Macaronichnus isp. is cross-cut by all other trace fossils, and it is therefore interpreted as the shallowest tier trace fossil. By comparison, Rosselia isp. represents the deepest tier structure, of which maximum penetration depth attains up to 2 m below the sediment surface.

PISCICHNUS WAITEMATA FILLED WITH MACARONICHNUS ISP.

FIGURE 30.2 Lithology and occurrence interval of Piscichnus waitemata and P. waitemata with Macaronichnus isp. in the uppermost part of the Yonaguni Formation cropped out at the Kubura-bari. 1—fine- to medium-grained sandstone with fragments of shells, 2—massive very finegrained sandstone or silty sandstone deposited in the inner shelf environments and 3—weakly stratified very fineto fine-grained sandstone deposited in shoreface environments. E. Pl.—Early Pleistocene, R. Gr.—Byukyu Groups, vf—very fine-grained, m—medium-grained, and vc—very coarse-grained.

Piscichnus waitemata occurring in the interval examined herein is a large, subcylindrical to cylindrical, pothole-like excavation structure and is vertical or slightly oblique to bedding planes (Figs. 30.3B,C and 30.4). Dimensions of P. waitemata observed are variable between 5 and 56 cm in diameter, and 9 and 53 cm in depth. Most specimens of P. waitemata in the interval occur as isolated structures. Normal grading is usually visible in the fill. The boundary between the Piscichnusfill observed and the host sediment is clearly recognizable based on the textural and lithologic differences. Some remarkable specimens of P. waitemata, of which fills are completely penetrated by densely packed Macaronichnus isp., were found in the interval (Figs. 30.2 and 30.5). The combination of a primary


FIGURE 30.3 Outcrop photographs of the Yonaguni Formation at Kubura-bari and general mode of occurrence of Piscichnus waitemata. (A) The P. waitemata-dominated interval of the Yonaguni Formation cropped out at Kubura-bari. (B) Many specimens of P. waitemata are observed in the massive very fine-grained sandstone or silty sandstone deposited in the inner shelf environments. (C) P. waitemata (arrows) occurs in the weakly stratified very fine- to finegrained sandstone deposited in the shoreface environments. Scale bars are 1 m long.

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FIGURE 30.4 Outcrop photographs of Piscichnus waitemata observed in the study interval. (A) Cross section view of specimens of P. waitemata. Schaubcylindrichnus coronus (arrow) cross cuts specimens of P. waitemata. (B,C) Plan view of specimens of P. waitemata. Arrow in (C) indicates a specimen of Schaubcylindrichnus coronus. Pencil is about 14 cm long.


FIGURE 30.5 Outcrop photographs of Piscichnus waitemata filled with Macaronichnus isp. (A) Seven specimens of P. waitemata filled with Macaronichnus isp. are observable. (B,C) Close-up view of the specimens of P. waitemata filled with Macaronichnus isp. Specimens of Macaronichnus isp. in the fill of Piscichnus waitemata are seen as the white circular or elongate spots. A boundary between the fill of Piscichnus and the host sediments is clearly visible. Most of the specimens of Macaronichnus isp. in the upper part of the Piscichnus-fill of C are nearly completely overprinted and obliterated by Bichordites monastiriensis. The coin in the lower right-hand corner of (C) is 2 cm in diameter.

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host structure (P. waitemata) and subsequently produced trace fossil (Macaronichnus isp.) is an example of a composite form (e.g., Chamberlain, 1975; Pickerill, 1994; Pickerill and Narbonne, 1995). Macaronichnus isp. in the fill of P. waitemata is sinuous, unbranched, and cylindrical structures without apparent wall or burrow lining. In cross section, Macaronichnus isp. is seen as circular or elongate spots having 3–5 mm in diameter (or width) (Figs. 30.5B,C). These burrows are oriented parallel or slightly oblique to bedding planes. Macaronichnus isp. is composed of lighter colored sediments rich in colorless minerals compared to the surrounding host rock (Figs. 30.5B,C). As described below, Macaronichnus isp. occurring within the fill of the Piscichnus-structure is well preserved in comparison to specimens in surrounding sediments. In other words, the occurrence of well-preserved specimens of Macaronichnus isp. is restricted to the fill of P. waitemata in the study interval. The density of Macaronichnus isp. gradually decreases toward the upper part of the Piscichnus-fill as a result of overprinting by subsequently produced deep-tier trace fossils, in particular, B. monastiriensis and Rosselia isp. (Figs. 30.5B,C). Detailed observation on the composite trace fossils revealed the following recurrent patterns, (1) few specimens of Macaronichnus isp. are found at the same level in the Piscichnus-bearing host sediment; (2) the boundary between the fill and the surrounding host sediments was identifiable as a smooth, and distinct

line; and (3) no specimen of Macaronichnus isp. crosses the boundary between the Piscichnus-fill and the surrounding host rocks. These facts strongly suggest that the burrowing and sediment reworking activities of the Macaronichnus-producer were restricted only to the part of the fill. Apart from the difference in mode of occurrence, Macaronichnus isp. observed in the host sediment also exhibits the same morphologic characteristics as the specimens occurring in the Piscichnus-fill. Identical aspects between them strongly suggest that they were produced by the same endobenthic animal. Two types of occurrences of Macaronichnus isp. in the host sediment are recognizable in the interval examined: bedded aggregation type and non-aggregation type. The first type appears in slightly muddy portions of the stratified sandstone interval deposited in the lower shoreface. In this case, the aggregations of Macaronichnus isp. occur as thinly and intermittently bioturbated layers less than 2–3 cm in maximum thickness (Fig. 30.6). The second one is observable as isolated single specimens throughout the Piscichnusbearing interval (Fig. 30.5C).

DISCUSSION Many examples of composite ichnofossils consisting of a distinctive combination of P. waitemata and Macaronichnus isp. occur in the uppermost

FIGURE 30.6 General mode of occurrence of bedded aggregation type of Macaronichnus isp. observed on the oblique surface of massive fine-grained sandstone deposited in shoreface environments. This aggregation is about 2 cm in maximum thickness. Macaronichnus isp. consists of colorless minerals dominated sediments. The coin is 2 cm in diameter.

DISCUSSION

interval of the Yonaguni Formation (Figs. 30.2 and 30.3). Judging from cross-cutting relationships among the ichnofossils occurring in the Piscichnus-bearing interval, the producing animals of Macaronichnus isp. invaded the fill of P. waitemata and reworked the sediment in the fill prior to the activity of other trace fossil producers. Non-deformed cylindrical morphology of Macaronichnus isp. is indicative of the weak sediment compaction of the sandy host rocks during the diagenetic process after production of the structure (Figs. 30.5 and 30.6). This suggests that the Yonaguni Piscichnus retain a nearly original shape and dimension. If so, the Macaronichnusproducers that invaded the Piscichnus-fill burrowed at least 30–40 cm beneath the sea floor. Cross-cutting relationships among the ichnofossils occurring in the sediments surrounding Piscichnus strongly suggest that Macaronichnus isp. apparently represent the shallowest tier ichnofossil. Therefore, the specimens of P. waitemata filled with Macaronichnus isp. can be interpreted to be a product of certain special behaviors of the Macaronichnus-producers. In other words, the Macaronichnus-producers invaded the Piscichnus-fill seem to have temporarily switched their behavioral pattern. The ichnofossil Chondrites, characterized by a systematic branched tunnel system, is known as one of the most famous representatives that penetrate fills of different trace fossils such as Diplocraterion, Gyrolithes, Planolites, and Thalassinoides (Krejci-Graf, 1936; Ehrenberg, 1942; Seilacher, 1964; Kennedy, 1967; Bromley and Frey, 1974; Ekdale and Bromley, 1984; Fu, 1991; Wetzel, 1991; Pickerill, 1994; Pickerill and Narbonne, 1995; Uchman and Wetzel, 1999; Miller, 2001). Previous authors have discussed the origin of composite forms based on the difference in consistency and/or food content level between the burrow fill and the surrounding host sediment. According to the previous interpretations, the Chondrites-producers may have invaded the primary host burrows filled with soft and enriched sediments in preference to the host sediments to exploit labile organic matter (e.g., Kennedy, 1967; Uchman and Wetzel, 1999). Piscichnus waitemata is well known as a trace fossil record of the feeding behavior of rays (Howards et al., 1977; Gregory et al., 1979; Gregory, 1991; Martinell et al., 2001; Kotake and Nara, 2002; Kotake et al., 2004). According to observations on the recent feeding excavations produced by rays, while the single feeding activity of a ray may be carried out during a very short interval of time, the substrate at the feeding area may sustain intense and deep sediment reworking

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(Howards et al., 1977; Gregory et al., 1979; Hines et al., 1997; Maruska and Tricas, 1998). In this sediment reworking process, many pothole-like excavations filled with loose and food-rich sediments containing oxygenated pore-water are produced. Indeed it is known that organic carbon content is elevated in the sediment of the feeding excavations produced by rays, and polychaetes or bivalves recolonized rapidly after the production of such excavations (Thrush et al., 1991). Therefore, such excavations must be a favorable micro-habitat for some endobenthic deposit feeders. This is because they can easily penetrate the fill and efficiently obtain organic material for their food without waste of energy. Opheliid polychaetes belonging to the genus Euzonus and Ophelia generally have been considered as the candidates for the producer of Macaronichnus on the basis of observations of recent animals (e.g., Clifton and Thompson, 1978; Nara, 1994; Gingras et al., 2002; Nara and Seike, 2004). This implies that the producer of Macaronichnus isp. examined herein also represents an endobenthic deposit-feeder. It seems likely that the Macaronichnus-producers have burrowed into the fill of P. waitemata to utilize enriched food resources. The Piscichnus-structure filled with nutrient-rich sediments appears to represent a spatiotemporally localized food resource for the Macaronichnus-producer. Since Macaronichnus isp. in the Piscichnus-bearing host sediments represents the shallowest tier trace fossil, the preservation potential of the ichnofossil must be extremely low because the shallowest tier trace fossils, such as Macaronichnus isp., are usually obliterated by other burrowers during the short interval of time after production of these ichnofossils. Few specimens of Macaronichnus isp. are preserved in the Piscichnus-bearing sediment. many well-preserved specimens However, of Macaronichnus isp. were preserved in the fill of P. waitemata. Because Macaronichnus isp. is cross-cut b all other ichnofossils, burrowing and reworking activity by the producers may have taken place prior to the activity of other burrowers during a very short period after the production of P. waitemata. As described above, the sediment of the Piscichnus-fill is characterized by softer and looser material than that of the surrounding sediment. Therefore, the Macaronichnus-producers could have easily and deeply invaded the sediment in the Piscichnus-fill in comparison with the surrounding sediment. The unusually deep burrowing of the Macaronichnus-producers within

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the fill of P. waitemata may have augmented preservation potential for the Macaronichnus burrows.

CONCLUSIONS The trace fossil Piscichnus waitemata produced by the feeding behavior of rays predominantly occurs in the uppermost part of the Middle Miocene Yonaguni Formation on the Yonaguni-jima Island, Okinawa, southwest Japan. The fill in some specimens of the Yonaguni Piscichnus is completely penetrated by densely packed Macaronichnus isp., the producing organisms invading the fill after the production of the Piscichnus-structure. The Piscichnus-structures with Macaronichnus isp. can be treated as examples of composite ichnofossils. Detailed analysis of morphology and mode of occurrence strongly suggests that the Macaronichnus-animals, which are considered as the shallowest tier burrower under the ordinary bottom conditions, deeply invaded the fill of the Piscichnus-structure to search for food and completely reworked the sediments within a short period after the production of the Piscichnusstructure. The Piscichnus–Macaronichnus combination examined herein seems to represent one of the best examples of ‘contemporaneous composite’ trace fossils described by Miller (2003). Soft substrate containing oxygenated pore-water in the fill of P. waitemata in comparison with the sediments surrounding the Piscichnus-structures allowed the Macaronichnus-animals to burrow deep in sediments up to 40 cm below the sea floor. In spite of the fact that Macaronichnus isp. occurring in the host sediments is usually characterized by a quite low potential of preservation, special and temporal behavior of the Macaronichnus-animals that invaded deeply into the fill of P. waitemata appear to have enhanced the preservation of the Macaronichnus burrows. Most previous authors have focused mainly on the trace fossils produced by the benthic invertebrates living on and below the seafloor. Bioturbation related to the activities of benthic vertebrates must be quite different from those of invertebrates in terms of the fundamental mechanism and the reworked sediment volume within a unit of time. This strongly suggests that the study of trace fossils produced by marine vertebrates is also very important to understand comprehensively the bioturbation that takes place in the marine sediments.

ACKNOWLEDGEMENTS The author thanks William Miller III for critical reading of the earlier version of the manuscript. This manuscript has improved by critical review by John W. Huntley and Leif Tapanila, to whom I express my sincere gratitude. Preparation of figures was supported by Michiaki Fujioka. This work was supported by the JSPS grants (no. 15540447).

References Bromley, R.G. and Frey, R.W. (1974). Redescription of the trace fossil Gyrolithes and taxonomic evaluation of Thalassinoides, Ophiomorpha and Spongeliomorpha. Bulletin of the Geological Society Denmark, 23, 311–335. Chamberlain, C.K. (1975). Trace fossils in DSDP cores from the Pacific. Journal of Palaeontology, 49, 1074–1096. Clifton, H.E. and Thompson, J.K. (1978). Macaronichnus segregates: a feeding structure of shallow marine polychaetes. Journal of Sedimentary Petrology, 48, 1293–1301. Ehrenberg, K. (1942). Uber einige Lebensspuren aus dem Oberkreideflysch von Wien und Umgebung. Palaeobiologica, 7, 282–313. Ekdale, A.A. and Bromley, R.G. (1984). Comparative ichnology of shelf-sea and deep-sea chalk. Journal of Palaeontology, 58, 322–332. Fu, S. (1991). Funktion, Verhalten und Einteilung fucoider und lophocteniider Lebensspuren. Senkenbergischen Naturforschenden Gesellschaft Frankfurt, 135, 1–79. Gingras, M.K., MacMillan, B., Balcom, B.J., Saunders, T. and Pemberton, S.G. (2002). Using magnetic resonance imaging and petrographic techniques to understand the textural attributes and porosity distribution in Macaronichnus-burrowed sandstone. Journal of Sedimentary Petrology, 72, 552–558. Gregory, M.R. (1991). New trace fossils from the Miocene of Northland, New Zealand: Rorschachichnus amoeba and Piscichnus waitemata. Ichnos, 1, 195–205. Gregory, M.R., Balance, P.F., Gibson, G.W. and Alying, A.M. (1979). On how some rays (Elasmobranchia) excavate feeding depressions by jetting water. Journal of Sedimentary Petrology, 49, 1125–1130. Hines, A.H., Whitlatch, R.B., Thrush, S.F., Hewitt, J.E., Cummings, V.J., Dayton, P.K. and Legengre, P. (1997). Nonlinear foraging response of a large marine predator to benthic prey: eagle ray pits and bivalves in a New Zealand sandflat. Journal of Experimental Marine Biology and Ecology, 216, 191–210. Howard, J.D., Mayou, T.V. and Heard, R.W. (1977). Biogenic sedimentary structures formed by rays. Journal of Sedimentary Petrology, 47, 339–346. Iryu, Y. and Suzuki, A. (1990). Depositional environment of Halimeda limestone of the Ryukyu Group on Yonaguni-jima. Fossil, 49, 13–22. Kennedy, W.J. (1967). Burrows and surface trace fossils from the Lower Chalk of southern England. Bulletin of the British Museum (Natural History) Geology, 15, 127–167. Kotake, N. and Nara, M. (1995). Sequence stratigraphy of the Kuburatagi Formation of the Yaeyama Group, Yonaguni-jima Island, Okinawa, southwest Japan. The Memories of the Geological Society of Japan, 45, 208–222.

REFERENCES

Kotake, N. and Nara, M. (2002). The ichnofossil Piscichnus waitemata: biogenic sedimentary structure produced by the foraging behavior using water jet. The Journal of the Geological Society of Japan, 108, 1–2. Kotake, N., Kondo, Y., Fujii, T. and Shibasaki, H. (2004). Palaeontologic and ichnologic interpretation for a peculiar mode of occurrence of shell concentrations in the lower part of the Tatamigaura Sandstone Member of the Tougane Formation (Middle Miocene), Hamada, western part of Shimane, Japan. The Journal of the Geological Society of Japan, 110, 733–745. Krejci-Graf, K. (1936). Zur Natur der Fucoiden. Senckenbergiana, 18, 308–315. Martinell, J., de Gibert, J.M., Domenech, R., Ekdale, A.A. and Steen, P.P. (2001). Cretaceous ray traces?: an alternative interpretation for the alleged dinosaur tracks of La Posa, Isona, NE Spain. Palaios, 16, 409–416. Miller, W., III. (2001). Thalassinoides–Phycodes compound burrow systems in Palaeocene deep-water limestone, Southern Alps of Italy. Palaeogeography, Palaeoclimatology, Palaeoecology, 170, 149–156. Miller, W., III. (2003). Palaeobiology of complex trace fossils. Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 3–14. Muruska, K.P. and Tricas, T.C. (1998). Morphology of the mechanosensory lateral line system in the Atlantic stingray, Dasyatis sabina: the mechanotactile hypothesis. Journal of Morphology, 238, 1–22. Nara, M. (1994). What is the producer of ‘trace fossil of Excirolana chiltoni’? — tracemaking mechanism of Macaronichnus segregates. Fossil, 56, 9–20. Nara, M. and Seike, K. (2004). Macaronichnus segregatis-like traces found in the modern foreshore sediments of the Kujyukuri-hama Coast, Japan. The Journal of the Geological Society of Japan, 110, 545–551.

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Nohara, T. (1971). Geology and palaeontology of Yonaguni-jima. Bulletin of Science and Engineering Division, University of Ryukyu, 14, 64–103. Ota, Y. and Omura, A. (1992). Contrasting styles and rates of tectonic uplift of coral reef terraces the Ryukyu and Daito Islands, southwestern Japan. Quaternary International, 15/16, 17–29. Pickerill, R.K. (1994). Nomenclature and taxonomy of invertebrate trace fossils. In: Donovan, S. (Ed.), The Palaebiology of Trace Fossils, Wiley, Chichester, pp. 3–42. Pickerill, R.K. and Narbonne, G.M. (1995). Composite and compound ichnotaxa, a case example from the Ordovician of Quebec, eastern Canada. Ichnos, 4, 53–69. Sakai, T., Hamada, S., Tsuji, K., Suzuki, I. and Kurokawa, M. (1978). Geology of Yonaguni-Island, Yaeyama Archipelago. Geological study on Ryukyu Islands, 3, 61–79. Seilacher, A. (1964). Biogenic sedimentary structures. In: Imbrie, J. and Newell, N. (Eds.), Approaches to Palaeoecology, Wiley, New York, pp. 296–316. Thrush, S.F., Pridmore, R.D., Hewitt, J.E. and Cummings, V.J. (1991). Impact of ray feeding disturbances on sandflat macrobenthos: do communities dominated by polychaetes or shellfish respond differently? Marine Ecology - Progress Series, 69, 245–252. Uchman, A. and Wetzel, A. (1999). An aberrant, helicoidal trace fossil Chondrites Sternberg. Palaeogeography, Palaeoclimatology, Palaeoecology, 146, 165–169. Wetzel, A. (1991). Ecologic interpretation of deep-sea trace fossil communities. Palaeogeography, Palaeoclimatology, Palaeoecology, 85, 47–69. Yazaki, K.( 1982). Geology of the Yonagunishima District. Quadrangle Series 1/50000, Miyako-jima (19) No. 7, Geological Survey of Japan, 57 pp.

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31 Meiobenthic Trace Fossils as Keys to the Taphonomic History of Shallow-Marine Epicontinental Carbonates Dirk Knaust

INTRODUCTION

SUMMARY : Beside the occurrence of numerous macroscopic invertebrate burrow and bioerosion trace fossils, meiobenthic trace fossils are common on micritic bedding planes in Middle Triassic marginalmarine carbonates of the Germanic Muschelkalk Basin and studied in detail for the first time. Their rapidly changing style of preservation together with the sedimentological context implies a peritidal (subtidal to supratidal) palaeoenvironment, in which most animals die on an exposed carbonate mud flat due to desiccation and sudden changes in substrate consistency. The uniqueness of this Fossil-Lagersta¨tte is the fact that many of the soft parts of the meiobenthic trace makers (foraminiferans, nematodes, nemerteans, annelids, arthropods and worm-like animals) are preserved in situ due to favourable circumstances in which the fossilisation of the decaying organic material takes place in a dysaerobic microenvironment after rapid burial. Even if the internal structure of the soft-bodied organisms is mostly destroyed due to early-diagenetic pyrite replacement, their morphology and size can be used to recognise higher taxa and as fingerprints to link a trace maker to a distinct meiobenthic trace fossil. The study of meiobenthic trace fossils is a new approach to solve multidisciplinary problems in ichnotaxonomy, taphonomy, palaeobiology, sedimentology, diagenesis and sequence stratigraphy.

An abundant and diverse ichnofauna in Middle Triassic (Muschelkalk) carbonates of the Germanic Basin has been the subject of numerous studies for the past two centuries. Several ichnogenera were established from here, such as Rhizocorallium, Trypanites, Balanoglossites and Pholeus. In the past decade, several thousands of trace fossils smaller than 1 mm in diameter have been collected from temporary outcrops. They offer the possibility to study the taphonomic history of this complex epicontinental carbonate setting in more detail. This chapter deals with aspects of how to study such meiobenthic trace fossils and to reveal their taphonomic history. The understanding of sub-macroscopic trace fossils certainly contributes—besides their macroscopic counterparts—valuable ecologic information and helps to improve palaeoenvironmental reconstructions (e.g., depositional setting, sequence stratigraphy). The presented case is from Middle Triassic carbonates, which were deposited in a shallow-marine environment on a carbonate platform. However, the principle and technique may be applied in a similar manner in both, carbonate and siliciclastic fine-grained sediments through the Phanerozoic. In fact, sediment stirring by interstitial meiofauna is a common feature in sediments of different nature and


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environment (e.g., Bromley, 1996; Pemberton et al., 2001). However, discrete traces (especially trails) produced by animals less than 1 mm in size are only occasionally described (e.g., Moussa, 1970; Wright and Benton, 1987; Metz, 1998; Uchman et al., 2004), whereas comprehensive studies of wide-ranging palaeoichnocoenoses in this scale are unknown to the author. The well-studied carbonates of the German Muschelkalk offer the opportunity to document and analyse a diverse meiofauna from an ichnological point of view, as well as to take different aspects of its taphonomic history into consideration. In addition, some of the producers are at least partly preserved at the end of some traces. Even if diagenesis has destroyed most of these soft-bodied animals, their remaining morphologies give a suggestion as to what higher systematic taxa they belong to and what kind of traces they generate.

LOCATION AND GEOLOGIC SETTING The studied trace fossils have been collected from two outcrops situated near the town of Weimar in Thuringia (Central Germany), which is a classical area of the German Triassic (Fig. 31.1). Samples from other areas (e.g., southern Germany) document that limestone beds with meiobenthic trace fossils are common over a large area, probably several thousands of square kilometres. Although similar trace fossils also occur in some limestone layers of the Lower Muschelkalk, their abundance is far lower and their preservation style not as good as of those studied from the Upper Muschelkalk. The Germanic Basin was an intracratonic basin with low relief and subsidence, which originated during the Late Permian and covered large parts of Europe in Mesozoic time (Fig. 31.1). The German Triassic is tripartite and consists of Buntsandstein (Lower), Muschelkalk (Middle) and Keuper (Upper) Group. Buntsandstein and Keuper consist mainly of continental deposits, whereas Muschelkalk is characterised by shallow-marine carbonates and evaporites (Fig. 31.2). The Muschelkalk succession reaches a thickness of about 250 m in most parts of the basin, thinning out toward the margins. There, the basin exhibits tidal signatures and was influenced by mixed clay and sand deposition. Previous studies of the German Muschelkalk have shown the validity of ichnological work for understanding different aspects of the depositional system (e.g., Knaust, 1998, 2004). Knaust et al. (1999) give an outline of the German

FIGURE 31.1 Palaeogeography of the Germanic Basin during the Middle Triassic, and the location of the studied sections near the town Weimar (Thuringia).

Triassic ichnology, whereas Knaust (in press) provides a more detailed overview of the ichnodiversity in the Middle Triassic Muschelkalk succession. During Upper Muschelkalk time (Upper Anisian–Lower Ladinian), the Germanic Basin was connected with the Tethys via the Burgundy Gate, from where a broad and shallow epicontinental sea transgressed into the basin. Deposition of a marlstone–limestone alternation is commonly interrupted by oolitic and bioclastic limestone beds, interpreted as high-energy event deposits (proximal tempestites, cf. Aigner, 1985). A subtidal depositional environment is likely for most parts of this succession, whereas most proximal facies exhibit intertidal to supratidal features (see below). The Upper Muschelkalk consists of metre-scale coarsening (shallowing)-upward cycles, interpreted as parasequences. They are thought to build the transgressive and highstand systems tracts of a 3rd order sequence with a maximum flooding surface around the cycloides Bed (Aigner and Bachmann, 1992). However, so far no general sequence stratigraphical model seems to be applicable to the whole Germanic Basin (see discussions in Knaust, 1997 and Vecsei and Duringer, 2003).

SEDIMENTOLOGY The Upper Muschelkalk succession generally consists of marlstone–limestone alternations with intercalations of decimetre-thick storm beds composed of bioclasts, ooids and intraclasts (Aigner, 1985; Fig. 31.3A). Ripple bedding, hummocky cross

31. MEIOBENTHIC TRACE FOSSILS AS KEYS TO THE TAPHONOMIC HISTORY OF SHALLOW-MARINE CARBONATES [m]

Lower Keuper

cycloides Bed

20

250 Upper Muschelkalk

cycloides Bed

Trochitenkalk Beds Meissner Fmormation

Middle Muschelkalk

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Micritic bedding planes with meiobenthic trace fossils and their producers preserved

[m]

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Lithologies: Marlstone Marly limestone Marlstone/limestone alternations 10

Bioclastic, oolithic or intraclastic limestone Dolomites and evaporites

100

Schaumkalk Beds

Terebratula Beds

5 50 Oolite Beds

0 Upper Buntsandstein

FIGURE 31.2 Gelmeroda.

Trochitenkalk Formation

Lower Muschelkalk

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Spiriferina Bed

Meiobenthic trace fossils

0

Stratigraphy and lithostratigraphic marker beds of the studied section,

SEDIMENTOLOGY

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FIGURE 31.3 Lithology and sedimentology of the studied Upper Muschelkalk succession. (A) Marlstone–limestone alternations with thick bioclastic/intraclastic limestone bed (storm bed) at the base and thickening-upward cycle above. Hammer (circled) for scale. (B) Top of a bioclastic limestone bed showing a thin micrite layer (with meiobenthic trace fossils), as well as an overlying marlstone unit containing a deformed micrite layer with tunnels of Balanoglossites triadicus (arrows). Scale bar = 1 cm. (C) Bedding plane with crystallaria, a calcrete feature originating by redistribution of chalky calcium carbonate along thin fractures. Diameter of the coin = 19 mm. (D) Bedding plane with wrinkle marks, sediment-filled fractures and meiobenthic trace fossils. Scale bar = 1 cm. (E) Micritic slab with wrinkle marks (‘Runzelmarken’) and sediment-filled fractures on bedding plane. Note the feather-like appearance of the micrite fill in the fractures and their reworking by straight to gently curved burrows (arrows), indicating an early stage of mud injection. Scale bar = 1 cm. (F) Nodule-like rounded micrite slab with different generations of fractures, a macroburrow, and meiobenthic trace fossils consisting mainly of straight to gently curved burrows. Scale bar = 1 cm. (G) Micritic bedding surface, altered by calcrete formation, showing large voids with a thin rim, interpreted to be formed due to gas escaping. Scale bar = 1 cm. –A: Troistedt, evolutus-spinosus zone. B–C,G: Troistedt, 2–4 m below cycloides. D–F: Gelmeroda, about 2 m below cycloides.

stratification, parallel (horizontal) to low-angle lamination and erosion structures (e.g., gutter and pot casts) indicate a deposition as proximal tempestites above the fair-weather wave base with frequent influence of storms (Knaust and Langbein, 1995).

In the investigated sections of outcrops Gelmeroda and Troistedt, meiobenthic trace fossils have been recognised together with their soft-bodied producers in a number of stratigraphical intervals of the Upper Muschelkalk (Fig. 31.2). Their stratigraphical

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31. MEIOBENTHIC TRACE FOSSILS AS KEYS TO THE TAPHONOMIC HISTORY OF SHALLOW-MARINE CARBONATES

deepest occurrence is recognised just above the massive skeletal limestone beds of the Trochitenkalk Formation, whereas the most prominent and bestpreserved meiobenthic trace fossils occur in numerous horizons within the Ceratites evolutus and C. spinosus zones. Higher horizons of the Ceratite Beds (Meissner Formation) also yield good material. Meiobenthic trace fossils occur in different parts of the coarsening-upward cycles (parasequences), but are most abundant in thin micrite veneers just below and above thick rudite and arenite beds (storm deposits). Burrows and trails occur on both (upper and lower) bedding planes and are preserved in positive or negative epirelief and hyporelief on very fine-grained (micritic) limestone layers with a pale grey colour, which are commonly bordered by a thin layer of dolomitic marlstone. The firm to hard sheets of micrite exhibit an uneven surface and a centimetre- to decimetre-scale relief consisting of irregular highs and depressions (Figs. 31.3B,D,F). In cross-section, a progressive degree of lithification can often be seen from the marlstone at the bottom to the micrite on the top. As the micritic surfaces, intercalated marlstone layers also contain a soft-bodied fauna, which is, however, in most cases altered and recrystallised into framboidal pyrite, for instance, and does not preserve any meiobenthic trace fossils. Internally, massive to planar, wavy or crinkled bedding is apparent. SEM analysis of fine-grained limestone of the Ceratites evolutus and C. spinosus zones has shown that the trace fossil bearing micrites and dolomicrites mainly consist of calcareous nannofossils (e.g., calcispheres). The micritic horizons are associated with several sedimentological features, which help to elucidate the palaeoenvironment: Wrinkle marks (‘Runzelmarken’) and pustules occur as patchy, irregular (swollen polygonal to semicircular), millimetre-scale surface textures (Figs. 31.3D,E and 31.4C). The thin, skin-like features modify the original sedimentary surface in a scrambling manner. Three main processes control the origin of wrinkle marks in marginal-marine environments: (1) windinduced shear; which affects the sediment surface under a very shallow cover of water (Reineck and Singh, 1980); (2) synsedimentary loading of millimetre-scale sand-over-mud doublets (Allen, 1984); and (3) activity of microbial mat communities, which were subsequently buried and loaded (Hagadorn and Bottjer, 1997). The observed wrinkle marks from the Upper Muschelkalk closely resemble those described by Reineck and Singh (1980) and Allen (1984), of which an inorganic genesis is likely, although mucusbounded veneers may have contributed too.

In contrast to under-mat traces commonly observed in the Proterozoic, some of the delicate wrinkle marks are sharply truncated by meiobenthic trails at the previous sediment surface and preclude an origin as microbial mats due to post-depositional sediment loading. Other traces were affected by the superficial deformation process. Occasionally, surfaces covered by wrinkle marks were preferred colonised by the trace makers. It is assumed that the described features originated due to pore-fluid seepage of the muddy sediment during temporary emersion (desiccation). Millimetre ripples occur on some fine-grained bedding planes and consist of broad, nearly straight and flattened crests (about 1 mm wide), separated by very narrow troughs. Transverse intersections and bifurcations are present. Cross-cutting by meiobenthic trace fossils occasionally occurs. Millimetre ripples are common in the Muschelkalk, and are known from modern tidal flats where they are produced by wind blowing on the surface of fine sediment covered by a thin water film (Reineck and Singh, 1980). Millimetre-scale voids are widespread, distributed along the fine-grained bedding planes, where they occur together with a diverse and differently preserved soft-bodied meiofauna (Figs. 31.3G, 31.4A and 31.6B). They have a rounded or irregular outline with a slightly raised rim. Some specimens contain blob voids with a fill of limonite, whereas others are empty. Comparisons with similar structures from modern muddy tidal flats suggest that most of the empty blobs were formed due to gas escaping as a result of decaying organic matter, whereas the limonite-filled blobs still have remains of decaying meiobenthic organisms in place. Mud cracks and fractures occur as a striking feature in form of linear fissures (Figs. 31.3D–F and 31.6C). They are typically several centimetres long, about 1–10 mm wide, and pinch out downward in a V-shaped manner after a few millimetres. Although some fractures connect in an irregular manner, polygonal patterns are rare. Fracture margins are in most cases raised a few millimetres against the surrounding bedding surface and form subtle ridges. Fracture fill consists of micrite, dolomicrite and/or calcite or dolomite. Some fractures with a micrite fill display ductile micro-deformations (small-scale displacements along the cracks due to smeared lime mud), indicating a synsedimentary origin. In a few cases, sediment-filled fractures were subsequently crossed by meiobenthic trails. Many of the elongated cracks were probably induced by shrinking processes

SEDIMENTOLOGY

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FIGURE 31.4 Sedimentary features, macroburrows and meiobenthic trace fossils on bedding planes. (A) Numerous Lockeia siliquaria (L) and an unidentified macroburrow (M) on upper bedding plane, cross-cut by many meiobenthic trace fossils (mainly straight to gently curved burrows, white arrows). Note the minute voids (black arrows), interpreted as gas escape structures, as well as chalky carbonate precipitations (C), interpreted as calcretes. (B) Same as A, with crystallaria (calcrete, C). (C) Upper bedding plane with diffuse wrinkle marks (‘Runzelmarken’, W), as well as a straight macroburrow (M) truncated by a Rhizocorallium spreite (R). Macroburrows were subsequently overprinted by numerous meiobenthic trace fossils, mainly consisting of straight to gently curved burrows (white arrows) and spherical to bilobate traces (black arrows). The change of outline in the latter clearly reflects shifting conditions of substrate consistency. (D) Same as C, with a false-branched macroburrow including vertical shaft (upper left) in different preservation, as well as straight to gently curved burrows and spherical to bilobate traces. (E) Lower bedding plane with macroburrows (M) and straight to gently curved burrows (meiobenthic, white arrows), cross-cut by a dolomite-filled crack (C) and minute cemented fractures (black arrows). (F) Arthropod trackway on upper bedding plane, consisting of paired ellipsoidal imprints, associated with the assumed producers preserved in sulphide mineral (white arrows). Meiobenthic traces include horizontal sine wave traces (black arrows), some of them containing a nematode-like trace maker at its termination (e.g., centre). A–D: Troistedt, evolutus zone. E–F: Gelmeroda, about 2–3 m below cycloides. All scale bars = 1 cm.

and the dewatering of an emerged mud layer. They are closely related to brecciation as well as the development of calcretes, although compaction processes also may have played a role.

Brecciation and minifaults are associated with discrete bedding planes and result in small-scale dislocations and ruptures (Fig. 31.4E). They indicate synsedimentary lithification and deformation of the

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FIGURE 31.5 Meiobenthic trace fossils on upper bedding planes. (A) Straight to gently curved burrows (white arrows) and vertical sine wave trail (black arrow), both with the producers preserved at their terminations, and overprinted by numerous laterally sinusoidal trails. (B) A wide elongated trail with V-shaped cross-section changes abruptly into straight to gently curved burrows. (C) Two vertical macroburrows (arrows) are accompanied by numerous straight to gently curved burrows and spherical to bilobate traces. Note the extreme change in morphology of the latter, indicating a rapid shift (desiccation) in substrate consistency. Many traces have their tiny producers preserved. (D) Meiobenthic trace fossils the same as in C, associated with irregularly bended minute trails (arrows). (E) Straight to gently curved burrows interchanging with spherical to bilobate traces (some with the producer preserved, white arrows). They are overprinted by loosely winding traces with a very tiny producer at their terminations (black arrows). (F) Wide elongated trails with striations, wedge-shaped in crosssection and with sediment levees displaying fine striations. A–B, D–F: Gelmeroda, about 2–3 m below cycloides. C: Troistedt, evolutus zone. All scale bars = 1 cm.

surfaces by setting off adjacent bedding surfaces a few millimetres. Sediment collapse as a result of pore-fluid seepage during subaerial exposure explains most of the deformational features, but a more complex origin including displacing growth of carbonate, wetting and drying cycles, thermal expansion and swelling clays as known from calcrete successions (Wright and Tucker, 1991) may be appropriate.

Calcretes are common in different stratigraphical levels of the studied sections, but very prominent in a horizon about 2–3 m below the cycloides Bed (Fig. 31.2), where they affect micrite layers with meiobenthic trace fossils. The finely crystalline (chalky) carbonate precipitations include features such as laminar crusts, nodules with circum-granular fracturing, honeycomb structures and crystallaria

SEDIMENTOLOGY

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FIGURE 31.6 Meiobenthic trace fossils on upper bedding planes. (A) Vertical sine wave trail with parts of the producer preserved in place. (B) Two horizontal sine wave traces, with their nematode-like producers partly preserved. Note the abundance of voids in different size. (C) A slender, gently curved trail with a nemertean-like producer preserved in situ. Note the minute cemented fractures. (D) Irregularly-bended minute trails. (E) Elongated trail with shallow levee and striations, displaying a short-elliptical arthropod at its end (white arrow). Note the imprints in front of the producer, obviously resulting from its appendices, activity. Other supposed arthropod traces reflect different substrate firmness (black arrow). Associated are a vertical sine wave trail (upper left) as well as tiny, irregularly arranged pits and grooves (lower left). (F) Segmented trace of an arthropod-like organism preserved in limonite. It changes its appearance from an interrupted to a continuous trail with stacked conical segments owing to the increasing firmness of the substrate. Gelmeroda, about 2–4 m below cycloides. All scale bars = 0.5 cm.

(Figs. 31.3C and 31.4A,B). The dense micritic to microsparitic groundmass of these structures is consistent with alpha calcretes, which are common in the vadose zone of arid areas (Wright and Tucker, 1991). The sedimentological features described above together with the stratigraphical context support an interpretation of the micrite layers with

meiobenthic trace fossils to be deposited in a marginal-marine, shallow subtidal to intertidal environment with occasional exposure. Furthermore, the bedding planes resemble cemented surface crusts as they occur on modern, muddy, carbonate tidal flats with extensive subaerial exposure (preferable in an upper intertidal to lower supratidal environment), such as northwest of Andros Island (Bahamas).

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MATERIAL AND METHODS The trace fossil bearing micrites are typically well cemented and alternate with marlstones. In fresh outcrops, those surfaces are often covered by marl and make the small trace fossils invisible. That might be one reason that meiobenthic trace fossils have been overlooked for a long time, whereas the macrofossil record is well known. Best conditions for collecting the tiny traces are given after a period (up to several months) of weathering. Most of the meiobenthic trace fossils already can be seen by the naked eye along micritic bedding planes in intense sunlight under varying angles. Over the past decade, several hundred slabs were recovered, each containing numerous meiobenthic trace fossils. After removing the slabs roughly from the dry-sticking marl, they were soaked in warm water for about half an hour and subsequently cleaned carefully with a soft water jet. For a first inspection, the dried samples were studied by incident light, whereas the full range of traces becomes visible under a microscope with up to 25 times of magnification. For documentation, a reflex camera was used in connection with the microscope, whereas most of the photographs published in this paper were taken with a digital camera (4.0 megapixels), which is able to capture an image size down to 1.55 x 1.2 cm. In addition, drawings of typical trace fossil outlines were taken from the digital images.

BIOTURBATION ACTIVITY OF MACROSCOPIC BURROWERS Besides meiobenthic trace fossils, bioturbation in the micritic layers is rare and restricted to a few ichnospecies of burrowing animals. Ichnodiversity is moderate with a trend to opportunistic colonisation. First of all, complex burrow systems with U-shaped components occur in some layers, most pronounced in a horizon about 2 to 3 m below the cycloides Bed (Figs. 31.2 and 31.3B). They are assigned to Balanoglossites triadicus, a firmground trace fossil that marks omission surfaces (Knaust, 1998, in press). The tunnels were produced by worm-like animals, which mainly thrive in a very shallow (intertidal) environment. Other shallow burrows include Protovirgularia isp., Lockeia siliquaria (Figs. 31.4A,B) and spreiten burrows of Rhizocorallium irregulare, indicative of dysaerobic conditions (Knaust in press).

On a few micrite surfaces, meiobenthic trace fossils are associated with subsurface macroburrows of unknown taxonomic affinity (Figs. 31.4A–D). The meandering tunnels have false T-shaped intersections, are depressed-ovate in vertical section and are up to 22 cm long and about 0.4–0.6 cm wide. The accompanying meiobenthic trace fossils, size, outline and preservation style of these macroburrows, are strongly influenced by sediment consistency. Generally, the tunnels stand in positive epirelief on the bedding plane. In one case, a tunnel changes gradually from a smooth, wide outline into a smaller one with an empty core and a thick wall (Fig. 31.4D). The smooth part shows two narrow, median ridges about 1 mm apart, whereas the walled portion contains external mud pellets with a diameter of about 1–2 mm and irregular shape and distribution. The opposite end of the tunnel continue with a bipartite surface expression with a median furrow and lateral pellets due to collapse of the burrow. This change in substrate consistency can be interpreted in terms of a drying mud flat with softground to firmground conditions, and is supported by truncation with Rhizocorallium spreiten (Fig. 31.4C). The described macroburrows resemble tunnels formed by mole crickets in recent floodplains (see Metz, 1990) and can be tentatively assigned to the activity of this group of insects. In contrast to similar tunnels of variegated mud-loving beetles (Coleoptera: Heteroceridae), these of mole crickets (Orthoptera: Gryllotalpidae) are commonly unbranched, exhibit coarser pellets and are larger (Metz, 1990). Another specimen contains arthropod trackways in addition to the common meiobenthic trace fossils, of which one is 40 mm in preserved length and about 1.5–2.0 mm in width (Fig. 31.4F). 12 to 14 tracks occur per centimetre and are continuously arranged (no series) in a staggered to asymmetric manner. They consist of paired ellipsoidal imprints with variable shape and size (ranging from 0.5–1.5 mm in length and 0.2–0.5 mm in width). The tracks are oblique, rarely perpendicularly oriented (while crossing a topographic high), and deepened to the mid-line. The generally gently curved trackway has an angular change, where after another centimetre the assumed producer is preserved in sulphide mineral. A total of three producers are preserved on the bedding plane in close association with the traces. They are 2.0–2.5 mm wide and 1.0–1.5 mm long and consist of platy (recrystallised) aggregates. The described trackways share some characteristics with those produced by straight to slightly oblique walking phyllopod crustaceans (e.g., notostracans) known as Merostomichnites.

MEIOBENTHIC TRACE FOSSILS

MEIOBENTHIC TRACE FOSSILS Meiofauna is in the size range between macrofauna and microfauna and includes organisms whose shortest dimension is generally smaller than 1.0 mm and larger than 0.06 mm (Giere, 1993). Following this classification of benthic organisms, most (but not all) of the trace fossils described below can be assigned to meiobenthic trace fossils, whose shortest dimension is between this size range. Even if their size is not always constant within one and the same trace due to behaviour, sediment consistency etc., as well as the occurrence of transitional forms, this classification serves as a rough guide to distinguish those trace fossils from their larger counterparts (e.g., macroburrows). The studied bedding planes contain a diverse and complex association of meiobenthic trace fossils with characteristic cross-cutting relationships, which represents an ichnocoenosis deriving from the work of a single epibenthic community. The degree of bioturbation on the bedding-plane commonly ranges between 0 and 20%. The preservation style includes positive or negative epirelief and hyporelief (mainly trails and burrows), and shows transitions to endorelief preservation (burrows). Many meiobenthic trace fossils have the producer preserved at the end of the trace. Since the study of meiobenthic trace fossils is a comparatively new field, the fairly high ichnodiversity needs a completely new approach in ichnotaxonomy to describe all the distinctive ichnotaxa in detail, which will be part of a different work. The following outline summarises the most common and conspicuous trace fossils in addition to a number of hitherto undescribed ichnotaxa. Straight to gently curved burrows (Figs. 31.3D,F, 31.4A–E, 31.5A–E and 31.7A): These unbranched surface traces with a width of about 0.3–1.0 mm and up to several centimetres in length are the most common and obvious meiobenthic trace fossils. Specimens with a sharp outline reveal crudely transverse annulations flanked by narrow marginal grooves, somewhat reminiscent of the ichnogenus Torrowangea. However, controlled by primary substrate conditions, gradual interchanges with spherical or bilobate traces (see below) and with widened diffuse furrows are common. Looping may occur, but is not typical and self-crossing is very rare. Many traces reveal their producer at the end, an irregular flat to elliptical microfossil preserved in white or transparent calcite, about 0.5–0.8 mm in length and 0.3–0.5 mm in width. These producers are interpreted

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as the remains of recrystallised tests of benthic foraminiferans (e.g., Involutinidae) as they are common in this interval of the Upper Muschelkalk (Pe´rez-Lo´pez et al., 2005). Benthic (and also some planktic) foraminifera are known to produce similar traces with the aid of their pseudopodia (Severin et al., 1982; Kitazato, 1988; Hilbrecht and Thierstein, 1996). Spherical to bilobate traces (Figs. 31.3D,F, 31.4C,D, 31.5C–E and 31.7B): This highly variable form is closely related to the former one and is the result of the same kind of producer operating in a muddy substrate characterised by a rapid consistency change from very soft to firm. The traces start with relatively large (up to 3 mm in diameter), spherical sediment aggregates, which are arranged like a string of beads with decreasing diameter down to about 0.2–0.5 mm, which corresponds to the size of the preserved producers. The shape of the spheres ranges from blurred ones in the initial stage of a trace to more pronounced bodies at its end. Some spheres are clearly bilobate and correspond to bilobated traces in the final part. In stiffer portions of the substrate, transitions to traces with irregular constrictions or rope-like annulations occur (see above). Locally, minute scratches are preserved. On undulating surfaces with wrinkle marks (interpreted to represent more wet and soupy portions), the shape of the traces changes back to spheres arranged in a string of beads. As for the straight to gently curved burrows, foraminiferans are the most likely producers, though tiny crustaceans such as ostracods might have been responsible for the bilobated variations of this trace. Horizontal sine wave traces (Figs. 31.4F, 31.5A, 31.6B and 31.7C): These laterally sinusoidal, unbranched trails and surface burrows are highly variable in size, wavelength and amplitude, and seem to represent several populations and/or species of their producers. They are comparable to Cochlichnus anguineus, but are very small and usually less than 0.2 mm in diameter, 1 mm in wavelength and 0.5 mm in amplitude. Periodically-interrupted trails indicate that only one moving phase is impressed due to sediment consistency. Some horizontal sine wave traces are preserved as compressed corkscrew-shaped burrows. High trace density, typical horizontal sine curves, and the fact that many specimens have the trace maker itself preserved in sulphide mineral at their end, clearly indicate that different nematode species were the responsible producers (cf. Moussa, 1970; Metz, 1998; Uchman et al., 2004). Thus, even if the microscopic structure of the soft tissues is not preserved, the softbody preservation of nematodes is a valuable addition

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FIGURE 31.7 Sketch with a summary of the described meiobenthic trace fossils. (A) Straight to gently curved burrows. (B) Spherical to bilobate traces. (C) Horizontal sine wave traces. (D) Vertical sine wave trails. (E) Loosely winding traces. (F) Elongated trails with striations. (G) Slender trails. (H) Irregularly-bended minute trails. (J) Irregular tiny pits. (K) Segmented trace. All scale bars = 1 mm.

to the geological record of nematodes otherwise mainly known from Cenozoic amber. Vertical sine wave trails (Figs. 31.5A, 31.6A,E and 31.7D): Sine-wave trails migrating in a vertical direction are similar to horizontal sine wave traces and occur in close association with these. They appear as a broken line (0.2–0.4 mm wide and several millimetres long) with pronounced impressions (troughs), intermittent by smooth highs. Wavelength varies between 0.5 and 1.0 mm, with short amplitude (0.1–0.5 mm). These features reflect a peristaltic movement of a worm by contracting concentric muscles on the lower and upper side of the body alternatively. This kind of locomotion is especially known from

parapodia-bearing nematodes, and indeed, nematodelike remains are preserved at some of the trails. Yet, other groups of animals may be able to produce similar traces, and short-elliptical producers too occur at the terminations of elongated and occasionally bilobated furrows with a periodical change in vertical direction. Loosely winding traces (Figs. 31.5E and 31.7E): This form consists of loosely winding, meandering to sinewave traces about 0.2–0.3 mm in diameter and some millimetres in length. Due to the variable shape, wavelength and amplitude are also variable but often decrease from the beginning of the trace to its end. These traces are similar to horizontal sine wave traces

PRESERVATION OF SOFT-BODIED MEIOBENTHOS

as described above, but commonly diverge from a strict sine-wave curve with a more variable shape. Some windings in the more loosely winding part of the traces show an affinity to Helminthopsis isp. A tiny, spot-like producer is preserved in sulphide mineral at some of the trace terminations, about 0.2 mm in size. Elongated trails with striations (Figs. 31.5F, 31.6E and 31.7F): These traces are preserved in negative epirelief in a length of up to several centimetres and a width of about 0.7–1.5 mm. They are straight or gently curved, wedge-shaped in cross-section or appear with a flat bottom. Sediment ridges are commonly pushed up along the margins and may display fine striations, which may continue towards the bottom. The producer is preserved in some instances and can clearly be identified as an arthropod with short elliptical outline (less than 1.5 mm long), probably a minute malacostracan crustacean. Alternatively, foraminiferans are known to produce similar traces. Slender trails (Figs. 31.6C and 31.7G): These traces comprise straight to gently curved, unbranched trails, up to several centimetres in length and about 0.1 mm in width. They are most reminiscent of the ichnospecies of Helminthoidichnites. In one case, an elongated soft-body is preserved in sulphide mineral at the trail’s termination. It is about 5 mm long, 0.1 mm wide, periodically constricted and seems to be annulated with many parapodia. Nemerteans would be good candidates to produce such slender trails, and the preserved soft-body actually looks like one. Irregularly-bended minute trails (Figs. 31.5D, 31.6D and 31.7H): These traces are usually less than 0.1 mm in width and a few millimetres in length, straight to irregularly curved, often characterised by abrupt changes of direction. The trails are variable in shape but often have the appearance of a broken line with relatively short (about 0.5 mm long) impressions occurring in intervals of about 1 mm. Worm-like animals or insect larvae are known to make similar traces. Irregular tiny pits (Figs. 31.6E and 31.7J): Diminutive but sharply outlined traces are preserved in very fine-grained portions of the micritic surfaces. They consist of irregularly arranged pits and grooves, usually less than 0.2 mm in width. Tiny limonite aggregates are assumed to be the producers, but could not be identified. Meiobenthic crustaceans

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or insect larvae are potential candidates for trace makers. Segmented trace (Figs. 31.6F and 31.7K): One trace is conspicuously segmented during its course. It is about 20 mm long and 0.7–0.9 mm wide, consisting of an interrupted trail in the first part and, due to a change in sediment consistency, changes into a continuous trail with stacked conical segments in the second part. An arthropod-like organism is preserved in limonite at the trace termination, probably belonging to malacostraca.

PRESERVATION OF SOFT-BODIED MEIOBENTHOS The newly discovered meiobenthic trace fossils along with the fossilized remains of their producers in a very good state of preservation can be regarded as an extraordinary fossil occurrence. They represent a Middle Triassic meiobenthic thanatocoenosis, in which the non-biomineralised tissues of meiobenthic organisms were fossilized to a certain degree, thanks to specific sedimentological circumstances such as anoxia and rapid burial with fine-grained sediment. Such conservation deposits (Fossil-Lagersta¨tte) comprise a wealth of taphonomic information, but are as yet poorly studied in detail. A prerequisite for preservation of soft-bodied animals is to exclude scavenging; this can result from stagnation due to anoxia or obrution due to rapid burial (Briggs, 2001). Such conditions were met in the epicontinental Germanic Basin, where a stratified water body, low oxygen and high salinity conditions were prevalent (Knaust, 2004). The micrites have preserved epibenthic organisms in situ, though only higher taxa can be recognised owing to very specific environmental controls. Early-diagenetic mineralisation had started during or shortly after decay of the meiobenthos, but owing to rapid degradation of soft parts, only the external morphology together with robust structural tissues such as arthropod cuticles, antennae and appendices are occasionally preserved. Soft tissues were mainly replaced by pyrite, although other sulphide minerals such as markasite may also have played a role. Pyrite is a mineral that appears relatively late in the early diagenesis compared to others (e.g., apatite and clay minerals). This circumstance results in a substantial loss of the original internal structure of the soft-bodies

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and sometimes in their complete obliteration. Pyrite follows organic matter as locus for precipitation and replicates the external appearance of the organisms by precipitating on the tissues, but destroys the microstructure of the tissues and prevents selective preservation. Microbial decay is an important step in the process, and the preserved meiobenthic carcasses are loci where microbes (e.g., bacteria) could have been mineralised. Finally, near-surface weathering is responsible for transferring pyrite into limonite and diagenetic alteration. The preservation of soft-bodied organisms in pyrite is rather rare compared to apatite or clay minerals (see Briggs, 2001). The preservation of soft-bodied meiobenthos of the Upper Muschelkalk is comparable to a certain extent with the Fossil-Lagersta¨tte of the Devonian Hunsru¨ck Slate of western Germany (Bartels et al., 1998), where isolated carcasses are exceptionally preserved in pyrite, but lack most of the details due to a specific taphonomic window.

3.

4.

5.

TAPHONOMIC HISTORY The ichnological evidence (chiefly meiobenthic trace fossils) is useful to reconstruct key taphonomic snapshots and palaeoenvironmental conditions of the studied Upper Muschelkalk interval (evolutus-spinosus zone) and its sedimentological context: 1. Mud deposition of the studied beds took place on an extensive, low-grade tidal flat with irregular relief (highs, troughs, ponds) and dysaerobic to anaerobic bottom conditions. Typically for quiet areas, such as protected epicontinental seas with fine-grained organic-rich sediments, the transition from the oxygenated layer to the anoxic zone occurs just below the sediment surface. It can be assumed, that large parts of the carbonate platform were subaerially exposed. Such broad, extremely flat expanses (mud flats) lack a modern counterpart but are familiar to us from other epicontinental seas (e.g., Proterozoic Belt Group in Canada, Upper Ordovician of Kentucky). 2. The softground became bioturbated by a lowdiverse macrobenthic community affecting the upper tier. This bioturbation mainly consists of bivalves leaving trace fossils such as Protovirgularia isp. and Lockeia isp., arthropods and insects (e.g., mole crickets). The animalhosting substrate experienced exposure and

6.

7.

8.

desiccation and, thus, may have rapidly changed its consistency from soft to firm. The surface and shallow sub-surface were colonised by diverse meiobenthos, including foraminiferans, nematodes, nemerteans, annelids (especially polychaetes), arthropods (ostracods, malacostracans and other crustaceans), and worm-like animals. As indicated by microfossils, brachyhaline to euhaline conditions were prevalent in the evolutus-spinosus zone (Kozur, 1974). Inorganic development of wrinkle marks (‘Runzelmarken’) and pustules took place as a result of sediment dewatering (pore-fluid seepage of the muddy sediment) and deformation (shearing) during temporary emersion (cf. Reineck and Singh, 1980; Allen, 1984). Meiobenthic organisms living on tidal flats were apparently trapped by rapid drying of the localised areas when grazing on the previously wet tidal flat. The change of width, outline and sharpness of edges along one and the same trace clearly indicates a rapid shift of sediment consistency from soft to firm, which is typical for emersion (Gra¨f, 1956; Knox and Miller, 1985; Uchman and Pervesler, 2006), either produced by strong offshore winds or in an intertidal environment. Other meiobenthos colonised subtidal areas such as shallow ponds or lagoons and might have been killed by anoxic bottom conditions or changes in salinity. After mass mortality, carcasses were probably covered by a thin biofilm of benthic blue-green bacteria or cyanobacteria, which usually live in extreme environments. Sediment instability due to rapid dewatering during low tide is responsible for localised synsedimentary deformation (loading) and firmground development. It is assumed that later, firmground surfaces were locally colonised by worm-like animals that produce Rhizocorallium irregulare and Balanoglossites triadicus. Dolomitisation, fracturing and brecciation of the thin and hardened micrite sheets occurred in a supratidal environment and included initial calcrete formation. The meiobenthos was buried (obrution) by marl owing to terrestrial influx, fine-gained lime, sand and gravel deposition due to storms, and possibly subsequent redistribution by tidal currents. Decaying of meiobenthic organisms by sulphate reducing bacteria took place within the anoxic zone, in which some nematodes are able to survive.

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CONCLUSIONS

9. Calcrete formation continued in a shallow subsurface vadose zone. 10. In a late-diagenetic stage, the soft-bodied fossils and their hosting sedimentary rocks were altered (e.g., recrystallisation, stylolitisation). Metastable aragonite and high-Mg-calcite were transformed into stable low-Mg-calcite. Afterwards, some soft-bodied fossils were limonitised in a sub-surface environment and finally weathered.

TIDALITY IN THE EPICONTINENTAL GERMANIC BASIN? Epicontinental (epeiric, epicratonic) basins are often regarded as not prone to tidal activity because of their isolation from the open ocean. Modern, partly enclosed marine basins such as the Baltic, Mediterranean or Gulf of Mexico exhibit only microtidal influence (tidal range 300 000 mg L1 (Kalff, 2002), a range that is orders of magnitude larger than the range of salinity variation in the ocean (33 000–35 000 mg L1). If the water balance remains negative, the subaqueous lake bottom is exposed and the lake shrinks. Human activity has accelerated the shrinking process in the Aral Sea (Wetzel, 2001), but even without human influence, the rate of exposure/ lake shrinkage can be extremely rapid. Most lakes are geologically ephemeral features of the landscape and tend to disappear over time. Life spans average about 20 thousand years and range from a few thousand (some glacially formed lakes) to more than 20 million years (tectonic lakes) (Wetzel, 2001; Kalff, 2002). The variability between lakes extant at one time and within a single lake over time contrasts with the relative homogeneity of the marine realm. As noted above, it has been documented that 9000 years passed between the initial burrowing in deep-sea sediments and the subsequent reburrowing by a Zoophycos-producing animal and that the environmental change during that period was negligible. (2) Lakes are affected by seasonal changes (mixis) and nutrient levels (trophy). Much of the early history of limnology was consumed by lake typology, the classification of lakes by mixing patterns, trophic status, geomorphology, etc. Lakes may be amictic (never mixing), monomictic (stratifying once per year), dimictic (stratifying twice per year), or holomictic (always mixed) and as oligotrophic (nutrient poor), mesotrophic (moderately nutrient rich), and eutrophic (nutrient rich). Meromictic lakes have deep, permanent chemical stratification, usually without organisms, but may fall into any of the above categories. In mesotrophic and eutrophic lakes that experience monomictic or dimictic patterns (often smaller mid-to high-latitude lakes), strong seasonal light and temperature regimes lead to summer warming and high productivity, forming an upper, less dense, oxygen-rich epilimnion surface layer that does not mix with the denser,

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colder hypolimnion. Organic matter sinking into the hypolimnion is degraded by aerobic bacteria, eventually leading to oxygen depletion at depth. DO levels remain low in the hypolimnion until the epilimnetic water cools sufficiently to become the same density as hypolimnetic water allowing mixing of the entire water column (overturn) and replenishment of DO. In contrast, oligotrophic lakes (such as the Laurentian Great Lakes and probably most early Paleozoic lakes) strongly stratify but only with temperature. The production of organic matter in the epilimnion and subsequent decomposition is insufficient to deplete DO in the hypolimnion. Physical mixing in all cases usually is a function of wind speed, wind duration, and fetch (Wetzel, 2001, Kalff, 2002). Lakes in low latitudes have less variation in surface temperature and light, but commonly have highly seasonal inputs of water and nutrients, and DO stratification is common. (3) The feedbacks between environmental parameters in lakes are complex and biologically important (Fig. 33.3). Probably the most significant for bottom-dwelling animals are processes leading to stratification and reduction of oxygen at depth. The implication of this is that deeper zones of most lakes since the late Paleozoic (all but the least productive–oligotrophic, ultraoligotrophic) become hypoxic or anoxic on a fairly regular basis. The recurring low oxygen conditions exert strong control on the benthic fauna and thus the suite of trace fossils that would be preserved. (4) Lake bottoms are composed of three, often distinct, zones based on wave action, the depth of light penetration, and the depth of the thermocline: the littoral zone, the transition zone (sublittoral), and the profundal zone. (5) Wave action in littoral zones of large lakes limits plant (macrophyte) growth, resulting in largely barren sandy zones. Continental shelves provide modern marine analogs of the physical processes, with large expanses of sand, mixed sand and mud, or mud. Surface features on the shallow seafloor include physically produced dunes, sandwaves, and ripples as well as tracks, trails, craters, and pits that are the surface representations of the infaunal activity. Much of the area is above storm wave base because large long duration storms generate waves that affect bottom sediments to a depth of half of the wavelength. In the marine realm, this is a mosaic of physically and animal-modified

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33. ECOLOGICAL AND EVOLUTIONARY CONTROLS ON THE COMPOSITION OF MARINE AND LAKE ICHNOFACIES

sediments, the setting of the Cruziana and Skolithos ichnofacies, in which plants play a minor role, just as they do in littoral zones of lakes. (6) Littoral zones in small lakes commonly are dominated by macrophytes that affect sediment characteristics and thus the infauna. Plants dampen wave action, allowing fine-grained particles to settle, they contribute organic matter to the sediment, and their structural complexity increases epifaunal abundance and diversity (Wetzel, 2001; Kalff, 2002). The roots of aquatic macrophytes, however, can be extensive and may mask recognizable biogenic structures. In fact, ancient lacustrine littoral zone sediments could be easily misinterpreted as rooted subaerial deposits. Thus, profuse plant growth in lake littoral zones could block development of a distinctive littoral ichnofauna produced by burrowing animals and replace it with root traces. (7) The sublittoral transition zone begins at the base of the littoral zone. This point corresponds with the depth of the photic zone (Wetzel, 2001) and the change from coarse to fine-grained sediments (Kalff, 2002). The change from coarse to fine sediments occurs at a predictable depth that is a function of the maximum fetch and the angle of slope of the lake bottom (Rowan et al., 1992). Below this depth, which is effectively the storm wave base, silt, clay, and organic particles accumulate; the depth of this transition can range from < 3 m in a small lake (fetch < 1 km) to > 40 m in very large lakes (fetch > 200 km). The width of the transition zone thus may vary from meters to kilometers depending on basin slope and the depth of the thermocline. Indeed, in shallower lakes and in larger, human constructed reservoirs, the transition zone may cover most of the lake bottom. (8) Littoral organic production that focuses lakeward along with planktonic production provides the base for sediment aerobic microbial production, the primary food supply for infaunal benthos (Wetzel, 2001). The average deposition rate in natural lakes without significant human disturbance is about 1 mm per year and contains optimally about 4% organic carbon in surface sediments. The biota of this zone consists primarily of epifaunal and infaunal macrobenthos (Table 33.1) and often contains the greatest density and diversity of animals, whose activities are more likely to be preserved in the stratigraphic record than those of littoral-zone animals.

(9) Profundal zones are marked by strong transitions in temperature and/or dissolved oxygen during stratification. Few benthic macroinvertebrates can withstand anoxic conditions for even short time periods. Even in oligotrophic lakes, cold bottom waters year round (often at or just above 48C) may limit the activity, diversity, and density of the benthos. The traces of benthic activity, however slow, might be expected to be preserved. (10) Tiering occurs in freshwater substrates. Although it is not as extensive or deep as in marine sediments, infaunal tiering has been described in the benthic literature, particularly for transitional zones (e.g., McCall and Fisher, 1982). The greatest numbers of benthic species are epifaunal; however, the highest population densities occur among the infaunal taxa. Unlike marine benthos, very few lake infaunal taxa construct permanent burrows because they are continually moving through the sediments. The extent of tiering in lake sediments depends upon oxygen availability, carbon resources, and the number of species present. In oligochaetes, for example, addition of a second species will force the first to feed deeper or shallower; a third species will dominate at a new depth (Keilty et al., 1988). Indeed, each species may feed on the other’s feces and associated bacteria, promoting greater oligochaete diversity (White et al., 1986).

BENTHIC ANIMALS IN LAKES VS. THE OCEAN Infaunal composition reflects the body plans represented and the extent to which these body plans have been modified for burrowing lifestyles. Environmental parameters discussed above are also important so far as they determine which animals will be present (Figs. 33.1–33.3).

Diversity and Body Plans Major groups of mega or macrofaunal animals that are known to burrow or have the potential to burrow in lakes or the ocean are listed in Table 33.1. The most striking difference between lake and marine benthos is in the greater diversity of burrowers in the ocean than in lakes. This is true on several taxonomic levels; there are many phyla of marine burrowers and many

BENTHIC ANIMALS IN LAKES VS. THE OCEAN

classes that contain burrowers within each phylum. In contrast, macrofaunal burrowers in lakes primarily belong to the Arthropoda, Mollusca, and Annelida (McCall and Fisher, 1982). Within each phylum, there are only a few orders that include burrowers in lakes, and those burrowers belong to a limited number of families (Table 33.1). Related to the differences in taxonomic distribution of burrowers in lakes vs. the ocean is a much wider range of body plans and adaptations for a benthic lifestyle among marine bottom-dwelling animals. Each phylum has a unique body plan, and the fact that there are at least eleven phyla of marine benthic animals testifies to the large number of fundamental body plans present on the ocean floor. Every phylum of marine organisms has at least one class that has special adaptations of the phylum’s basic body plan for burrowing. Some examples include (1) modification of bivalve shell shape, thickness and ornamentation for different styles of burrowing and living at different tiers within the substrate (Stanley, 1970); (2) development of a massively muscular foot and streamlined shell by the infaunal carnivorous naticid gastropods (Trueman, 1968); (3) ability of the lophophorate Phylum Phoronida to burrow and construct vertical tubes, in contrast to the other lophophorate phyla (Bryozoa, Brachiopoda) that are almost uniformly sessile; (4) modification of appendages of decapod crustaceans for rapid and deep burrowing, including the greatly enlarged chelae of thalassinid shrimp that manipulate sediment, allowing construction and maintenance of burrows greater than one meter deep (Griffis and Suchanek, 1991); (5) diverse modifications of the segmented polychaete worm body plan such as for active pumping and infaunal filter feeding (Chaetopterus) and for surface deposit feeding by sediment-collecting tentacles radiating out from the anterior of the body oriented vertically in the sediment (terebellids; Barnes, 1968); (6) development in the worm-like Phylum Echiura of food gutters up to a meter long that funnel sediment to the mouth (Gage and Tyler, 1991); and (7) modification of the echinoderm water vascular system to allow irrigation and burrowing in irregular echinoids, and even construction of semi-permanent dwelling burrows by small holothurians (Gage and Tyler, 1991). Because only a few groups dominate the benthos of lakes, the number of body plans available for burrowers is smaller than in the marine realm, and in general, there has been less modification of the body plans for adaptation for an infaunal lifestyle. For example, many of the freshwater gastropods have terrestrial pulmonate origins (Thorp and Covich, 2001) with few adaptations for burrowing.

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The unionid, sphaeriid, and corbiculid clams are all siphonate and include some that live on the surface and others that can burrow a decimeter or more beneath the sediment–water interface and are locally significant bioturbators (McCall et al., 1979; McCall and Fisher, 1982; White et al., 1986). Burrowing activity may laterally displace sediments, but few species are expected to leave the types of traces seen in their marine counterparts. In spite of high diversity, particularly in the southeastern United States, the range of shell thickness and of shell shapes is limited, and there is no clear relationship that has been documented in the lacustrine realm between mode of life and shell morphology, as there has been for marine bivalves (Stanley, 1970). One genus, Pisidium (Sphaeriidae), does have a greatly reduced incurrent siphon (Mackie et al., 1980), allowing it to burrow through fine sediments where it feeds on bacteria. Crustaceans include isopods, amphipods, and decapods. Isopods are mostly epifaunal occurring in organic matter deposits. Burrowing amphipods (e.g., Monoporeia) are common inhabitants of cooler, oligotrophic lakes and may reach densities greater than 5 000 m2. Unlike most marine and freshwater taxa, these amphipods are adapted for moving through the top few centimeters of fine sediments where they feed on organic matter and associated bacteria and may completely mix surficial sediments (Wetzel, 2001). Large decapods (crayfish) may be common in lakes, particularly where there are extensive macrophyte beds. Most crayfish could be considered epifaunal or burrowers in floodplain sediments, but occasionally numerous burrows may occur in the bottom of small lakes. Insects constitute a high percentage of the species diversity and biomass in lakes, and insect larvae, nymphs, and naiads are abundant in both shallow and profundal lake sediments (Brinkhurst, 1974; Merritt and Cummins, 1996). Unlike marine groups that evolved in the ocean and have remained there hundreds of millions of years, insects are evolved on land and are secondarily aquatic. Most lake taxa are thought to be derived from stream species and are still constrained by respiratory mechanisms and by having an air-breathing adult stage (Merritt and Cummins, 1996). The switch from obtaining oxygen from air to obtaining oxygen from water has occurred in numerous ways, all requiring evolutionary innovation (Ward, 1992). Almost all aquatic insects have some respiratory exchange through the cuticle covering the body. The epicuticle commonly has been thinned by evolutionary loss of one or more layers, which increases oxygen permeability. Small size increases surface to volume ratio and maximizes respiratory

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TABLE 33.1

Common Burrowing Macrobenthic Animals in Marine and Lacustrine Environments

Burrowing Marine Benthos Phylum Cnidaria: Order Ceriantharia – burrowing anemones, some extend > 50 cm Phylum Nemertea – mobile infaunal carnivores, active decimeters beneath SWI Phylum Sipuncula – burrowing deposit feeders; densities up to 400 m2 in deep sea Phylum Annelida Class Polychaeta – 20 families of burrowers, including surface and subsurface deposit feeders and suspension feeders; abundant and ubiquitous Class Oligochaeta – small deposit feeders, abundant in deep-sea, tolerant of low oxygen Phylum Mollusca Class Bivalvia – most are burrowers at diverse depths beneath SWI; many shallow-water forms are suspension feeders, deposit-feeders dominate deep-water Class Scaphopoda – burrowers that typically feed on protists Class Gastropoda – many disrupt surface sediments; some burrow (e.g., Naticidae) Class Aplacophora – small burrowers, abundant in deep-sea Phylum Arthropoda Subphylum Crustacea Class Malacostraca Order Stomatopoda (mantis shrimp) – carnivores that hide in burrows, crevices Order Amphipoda – many active deposit feeders; some produce discrete burrows Orders Isopoda, Tanaidacea – small active burrowers in diverse environments Order Decapoda: Callianassidae – deep burrowing decapods, cause rapid sediment overturn, diverse feeding styles, abundant and widely distributed Subphylum Chelicerata Class Merostomata (horseshoe crabs) – shallow burrowers preying on infauna Phylum Echinodermata Class Asteroidea (starfish) – mostly carnivorous, some burrow shallowly in deep sea Class Echinoidea (sea urchins) – many irregular echinoids (sand dollars, heart urchins, spantangoids) are active and deep burrowers and are common in deep-sea sediments) Class Holothuroidea (sea cucumber) – many burrowers; includes suspension and shallow and deep deposit feeders; very abundant in deep sea Class Ophiuroidea (brittle and basket stars) – numerically dominate deep-sea; suspension or deposit feeders or carnivorous; live in or on the sediment Phylum Echiura – produce U-shaped burrows; activity in deep-sea produces mounds; locally abundant in deep-sea and in eastern Pacific coastal zones Phylum Priapulida – small infaunal deposit feeders; up to 200 m2 Phylum Hemichordata: Class Enteropneusta – sediment ingesters/excreters that leave their marks on deep-sea sediments Phylum Chordata: Amphioxus – burrows in clean sand Burrowing Lacustrine Benthos Phylum Arthropoda Subphylum Insecta Order Diptera Family Chironomidae – most diverse, widespread infaunal animals in lakes, often abundant, most confined to silk-lined burrows 5 cm beneath SWI, primarily particle feeders Family Chaoboridae – mostly planktonic predators, but burrow in surface sediment to escape predation Order Ephemeroptera – several genera well adapted to burrowing (tusks and legs), particularly the genus Hexagenia, particle gatherers Order Odonata – several genera, predatory, generally bury just enough to be concealed from prey (Numerous Orders and Genera at land/lake margin, e.g., horsefly larvae, beetle adults and larvae, mole crickets) Subphylum Crustacea Order Amphipoda: Monoporeia – important sediment reworkers; generally shallow burrowers, particle feeders (continued)

BENTHIC ANIMALS IN LAKES VS. THE OCEAN

TABLE 33.1

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(Continued)

Burrowing Lacustrine Benthos Order Mysidacea: Mysis, Neomysis, Taphromysis – mostly benthic and planktonic predators, migrate from water column to burrow in sediment, often up to 4–5 cm deep Phylum Mollusca Class Gastropoda – several families, epifaunal, often leave tracks as they feed on organic particles and benthic algae Class Bivalvia (filter feeders) Family Unionidae – may move deeply within sediments, > 20 cm deep Family Sphaeriidae – move shallowly within sediments, < 2 cm deep Family Corbiculidae – may move deeply within sediments, > 10 cm deep Family Dreissenidae: Dreissena – generally shallow, < 10 cm deep Phylum Annelida Class Polychaeta: Manayunkia – shallow burrowers in sands and fine sediments, may be locally abundant Class Oligochaeta Families Tubificidae, Lumbriculidae – small, conveyer-belt deposit feeders, some species tolerate (and dominate) low oxygen conditions, often very abundant even in deep lakes. Complied from Brinkhurst (1974), Ricketts et al. (1985), Kozloff (1987), Gage and Tyler (1991), Levinton (1995), Merritt and Cummins (1996) and Thorp and Covich (2001).

exchange through the body wall. Many families have developed tracheal gills along the abdomen or thorax. The ephemeropteran Hexagenia creates a current with its large tracheal gills that aerates its U-shaped burrow extending 15 cm or more beneath the sediment–water interface, but most are confined to the upper few centimeters of the substrate. Chironomid larvae, the most diverse and abundant lake macrobenthic family of insects (Order Diptera), have a very thin cuticle covering an highly tracheated body wall that enhances respiratory exchange; their small size and presence of hemoglobin in some taxa increases their oxygen uptake and allows them to live in low oxygen substrates (Ward, 1992). There are fewer reports in the literature of adaptations for burrowing in sand and mud. Perhaps the most adapted is the large ephemeropteran Dolania that has greatly reduced legs and gills with protective coverings on the head and ‘shoulders’ (Edmunds et al., 1976). This taxon burrows deeply into the sand and is rarely collected by normal methods. Some insects (Heptageniidae including Hexagenia) have anterior ‘tusks’ used in burrowing (Hunt, 1953). Some have either hairs or modified gills to protect the gills from sediment (Ward, 1992), and others have forelegs modified for digging (Merritt and Cummins, 1996). Most infaunal insects, however, appear to have typical insect legs without the special adaptations for rapid and efficient burrowing that are common among crustacean burrowers (e.g., Ward, 1992; Merritt and Cummins, 1996). Dipteran larvae, the most common infaunal insects, have no real legs, and

most of the Chironomidae remain in silk-lined burrows just below the SWI during their entire larval cycle. The planktonic dipteran Chaoborus, along with mysids, moves in and out of bottom sediments on a daily basis often burrowing as much as 4–5 cm to escape predation (Wetzel, 2001). There are also a number of burrowers along the shore–lake interface that leave distinctive traces: horsefly larvae (Tabanidae), adults and larvae of variegated mud loving beetles (Heteroceridae), and pygmy mole crickets (Tridactylidae) (Merritt and Cummins, 1996). Oligochaetes are often the dominant component of the lake benthos both in numbers and diversity, and many taxa with hemoglobin are adapted to low DO conditions (Brinkhurst and Cook, 1980). The families Tubificidae and Lumbriculidae feed with their heads deep in the sediment, often in anoxic conditions, defecating either in the subsurface or at the sediment–water interface. This conveyor-belt mode of feeding reworks surficial sediments and may homogenize sediments to a depth of several centimeters or more depending on the sedimentation rate (Robbins et al., 1977). As noted above, many species may occur together where they partition the bacterial components of the sediments (Keilty et al., 1988).

Reproduction and Dispersal Unlike nonmarine aquatic animals, most marine macrobenthic animals produce planktonic larvae, some of which feed on plankton before settling

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(Levinton, 1982). Reproduction and life cycles of lake macrobenthic animals are more complex than those of their marine counterparts. Immature insects go through several stages involving numerous molts before abandoning the lake bottom to emerge as flying adults. The adults mate and lay eggs before dying, and the eggs sink to the lake bottom where they hatch. Most insect life cycles are univoltine (one generation per year), but in tropical or temperate lakes two or more generations may occur, and in high latitudes, life cycles may take two to several years (Merritt and Cummins, 1996). In general, the short life span of most insect benthos may limit the size and complexity of the traces produced, and the same may be true for both oligochaetes and burrowing amphipods (e.g., Brinkhurst and Cook, 1980). The long-lived unionid clams tend to remain in place but may not mature for many years, and they must be near the sediment–water interface to transfer larval glochidia to fish, limiting burrowing behavior (Burch, 1975). Sphaeriids, however, are very mobile and mature quickly giving birth to small clams that must be in well-oxygenated sediments for best survival (Burch, 1972).

Implications for Ichnofacies The wide variety of body plans and modifications of body plans of marine infaunal burrowers implies a wide range of potential behavior. This was implicit in Seilacher’s ichnofacies paradigm; the assumption was that the optimal behavior can be achieved in any marine environment because diversity of animal body plans allows a wide variety of behavior at all depths below the sediment–water interface (Figs. 33.1 and 33.2). That is not the case for lakes, however, where (1) macrobenthic burrowers belong primarily to a few phyla, which may limit diversity of body plans; (2) extensive evolutionary modifications of the dominant insects needed to transform air breathers to aquatic animals capable of oxygen uptake from water have occurred, although insects remain small and generally are restricted to the sediment surface zone and a few centimeters beneath it; (3) anatomical specialization for burrowing speed and efficiency is not common among infaunal animals, limiting the effects of burrowers on the sediment; and (4) reproductive styles and life cycles constrain the range of behavior of burrowers by, for example, limiting the length of time spent in the sediment, or the depth beneath the sediment–water interface required for successful reproduction. All of these restrictions on the potential range of behavior imposed by the limited

diversity and body plans act to narrow the diversity of biogenic structures that are produced and therefore impact the composition and character of the ichnofacies.

COMPARISON OF MARINE VS. LACUSTRINE ICHNOFACIES Marine ichnofacies commonly are complex, and are typically characterized by diverse traces produced by animals with a broad range of body plans and life cycles living at all depths beneath the SWI. Biogenic structures are present in most marine sedimentary sequences (Fig. 33.4). If shallow tier traces are eroded, those produced deeper in the sediment will be preserved. The abundance of trace fossils and the pervasiveness of bioturbation are reflected by the fact that ichnofabric indices for characterization of bioturbation originally contained a category for sediments that had been reworked more than once (Droser and Bottjer, 1986; Bromley, 1996). Ichnofacies in lacustrine sediments include fewer types of trace fossils that record a narrower range of behavior. Traces in lake bottom sediments tend to be small and simple, reflecting their producers’ diminutive size and simple behavior, which may result from a lack of specialized anatomical/behavioral adaptations for burrowing. Traces in lake sediments typically are produced at shallow tiers at or a few centimeters below the SWI (Fig. 33.5), due to the burrowers, inability to deal with low dissolved oxygen levels at depth beneath the sediment–water interface as well as

FIGURE 33.4 Biogenic structures and bioturbation in Permian marine turbidites, Bluff, New Zealand. View is of oblique section; top of bed is top of photo. Note abundance of penetrative biogenic structures with complex fill structure. Scale: 15 cm ruler.

IMPLICATIONS AND SIGNIFICANCE

FIGURE 33.5 Biogenic structure (Cochlichnus) on bedding plane of Permian lacustrine turbidite, Shackleton Glacier area, Transantarctic Mountains, Antarctica. Trace is confined to bedding plane surface, which otherwise is little disturbed by bioturbation. Scale: 15 cm ruler.

to the animals’ small size and (for insects at least) limited time in the sediment prior to their emergence as adults. Animals with body plans that allow them to use the deep-tier ecospace in lake bottoms are less common. The shallow traces produced near the SWI are prone to erosion, and when they are eroded, the absence of deep-tier burrows or bioturbation results in sediment that retains no preserved record of benthic activity. The results are assemblages of small, simple, near-surface trace fossils (e.g., Maples and Archer, 1989; Miller and Collinson, 1994; Buatois and Mangano, 1995) in rocks that are characterized by low levels of bioturbation (Miller and Labandeira, 2002; Miller et al., 2002).

Why Do Marine and Lacustrine Ichnofacies Differ? The most obvious cause of the difference in the ichnofacies is the difference in the animals present in the marine and lacustrine realms, particularly with respect to the limited body plans and the paucity of evolutionary adaptations for burrowing of lake infaunal animals. Reasons for the reduced diversity and styles of macrobenthos are more complex. An important effect must be that of the estuarine filter that has limited upstream colonization of freshwater systems by marine animals throughout the Phanerozoic (Miller and Labandeira, 2002; Park and Gierlowski-Kordesch, 2005). Fundamental controls on lake environmental parameters must be major determinants of lacustrine macrobenthic composition. In spite of the late Paleozoic and Cretaceous events (e.g., Robinson

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et al., 2004; Kiehl et al., 2005) throughout the Phanerozoic, the oceans have provided a large interconnected body of water of stable composition, permitting a long evolutionary history. In contrast, lakes are strongly affected by changes at all scales in time and space (Fig. 33.3). Lakes may have strong seasonal changes in productivity, and thus in DO, that affect the macrobenthos on a yearly or semi-yearly basis. On a scale of hundreds to thousands to tens of thousands of years, lake salinity can change by an order of magnitude, and lake surface area can increase or decrease due to sedimentation and precipitation/evaporation balances. Lakes can dry up and cease to exist. The effects of instability are confounded by the lack of connection among lakes; when conditions deteriorate, there is no refuge for the organisms. Geographic isolation of lakes inhibits mixing of noninsect faunas and the spread of evolutionary novelties generated in isolated populations. An additional persistent factor is the fact that lakes are the dumping grounds of continental particulate inorganic and organic debris and dissolved materials, and this often results in saline and/or alkaline lake systems that will sustain a very different biota from fresh water lake systems. A common result of this influx and its interaction with the complex lacustrine chemical, physical, and biological processes is reduced DO and anoxia, which is deleterious to the macrobenthos and restricts the ichnofacies that reflects their legacy.

IMPLICATIONS AND SIGNIFICANCE Delineation of differences between ichnofacies characteristics of marine and freshwater deposits will aid in reconstruction of depositional environments. Many of the physical processes active in lakes are the same as those in the ocean, although they typically differ in scale. The biological fingerprint of fresh water vs. marine ecosystems is particularly useful; macrobenthic aquatic organisms other than mollusks are unlikely to be preserved, leaving the trace fossils and bioturbation as the primary macrofauna record. In their role as recipients and catalogers of material scraped from drainage basins, lakes record the history of the interplay of climate, topography, and tectonics (Bohacs et al., 2000). The macrobenthos is sensitive to fluctuation of the environmental parameters at all scales (Figs. 33.2 and 33.3), so the trace fossils and bioturbation produced by the macrobenthos peserves unique paleoenvironmental and paleoclimatic information.

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Compilations of the temporal distribution of body fossils in freshwater deposits have yielded a picture of the evolution of freshwater faunas (Gray, 1988; Park and Gierlowski-Kordesch, 2005), but provide little information about the abundance and ecospace use by burrowers in lake substrates through time. Analysis of bioturbation in Permian through Jurassic aquatic continental facies (fluvial and lacustrine) indicates that colonization by macrobenthos of freshwater substrate habitats was delayed relative to rapid colonization of marine substrates in the latest Neoproterozoic–early Paleozoic (Miller et al., 2002). Evaluation of lacustrine ichnofaunas and ichnofabrics through the entire Phanerozoic are needed to document the entire colonization history of freshwater ecosystems and facilitate comparison with that of marine habitats. The paucity of deep and pervasive bioturbation effectively removes organic matter buried in lake bottoms from the carbon cycle. Although the time that organic matter would be sequestered in lake sediments is limited by the high probability of erosion over tens to hundreds of thousands of years, on a global scale, carbon removal may have an important effect. On a shorter time scale, bioturbation in lakes has been demonstrated to affect physical and chemical parameters of lakes (McCall and Fisher, 1982; Krantzberg, 1985; Svensson and Leonardson, 1996); these effects would be magnified if lake bioturbation were as deep and pervasive as that in the marine realm.

water volume, as are conditions in the world ocean. As a result, lake ichnofacies are limited and controlled by both physical and biological constraints. Most benthic taxa of lakes do not have the burrowing capabilities or adaptations for altering sediment redox potentials and thus, are limited to the top few centimeters of sediment, and the majority burrowing macrobenthic taxa occupy a narrow range of benthic conditions below the lake depth where wave action continually resuspends bottom sediments but above the lake depth of the hypolimnion. In many lakes, this may represent only a fraction of the total bottom area. Even in oligotrophic lakes, cold bottom water temperatures may restrict the benthos. Lacustrine ichnofacies will reflect the fundamental differences between lake and marine histories as well as their differences in biological, physical, and chemical processes, and are potentially powerful tools for the recognition and interpretation of ancient lake facies.

ACKNOWLEDGEMENTS Supported by NSF OPP 0126146 and OPP 0440954 to Miller and the Center for Reservoir Research to White. We appreciate the constructive suggestions of reviewers Lisa Park and A. A. Ekdale.

References CONCLUSIONS The theoretical underpinning for the ichnofacies concept is that there is an optimal behavior for each set of environmental conditions and that there will be animals present with body plans and life histories that allow that optimal behavior. Whereas this applies to the marine realm where substrate habitats were colonized by at least ten phyla near the beginning of the Phanerozoic and where conditions have remained relatively unchanged since, allowing for extensive adaptation and specialization, it is not appropriate for ephemeral ancient or modern lake ecosystems. Infaunal macrobenthos in lakes belong largely to three phyla and have a limited range of body plans relative to their marine counterparts. Infaunal activity in lakes is constrained by the complexity and variability of environmental conditions within lakes that are strongly affected by drainage basin processes and seasonality and that are not buffered by immense

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34 Trace Fossils in an Archaeological Context: Examples from Bison Skeletons, Texas, USA Dixie L. West and Stephen T. Hasiotis

archaeological context. Insect-feeding and -pupation behavior leave traces that can be distinguished from other taphonomic signatures including: weathering, root etching, gnawing, prehistoric human-food processing, and damage sustained through excavation and subsequent preservation. Humans create trace fossils; however, conventional ichnology does not recognize them as tracemakers (Ekdale et al., 1984; Bromley, 1996). In the context of understanding organism–medium interactions, it is, however, necessary to recognize human–medium interactions as trace fossils, particularly those that are pre-Holocene in age. It is our hope that eventually structures and traces produced by humans will be recognized as true trace fossils, since we are part of the Kingdom Animalia, not above it. Archaeologists have relatively little experience in the recognition of trace fossils on bones. Until recently, traces and marks (sensu Seilacher, 1953) made by agents other than weathering, roots, carnivore gnawing and digestion, and humans have been ignored—largely because archaeologists have failed to recognize these ichnofossils and their significance. Humans can extensively modify animal carcasses during butchering, transport, and processing to extract food; this activity creates traces on bone (e.g., Noe-Nygaard, 1989; Fagan, 2000). Indeed, one of the chief goals of humans, past and present, has been preventing other predators or scavengers from destroying their food sources. Insects are rarely left with acceptable microclimatic parameters on butchered carcasses for feeding and pupating. Subsequently, invertebrate trace fossils rarely develop or survive in

SUMMARY : Bones from the Folsom-age (11,500 –11,000 BP) bison kill site in Lipscomb, Texas, contain shallow to deep penetrative holes, ovoid chambers, surface-etched trails, tunnels and channels, and short, U-shaped notches attributed to a variety of insect behaviors. These trace fossils provide information on the seasonality of death and site-formation processes including when the bison were killed, the position of the carcasses on the landscape, stages of faunal succession and decomposition within the carcasses, rate and depth of burial, and butchering techniques. Invertebrate trace fossils can be distinguished from other taphonomic features including root etching, weathering, and human trace fossils—both ancient and modern. The occurrence of trace fossils on these 11,000-year-old bones is probably an unusual event; this is one of the few Paleoindian sites where the prey animals were dispatched during the summer, an optimal time for arthropod and microbial interactions on carcasses in temperate zones. Identification of the tracemakers can also potentially provide information on the environment and climate of the southern High Plains during the terminal Pleistocene.

INTRODUCTION This chapter describes ichnofossils on late Pleistocene-aged bison bones from a Paleoindian kill site at Lipscomb, Texas, USA. It provides a useful guide to differentiate the traces and marks left on bones by different organisms and agents in an


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34. TRACE FOSSILS IN AN ARCHAEOLOGICAL CONTEXT: EXAMPLES FROM BISON SKELETONS, TEXAS, USA

an archaeological context because of the season in which the animal was killed or because of human disturbance of the carcasses at kill sites. Since they occur infrequently, archaeologists do not recognize invertebrate trace fossils, or they are mistaken for other types of bone damage. Application of insect research to anthropological studies is similar to that of forensic anthropology, the discipline that frequently uses insect remains and behavior to infer time, season of death, condition, possible transportation and other questions related to the death of a human body (Sutton, 1995). Archaeologists can use forensic anthropology to identify ancient trace fossils and their tracemakers by comparing them with known tracemakers of extant traces on bone. Insects as producers of trace fossils on bones are rarely addressed in the archaeological literature. There are a few exceptions: (1) the rate of carcass skeletonization by insects (Payne, 1965); (2) the use of fly pupae to determine the season of death (Guthrie, 1990); (3) insect impacts on soft tissue preservation and decomposition (Lyman, 1994); and (4) the role of insects in disarticulation of remains (Lyman, 1994). Actualistic studies by Behrensmeyer (1978) recognized traces made by moth larvae in modern bovid horn cores in East Africa, and Haynes (1991) recorded insect activity on elephant bones. In an archaeological context, Gautier (1993) described trace fossils in Paleolithic Europe. Todd (1987) identified insect damage on bison bones from the Horner Site. Kitching (1980) recorded insect pupation burrows on gazelle leg bones from Pliocene deposits in Makapansgat, a South African cave. Jodry and Stanford (1992) recognized insect damage on bison bones from Stewart’s Cattle Guard.

ARCHAEOLOGICAL SETTING AND PREVIOUS ANALYSES The Lipscomb Bison bone bed is located in the southern high plains of the Texas panhandle. Paleontologist C.B. Schultz first excavated this Paleoindian kill site in 1939 and 1946 (Barbour and Schultz, 1941; Schultz, 1943; Hofman et al., 1989a,b). Located in an area measuring 30.7 m north to south, 6.3 m east to west, the bones represent an extinct form of bison (Bison antiquus taylori) (Schultz, 1943, Hofman et al., 1989a). Artifacts associated with the bones included complete and broken Folsom-type dart points, scrapers or knives, flakes and flake tools, and limestone slabs (Barbour and Schultz, 1941; Hofman et al., 1989a). Early investigations revealed that 14 overlapping skeletons were still articulated,

and that minimal processing had occurred on many of the other carcasses. Hofman et al. (1989a: 153) stated, ‘It is difficult to postulate why so many articulated animals had been left in the concentration . . . . Perhaps there was more food than necessary, and after the butchering of a sufficient supply had been completed only the pelts were taken from the remaining animals. Burial must have taken place shortly afterward, or the carnivores would have dismembered the skeletons.’ Erosion left the bones 17.8 cm below the surface at the northeast end and 76.2 cm at the southwest edge of the site (Schultz, 1943; Hofman et al., 1989a). This resulted in differential preservation of the bones with those at the northeast edge of the site experiencing the most surface weathering and rootlet damage (Hofman et al., 1989a). Further investigations of the site were conducted by Hofman and Todd in the 1980s and early 1990s (Hofman et al., 1989a,b). This Folsom-age bison bone bed represents 55 individuals killed en masse during the late summer or early fall, based on minimum number of individuals (MNIs) of astragali along with tooth eruption patterns and wear (Todd, 1987; Hofman et al., 1989a; Todd et al., 1990). Hofman et al. (1989b) argued that processing or camp activities occurred near the kill site, based on recovered stone artifacts, fractured bones, and evidence of individual fires adjacent to the dense bone bed. To date, Lipscomb represents the largest and most well-preserved Folsom-aged bison kill site known. Bones excavated from this site are currently housed in the Morrill Paleontological Collection at the University of Nebraska State Museum in Lincoln. A cursory analysis of the bison bones recovered from the 1930s excavations at Lipscomb revealed a left calcaneum with distinctive dermestid pupation chambers (Martin and West, 1995; West and Martin, 1997, 2002). This insect damage supported a summer killingepisode proposed by Todd et al. (1990). The animals were killed early enough during the warm season that the large parts of the discarded carcass were dry enough for dermestids to feed and pupate prior to the onset of cold weather (Martin and West, 1995; West and Martin, 1997). Broken long bones are evidence of marrow extraction and Todd et al. (1990) observed few broken long bones in the Lipscomb assemblage. Marrow extraction usually results in the disarticulation and removal of skin from the limbs. West and Martin (1997, 2002) suggested that when Paleoindian hunters processed the animals, they probably discarded nonmeaty, lower limbs as single units with the skin attached. The skin dried over the articulated knee joints and lower limbs, and dermestid larvae fed on dried tissues in dark, desiccated areas between the

547

INVERTEBRATE TRACES

mummified skin and bone. Prior to pupation, these beetles bored into adjacent solid bone. The presence of pupation chambers also suggests that carnivore scavenging, if it did occur, left some bones encased within mummified tissue, a situation conducive to the completion of the dermestid life cycle (West and Martin, 1997, 2002).

APPROACH AND METHOD Previous studies (Martin and West, 1995; West and Martin, 1997, 2002) described dermestid pupation chambers on a left calcaneus. West (unpublished data, 1996) recognized that multiple traces were found on other bison bones at this site and that they should be described. In 2004, West examined the Lipscomb collections at the University of Nebraska. Surface modifications on the bones were more extensive than previously thought. Traces included small and large pits, tunnels, notches, swirls and superficial scratches, channels; broad, smooth, short grooves; thin, curvilinear, branching grooves; and eroded bone surfaces. Proposed modifying agents included: insects, rodents, root etching, ancient and modern humans, and weathering. The assemblage represents an excellent example of multiple, sometimes overlapping, events occurring on bones in an archaeological context. Eighty-six bones with ichnofossils of different behaviors were examined at the Department of Geology, University of Kansas. There, ichnofossils were identified, measured, digitally photographed, and casts made with silastic rubber. Irregular-shaped ichnofossils were difficult to measure. Scallops and channels often ran across and through the bone surfaces into the interior of the bones, making measurements impossible. In some cases, ichnofossils were compound with scallops running through, or becoming, channels or holes. Some traces, including scratches, were so superficial and indistinct that measuring was difficult. Distinct and clearly delineated traces including pits and tunnels provided the most accurate length and width measurements. The most accurate measurements for meandering channels and swirls were widths.

ICHNOLOGY—ARCHITECTURAL AND SURFICIAL MORPHOLOGY, TRACEMAKER, AND DISCUSSION Traces on the Lipscomb bones are divided into four major groups based on the producer: (1) small and

large pits, tunnels, notches, scallops, scratches, and channels probably made by invertebrates, (2) broad, short, smooth grooves attributed to rodent gnawing, (3) thin, curvilinear, branching grooves recognized as root etching, and (4) superficial striations, V-shaped grooves, and breaks ascribed to ancient and modern human behavior. Pock-marked and exfoliated surfaces due to weathering of the bone may be mistaken for bone-modifying activity of plants, invertebrates, or vertebrates. The four categories of trace fossils are described according to their architectural and surficial morphologies following Hasiotis and Mitchell (1993) and Hasiotis et al. (2004). These descriptions are followed by interpretations of the tracemakers.

INVERTEBRATE TRACES Small Pits Small pits range from 3.3 to 8.1 mm in length and from 2.1 to 5.0 mm in width (Table 34.1). Some of these pits are nearly round, but most are elliptical shaped (Fig. 34.1A). These pits are rarely found on the central areas of the diaphyses of long bones, ribs, and vertebrae. They are most frequently found on parts of bones associated with, or near, tightly connected joints, as well as on the bones of the non-meaty lower legs, from just above the hock down to the hoof (Figs. 34.1B,C). Walls of the pits appear rough and irregular, characterized by very small scratches with no preferred direction. The pit walls appear gnawed or scraped rather than smooth. The pit shape is probably based on how the tracemaker approached the bone. A round-shaped pit suggests that the tracemaker excavated perpendicular to the bone surface. An ovoid-shaped pit resulted if the tracemaker excavated the bone at an angle to the bone surface. Small pits (Table 34.1; Fig. 34.1D) are similar both in size and morphology to the chambers earlier described on a calcaneus from Lipscomb by West and Martin (1997, 2002). They identified those pits (7.3 and 7.1 mm in length and 3.9 and 4.1 mm in width) as dermestid pupation chambers. These smaller, flask-shaped holes in our sample are likely the pupation chambers of dermestid larvae. Dermestids, during larval stages de-flesh dried carcasses, and can bore into hard substances within the vicinity of carcasses to pupate (Martin and West, 1995; West and Martin, 1997). Media used by dermestids include bones, hoof sheaths, antlers, and horn cores. Very specific parameters are necessary for these small beetles to successfully complete their life

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A

B

C

D

E

F

G

H

FIGURE 34.1 (A) Small pits on distal end of bison radius (16719-39). The pits can be either round or elliptical. (B) Distal end of bison femur (16189-39) with small pit on medial condyle. Dendritic patterns of rootlet etching are also prevalent on the bone surface. (C) Small pit on proximal end of immature bison metatarsal (16716-39). (D) Small pit on bison astragalus (16816-39). (E) Scallops leading to a large, ovoid pit on bison astragalus (16585-39). (F) Large, circular pit on distal end of bison metacarpal (16716-39). (G) Groove leading to large, ovoid pit on shaft of bison metacarpal (16697-39). Faint scratches can be seen on the bone shaft to the left of the groove. (H) Large, ovoid pit on shaft of bison phalanx 1 (16275-39).

549

INVERTEBRATE TRACES

TABLE 34.1 Locations and Measurements in Millimeters of Small Pits on the Lipscomb Bison Bones Bone

Catalog Number

Cervical vertebra

TABLE 34.2 Characteristics of Dermestid Activities on Carcasses (modified from West and Martin, 1997) (1) Adults visit carcasses at the butyric (desiccated) stage of

Length

Width

16193-39

7.1

3.1

decomposition.

Humerus

16719-39

8.1

5.0

(2) Adults copulate at temperatures above 108C.

Radius Femur

16719-39 16819-39

7.9 4.1

3.7 3.4

(3) The duration of the life cycle requires at least 42–46 days.

Femur

16819-39

3.9

3.9

(4) Larvae consume only drying flesh. (5) Larvae are negatively phototrophic.

Astragalus

16816-39

6.8

3.4

(6) Pupation chambers are flask shaped and the girth of the

Astragalus

16546-39

6.8

3.3

chamber is the most reliable identifying measurement.

Calcaneus

Lipscomb TX

5.7

4.2

(7) Grooves on bones may be created as larvae prepare to pupate.

Calcaneus

Lipscomb TX

6.1

4.2

(8) Walls of pupation chambers appear gnawed rather than smooth.

Calcaneus

Lipscomb TX

6.3

3.6

(9) Chamber size is variable with warmer species creating larger

Calcaneus Calcaneus

Lipscomb TX 16229-39

– 3.8

3.3 3.1

pupation chambers than those in cold climates (Hinton, 1945).

Calcaneus

16229-39

6.0

3.3

Metapodial

16716-39

5.4

3.6

Phalanx 1

16585-39

5.8

3.6

Phalanx 1

16585-39

6.7

4.0

Phalanx 1

16585-39

–

3.2

Phalanx 1

16294-39

6.6

2.1

Phalanx 1 Phalanx 1

16548-39 16677-39

3.3 7.1

2.7 4.0

Phalanx 1

16515-39

4.2

2.7

Phalanx 2

16512-39

5.9

3.9

Phalanx 3

16585-39

6.5

4.5

Phalanx 2 + 3

16148-39

5.9

4.9

cycle (Table 34.2), and these include temperature, light, and moisture. Dermestid infestation is supported by the fact that the pits are most frequently associated with tightly connected areas around articulated joints on nonmeaty, lower limb bones (West and Martin, 1997). These areas would have been protected from light and, depending on position of the animal at death, could have dried at a relatively rapid rate (Table 34.3). If the animals fell on their sides with legs extended at the time of death, the lower limbs would have dried relatively rapidly. If animals sank with their legs under the torsos, body fluids would have drained into the lower legs, hampering desiccation. The massive trunk regions, containing wet gut contents, almost certainly would have dried more slowly. Location of the carcass within the mass-death site would have also been crucial. Carcasses of bison that died, or were discarded by hunters, at the edge of the death site would have dried more rapidly than carcasses of animals in the center of the heap. It is likely that some parts of the carcass did not dry before the onset of cold weather, an event that would have interrupted the

TABLE 34.3 Locations and Measurements in Millimeters of Large Pits on the Lipscomb Bison Bones Bone

Catalog Number

Atlas vertebra

16702-39

Length 13.4

Width 8.8

Atlas vertebra

16716-39

16.2

10.2

Humerus

311-46

19.1

9.9

Femur

16819-39

8.6

8.5

Astragalus

16816-39

11.9

7.1

Astragalus

16107-39

6.9

6.9

Astragalus

16585-39

10.8

6.1

Astragalus Astragalus

16585-39 16546-39

– 15.9

7.6 11.6

Astragalus

16546-39

–

9.1

Calcaneus

16585-39

8.1

6.9

Metapodial

16716-39

7.6

7.1

Metapodial

16716-39

9.8

7.5

Metapodial

16716-39

9.9

4.6

Metapodial

16697-39

12.1

5.8

Metapodial Scapula

No number 16762-39

17.2 21.9

14.3 14.7

Phalanx 1

16810-39

12.0

5.9

Phalanx 1

No number

10.4

8.1

Phalanx 1

16677-39

11.8

8.1

Phalanx 1

16294-39

11.6

8.5

Phalanx 1

6529-39

7.1

6.7

Phalanx 1

16515-39

–

9.6

Phalanx 1 Phalanx 1

16500-39 16585-39

10.5 13.2

5.3 7.1

Phalanx 1

16585-39

11.6

9.5

Phalanx 2

16585-39

11.6

–

Phalanx 3

16585-39

9.6

5.7

Phalanx 3

No number

–

–

Phalanx 3

16224-39

9.3

5.3

Phalanx 2 + 3

16148-39

14.5

8.8

– Could not be measured.

550


dermestid life cycle. Very few pits on the bones were associated with the torso.

Large Pits Like small pits, these traces are circular or ovoid in shape, but measure 4.6–14.7 mm in width. Larger pits are associated with joints (Fig. 34.1E) and the ends of long bones (Fig. 34.1F), but also occur on the shafts of bones (Figs. 34.1G,H). The pit walls appear rough, characterized by very small scratches with no preferential orientation. Many of these pits are larger than those previously described from the assemblage (West and Martin, 1997, 2002). It is possible that the tracemaker was a Pleistocene dermestid that was larger than the extant species because of the large size of the pits. Extant Dermestis maculates chews chambers in wood, with widths measuring between 2.10 and 3.75 mm; these are smaller than the width measurements of the large pits in our sample (Table 34.4). Tobien (1965) recorded widths of dermestid pupation chambers that reached 6.80 mm. Rogers (1992) attributed the very large borings on Prosaurolopus bones (Table 34.4) to dermestids and Hasiotis et al. (1999) noted insect damage on bones during the Jurassic. Crowson (1981) reported the body fossil of a Lower Cretaceous dermestid encased in amber from Lebanon. Dermestids certainly existed during the late Pleistocene and, depending on the species, the size could have varied. Currently, TABLE 34.4 Specimen Prosaurolopus

700 species of the family Dermestidae are known; 125 of these occur in North America (Timm, 1982). It is possible that two, or more, species of Dermestidae, with slightly different microclimatic parameters, fed on the Lipscomb bones and left both small and large pupation chambers. Currently, we can only hypothesize that the constructor of these large pits is the larva of some unknown beetle.

Tunnels Tunnels are spherical to elliptical shaped, linear borings that penetrate and may pass through the bones (Figs. 34.2A–C). Tunnels vary from 7.0 to 16.0 mm in length and 4.8–9.6 mm in width (Table 34.5). They can deeply penetrate, sometimes extending into the medullary cavity of long bones and continuing through to the opposite side of the bone (Figs. 34.2D,E). The location of tunnels and their measurements are given in Table 34.5. The walls of most tunnels appear rough, characterized by very small scratches, but some tunnel walls appear smooth and polished with no surface irregularities. Like pits, the tunnel shape is probably a function of the angle of excavation of the tracemaker. The round cross section of a tunnel indicates that the tracemaker excavated perpendicular to the bone surface. If the tracemaker excavated the bone at an angle to the bone surface, the result was an ovoid-shaped tunnel.

Ages, Locations, and Measurements of Dermestid Borings

Age

Location

Number Measured

Upper Cretaceous

Two Medicine Formation,

2

Length Range (mm)

Width Range (mm)

Source

37.8 and 43.0

13.2–16.6 and 8.7-10.1

Rogers (1992)

7.0–19.7

2.0–6.8

Tobien(1965)

4–5

Kitching (1980)

5

3.84–4.55

Martin and West (1995)

51

1.87–4.00


4.6–5/0


4

Reed (1958)

2.10–3.75

West and Martin (1997)

Montana Miocene Gazelle

Pliocene

42 Makapansgat, South Africa

Stegamastodon

Late

Idaho

Pliocene Bison latifrons horncore

Pleistocene, 400 000–

Comanche Co., Kansas

Stagmoose

100 000 BP Pleistocene

Kansas River

(Cervalces)

(ca. 15 000

Sandbar,

antler

BP)

Bonner Springs

Dog carcass

Modern

Knoxville,

hides Wood

3

Tennessee Modern

KU dermestid colony

36

INVERTEBRATE TRACES

A

B

C

D

E

F

G

H

FIGURE 34.2 (A) Large, round tunnel on distal shaft of bison phalanx 1 (16548-39). (B) Elliptical-shaped tunnel on proximal end of bison metacarpal (16500-39). (C) Large, round tunnel on root-etched bison metatarsal shaft (16716-39). (D) Large tunnel on the anterior side of the distal shaft of a bison metapodial (16585-39). The tracemaker took advantage of a foramen that naturally occurred on this bone. (E) The same tunnel as shown in (D) emerging from the anterior side of the distal shaft of a bison metapodial (16585-39). (F) Notch on the shaft of a bison calcaneus (16585-39). (G) Notch on the edge of the proximal end of a bison scapula (16762-39). An elliptical tunnel also occurs on the articular surface of this bone. (H) Notch on the lateral side of a bison metatarsal shaft (16340-39).

551

552


TABLE 34.5 Location and Measurements in Millimeters of Tunnels on Lipscomb Bison Bones Bone

Catalog Number

Scapula

16762-39

Length

Humerus

16464-39

11.1

Femur Femur

16819-39 Lipscomb, TX

10.0 13.9

Width

TABLE 34.6 Locations and Measurements in Millimeters of Notches on the Lipscomb Bison Bones Bone

Catalog Number

Atlas vertebra

16716-39

Length –

Width 10.0

6.4

Patella

16668-39

23.3

12.3

5.9 7.4

Astragalus Calcaneus

16816-39 16585-39

– –

7.5 6.7 9.1

Metapodial

16585-39

12.4

6.6

Metapodial

16356-39

12.1

Metapodial

16500-39

12.2

6.4

Scapula

16762-39

–

7.4

Metapodial

16500-39

14.3

8.6

Scapula

16269-39

–

12.2

Scapula

16762-39

11.8

6.9

Phalanx 3

16585-39

–

4.3

Scapula

16762-39

10.4

5.4

Phalanx 1

No number

–

8.1

Phalanx 1

16677-39

12.2

5.8

Phalanx 1

16677-39

21.6

10.2

Phalanx 1 Phalanx 1

16548-39 16500-39

8.6 10.5

7.6 6.2

Phalanx 1 Phalanx 1

16677-39 16677-39

15.3 –

11.4 9.4

Phalanx 1

16585-39

15.1

4.8

Phalanx 1

16677-39

–

7.0

Phalanx 1

16585-39

16.0

9.6

Phalanx 1

16515-39

–

14.8

Phalanx 1

No number

7.0

5.3

Phalanx 1

16140-39

–

9.4

Phalanx 1

No number

–

4.8 – Could not be measured.


Because tunnels are continuous, they cannot be defined as pupation chambers. It is likely that larvae, excavating a place to pupate, created the tunnels. The large size of some tunnels might indicate that more than one larva used the same tunnel, enlarging it as they gnawed. Sometimes the tracemakers were opportunistic and took advantage of foramina and sulci, which are naturally occurring holes in bones for the passage of nerves and blood vessels, as paths of least resistance, enlarging these as they gnawed or scraped (Figs. 34.2D,E). The larva of an unknown beetle excavated the tunnels as well as the large pits, based on the size of the tunnel.

Notches Notches, unlike tunnels or pits, are cup-shaped depressions (Figs. 34.2F–H). They measure from 4.3 to 14.8 mm in width (Table 34.6) and occur on the ends of bones as well as on the shafts. The width of notches is well within the size limits of both small and large pits as well as tunnels. Most notches, like pits, have rough walls, but several have very smooth walls with no surface irregularities. The orientation of a notch, like a tunnel, records the path of movement of the tracemaker. The tracemaker created a notch on the edge of a bone by gnawing between soft tissues encasing the bones and the bones themselves. If the tracemaker had gnawed directly into the bone, this would have created a pit or tunnel.

Like pits and tunnels, notches represent feeding or excavating, rather than reproductive, behavior. The depth of the notch records how closely the organism passed to the bone edge as it gnawed through surrounding tissues, rather than the width of the actual organism. Apparently, as invertebrates moved through a carcass, bones sometimes simply impeded the route; undeterred larvae simply gnawed the bone surface as well as tissues surrounding the bone. Because notches and tunnels probably represent the same type of behavior, width sizes can be similar (Table 34.6). Caution is necessary; however, the width of a notch depends on how closely gnawing occurred to the actual bone surface. Arthropods that passed close to bones would gnaw deeper into bone surfaces leaving notches with larger widths than arthropods that did not pass as closely to the bone surface. Often, the length of the notch could not be easily measured (Table 34.6), and this measurement provides little information on the actual activity.

Scallops and Scratches Scallops are meandering trails of crescentshaped, shallow etchings on the surface of the bone (Figs. 34.3A–E). Scallops in the Lipscomb assemblage range from 4.3 to 16.1 mm wide. Like notches, scallops can be quite short (e.g., 5.1 mm) or they can extend along the surface of the bone for some distance (e.g., 46.6 mm; Table 34.7). On the other hand, scratches are superficial traces that are faint, and sometimes

INVERTEBRATE TRACES

A

B

C

D

E

F

G

H

FIGURE 34.3 (A) Scallops on bison astragalus (16223-39). (B) Close-up of scallops on bison astragalus (16223-39). (C) Scallops on distal end of bison astragalus (16180-39). (D) Close view of scallops on distal end of bison astragalus (16180-39). (E) Scallops on distal end of bison calcaneus (16229-39). (F) Scratches on bison astragalus (16107-39). (G) Scratches on bison metatarsal shaft (16340-39). (H) Scratches on bison astragalus (16585-39).

553

554


TABLE 34.7 Locations and Measurements in Millimeters of Swirls on the Lipscomb Bison Bones Bone

Catalog Number

Humerus

16719-39

Length –

Width –

Humerus

16381-39

–

13.4

Radius Astragalus

16719-39 16107-39

14.2 34.4

12.5 8.8

Astragalus

16816-39

–

–

Astragalus

16585-39

22.0

10.4

Astragalus

16585-39

24.6

10.5

Astragalus

16107-39

17.0

12.6

Astragalus

16585-39A

19.2

9.8

Astragalus

16585-39A

46.6

8.5

Astragalus Astragalus

16546-39 16546-39

14.9 22.4

9.0 13.1

Astragalus

16546-39

38.6

9.1

Astragalus

16180-39

33.9

10.3

Astragalus

16180-39

13.4

7.1

Astragalus

16107

34.4

8.8

Astragalus

16223-39

35.4

11.4

Astragalus

16585-39

26.4

9.5

Astragalus Autopodium

16546-39 16148-39

– 18.4

9.6 10.2

Calcaneus

16667-39

37.4

12.6

Metapodial

16356-39

–

–

Metapodial

16716-39

6.7

9.9

Metapodial

16716-39

–

–

Phalanx 2

16152-39

5.1

11.3

Phalanx 2

16585-39

–

16.1

Phalanx 3 Phalanx 1

No number 16130-39

– –

4.3 14.5

Phalanx 1

16346-39

11.7

6.9

Phalanx 1

16515-39

–

8.1

Phalanx 1

No number

–

7.3

Phalanx 1

No number

33.4

11.5

Phalanx 1

16294-39

9.4

6.4

Phalanx 1

16515-39

21.1

6.1

Phalanx 1 Phalanx 1

16585-39 16585-39

21.8 21.2

13.2 10.0

Phalanx 1

16585-39

–

9.5

Phalanx 1

16585-39

–

6.1

Phalanx 1

16585-39

22.8

11.1

Phalanx 1

16585-39

31.0

7.6


crisscross one another on the bones (Figs. 34.3F–H). Unlike scallops, scratches are not deep enough to leave distinct, measurable, trails on the bones. Scratches were only observed on cortical bone in the Lipscomb assemblage. Scratches are so subtle that they could not be detected on softer, cancellous tissues, and probably would have been readily

FIGURE 34.4 femur.

Dermestid damage on modern antelope

erased by weathering and rootlet etching on the softer bone. Scratches could not be accurately measured. Scalloping suggests an activity that follows the path of least resistance, rather than passing through bones like notches and tunnels. The traces seem to represent a type of grazing behavior that follows the surface of the bones rather than passing through them. It is possible that the tracemaker fed on the periosteum, the surrounding connective tissue of the bone, rather than the bone itself. The morphology of the scallops provides information on a sweeping, gnawing durophagous behavior of an invertebrate as it gnawed the bone surface with its mandibles. Some of the wider scallops might represent the activities of more than one individual gnawing at the same location. The relatively large width of some scallops suggests that an arthropod other than Dermestis maculatis probably created these traces. Hasiotis (2004) recorded the voracious nature of dermestid feeding activities on an antelope carcass in Wyoming during late June 2004 (Fig. 34.4). Dermestids ravaged the proximal end of a femur leaving it ragged, but no scallops or scratches like those found on the Lipscomb assemblage were observed. Scratches represent ephemeral traces similar to termite damage identified by others. Derry (1911) identified termite damage on bones in Africa. Watson and Abbey (1986), performing actualistic experiments with termites and bones, showed that termites gnaw on bones, leaving distinct scratches with their mandibles, as they extract nitrogen. Although it is possible that termites gnawed the bones after they were in the ground for a time, previous work by Watson and Abbey (1986) suggests that termites are more likely attracted to fresh bones.

555

HUMAN MODIFICATIONS

Channels

Thin, Curvilinear, Branching Grooves

Channels are much like notches in that they have U-shaped cross section (Figs. 34.5A–C). Channels occur on the surfaces of the bones and can extend for some distance, unlike notches that occur on bone edges. Channels cut into the surfaces of bones much more deeply than scallops. Channels vary considerably in size from 2.9 to 23.1 mm in width (Table 34.8) and can be straight or curved. Channels can lead to tunnels or pits. The walls appear rough and show minute, non-directional striations, and do not contain swirl patterns. The great variation in channel width suggests that more than a single arthropod—adult or larva—created these marks. It is interesting to note that some channels are oriented in a straight line. Although we assume that these channels were made by arthropods, the identity of the tracemaker is unknown.

The surfaces of many bones display an irregular, dendritic pattern of grooves (Figs. 34.5F–H). The grooves are semicircular in cross section and vary in width from 0.1 to 1 mm. They are typically shallow although some penetrate the bone to a moderate depth. The grooves are not present on all bones, but cover nearly 100% of the surface of some bones (Fig. 34.5H), almost obliterating the surface of the original bone surface. The walls of these grooves appear smooth. These dendritic groove patterns represent acid etching by plant roots. Roots can potentially remove much of the periosteal layer and cancellous tissues of bone, erasing tool-cut marks or carnivore gnawing (Maltby, 1985; White, 1992). Roots may also cause splitting and fragmentation of bones (Behrensmeyer, 1978). Narrow, intersecting grooves are created as plant roots excrete humic acids to break down and extract nutrients from nearby resources including bones (Lyman, 1994). The intensity of root etching is highly dependent on: (1) depth of the burial of the bone assemblage; (2) density of the soil in which plant roots are growing; (3) the amount of water nourishing the roots; and (4) the configuration of roots which can attach to a given bone assemblage. Root acids readily destroy bones in tropical climates (Warren, 1975); root etching on buried bones in a temperate climate is much slower (Stewart, 1979). Root etching can be as intense on the interior of long bone fragments, suggesting that roots seek out avenues of least resistance to chemical breakdown (West, 1997). The recent age and sedimentological context of the Lipscomb site suggests that root etching is a much more recent phenomenon, rather than having occurred shortly after burial. Figure 34.5H shows a root hair preserved in the lower right-hand corner of the bison astragalus. This illustrates that root etching was still ongoing when the bones were excavated. Shallow ichnofossils, including scallops and scratches, could be easily obliterated by the extensive root-acid etching observed on many of the Lipscomb bones.

Broad, Smooth, Short Grooves Short, smooth, parallel traces appear on the edges of bones and are sometimes accompanied by similar traces on the opposing bone faces. These traces are V or rectangular in cross section and the walls are smooth (Figs. 34.5D,E; Table 34.9). This damage on the Lipscomb assemblage resembles damage by rodent gnawing. Rodents gnaw on hard substances to adjust the chisel edges of their incisors or to extract minerals (Brain, 1969; Gautier, 1993). Some rats are carnivorous, however, and willingly eat flesh and cartilage if given the opportunity. This scavenging behavior can potentially damage bones and has been documented in forensic anthropology cases (Ubelaker and Scammell, 1992: 287–289) and the archaeological record (Gautier, 1993). The physics of the size of the mouth and size of the bone dictates the preferences of bones that will be gnawed. Rodents often choose thin, flat bones or bones with sharp edges that can fit the radius of their bite (e.g., Bromley, 1975). The general absence of carnivore activity reflected at Lipscomb suggests that the assemblage was probably not significantly altered or depleted by large scavengers (Hofman et al., 1989a: 153). We identified distinctive, short, broad, parallel striations indicative of rodent gnawing, on three of the Lipscomb bones, however. This gnawing probably occurred prior to burial when rodents were scavenging for meat, extracting minerals, or sharpening their incisors.

HUMAN MODIFICATIONS Linear, V-Shaped Grooves (Chop Marks) A calcaneus and astragalus from the Lipscomb assemblage possessed multiple, V-shaped grooves (Figs. 34.6A,B). These rare grooves occur on the edges of bones associated with the lower limbs.

556


FIGURE 34.5 (A) Channel on distal end of bison astragalus (16546-39). (B) Curving channel on bison centroquatro (386-46). (C) Channel on proximal end of bison calcaneus (xx116-39). (D) Short, parallel grooves on the proximal (lower right edge) of a bison phalanx 1 (16275-39). (E) Close-up of parallel grooves on proximal edge of bison phalanx 1. (F) Dendritic marks made by root etching on bison calcaneus (16585-39). (G) Close-up of dendritic patterns on bison calcaneus. (H) Surface of bison astragalus (16575-39) nearly obliterated by root etching.

HUMAN MODIFICATIONS

TABLE 34.8 Location nd Measurements in Millimeters of Channels on Lipscomb Bison Bones Bone

Catalog Number

Humerus

311-46

Femur

16819-39

Femur Femur

Length

Girth

24.2

23.1

–

5.9

16719-39 Lipscomb TX

19.3 –

15.6 10.4

Astragalus

16585-39

36.8

16.5

Astragalus

16107-39

–

5.9

Astragalus

16816-39

19.3

5.1

Astragalus

16546-39

–

7.4

Calcaneus

16116-39

45.1

7.2

Metapodial

16716-39

21.4

8.9

Metapodial Metapodial

16697-39 16340-39

– 14.2

5.1 6.1

Metapodial

16716-39

–

10.2

Metapodial

16767-39

–

8.5

Centroquatro

386-39

–

12.3

Scapula

16762-39

11.8

6.9

Scapula

16762-39

10.4

5.4

Phalanx 2

16152-39

–

2.9

Phalanx 1 Phalanx 1

16487-39 16294-39

– 16.7

8.1 9.8

Phalanx 1

16515-39

–

5.0


TABLE 34.9

Bone

Locations of Rodent Gnawing on Lipscomb Bison Bones Catalog Number

Location

Femur

Lipscomb TX

Astragalus

16223-39

Anterior/medial Anterior/lateral

Phalanx 1

16275-39

Proximal/medial

These grooves are short, parallel, and have smooth surfaces. These grooves likely represent chop marks produced by humans butchering the carcass. Animal carcasses are butchered for easy transport and storage, convenient cooking, and consumption. Cut lines, chopping marks, abrasions, and scrapes are an incidental part of the disarticulation, meat extraction, and skinning process of animal carcasses (West, 1997). They occur on a carcass where soft tissue is not present to absorb the cuts (Johnson, 1983). Chopping leaves characteristic multiple, parallel, V-shaped grooves. Location and angle of chop marks on bones provide information on how muscle and fat were removed and how carcass parts were separated. The locations of these chop marks associated with bones of the mid limb, just above the hock, support

557

the earlier scenario proposed by West and Martin (2002) that human hunters knocked lower legs from carcasses during the butchering process (Table 34.10). The paucity of cut marks on other bones of the skeleton suggests that hunters carefully filleted meatrich parts of carcasses, or did not butcher some of the carcasses, leaving them intact.

Superficial Striations and Pockmarked Bone Surfaces Very fine-grained elongate striations cover some bones (Fig. 34.6C). Other bones possess pockmarked surfaces that are lighter in color than the surrounding darker, discolored bone (Fig. 34.6D). The proximal end of a calcaneus (Fig. 34.6E) shows a deep groove. The groove walls are lighter colored than the surrounding bone and are extremely smooth and polished. Field recovery and laboratory preparation methods left very distinctive marks on some bones (Figs. 34.6C–E). Scraped areas on otherwise darkly discolored bones indicate that excavators gouged some bones with metal tools during field excavation or subsequent cleaning. Very fine-grained, elongate striations cover some bones. Paleontologists apparently cleaned soil from soft bones prior to applying a preservative coating to the bone surfaces. Brush scrubbing left striations and removed the original, stained, outer bone layer. The proximal end of a calcaneus (Fig. 34.6E) shows a deep groove that resembles channeling made by insect larvae. This groove, however, has very smooth walls. The bone was probably drilled with some type of metal instrument, possibly for radiocarbon dating.

Broken Bones The Lipscomb bones were, for the most part, complete. Few bones were fractured. Only one bone in our study exhibited a curvilinear fracture with smooth walls. Other bones possessed rectilinear fractures with rough surfaces. The fracture walls often are lighter colored than the surrounding, darker colored bone surface. Bone breaks in a variety of ways, but in predictable fashion, based on its collagen content. Fresh or green bones break in smooth fractures that run down the bone shaft. Dry or mineralized bone shatters into straight-edged fragments with uneven or jagged break surfaces (Behrensmeyer, 1978; West, 1997). Todd et al. (1990) determined that the Lipscomb bison were killed during summer when bison marrow would have been poorest in quality, based on tooth

558


A

B

C

D

E

F

FIGURE 34.6 (A) Chop marks on shaft of bison calcaneus (16498-39). (B) Chop marks on bison astragalus (16180-39). (C) Close view of brush mark on bison calcaneus (16229-39). (D) Modern archaeological damage on bison astragalus (16585-39). The tool has cut through the original darkened surface of the bone. (E) Groove on bison calcaneus created by modern human drilling. (F) Weather cracking on bison metacarpal (16356-39).

eruption sequences. With such a large number of animals, it is likely that Paleoindians took as many hides and as much meat as they could process and carry, and left the carcasses unscathed for the most part. A green break occurred on a metapodial (Figs. 34.2D,E). It is possible, however, that this break occurred during the killing episode when the animals were lunging and milling around trying to escape. Hunters would have preferred breaking upper limb bones, including humeri and femora, because these bones contained larger amounts of marrow than lower

limb bones. The green breaks in the Lipscomb assemblage are probably purely incidental.

WEATHERED BONE Pockmarked, cracked, and exfoliated surfaces due to weathering of the bone may be mistaken for bonemodifying activity of plants, invertebrates, or vertebrates. Weathering, characterized by cracking and

DISCUSSION AND CONCLUSIONS

TABLE 34.10

Bone

Locations of Human Chop Marks on Lipscomb Bison Bones

Catalog Number Location

Multiple/single

Astragalus 16180-39

Anterior/lateral

Multiple

Astragalus 16170-39

Posterior/medial Multiple

Astragalus 16223-39 Calcaneus 16498-39

Proximal/medial Multiple Anterior Multiple

Phalanx 1

16275-39

Proximal/lateral

Multiple

Phalanx 1

16294-39

Distal

Multiple

Phalanx 1

16585-39

Distal

Single (spall)

exfoliation (Fig. 34.6F), begins when hide, meat, fat, and fascia encasing skeletons are removed, and bones are exposed to the elements. Behrensmeyer (1978: 153) defined weathering as ‘the process by which the original microscopic organic and inorganic components of bone are separated from each other and destroyed by physical and chemical agents operating on the bone in situ, either on the surface or within the soil zone.’ Absence of carnivore activity on the Lipscomb bones suggests quick burial (Hofman et al., 1989a). Rapid burial, as suggested by Hofman et al. (1989a) could account for the excellent condition of some bone surfaces (see Fig. 34.1D). Unscathed bone surfaces might be accounted for by reasons other than rapid burial. During the terminal Pleistocene, climate may have been different—cooler with fewer extremes in temperature fluctuations—from the current climate of the southern High Plains (Graham and Lundelius, 1984). The Pleistocene climate likely slowed weathering processes. Also, densely packed, articulated, hide-covered bones representing 14 unbutchered animals weathered slowly compared to bones from carcass parts that had hide, meat, and fat removed by human hunters. Erosion left the bones 17.8 cm below the surface at the northeast end and 76.2 cm at the southwest edge of the site (Schultz, 1943; Hofman et al., 1989a). This resulted in a differential preservation, as deeply buried bones experienced the least surface weathering and root damage, and shallowly buried bones experienced the most weathering and root damage.

DISCUSSION AND CONCLUSIONS Insects leave traces in anthropogenic as well as natural contexts. It is reasonable that, under sufficient light, temperature and moisture parameters, feeding, and growth, pupation activities can occur any time

559

carcasses attract Coleoptera and other invertebrates. This can occur even if the bone had been anthropogenically altered. The current study supports the hypothesis that invertebrate modifications on bones can occur in both the context of a hunting (anthropogenic) episode as well as in natural death sites. Human traces include V-shaped grooves (cut or chop marks) and bones broken for extracting marrow. Some paleontologists believe that humans should not be considered tracemakers. We argue that in an archaeological context, humans do leave traces of their activities on bones, and can potentially alter animal-bone assemblages to such an extent that other organisms that normally feed and pupate on carcasses are impacted. Archaeologists have had relatively little training in the recognition of invertebrate traces on bones probably because ichnofossils are a relatively rare phenomenon in archaeological sites. Because of their rarity, when invertebrate ichnofossils do occur, archaeologists do not recognize traces, or they mistake them for other types of damage on bones. Traces can provide information on post-mortem and preburial history—site-formation processes—of death sites. Our observations of coleopteran activities on the bison bones from the Folsom-aged Paleoindian bison kill site near Lipscomb, Texas, support evidence from tooth eruption and wear that the bison were killed during summer (Todd et al., 1990). Our research also demonstrates that traces can be compound. One or more invertebrates may have simultausly created different traces on the bone. Sometimes, channels ended up as large pits, and scratches could overlap with scallops. Through time, traces such as root etching probably erased traces produced earlier in the history of the bone assemblage. Final episodes of weathering may have also completely erased earlier ichnofossils. Location of traces on the Lipscomb bones suggests that parts of carcasses desiccated and became accessible to tracemakers at different times. Bones associated with the lower legs and bones on the fringes of the large bison accumulation appear to have dried more quickly than bones in the center of the accumulation. Invertebrates, including Dermestids and other beetles, fed and pupated at a quicker rate in these particular regions, completing their life cycles prior to the onset of cold weather. Our research also shows that ichnofossils might be easily misidentified in an archaeological context. If the zooarchaeologist or paleontologist does not take into account that invertebrates can attack bone assemblages, the trace might be easily mistaken for carnivore gnawing or some other form of unidentified

560


weathering damage. On the other hand, modern human modifications might also be misidentified as invertebrate traces (see Fig. 34.6E). Although the groove might, upon first glance, appear to be made by invertebrates, the smooth wall surfaces indicate that humans created this particular modification. Accurate identification of more recent traces, like those found in the late Pleistocene Lipscomb site, may provide clues to identifying traces on bones in deep time. This study shows clearly that damage to bone comes in a range of morphologies produced by insects and vertebrates that occurs just after death, during decay, and after burial. The pits, holes, scratches, scallops, and grooves have distinct morphologies that can be differentiated from abiotic modifications to bone. Finally, our study shows that trace fossil production is ongoing. They can commence upon, or shortly after, the death of the animal, occur during the burial process or as bones erode, and continue as modern archaeologists and paleontologists excavate and preserve bones. This situation is common to trace fossils produced in the continental realm, where various media are overprinted by several to multiple generations of bioturbation in association with syndepositional, post-depositional, and pedogenic processes (e.g., Hasiotis, 2002).

ACKNOWLEDGEMENTS We thank William Miller III for inviting us to contribute this chapter to the book. Access to the Lipscomb bison bones was granted with the permission of George Corner of the University of Nebraska, Lincoln. We are indebted to the students of University of Kansas IchnoBioGeoScience research group for stimulating research and discussions on the breadth and depth organism–medium interactions. Richard Bromley and an anonymous reviewer provided helpful comments and suggestions that greatly improved the chapter. We thank Brian Platt and Jon Smith for their help in preparing the chapter for publication.

References Barbour, E.H. and Schultz, C.B. (1941). A new fossil bovid from Nebraska with notice of a new bison quarry in Texas. Bulletin of The University of Nebraska State Museum, 2(7), 63–68. Behrensmeyer, A.K. (1978). Taphonomic and ecologic information from bone weathering. Paleobiology, 4, 150–162. Brain, C.K. (1969). The contribution of Namib Desert Hottentots to an understanding of Australopithecine bone accumulations.

Scientific Papers of the Namib Desert Research Station No. 39, pp. 13–32. Bromley, R.G. (1975). Comparative anatomy of fossil and recent echinoid bioerosion. Palaeontology, 18, 725–739. Bromley, R.G. (1996). Trace Fossils—Biology, Taphonomy, and Applications, Chapman & Hall, London, 361 pp. Crowson, R.A. (1981). The Biology of the Coleoptera, Academic Press, New York, 802 pp. Derry, D. (1911). Damage done on skulls and bones by termites. Nature, 86, 245–246. Ekdale, A.S., Bromley, R.G. and Pemberton, S.G. (1984). Ichnology: The Use of Trace Fossils in Sedimentology and Stratigraphy, Socirty of Economic Palcontologists and Mineralogists, Short Course, 15, pp. 1–317. Fagan, B.M. (1955). Ancient Lives—An Introduction to Archeology. Prentice Hall, Upper Saddle River NJ, 428 pp. Gautier, A. (1993) Trace fossils in archaeozoology. Journal of Archaeological Science, 20(5), 511–523. Graham, R.W. and Lundelius, Jr, E.L. (1984). Coevolutionary disequilibrium and Pleistocene extinctions. In: Martin, P.S. and Klein, R.G. (Eds.), Quaternary Extinctions: A Prehistoric Revolution, University of Arizona Press, Tuscon, Arizona, pp. 223–249. Guthrie, D. (1990). Frozen Fauna of the Mammoth Steppe: The Story of Blue Babe, University of Chicago Press, Chicago, 338 pp. Hasiotis, S.T. (2002). Continental Trace Fossils, Tulsa, Oklahoma, SEPM, Short Course Notes Number, 52, 132 pp. Hasiotis, S.T. (2004). Reconnaissance of Upper Jurassic Morrison Formation ichnofossils, Rocky Mountain region, USA: environmental, stratigraphic, and climatic significance of terrestrial and freshwater ichnocoenoses. Sedimentary Geology, 167, 277–368. Hasiotis, S.T. and Mitchell, C.E. (1993). A comparison of crayfish burrow morphologies. Triassic and Holocene fossil, Paleo- and Neo-ichnological evidence, and the identification of their burrowing signatures. Ichnos, 2, 291–314. Hasiotis, S.T., Fiorillo, A.R. and Laws, G.R. (1999). A preliminary report on borings in Jurassic dinosaur bones. Trace fossil evidence of beetle interactions with vertebrates. In: Gillette, D.D. (Ed.), Vertebrate Fossils of Utah, Miscellaneous Publication 99-1, Utah Geological Survey, pp. 193–200. Hasiotis, S.T., Wellner, R.W., Martin, A. and Demko, T.M. (2004). Vertebrate burrows from Triassic and Jurassic continental deposits of North America and Antarctica: their paleoenvironmental and paleoecological significance. Ichnos, 11, 103–124. Haynes, G.A. (1991). Mammoths, Mastodonts, and Elephants: Biology, Behavior, and the Fossil Record, Cambridge University Press, New York, 427 pp. Hofman, J.L., Todd, L.C., Schultz, C.B. and Hendy, W. (1989a). The Lipscomb bison quarry: continuing investigation at a Folsom kill-butchery site on the Southern Plains. Bulletin of the Texas Archeological Society, 60, 149–189. Hinton, H.E. (1945). A monograph of the bectles associated with stored products, British museam: London, United Kigdom. Hofman, J.L, Todd, L.C. and Schultz, C.B. (1989b). Further investigation of the Folsom bison kill at Lipscomb, Texas. Current Research in the Pleistocene, 6, 16–17. Jodry, M.A. and Stanford, D.J. (1992). Stewart’s Cattle Guard Site : an analysis of bison remains in a folsom kill - butchery campsite. In: Stanford, D. and Day, J. (Eds.), Ice Age Hunters of the Rockies, Denver Museum of Natural History and University Press of Colorado, Boulder, Colovado, pp. 101–168.

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Johnson, E. (1983). A framework for interpretation in bone technology. In: Le Moine, G.M. and MacEachern, A.S. (Eds.), A Question of Bone Technology, Calgary Archaeological Association, Calgary, pp. 55–93. Kitching, J. (1980). On some fossil Arthropoda from the Limeworks, Makapansgat, Potgietersrus. Palaeontologia Africana, 23, 63–68. Lyman, R.L. (1994). Vertebrate Taphonomy, Cambridge University Press, Cambridge, 550 pp. Maltby, J.M. (1985). Patterns in Fannal Assemblage Variability. In: Barker, G. and Gamble (eds). Beyond Domestication in Prehostonic Europe. Academic press, London, pp. 34–74. Martin, L.D. and West, D. (1995). The recognition and use of Dermestid (Insecta, Coleoptera) pupation chambers in paleoecology. Palaeogeography, Palaeoclimatology, Palaeoecology, 113, 303–310. Noe-Nygaard, N. (1989). Man-made trace fossils on bone. Human Evolution, 4, 461–491. Payne, J. (1965). A summer carrion study of a baby pig Sus scrofa. Ecology, 46(5), 592–602. Reed, H.B., Jr. (1958). A study of dog carcasses in Tennessee with special reference to the insects. American Midland Naturalist, 59(1), 213–245. Rogers, R. (1992). Non-marine borings on dinosaur bones from the Upper Cretaceous Two Medicine Formation, Northwestern Montana. Journal of Vertebrate Paleontology, 12, 528–531. Seilacher, A. (1953). Studien zur Palichnologie. I. Uber die Mehtoden der Palichnologie. Neues Jahrbuch fur Geologie und Palaontologie, Abhandlungen, 96, 421–452. Schultz, C.B. (1943). Some artifact sites of early man in the Great Plains and adjacent areas. American Antiquity, 3, 242–249. Stewart, T.D. (1979). Essentials of Forensic Anthropology, Charles C. Thomas, Springfield, IL, 300 pp. Sutton, M.Q. (1995). Archaeological aspects of insect use. Journal of Archaeological Method and Theory, 2(3), 253–298.

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Timm, R.M. (1982). Dermestids. Field Museum of Natural History Bulletin, 53(2), 14–18. Tobien, H. (1965). Insekten-Frasspuren an tertiren und pleistozanen Saugetier-Knochen. Senckenbergiana Lethaea, 46, 441–451. Todd, L.C. (1987). Taphonomy of the Horner II Bone Bed. In: Frison, G.C. and Todd, L.C. (Eds.), The Horner Site: The Type Site of the Cody Cultural Complex, Academic Press, Orlando, pp. 107–198. Todd, L.C., Hofman, J. and Schultz, C. (1990). Seasonality of the Scottsbluff and Lipscomb bison bonebeds: implications for modeling Paleoindian subsistence. American Antiquity, 55(4), 813–827. Ubelaker, D. and Scammell, H. (1992). Bones: A Forensic Detective’s Casebook, Edward Burlingame Books, New York, 317 pp. Warren, C.P., (1975). Plants as decomposition vectors of human skeletal remains. Paper presented at Indian Academy of Sciences, 91 Annual Meeting, Butler University. Watson, J. and Abbey, H.M. (1986). The effects of termites (Isoptera) on bone: some archaeological implications. Sociobiology, 11, 245–254. West, D.L. (1997). Hunting Strategies in Central Europe during the Last Glacial Maximum. BAR International Series, 672, 153 pp. West, D.L. and Martin, L.D. (1997). Insects and the archaeological record: Dermestid ichnofossils. In: Hannus, L., Rossum, L., and Winham, R. (Eds.), Proceedings of the 1993 Bone Modification Conference, Hot Springs, South Dakota, Augustana College Occasional Paper No.1. Sioux Falls, South Dakota, pp. 88–97. West, D.L. and Martin, L.D., (2002). Insect trace fossils as environmental/taphonomic indicators in archaeology and paleoecology. In: Dort,Jr., W. (Ed.), Institute for Tertiary W.Quaternary Studies: Ter-Qua Symposium Series, 3, pp. 163–174. White, T. (1992). Prehistoric Cannibalism at Mancos 5MTUMR-2346, Princeton University Press, Princeton, 492 pp.

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35 Ichnofacies of an Ancient Erg: A Climatically Influenced Trace Fossil Association in the Jurassic Navajo Sandstone, Southern Utah, USA A.A. Ekdale, Richard G. Bromley, and David B. Loope

INTRODUCTION

SUMMARY : Arid eolian environments usually exhibit a paucity of organism traces, but some eolianite facies in the geologic record contain a great abundance of trace fossils, which characterize a distinctive ichnofacies, herein termed the Entradichnus Ichnofacies. This arid landscape ichnofacies is exemplified by a locally dense and diverse invertebrate trace fossil assemblage, which is preserved in the Navajo Sandstone, a Jurassic eolianite exposed in the Paria Canyons Primitive Area in southern Utah. The trace fossils (Planolites, Palaeophycus, Skolithos, Arenicolites, Entradichnus, Taenidium and Digitichnus) all appear to be the products of shallow burrowing by desert-dwelling arthropods, such as beetles and other insects, that kept pace with the dune migration. The paleoclimate was monsoonal, characterized by rainy summers and windy (but relatively dry) winters. The burrowed beds were produced during long-lived pluvial intervals that brought higher than usual amounts of moisture to the Navajo dune fields. Most of the sand in the Navajo at the study site was deposited as dry grain flows during the winter months, and the only possibility of rainfall or dew precipitation came during the summer months. Nevertheless, the burrowers apparently were active year-round and exploited resources within both dry and damp sand.

It is widely understood that the most important practical applications of ichnology are in the area of paleoenvironmental interpretation. The analysis of trace fossils and trace fossil associations provides powerful tools for interpreting the bathymetry, salinity, oxygen concentration, hydrodynamic energy and substrate consistency in subaqueous settings (Seilacher, 1964, 1967a; Ekdale et al., 1984; Frey and Pemberton, 1984; Ekdale, 1988; Pemberton et al., 1992, 2001; Bromley, 1996; McIlroy, 2004) and for interpreting substrate character and soil formation in subaerial settings (Retallack, 1984, 2001; Donovan, 1994; Buatois et al., 1998; Genise et al., 2000). Paleoclimatology is a major interest in historical geology, yet paleoclimatologic applications of ichnology have received only limited attention (Bown and Laza, 1990; Hasiotis and Dubiel, 1994; Genise, 1997; Genise et al., 2000; Retallack, 2001). The eolian realm, especially ancient erg settings (inland sand seas), offers significant promise for using trace fossils to assist in interpreting paleoclimatic conditions (Loope and Rowe, 2003). Eolian facies in the geologic record typically are depauperate—and often entirely devoid—of trace fossils. Although a plethora of organism traces may


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GEOLOGIC SETTING

be observed quite commonly in modern sand dunes, only rarely are trace fossils seen in ancient eolianites. The reason for this apparent discrepancy may lie at least partly in the sedimentology of sand dunes. An eolian dune usually has a gently, sloping windward side (the stoss), which is erosional, and a more steeply dipping leeward side (the foreset or slip face), which is depositional. This dual character of a sand dune as both an erosional and depositional environment is what allows the dune to move forward in accordance with the predominant wind direction. However, the situation is different for echo dunes, which are builtup against a cliff, because deflation erosion is much reduced, and the preservation potential for trace fossils is correspondingly raised (Forno´s et al., 2002). The vast majority of organism traces observed in the loose sand of modern dunes are seen on the erosional stoss side of the dune, and thus they are rarely preserved in the ancient record. There often seems to be more animal life on the stoss side, apparently because of its lower dip angle, broader surface area and more abundant vegetation. As can be observed in modern dunes, traces also do occur on the depositional slip face of the dunes, where they may be deformed by caving and slumping of the loose sand on the more steeply dipping slope. Many of the trace fossils recorded in ancient eolian systems occur in subaqueous (or at least moist) interdune facies rather than in the subaerial dunes themselves (Hanley and Steidtmann, 1973; Ahlbrandt et al., 1978; Gradzinski and Uchman, 1994; Buatois et al., 1998; Smith and Mason, 1998). Nevertheless, well-preserved trace fossils have been described in the foreset cross-strata of ancient dunes in a number of inland erg settings (McKee, 1944; Brady, 1947; Hanley et al., 1971; Walker and Harms, 1972; Picard, 1977; Ekdale and Picard, 1985; Sadler, 1993; Braddy, 1995; Loope and Rowe, 2003).

GEOLOGIC SETTING The Jurassic Navajo Sandstone was deposited as enormous eolian dunes (probably mainly transverse dunes) in an immense erg in the arid continental interior of the western United States (Kocurek and Dott, 1983; Blakey, 1994; Loope et al., 2004). With a stratigraphic thickness reaching 0.75 km and an areal extent of more than 0.33 million km2, the Navajo Sandstone is one of the thickest and most extensive stratigraphic units in North America. Although clearcut biostratigraphic indicators are few, the Navajo

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FIGURE 35.1 Idealized column of the studied portion of the eolian Navajo Sandstone (Lower Jurassic) and location map of the primary study area at Coyote Buttes, Kane County, southern Utah (modified from Loope, 2006, Fig. 1).

Sandstone generally is regarded as Early Jurassic in age (Peterson and Pipiringos, 1979). The massive Navajo Sandstone is a familiar sight to geologists and tourists alike, as it forms the spectacular ‘White Cliffs’ in some of America’s most famous and scenic national park lands, including Zion, Capitol Reef, and Canyonlands National Parks, Dinosaur, Grand Staircase-Escalante and Rainbow Bridge National Monuments, Glen National Recreation Area and Paria Canyons Primitive Area. This study focuses on the North Coyote Buttes section of the Paria Canyons Primitive Area along the Utah–Arizona border in Kane County, Utah, where

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35. ICHNOFACIES OF AN ANCIENT ERG

the Navajo Sandstone is exceptionally well exposed (Fig. 35.1; see also Loope et al., 2001; Loope and Rowe, 2003).

ORGANISM TRACES IN DUNES Despite the meager record of eolian trace fossils in general, it is clear that many organisms indeed live in dune fields. Even though standing water and vegetative cover may be sparse, a surprisingly large diversity of invertebrates and vertebrates is known to inhabit dune fields all over the world today (Cloudsley–Thompson and Chadwick, 1964; Crawford, 1981, 1986, 1991; Louw and Seely, 1982; Wallwork, 1982; Cloudsley-Thompson, 1991; Costa, 1995). As mentioned earlier, it is mainly those traces on the depositional side of dunes that are preserved in the fossil record. The traces may be seen in the avalanching slip face as well as in the plinth at the base of the slip face, where wind ripple strata accumulate. Although the eolian trace fossil record is extremely sparse and highly localized, trace fossils in eolianites may be locally abundant and diverse (White and Curran, 1988; Curran and White, 1991, 2001; Curran, 1994; Phelps, 2002). Surface tracks and trails are rarely preserved, so eolian trace fossils are mainly shallow burrows of invertebrates and undertracks of vertebrates. For effective preservation of traces, the dune sand needs to be slightly moist, i.e., neither totally dry nor totally saturated with water (McKee, 1947; Sadler, 1993; Forno´s et al., 2002; Phelps, 2002). This obviously was the case for the Navajo Sandstone trace fossils described in this chapter. As observed in modern dunes, unlined traces that were created in loose, dry sand could not have persisted without collapsing and crumbling when succeeding sediment layers were deposited by the action of the desert winds. Most of the Navajo Sandstone trace fossils are sharply defined and show little evidence of caving-in under totally dry conditions or of slurrying in water-saturated conditions, and there is little evidence to suggest that the burrows remained open for some time. Thus, it appears that the sand was damp (but not soaked) when the burrows were created. Some of the burrows exhibit meniscate backfill that must have been produced as the animal moved through the sediment, and other burrows contain structureless fill that may have been passive.

TRACE FOSSILS Locally abundant invertebrate trace fossils at Coyote Buttes were preserved in the eolian cross-strata of Navajo Sandstone. They include the following ichnotaxa (listed here in approximate order of abundance): Planolites beverleyensis, Palaeophycus tubularis, Skolithos linearis, Arenicolites (two ichnospecies), Entradichnus meniscus, Taenidium serpentinum, and Digitichnus laminatus. Planolites beverleyensis—The most abundant burrows are simple, unlined, unbranched, non-meniscate, horizontal burrows that often occur in very dense patches with numerous cross-overs (Fig. 35.2). In most cases, there is no regular geometric pattern to the courses of the trails, which appear like random scribbles on the bedding plane (sensu Seilacher, 1967b). The burrow fill is similar to but slightly darker than the surrounding sediment. Dimensions: tunnel diameter is 5 mm. Palaeophycus tubularis—Thinly walled burrows, oriented parallel to subparallel to the slipface, are evident at several sites, where the dark-colored linings render them quite visible (Fig. 35.3). The burrow fill is the same as the surrounding sediment. They exhibit approximately the same size range and geometric aspect of the associated Planolites, which are unwalled, so it is possible that the Paleophycus and Planolites were made by the same organisms behaving in different ways. However, the reason why the organism lined its burrow in one place and not in another is unclear. Dimensions: tunnel diameter is 5 mm. Skolithos linearis—Short, unlined, vertical shafts are common at all sites. They are oriented more or less perpendicularly to the dipping foreset laminae, and thus they occur at an angle to the horizon. Because the burrow fill is the same as the surrounding sediment, and the burrow margins are somewhat indistinct, these shafts often are only faintly visible in vertical section. Cylindricum, an ichnogenus that is sometimes applied to short vertical burrows, is regarded here as a junior synonym of Skolithos. Dimensions: shaft diameter is variable and averages about 5 mm; shaft length is up to 3 cm. Arenicolites ispp.—Paired burrow openings commonly were observed in plan view, and ‘U’ burrows with two shafts were observed in vertical section in a few instances. A faint protrusive spreiten structure was observed in some specimens in the field, but a clear spreite could not be documented with certainty, so these ‘U’ burrows are assigned provisionally to Arenicolites. Two ichnospecies may be differentiated

TRACE FOSSILS

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A

B

FIGURE 35.2 (A,B) Planolites beverleyensis (plan view) in Navajo Sandstone at Coyote Buttes, southern Utah. Scale bar equals 8 cm.

on the basis of size and shape. A. isp. 1 is the smaller form. On a number of bed surfaces one can observe a paired arrangement of shaft openings (Fig. 35.4), which suggests ‘U’ burrows, but a subsurface connection of two shafts to form a ‘U’ could not be demonstrated with certainty in most cases. The shafts appear to be unlined. Dimensions (A. isp. 1): shaft diameter is about 2 mm; space between paired shaft openings is about 2 mm. A. isp. 2 is the larger

form. The ‘U’ is broadly bow-shaped and shallow in depth in the sediment, and it is oriented perpendicularly to the slipface. The burrows are unlined. Dimensions (A. isp. 2): shaft diameter is 5 mm; span of the bow-shaped ‘U’ is about 5 cm wide and 2 cm deep. Entradichnus meniscus—As described by Ekdale and Picard (1985) in the slightly younger Entrada Sandstone to the northeast of Coyote Buttes (Fig. 35.5),

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FIGURE 35.3 Paleophycus tubularis (plan view) in Navajo Sandstone at Coyote Buttes, southern Utah. Scale bar equals 3 cm.

FIGURE 35.4 Arenicolites isp. 1 (plan view) in Navajo Sandstone at Coyote Buttes, southern Utah. Tiny black stars indicate paired openings to the U-shaped burrows. Scale bar equals 6 cm.

Entradichnus meniscus consists of a long, horizontal, unwalled, meniscate trail that was created as a shallow burrower moved-up the slip face of a dune in a fairly straight or gently curved line. The animal pushed small packets of sand behind itself as it moved through the sediment across the slip face, creating a string of slightly flattened menisci. Some minor surface collapse also occurred as the animal moved forward, which contributed to the crescentic aspect of

the trail’s internal structure. The menisci of Entradichnus meniscus differ from those of Beaconites barreti in lacking evidence of fecal material. The trails usually are gently curved, and they are preserved in epirelief. In some cases, clusters of Entradichnus radiate irregularly from a central mass of burrows, suggesting a hatching and subsequent dispersal of burrowers (Fig. 35.6). Dimensions: trail is 5–7 mm wide and up to 15 cm long.

TRACE FOSSILS

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FIGURE 35.5 Entradichnus meniscus (plan view) preserved in convex epirelief in the eolian Entrada Sandstone (Middle Jurassic) from the type locality south of Moab, Grand County, Utah (see also Ekdale and Picard, 1985). Scale bar equals 3 cm.

FIGURE 35.6 Clusters of radiating Entradichnus meniscus (plan view) in Navajo Sandstone at Coyote Buttes, southern Utah. Scale bar equals 10 cm.

Taenidium serpentinum—Thinly lined, meniscate burrows occur sparsely at all sites, typically in full relief within sand beds. They are mostly subparallel to the slipface, and they curve slightly upwards and downwards as well as sideways in the sediment. In contrast to Entradichnus meniscus, the menisci in Taenidium serpentinum are less regular in shape

and spacing, and there is no evidence of roof collapse in the burrow. Dimensions: tunnel diameter is 5 mm. Digitichnus laminatus—Short, stout, finger-shaped burrows are sparsely present at one site. They are oriented vertically with respect to the horizon in the dipping foreset laminae, and thus they occur at an angle to the bedding plane. The burrow shafts are

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unlined, and the burrow fill is either structureless or horizontally laminated. Dimensions: shaft diameter is about 1 cm, and shaft length is about 3 cm. Vertebrate tracks—Vertebrate tracks also are preserved in the eolian foreset beds of Navajo Sandstone at Coyote Buttes. They include Grallator (presumably made by theropod dinosaurs) and Brasilichnium (presumably made by therapsids). These are tetrapod trackways, which were described briefly by Loope and Rowe (2003), and which are examined more thoroughly in their sedimentologic context by Loope (2006). Thus, discussion of the vertebrate tracks in the Navajo Sandstone is not included in this paper.

TRACE MAKERS Even though the diversity of invertebrate ichnotaxa in the Navajo Sandstone at Coyote Buttes is fairly high (seven ichnospecies), it is possible that the traces were made by a very small diversity of biotaxa. In fact, because five of the seven ichnotaxa (i.e., Arenicolites, Palaeophycus, Planolites, Skolithos, and Taenidium) exhibit nearly the same size range and preservational mode, they may very well have been produced by the same species of burrowing organism, the differences in trace fossil morphology resulting from differences in organism behavior and/or substrate character. All the burrowers clearly were invertebrate animals, as the small size and characteristic morphologies of the burrows are inconsistent with any known vertebrate taxa inhabiting the Early Jurassic landscape, and the preservation mode and typical geometries of the burrows are inconsistent with any known vascular plant taxa occurring in western North America at this time. It is most likely that the burrowers were arthropods (i.e., insects, arachnids and/or myriapods), as many types of modern arthropods are known to produce distinctive burrows in modern dunes (Ahlbrandt et al., 1978; Phelps, 2002), and also because trace fossils of burrowing arthropods have been reported in other Mesozoic occurrences in the region (Hasiotis and Dubiel, 1994; Hasiotis, 2003). The body fossil record of terrestrial arthropods in the Jurassic is very poor, and the body fossil record of arthropods in eolianites of any age is exceedingly sparse. Thus, we may only conjecture regarding the taxonomic affinities of the trace makers in the Navajo Sandstone. Based on trace fossil size and morphology, reasonable candidates for the producers of the Jurassic Arenicolites, Palaeophycus, Planolites, Skolithos, and

Taenidium in the Navajo Sandstone would be insects. Similar burrows are produced in modern eolian dunes by various kinds of beetles (Order Coleoptera), including especially darklings (tenebrionids), histers (histerids) and scarabs (scarabaeids), which are very common and widespread inhabitants of desert ecosystems all over the world today (CloudsleyThompson and Chadwick, 1964; Crawford, 1981; Wallwork, 1982; Phelps, 2002). Desert sand roaches (Order Dictyoptera) create meniscate backfilled burrows resembling Taenidium in many deserts today (Crawford, 1981; Wallwork, 1982; Phelps, 2002). Entradichnus was interpreted by Ekdale and Picard (1985) to represent the plowing trails of larvae of crane flies (tipulids, Order Diptera), based on their similarity to trails made by crane fly larvae in modern desert dunes (Ahlbrandt et al., 1978). The plug-shaped Digitichnus shafts could be made by a variety of infaunal arthropods, possibly including scarab beetles and certain spiders that are known to dig shallow pits that resemble Digitichnus (Phelps, 2002). Arachnids, such as scorpions and spiders, are also known as producers of distinctive burrows in eolian dunes today (Curran, 1994; Phelps, 2002), although the body fossil and trace fossil records of Early Jurassic arachnids are exceedingly sparse, and none of the burrows observed in this study in the Navajo Sandstone exhibit any definitive characteristics to suggest arachnid producers. Nevertheless, because diverse arachnids are common components of modern dune ecosystems (Crawford, 1981; Wallwork, 1982; Costa, 1995), as well as Cenozoic continental facies (Codington, 1992; Phelps, 2002), the possibility that arachnids burrowed in the Navajo Sandstone dunes cannot be ruled out. There is no evidence in the trace fossil assemblage at Coyote Buttes of complexly branched and/or chambered burrow systems that could be interpreted as multi-celled domiciles or brooding structures of semi-permanent populations of social insects, such as ants, bees, wasps or termites.

PALEOECOLOGIC INTERPRETATIONS This trace fossil assemblage in the Navajo Sandstone appears to be an ichnosuite of trace fossils representing a single ichnoguild of very shallow-tier, mostly horizontal burrows. Terrestrial arthropod taxa exhibit a wide range of feeding habits. While there is no direct or circumstantial evidence from the Navajo Sandstone burrows that the trace makers were sediment-ingesting deposit feeders, similarly there

PALEOCLIMATIC IMPLICATIONS

is no direct evidence that they were grazing herbivores or predatory carnivores either. Most of the Navajo Sandstone trace fossils were simple dwelling and/or unorganized grazing traces. It is possible, although not entirely certain, that the most abundant trace fossils were produced during very short intervals of time (i.e., in a matter of weeks) when an opportunistic explosion of many insects appeared on the scene to consume new plant material and organic detritus (including insect carcasses) that were accumulating as a result of short-lived wet conditions. This interpretation is suggested by observations of a common clustering pattern of burrows in some beds (Fig. 35.6; see also Loope and Rowe, 2003, Fig. 3b), possibly indicating a periodic hatching and dispersal of a new cohort of larval insects. The trace fossil association reflects a single ichnoclade of burrowers (sensu Ekdale and Lamond, 2003) that dug open, unbranched tunnels and shafts in the sand, which were filled either actively or passively with the surrounding host sediment. With only a few exceptions (Palaeophycus and Taenidium), the Navajo Sandstone burrows are unlined, and none appear to contain fecal material. Adult insects today generally do not ingest sediment as food, as for example earthworms do (Ratcliffe and Fagerstrom, 1980), and in subaerial settings adult insects typically do not line their burrows with mucus or agglutinated sediment. However, it has been reported that some insect larvae produce organic secretions that have a potential of stabilizing burrow walls with a thin lining (Ratcliffe and Fagerstrom, 1980), although such a wall lining has not been reported in larval insect burrows in modern eolian dunes. The feeding habits of most desert arthropods today are poorly known, apart from the anecdotal observations of some of the most common taxa (Cloudsley-Thompson and Chadwick, 1964; Cloudsley-Thompson, 1991; Costa, 1995). The arachnids are carnivores, whereas the insects include a broad spectrum of carnivores, herbivores, detritivores (including coprophages) and omnivores. There is no obvious aspect of the horizontal burrows (e.g., Planolites and Palaeophycus) in the Navajo Sandstone to suggest that they were produced for purposes of predation, although some of the vertical burrows (e.g., Skolithos and Digitichnus) may have been domichnia of stationary predators. There is no direct evidence of vascular plants, such as macroscopic plant fossils or root structures, in the Navajo Sandstone beds that contain the burrows described here. Therefore, a year-round source of lush plant growth to serve as food for herbivorous

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insects seems unlikely. However, a wide variety of blue-green algae (cyanobacteria), green algae and fungi are known to grow on and in modern desert soils, including eolian sand (Friedmann and Galun, 1974), and such microbial growth may serve as an important food source for small invertebrates (Costa, 1995). Thus, it is possible that the Jurassic burrowers in the Navajo dunes may have survived by feeding upon algal films or fungi that grew on sand grains during damp times. However, if there were abundant vascular plants inhabiting other parts of this inland erg environment, such as wetter interdune areas, plant detritus may have blown into the relatively dry dunes and provided a food source for the foraging insects there. In the unvegetated dune fields of the modern Namib Desert, Seely (1978) documented abundant populations of darkling (tenebrionid) beetles that apparently feed upon plant detritus that periodically blows in from adjacent areas.

PALEOCLIMATIC IMPLICATIONS The paleoclimatic implications of cyclical bed forms and primary sedimentary structures in the Navajo Sandstone in southern Utah have been related to monsoonal conditions, in which dry and wet seasons alternated annually with different prevailing wind directions and average wind velocities (Chandler et al., 1992; Chan and Archer, 1999, 2000; Loope et al., 2001; Loope and Rowe, 2003; Loope et al., 2004). The two components of the annual monsoonal cycle in the Navajo Sandstone are (a) bundles of 20–50 individual grainflow layers representing the southeastward migration of dunes under the influence of prevailing northwesterly winds during the winter dry season, and (b) thin wedge-shaped layers of wind-rippled sand that were pushed up against the slip face during the rest of the year by northeasterly winds moving obliquely up the dune slope. In this low-latitude setting in the Northern Hemisphere, rain was most likely during the summer months (Loope et al., 2001; Loope and Rowe, 2003). The trace fossil assemblage at Coyote Buttes is consistent with a monsoonal climatic setting. The invertebrate trace fossils described here occur most profusely in the grain flow layers on the dune slip faces. The trace fossils may have been produced—or at least preferentially preserved—in damp sand in the foresets of large dunes, possibly during rainy seasons, when the cyclical influx of moisture into the Navajo desert permitted insects to take advantage of the algal growth in the sand.

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This trace fossil assemblage appears to reflect the periodic activity of insects, possibly r-selected opportunists, which took rapid advantage of rainy intervals in a monsoonal climate to feed and flourish. However, the sedimentologic context of the trace fossil occurrences suggests that the burrowing events were not simply related to annual cycles of wet and dry seasons. Instead, the burrowed beds appear to coincide with long-lived pluvial episodes that may have lasted for thousands of years during the history of the Navajo erg (Loope and Rowe, 2003). This scenario would explain why the burrows are very profuse in grainflow layers in certain parts of the Navajo Sandstone and absent from most of the rest of the formation. The insect fauna flourished only during these more hospitable pluvial intervals, and their traces therefore reflected the variable paleoclimatic conditions that affected this ancient erg environment. The types of vegetation available to the hungry Jurassic insects is not known, as there are no macroscopic plant fossils or rhizoliths preserved in these sandstone beds, and no palynomorph studies have been attempted. Because there were no grasses or any other angiosperms existing on Earth at this time, and because arid conditions are not very conducive to gymnosperm growth, the dune flora may have consisted mainly of microscopic algae that periodically came to life and spread rapidly in the wet sand (Friedmann and Galun, 1974). The trace-making organisms apparently were surface or near-surface

dwellers that fed at least partly upon the algal coatings of sand grains. Many desert insects today exhibit seasonal activity cycles (Wallwork, 1982; Cloudsley-Thompson, 1991; Heatwole, 1996), including several groups of burrowing beetles, such as those that may have been responsible for producing the Navajo Sandstone burrows. The fluctuating monsoonal conditions in the Jurassic Navajo erg facilitated the cyclical activity of the resident insect fauna.

ENTRADICHNUS ICHNOFACIES The three most widely accepted ichnofacies in continental settings are (a) the Coprinisphaera Ichnofacies, representing moist, herbaceous paleosols (Genise et al., 2000), (b) the Scoyenia Ichnofacies, representing floodplains and ephemeral streams (Seilacher, 1964; Buatois et al., 1998), and (c) the Mermia Ichnofacies, representing shallow and deep lakes (Buatois and Mangano, 1995; Buatois et al., 1998). The Navajo Sandstone trace fossil assemblage reported here clearly does not fit within any of these three welldocumented non-marine ichnofacies. We hereby name a fourth terrestrial ichnofacies, the Entradichnus Ichnofacies, for the recurrent trace fossil assemblage that typifies sparsely vegetated and unvegetated eolian dune fields in arid climatic settings (Fig. 35.7; Table 35.1). We offer the Navajo

FIGURE 35.7 Idealized sketch of the typical ichnotaxa in the Entradichnus Ichnofacies. A1, Arenicolites isp. 1; A2, Arenicolites isp. 2; D, Diplocraterion parallelum; Dt, Digitichnus laminatus; E, Entradichnus meniscus; F, footprint of vertebrate; Pa, Palaeophycus tubularis; Pl, Planolites beverleyensis; Sk, Skolithos linearis; T, Taenidium serpentinum. (Note: Diplocraterion parallelum was not documented with certainty in the Navajo Sandstone at the Coyote Buttes study site.)

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ENTRADICHNUS ICHNOFACIES

TABLE 35.1 Ichnogenus Arenicolites Digitichnus

Ichnotaxa that Typify the Entradichnus Ichnofacies in Eolianites

Formation (Reference)

Locality

Age

Navajo (8) Tumlin(?)(5)

Utah, USA Poland

Jurassic, Early Triassic, Early

Sossus (6)

Namibia

Pliocene–Holocene

Entrada (4)

Utah, USA

Jurassic, Middle

Navajo (8)

Utah, USA

Jurassic, Early

Diplocraterion

Navajo (?) (8)

Utah, USA

Jurassic, Early

Tumlin (5)

Poland

Triassic, Early

Entradichnus

Entrada (4)

Utah, USA

Jurassic, Middle

Utah, USA Arizona, USA

Jurassic, Early Permian, Early

Palaeophycus

Navajo (8) Coconino( ) (1) Navajo (8)

Utah, USA

Jurassic, Early

Tumlin (5)

Poland

Triassic, Early

Casper( ) (2)

Wyoming, U.S.A

Permian, Early

un-named eolianite (7)

Mexico

Pleistocene–Holocene

Tsondab (6)

Namibia

Eocene–Miocene

Navajo (8)

Utah, USA

Jurassic, Early

Tumlin (5) Casper( ) (2)

Poland Wyoming, USA

Triassic, Early Permian, Early

Cedar Mesa( ) (3)

Utah, USA

Permian, Early

Skolithos


Mexico


Navajo(8)

Utah, USA

Jurassic, Early

Taenidium


Mexico


Planolites

Sossus (6)

Namibia

Pliocene–Holocene

Tsondab (6)

Namibia

Eocene–Miocene

Navajo (8) Coconino( ) (1) Casper( ) (2)

Utah, USA Arizona, USA

Jurassic, Early Permian, Early

Wyoming, USA

Permian, Early

References: 1. Brady, 1947; 2. Hanley et al., 1971; 3. Loope, 1984; 4. Ekdale and Picard, 1985; 5. Gradzinski and Uchman, 1994; 6. Smith and Mason, 1998; 7. Phelps, 2002; 8. this chapter. Question mark after formation name indicates uncertain ichnogeneric identification in the field. Asterisk after formation name indicates current ichnogeneric assignment of a previously un-named or differently named trace fossil based on the ichnotaxonomic scheme employed in this chapter.

Sandstone trace fossil association described herein as a typical example of this new ichnofacies. Buatois et al. (1998, Fig. 5) reported a typical trace fossil association in Mesozoic dune and interdune facies that includes twelve ichnogenera, six of which occur in the Navajo Sandstone in the outcrops at Coyote Buttes. Descriptions of similar trace fossil associations have been reported in eolian sequences of other ages at other localities, including the Permian Coconino Sandstone in northern Arizona (Brady, 1947), Permian Cedar Mesa Sandstone in southern Utah (Loope, 1984, 1985), Permian Casper Sandstone in southern Wyoming (Hanley et al., 1971), Jurassic Entrada Sandstone in eastern Utah (Ekdale and Picard, 1985), Tertiary Tsondab Sandstone in Namibia (Smith and Mason, 1998), and Quaternary eolianite beds in Sonora, Mexico (Phelps, 2002).

Thus, this is a very widespread, recurrent trace fossil association that typifies arid eolian paleoenvironments. The ichnotaxonomic status of the eponymous ichnotaxon of the Entradichnus Ichnofacies is worth noting briefly here, although a thorough ichnotaxonomic treatment is beyond the scope of this present chapter. Ekdale and Picard (1985, p. 8) stated that Entradichnus differs from Taenidium in being unlined, unbranched and always oriented along a single bedding plane (Fig. 35.5). Entradichnus meniscus typically is long and straight to gently sinuous with a uniform width of approximately 5 mm throughout the entire length of the tunnel. The menisci are composed of the same sediment as the host sediment, and there is no evidence of fecal matter in the menisci, as sometimes occurs in Taenidium.

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D’Alessandro and Bromley (1987) regarded Entradichnus as a junior synonym of Taenidium at the ichnogeneric level, based on the mensicate internal structure in the tunnel. They equivocated slightly, however, and remarked that ‘Entradichnus meniscus may belong here [in Taenidium serpentinum], although the menisci appear to be closely spaced and rather flat’ (D’Alessandro and Bromley, 1987, p. 754). In the example from the Navajo Sandstone reported here, as well as in the Entrada Sandstone where it was first described, Entradichnus is straight or gently curving with very regular crescentic menisci and without a wall lining, and its course follows a single plane, exposing the trail in positive and/or negative semirelief on tops of beds. Taenidium, in contrast, is more sinuous with a thin but distinctly dark-stained lining and with irregularly shaped menisci, and in the Navajo Sandstone it usually occurs in full relief within a sand lamina. Brady (1947) erected the new ichnogenus Scolecocoprus and two new ichnospecies, S. cameronensis and S. arizonensis, for mensicate trace fossils in the eolian Coconino Sandstone in northwestern Arizona. He inappropriately listed Scolecocoprus as a new genus of oligochaete annelid, and he mistakenly interpreted it as a worm burrow filled with fecal pellets. D’Alessandro and Bromley (1987) emended the diagnosis of S. cameronensis and reassigned it to the ichnogenus Taenidium, as T. cameronensis. However, they did not consider the other ichnospecies, S. arizonensis, which appears in the original published photograph (Brady, 1947, pl. 69, Fig. 2) to be very similar to the type specimens of Entradichnus meniscus (Fig. 35.8; see also Ekdale and Picard, 1985, pl. 2,

Fig. A,B). However, Brady’s (1947) description of S. arizonensis was too vague to assert that it is identical to E. meniscus. Therefore, in consideration of the present ambiguity regarding the ichnotaxonomic status of E. meniscus, we provisionally retain it as a valid ichnogenus and ichnospecies. The most distinctive hallmark of the Entradichnus Ichnofacies is Entradichnus itself, since most of the other ichnotaxa in this association (e.g., Arenicolites, Palaeophycus, Planolites, Skolithos and Taenidium) are facies-breaking traces that may be found in other nonmarine and marine ichnofacies as well. Entradichnus is common in many eolianites from at least the Permian to the present and is unknown in non-eolian settings. Thus, despite the ichnotaxonomic questions regarding Entradichnus, it is the most apt name for this eolian ichnofacies.

CONCLUSIONS The invertebrate trace fossil assemblage in the Navajo Sandstone at Coyote Buttes consists of Planolites, Palaeophycus, Skolithos, Arenicolites (two ichnospecies), Entradichnus, Taenidium, and Digitichnus. This diverse association of ichnotaxa represents essentially a monotypic ichnoguild of shallow-tier burrows characterizing an arid eolian habitat that apparently was devoid of macroscopic vegetation. By comparison with modern trace-making dune dwellers, it can be reasonably inferred that the Jurassic trace-making organisms were insects, including especially beetles, and perhaps also arachnids.

FIGURE 35.8 Entradichnus meniscus (plan view) in the eolian Coconino Sandstone (Permian) along the Colorado River in the Grand Canyon, Coconino County, Arizona (see also Brady, 1947). Lens cap is 5 cm in diameter.

ACKNOWLEDGEMENTS

The trace fossils occur mostly in the sand layers that accumulated as grain flows on the dune slip faces during long-lasting pluvial intervals when insects flourished and exploited the periodic algal growth in the sand and/or in-blown organic detritus for food. Thus, the trace fossil record supports the interpretation of a monsoonal climatic regime for the Jurassic Navajo erg. This assemblage of trace fossils in the Navajo Sandstone exemplifies the Entradichnus Ichnofacies, which represents arid eolian paleoenvironments in the geologic record, extending from at least the Late Paleozoic to the present.

ACKNOWLEDGEMENTS This study was funded in part by an NSF grant (EAR02-07893) to D. B. L. We thank Luis Buatois, William Miller III, William Phelps and Leif Tapanila for their valuable comments during preparation of this manuscript.

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36 Endobenthic Response through Mass-Extinction Episodes: Predictive Models and Observed Patterns Jared R. Morrow and Stephen T. Hasiotis

INTRODUCTION

SUMMARY : Three hypothesized endobenthic behavioral responses to ecological perturbations—positive, negative, and no feedback—are compared to existing, empirical endobenthic records of the ‘big five’ Phanerozoic mass extinctions—latest Ordovician, Late Devonian, end-Permian, endTriassic, and end-Cretaceous—and evaluated against new data on ichnofaunal changes associated with the Late Devonian mass extinction in western Utah, USA. All of the ‘big five’ events are characterized by negative responses within the endobenthic realm, which vary in proportion to the severity and signature of the extinction. Responses of short-term positive and no feedback are superimposed on the overall negative endobenthic trends, indicative of other such influences on behavior as feeding strategy, oxygen tolerance, and facies preference. Infaunal ecosystem response across the end-Cretaceous mass extinction appears to be characterized by abrupt collapse and rapid recovery; this pattern is significantly different from those observed in the other four of the ‘big five’ mass-extinction events and is related likely to a large extraterrestrial impact. We suggest that detailed records of endobenthic response across mass-extinction episodes can provide a new tool for assessing the overall nature of extinction, and testing for extraterrestrial impacts as a primary driving mechanism.

The application of ichnology to document the record and potential causes of mass extinction is just beginning. The purpose of this chapter is to review the trace-fossil studies of the ‘big five’ Phanerozoic mass extinctions—latest Ordovician, Late Devonian, endPermian, end-Triassic, and end-Cretaceous—and to provide new data on trace-fossil responses across the Late Devonian mass-extinction interval from the intracratonic Pilot basin, western Utah, USA. These studies are evaluated in light of three hypothesized, end-member endobenthic ecosystem responses, introduced herein. Comparisons of hypothesized and empirical endobenthic responses are discussed, with goals of evaluating proposed mass-extinction mechanisms and suggesting potentially important and fruitful directions for future, integrated ichnological and mass-extinction research. Detailed work documenting the responses of endobenthic ecosystems to mass extinction is in its infancy as compared to the study of epifaunal clades (e.g., Twitchett and Barras, 2004). This paucity may be due, in part, to the perception that Phanerozoic tracefossil (or ichnofossil) morphotypes are too conservative and long ranging to record meaningful patterns across biotic crisis intervals (e.g., Bottjer and Droser, 1994). Further lacking are detailed ichnofossil analyses


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576

36. ENDOBENTHIC RESPONSE THROUGH MASS-EXTINCTION EPISODES

conducted at the same high stratigraphic resolution as studies of coeval epifaunal fossil groups. Contrary to this view, other studies of both marine and continental endobenthic palaeoecosystems have demonstrated clearly the potential quantitative information recorded by ichnofossils, including insight into organism response to such rapidly changing environmental parameters as oxygen levels, nutrient supply, substrate composition, and palaeohydrology (e.g., Ekdale and Bromley, 1984; Ekdale et al., 1984; Bromley, 1990; Savrda and Bottjer, 1991; Twitchett and Wignall, 1996; Wignall et al., 1998; Twitchett, 1999; Hasiotis, 2002; Pruss and Bottjer, 2004; Robertson et al., 2004; Rodriguez-Tovar et al., 2004; Twitchett and Barras, 2004; Twitchett et al., 2004; Pruss et al., 2005; Rodrı´guez-Tovar, 2005). Given the potential use of ichnofossils to further document and understand biotic crisis intervals, future high-resolution studies across mass-extinction intervals should provide critical new insights into ecosystem responses, environmental effects, and driving mechanisms of an event.

BACKGROUND Major advances have been made in our conceptual understanding of how epifaunal ecosystems respond to mass extinctions. Extinction magnitude is calculated typically as a percentage of taxa lost relative to standing biodiversity through a relatively short geologic interval (e.g., stage) (Raup and Sepkoski, 1982; Sepkoski, 1996). Other studies (e.g., summarized in McGhee, 1996) evaluate the magnitude of biotic crises by comparing taxonomic turnover based on extinction and origination rates over a short interval; mass extinction is characterized by greatly accelerated extinction superimposed against a background of suppressed origination. Such analyses led to the recognition of five first-order mass-extinction episodes during the Phanerozoic, comprising the latest Ordovician, Late Devonian (Frasnian–Famennian, F–F), end-Permian (Permian–Triassic, P–Tr), end-Triassic (Triassic–Jurassic, Tr–Jr), and end-Cretaceous (Cretaceous–Tertiary, K–T; equivalent to the Cretaceous–Palaeogene, or K–P, of some researchers) (Fig. 36.1; Raup and Sepkoski, 1982; Sepkoski, 1996). Detailed studies have documented the pattern, mode, and potential ultimate and proximal causes of these biotic crises (e.g., Erwin, 1993; Hart, 1996; McGhee, 1996; Ryder et al., 1996; Walliser, 1996a; Hallam and Wignall, 1997; Koeberl and

MacLeod, 2002). Several persistent patterns or extinction models have emerged (e.g., Hart, 1996), although rates and patterns of biodiversity collapse and expansion across extinction intervals vary widely. This indicates numerous potentially interrelated physical, chemical, and such biological factors as environmental tolerance, geographic distribution, feeding and living behaviors, and genetics. Temporal (stratigraphic) and spatial (palaeogeographic) patterns of epifaunal clades that survive Phanerozoic biotic crisis intervals indicate several general survival strategies, including pre-adaptation, ecological generalization, niche opportunism, refugia, and chance (Harries et al., 1996). Kauffman and Harries (1996) developed a conceptual model for mass extinction with three distinct phases within a biotic crisis episode based on common patterns of extinction and post-extinction response observed in fossil taxa —extinction, survival, and recovery. Phanerozoic mass extinctions profoundly affected all low-latitude, marine, epifaunal trophic levels, from primary producers to high-level consumers. During four of the ‘big five’ mass extinctions (Late Devonian, end-Permian, end-Triassic, and end-Cretaceous), some biodiversity loss is documented in paralic and continental settings. The effects of mass extinction were also experienced in high palaeolatitudes, although this is based on smaller datasets (Erwin, 1993; McGhee, 1996; Sheehan et al., 1996; Hallam and Wignall, 1997; Erwin et al., 2002). Proposed causes of biotic crises consist of Earth-bound and extraterrestrial driving mechanisms. Potential mechanisms include an integration of (1) fundamental, ultimate causes and (2) proximal causes directly responsible for observed biotic and geologic effects. Postulated ultimate mechanisms include global environmental changes during the transition from greenhouse to icehouse worlds, shifting tectonic plate configurations, superplume activity and volcanism, secular changes in carbon cycling and weathering due to terrestrial ecosystem evolution, and changing orbital parameters. Also included here are such extraterrestrial triggers as bolide impacts and high-energy electromagnetic phenomena. Numerous possible proximal causes resulting from the ultimate driving mechanisms include global warming/cooling, glaciation, atmospheric pollution, sea-level fluctuations, anoxia, primary productivity collapse, oceanic overturn, sudden ocean-floor methane release, and oceanic circulation changes (Fig. 36.2; see also references cited earlier).

ENDOBENTHIC ECOSYSTEMS AND EXTINCTION

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FIGURE 36.1 Phanerozoic biodiversity of marine animals, continental tetrapods, vascular land plants, and insects. Marine animal biodiversity is given in number of genera, while (inset) tetrapod and insect abundances are given in number of families, and plant abundance is given in number of species. Arrows denote the ‘big five’ mass-extinction events: (I) latest Ordovician; (II) Late Devonian; (III) end-Permian; (IV) end-Triassic; and (V) end-Cretaceous. Modified from Benton (1985), Niklas et al. (1985), Labandeira and Sepkoski (1993), and Sepkoski (1996).

ENDOBENTHIC ECOSYSTEMS AND EXTINCTION Trace fossils are useful for reconstructing ancient palaeoenvironmental, palaeohydrologic, palaeoecologic, and palaeoclimatic settings because they record organism–substrate interactions (Ekdale et al., 1984; Hasiotis, 2002). Trace fossils can serve as proxies for larger processes operating within ancient trophic systems (Fig. 36.3). Organism–substrate interactions indicate the physical, chemical, and biological character of the environment at the time of emplacement (e.g., Ekdale et al., 1984; Bromley, 1990; Hasiotis, 2002). Substrate texture and consistency, oxygen levels, nutrient content, redox conditions, depositional energy, and sedimentation rate are among the factors

controlling the diversity and distribution of trace fossils. Ichnofacies are recurrent associations of ichnofossils that indicate such environmental characteristics as bathymetry, salinity, and substrate conditions. The vertical tiering of ichnofossils within these ichnofacies provides information on the endobenthic communities’ response to changes in the sedimentation rate and nutrient and oxygen supply, as well as other environmental perturbations (Fig. 36.4; Bromley, 1990). Tiering is the vertical distribution of various behaviors from surface and shallow deposit feeders along with stationary suspension feeders to deeper deposit feeders, down to the deepest tiers, representing deposit-feeders and bacteria gardeners in anoxic sediments (Fig. 36.5; Bromley, 1990; Savrda and Bottjer, 1991). The intensity of bioturbation and

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Cosmic radiation Geophys. parameters

Impact

Bolide passing

Chemo.-phys. conditions, land surface

Insolation Incurring radiation rate

Tidal forces, rotational speed

Chemo.-phys. conditions, atmosphere

Atmospheric dust

Biological productivity

BIOTOPE

SEA LEVEL

CLIMATE Chemo.-phys. conditions, sea water

Magnetic shield

T

C

Biological innovation

E

Ocean convection & currents Tectonics e.g., Plate tectonics, orogeny

Sedimentation

Magnetic reversal

Volcanism

Magmatism Mantle convection Core alterations

L

I

Cosmic dust

Astrophys. parameters e.g., Ecliptic, precession Solar energy

C

L

R

C O

S

I

M

U

FIGURE 36.2 Flow-chart showing multiple possible interacting telluric (Earth-bound) and cosmic (extraterrestrial) factors that can affect ecosystems or biotopes, potentially driving biotic crises and mass extinctions. Chart shows both ultimate (e.g., impact, solar energy fluctuation, mantle convection changes) and proximal (e.g., climate and sea-level changes) mechanisms potentially involved in the process. Modified from Walliser (1996b).

sediment mixing is termed ichnofabric, and is measured on an ichnofabric index (ii) scale of 1–5 from no bioturbation (laminated sediment) to completely disturbed bedding with few discrete burrows and little unmixed fabric (Droser and Bottjer, 1986). Ichnofabric index 6 is complete bioturbation (homogenized sediment) with no distinct burrows preserved. The diversity and distribution of ichnofossils, their tiering relations, and resultant ichnofabrics comprise a fundamental empirical dataset that can be used to evaluate endobenthic ecosystem response across mass-extinction intervals. As part of the ichnologic patterns, burrow diameter is a proxy for body size and is a fundamental character of organism biology, behavior, and ecology (e.g., Twitchett and Barras, 2004). Such traces as Ophiomorpha, Spongeliomorpha, and Thalassinoides are

attributed to crustaceans, which in modern and ancient examples are the last to reappear in environments that experienced anoxia (Harper et al., 1991; Twitchett and Barras, 2004). Based on available case histories, mass-extinction events are characterized by a moderate to major decrease in all of these endobenthic parameters (e.g., Twitchett and Wignall, 1996; Twitchett, 1999; Pruss and Bottjer, 2004; Twitchett and Barras, 2004). Initial post-extinction conditions can be characterized by non-burrowed, laminated deposits or by very low ichno- and biodiversity with organisms typified by small size compared to pre-extinction taxa. Later post-extinction conditions are distinguished by an increase in shelly fauna diversity, ichnodiversity, ichnofabric index, burrow diameter, and tiering depth.

PREDICTIVE MODELS OF ENDOBENTHIC RESPONSE

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FIGURE 36.3 Major biotic and abiotic components and potential nutrient flow in a shallowmarine, detrital food chain. DOM—dissolved organic matter; POM—particulate organic matter; ‘t’ next to epifaunal benthic and endobenthic biota indicates potentially preservable trace fossils. A detritus-based benthic marine ecosystem may serve as a good analog for modeling the character of stressed benthic communities during the extinction and survival phases of a biotic crisis. Across the biotic crisis interval, major biodiversity and biomass loss within such epifaunal clades as nektonic heterotrophs, phytoplankton, zooplankton, protozoans, higher predators, selected suspension feeders, and grazers would drive potentially a profound shift in nutrient flow within the ecosystem, accompanied by a short-term, significant increase in the relative amount of organic material sequestered into sediments. Modified from Wood (1987).

PREDICTIVE MODELS OF ENDOBENTHIC RESPONSE

Three end-member endobenthic ecosystem responses during mass-extinction episodes are hypothesized:

The primary controlling environmental factors that potentially affect endobenthic ecosystem response across a mass-extinction interval include substrate changes due to fluctuating sea level or sedimentation rate; food availability (live epifaunal and dead detrital organic sources); temperature fluctuation; and changes in benthic oxygenation levels and other water chemistry parameters (e.g., toxic minor and trace elements). Other variations possibly affecting both aquatic (marine to freshwater) and terrestrial settings include geologically sudden, global-scale temperature-climate change and decreased photosynthesis due to reduced incoming sunlight.

(1) Positive Feedback/Response: a thriving lowdiversity, high-abundance infauna, due to increase in food sources (dead epifaunal organisms, increased delivery of detrital organic matter into sediments, etc.), and possible buffering from toxic, element-enriched, oxygen-depleted water masses in the upper water column due to protection by the endobenthic mode of life. Opportunistic expansion of selected endobenthic organisms could be tied to short-term benthic oxygenation promoted by debris-flow and turbidite events into dominantly anoxic basins, which may increase with falling sea level. More vigorous oceanic circulation during glacial episodes

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Decreasing Oxygen Availability

Mixed Layer Transition Layer (tiered) Historical Layer (ORI)

Increasing Organic Carbon Preservation

FIGURE 36.4 Expected changes in burrow stratigraphy and bioturbation density with decreasing benthic oxygen availability. Burrow diversity, diameter, and penetration depth of transition-layer burrows preserved within historical layer ichnofabrics define the oxygen-related ichnocoenoses (ORI), providing a method of evaluating palaeo-oxygenation levels. During a mass-extinction interval, the ichnofabrics associated with benthic oxygen levels and ORI may also be temporarily affected by other environmental controls such as fluctuating water chemistry, abrupt changes in detrital organic nutrient supply and flow, and overall biomass decline. Modified from Savrda and Bottjer (1991).

FIGURE 36.5 Schematic diagram outlining the magnitude of bioturbation and hierarchy of expected trace-fossil tiers within a marine benthic setting, with a list of predicted relative preservation potential of selected physical and palaeoecological parameters including amount of bioturbation, percentage of work represented by the ichnocommunity, percentage of discrete biogenic structures preserved, percentage of work of individual tiers that is preserved, and representative characteristic ichnogenera. Modified from Bromley (1990).

OBSERVED ENDOBENTHIC RESPONSES ACROSS MASS-EXTINCTION INTERVALS

may increase benthic oxygenation and encourage endobenthic occupation in deeper water habitats not exposed during eustatic sea-level fall. (2) Negative Feedback/Response: infauna suffer equal to, or worse than, the epifauna due to changes in water-mass chemistry, lowered benthic oxygenation levels, decline in suspended or detrital food sources, and disruption and collapse of the trophic food web. This response would be recorded by a decrease in endobenthic biodiversity, decline in ichnofabric index, or reduction of endobenthic tiering. If this pattern is observed, an important consideration is whether this response was in-phase or out-ofphase with biodiversity and ecosystem changes in the epifaunal realm. An out-of-phase pattern may indicate an initial interval of endobenthic biodiversity increase or stasis due to a short-term increase of detrital food sources, followed by endobenthic biodiversity reduction when overall biomass is reduced and food sources decrease later in the mass-extinction interval. During postextinction biotic recovery, a reverse pattern may be evident, with endobenthic ecosystems recovering only after re-establishment of a robust epifaunal food source and active cycling of detrital organic material into the substrate. (3) No Feedback/Response: infauna apparently unaffected by the biotic crisis and its associated palaeoenvironmental changes. Local endobenthic biodiversity changes due to changing substrate type must be distinguished from larger scale ecosystem changes. This pattern may show as ichnodiversity plateaus within a longer period of endobenthic re-establishment during the postextinction recovery. If this feedback/response pattern is observed during the crisis interval, it has important implications for understanding the severity, length, and selectivity of the biotic crisis and identifying the most viable mechanism for the mass extinction.

OBSERVED ENDOBENTHIC RESPONSES ACROSS MASS-EXTINCTION INTERVALS Endobenthic case histories from the latest Ordovician, end-Permian, end-Triassic, and endCretaceous events (cf. Twitchett and Barras, 2004), together with new ichnological data on the Late Devonian biotic crisis, are summarized below to

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demonstrate the use of trace fossils and endobenthic behavior to better understand mass extinctions. These results are evaluated based on the hypothesized endobenthic biotic responses, with the goal of elucidating further the overall ecosystem responses to the events, and suggesting how endobenthic datasets may help constrain current and future models of massextinction mechanisms.

Latest Ordovician Mass Extinction Only a few studies discuss the record of ichnofaunal community changes during the latest Ordovician mass extinction (e.g., McCann, 1990; Sheehan et al., 1996; Twitchett and Barras, 2004). An estimated 22% of marine families and 57% of marine genera were eliminated during this extinction episode, making it the second largest of the ‘big five’ events after the end-Permian crisis (Benton, 1995; Sepkoski, 1996; Brenchley, 2001). During the Late Ordovician, biotic provincialism was high, with different endemic faunas occupying relatively isolated, low-latitude, epicontinental marine niches (Sheehan et al., 1996). The overall pattern of biotic loss during the extinction was complex, and no single feeding strategy was favored for survival (Sheehan et al., 1996). Detailed studies of faunal groups affected have shown that the latest Ordovician extinction event occurred in two distinct pulses or phases, separated by a 0.5–2 million year interval characterized by low diversity, cosmopolitan, eurythermal faunas (Brenchley, 2001). Taxonomic groups affected most severely by the event include the graptolites, brachiopods, trilobites, conodonts, bivalves, rugose and tabulate corals, and plankton. It is unclear how the loss of such epifaunal to shallowendobenthic skeletonized taxa as trilobites potentially affected the trace-fossil record of the extinction interval, although newly evolved Ordovician rockboring mytilacean bivalves and many other suspension-feeding bivalve groups also suffered significant losses (Pojeta and Palmer, 1976; Hallam and Miller, 1988). The latest Ordovician extinction is attributed to pronounced low-latitude climate cooling, eustatic sealevel fluctuations, global-scale carbon-cycle perturbations, and possible oceanic overturn driven by Southern Hemisphere glaciation (Brenchley et al., 1994; Berry et al., 1995; Sheehan et al., 1996, and references therein). In deep-marine strata of the Welsh Basin, the Late Ordovician to earliest Silurian interval is characterized by a gradual ichnodiversity increase, punctuated by a short-term loss of 50% of ichnogenera during

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Comparison of extinction selectivity and feeding strategies among bivalve taxa (Sheehan et al., 1996, and references therein) indicates that benthic detritus feeders suffered slightly lower extinction rates than benthic suspension feeders. This suggests that latest Ordovician to earliest Silurian extinction and early post-extinction endobenthic community changes show a negative feedback response indicated by overall ichnodiversity decrease, as well as the possibility of a shorter term, positive feedback response within taxa able to utilize detrital food sources and exploit newly opened, oxygenated niches in previously anoxic settings (Table 36.1).

the latest Ordovician mass-extinction event (McCann, 1990; Twitchett and Barras, 2004). This trace-fossil decrease is best documented within sandstone facies occurring in a sequence of mixed, turbiditic sandstones and mudstones spanning the Upper Ordovician to lowest Silurian interval. Of eight total ichnogenera recorded in the pre-extinction Upper Ordovician sandstone beds—Chondrites, Circulichnus, Cochlichnus, Gordia, Helminthopsis, Palaeophycus, Planolites, and Protopalaeodictyon—only four, Chondrites, Helminthopsis, Palaeophycus, and Planolites, are present in basal Silurian rocks (McCann, 1990). In the McCann (1990) study, no such data on possible endobenthic ecosystem deterioration as decreasing burrow size, tiering depth, and burrow complexity are given. As a possible proxy of oxygenrelated ichnocoenoses changes (ORI) (Fig. 36.4), Sheehan et al. (1996) notes an increase in the degree of deep-marine bioturbation during the event, which is linked to more vigorous ocean circulation and an increase in bottom-water oxygenation driven by the glaciation. Although this pattern may at first appear to contradict the data presented by McCann (1990), the increase in trace fossils noted by Sheehan et al. (1996) is strongly facies controlled, corresponding to a shift from black laminated shale below to bioturbated mudstone above. This contradiction can be resolved best through future detailed, integrated ichnological studies across the mass-extinction interval developed in similar facies and in multiple palaeoenvironmental settings.

Late Devonian Mass Extinction There have been few systematic ichnological analyses examining specifically the Late Devonian (Frasnian–Famennian, F–F) mass-extinction event. Trace fossils, however, are common to abundant features reported from numerous marine, paralic, and continental Late Devonian boundary sections (e.g., Gutschick and Rodriguez, 1977, 1979; Bridge and Droser, 1985; Jordan, 1985; Craft and Bridge, 1987; Gordon, 1989; Halperin and Bridge, 1989; Hasiotis and Piechocki, 1990; Over, 1992; Schindler, 1993; Wegweiser et al., 1995; Hasiotis et al., 1999; Phelps and Droser, 1999, 2001; Morrow and Sandberg, 2003). Stepped extinction prior to the F–F boundary is associated with worldwide collapse of low-latitude, coral- and stromatoporoid-dominated reef ecosystems (Copper, 2002), an abrupt reduction in global biomass,

TABLE 36.1 Summary of Observed Endobenthic Responses During ‘Big Five’ Phanerozoic Mass-Extinction Events, Based on Previously Published Accounts and New Data for the Late Devonian Crisis Interval, Presented Herein Phasea/Responseb Mass Extinction Latest Ordovician Late Devonian

Extinction

Survival

Early Recovery

Late Recovery

1, 2

1, 2

2

2(?)

Strong facies control

Comments

1(?), 2

1(?), 2

2

2

Protracted extinction interval with opportunistic

End-Permian

1, 2

1, 2

2, 3

2, 3

colonization Protracted recovery interval with opportunistic infaunas and ichnodiversity plateaus; more rapid recovery at higher palaeolatitudes?

End-Triassic End-Cretaceous

2

2

2

2(?)

Shorter recovery interval?

1, 2

1, 2

2

2(?)

Abrupt onset and very rapid recovery

a

Phase refers to conceptual phases of mass extinction proposed by Harries et al. (1996) and Kauffman and Harries (1996). bResponse refers to predicted feedback/response hypotheses discussed in text: 1—positive feedback/response; 2—negative feedback/response; 3—no feedback/response. See text for discussion and studies used in compiling this table.


and loss of up to 82% of marine tropical to subtropical species (McGhee, 1996). Research has demonstrated that the crisis simultaneously affected genetically and ecologically diverse epibenthic, nektonic, and planktonic organisms from all trophic levels of the low-latitude marine biosphere. The crisis also affected Late Devonian continental settings (McGhee, 1996). The five primary epifaunal biological signals associated with the F–F mass extinction (McGhee, 1996) were: (1) biodiversity losses in marine and continental ecosystems; (2) much more severe biodiversity loss within the marine setting for fish clades with genera inhabiting both marine and freshwater settings; (3) biodiversity of low-latitude ecosystems was decimated, while higher latitude biodiversity was possibly less reduced; (4) biodiversity in shallowmarine settings was much more affected than that in deep-marine settings; and (5) geographic ranges of low- to mid-latitude taxa were compressed latitudinally towards the equator. In low-latitude marine settings, a fundamental characteristic of the F–F crisis interval is its association with widespread anoxic and dysoxic strata, including dark-grey to black, organic-rich, nodular limestone and shale of the Kellwasser Limestone facies. This is best developed at the type area in the Harz Mountains, Germany, and in surrounding regions of Western and Central Europe and North Africa (e.g., Sandberg et al., 1988; Walliser et al., 1988; Schindler, 1993, Walliser, 1996a). Although of different character than typical Kellwasser Limestone strata, upper Frasnian anoxic and dysoxic strata are distributed widely on virtually all low-latitude Devonian continents (see, e.g., references in McGhee, 1996). Late Frasnian ocean anoxia is evidenced by major, global-scale elemental, isotopic, and organic carbon fluctuations, indicating changes in redox conditions, productivity, organic carbon burial, or terrestrial sediment influx (e.g., Buggisch, 1991; Joachimski and Buggisch, 1993; Algeo et al., 1995; Bratton et al., 1999; Murphy et al., 2000; Joachimski et al., 2002; Bond et al., 2004; Bond and Wignall, 2005).

F–F Boundary Trace-Fossil Record, Pilot Basin, Western Utah, USA The Upper Devonian to Lower Carboniferous, upper- to lower-slope Pilot Shale, deposited in the intracratonic Pilot basin, western Utah and east-central Nevada, USA, contains a well-documented, fossiliferous, and relatively complete marine record across the F–F boundary (Sandberg et al., 1988, 1989, 1997, 2003). Trace fossils are a common to abundant biotic component of the Pilot Shale (e.g., Gutschick and

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Rodriguez, 1977, 1979), occurring in siltstones and shales, preserved in calcareous concretions and nodules, and developed in turbiditic, debris-flow sandstones, and sandy limestones. As an example of the use of ichnology to further evaluate the F–F mass extinction, a series of trace fossils from the Pilot Shale at Coyote Knolls, western Utah, are documented in Figs. 36.6 and 36.7. During the F–F boundary interval, the Pilot basin remained largely dysoxic to anoxic (Sandberg et al., 1988, 1997, 2003; Bratton et al., 1999; Bond and Wignall, 2005), indicated by thick units of dark-grey to black, organicrich, laminated siltstone and shale. Common highenergy, turbiditic debris-flow events into the basin, however, temporarily broke down the redox boundary, bringing in oxygenated water masses with abundant platform-derived quartz sand, bioclastic material, and rip-up clasts. These oxygenation events allowed the short-term proliferation of endobenthic organisms, providing a series of ichnological ‘snapshots’ within a similar, recurring depositional facies across the Late Devonian mass-extinction interval (Figs. 36.7A–H). What becomes readily apparent when comparing pre-extinction interval, late Frasnian trace fossils (Figs. 36.6 and 36.7B–E, Late rhenana to linguiformis conodont zones) to recovery interval, early Famennian ichnofaunas (Figs. 36.6 and 36.7F–H, Early to Middle triangularis Zones) is a striking decrease in ichnodiversity, ichnofabric index, burrow size, and tiering depth. Late Frasnian ichnofaunas are diverse and widespread, including Chondrites, Cruziana, Phycodes, Planolites, Rhizocorallium, Rusophycus, Skolithos, Teichichnus, and Thalassinoides (Figs. 36.6 and 36.7B–E; Gutschick and Rodriguez, 1977, 1979). In the late Frasnian Late rhenana Zone, fine- to medium-grained sandy turbidite beds contain abundant Phycodes, Planolites, Rhizocorallium, and Thalassinoides (Figs. 36.6 and 36.7B). The latest Frasnian linguiformis Zone interval is composed of resistant, highly bioturbated ledges of turbiditic, medium- to coarse-grained quartz sandstone and quartzite interbedded with non-bioturbated, darkgrey to black, anoxic shale and siltstone (Figs. 36.6 and 36.7C–E). Few trace fossils are observed in the boundary section above this position. The first common trace fossils to reappear are found about 10 m above the F–F boundary in the earliest Famennian Early triangularis Zone, where turbiditic, skeletal, debris-flow sandstones contain mostly simple mazes of Thalassinoides and few box-work Thalassinoides (Figs. 36.6 and 36.7F, G). Above these in the Middle triangularis Zone, debris-flow conglomerate and sandstone with contorted bedding contain Planolites and Scolicia (Figs. 36.6 and 36.7H).

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FIGURE 36.6 Stratigraphic section of highest part of Guilmette Formation and lower part of lower member of Pilot Shale on ridge west of Coyote Knolls, Tule Valley, western Utah, USA (star on inset map), including the Late Devonian (Frasnian–Famennian, F–F) boundary massextinction interval. Ichnotaxa ranges, ichnofabric indices, and relative endobenthic tier depths are shown. Uppercase bold letters next to lithologic column denote locations of accompanying outcrop photographs (Fig. 36.7), including selected examples of bioturbation across the extinction interval. Also shows microfossil samples used to constrain conodont biozonation. Section modified from Sandberg et al. (1997). Detailed locality descriptions are given in Sandberg et al. (1989, 1997).

Preliminary ichnologic studies in Pilot basin show that the overall pattern of endobenthic ecosystem response during and after the F–F mass extinction was that of a protracted negative feedback interval. Ichnodiversity, ichnofabric index, burrow depth, burrow size, and tiering were greatly reduced during the extinction, survival, and early recovery stages. This seems to have begun in the latest Frasnian linguiformis Zone about 7 m below the boundary, and continued into the earliest Famennian Early triangularis Zone, nearly 10 m stratigraphically above the boundary. In general, early Famennian burrows are of much lower diversity, are smaller, and are more widely spaced than Frasnian forms. Thalassinoides in the Famennian (Figs. 36.7F,G) are infilled with coarse sand and skeletal material, indicating a change in

available sediment sources within the debris-flow units and, perhaps, a shift in available food resources. This trace-fossil pattern may in fact indicate the predicted drastic reduction in biomass production during the extinction interval, accompanied by a shift in food sources from dark, organic-rich mud abundantly available in the pre-extinction interval, to detrital material dominated by coarse bioclastic debris. In younger strata, ichnodiversity remains low until the middle Famennian (marginifera Zone), where recovery is represented by the reappearance of common trace fossils including Cruziana and Rusophycus (Gutschick and Rodriguez, 1977, 1979). Although more detailed data are needed, these preliminary observations suggest that the endobenthic post-extinction recovery phase may have been

OBSERVED ENDOBENTHIC RESPONSES ACROSS MASS-EXTINCTION INTERVALS A

B

Ph

Ph Rh

C

D

Th

E

F

Th Th

Ph G

H

Th

Sc

Pl Sc

FIGURE 36.7 Selected outcrop photographs across the F–F boundary interval, Coyote Knolls, Utah (Fig. 36.6), illustrating representative styles and changes of endobenthic behavior through the mass-extinction interval. See text for discussion. (A) Outcrop overview of lower part of lower member of Pilot Shale, showing slope and rounded ledge-forming, dysoxic to anoxic siltstone and shale units punctuated by thin, resistant ledges of turbiditic, skeletal, debris-flow sandstone and conglomerate. Location of F–F boundary is indicated. Letters correspond to trace-fossil photographs described below and indicated in Fig. 36.6. (B) Epirelief (upper bedding plane) view of mostly Phycodes (Ph) and sparse Rhizocorallium (Rh) in an upper Frasnian (Late rhenana conodont zone), fine- to medium-grained sandy turbidite bed. (C) Cross-sectional view of uppermost Frasnian (linguiformis Zone), resistant, highly bioturbated ledges of light-weathered, turbiditic, medium- to coarse-grained quartz sandstone and quartzite interbedded with nonbioturbated, dark-grey to black, anoxic shale and siltstone. Hammer is 30 cm long. (D,E) Hyporelief (lower bedding plane) views of resistant, turbiditic sandstone ledges in Fig. 36.7C, showing pervasive bioturbation (ii 3–5) comprising mostly cross-cutting Thalassinoides (Th) and Phycodes (Ph), with possible poorly preserved Planolites and Teichichnus. (F,G) Epirelief views of simple, lowermost Famennian (Early triangularis Zone) Thalassinoides (Th) in turbiditic, skeletal, debris-flow sandstone ledges. Note coarse burrow-fill consisting of poorly sorted, mixed sandy and skeletal material. (H) Epirelief view of lower Famennian (Middle triangularis Zone) Planolites (Pl) and Scolicia (Sc) in turbiditic, debris-flow conglomerate and sandstone with contorted bedding produced by post-depositional slumping.

585

586


protracted, extending as much as 1–3 million years after the F–F boundary event. This is consistent with patterns observed in the epifaunal realm (McGhee, 1996), and thus, it appears that the F–F boundary ichnofaunal community displayed an extended negative feedback response that was in phase with epifaunal biodiversity loss and recovery (Table 36.1).

End-Permian Mass Extinction In contrast to the other four of the ‘big five’ massextinction episodes, a relatively abundant number of detailed studies have documented and evaluated marine endobenthic response across the end-Permian mass-extinction interval (e.g., Bottjer et al., 1988; Schubert and Bottjer, 1995; Twitchett and Wignall, 1996; Wignall et al., 1998; Zonneveld et al., 1998, 2002; Twitchett, 1999; Fraiser and Bottjer, 2000; Twitchett et al., 2001, 2004; MacNaughton et al., 2002; Wignall and Twitchett, 2002a, b; MacNaughton and Zonneveld, 2003; Pruss and Bottjer, 2004; Twitchett and Barras, 2004; and Pruss et al., 2005). It is now recognized that major biodiversity loss in the later part of the Permian comprised two distinct mass extinctions—one at the end of the Middle Permian and a second, more severe event at the end of the Late Permian (Stanley and Yang, 1994; Hallam and Wignall, 1997; Erwin et al., 2002). The endPermian mass extinction is characterized by the selective disappearance of several important, longranging, epifaunal, suspension-feeding dominated groups, including members of the articulate brachiopods, crinoids, blastoids, rugose and tabulate corals, and bryozoans (Hallam and Wignall, 1997). Furthermore, recent refinements in biocorrelation (e.g., Twitchett et al., 2001) and in the quality of fossil datasets show that the extinction event also affected vertebrates, plants, and insects in the continental realm (Fig. 36.1; Erwin et al., 2002). Endobenthic palaeocommunities, discussed below, also suffered heavily. Overall marine species-level loss at the end-Permian mass extinction is estimated to have been 76–88% (Stanley and Yang, 1994), and total family-level extinctions in the marine and continental realms may have exceeded 60% (Benton, 1995). Postulated Late Permian extinction mechanisms include extraterrestrial impact, marine transgression and anoxia, Siberian flood basalt volcanism, oceanic overturn, and large-scale sea-floor methane release (e.g., Hallam and Wignall, 1997; Wignall, 2001; Erwin et al., 2002). Serious doubts have been raised recently about existing data supporting a catastrophic impact

hypothesis (Koeberl et al., 2004; Langenhorst et al., 2005). Current models appear to favor climatic deterioration and ecosystem collapse driven by interacting, positive feedback mechanisms of closely timed transgression and anoxia, Siberian flood basalt eruptions, and possible methane release from gas hydrates, which is evoked to explain a major, global-scale negative d13C isotopic excursion at the end-Permian (Erwin, 1993; Krull and Retallack, 2000; Twitchett et al., 2001). Detailed ichnological studies across the latest Permian–Middle Triassic interval demonstrate the long duration of post-extinction survival and recovery intervals for endobenthic ecosystems (Table 36.2), which mirror patterns in the epifaunal realm (e.g., Schubert and Bottjer, 1995, Twitchett et al., 2004). Full recovery of ichnodiversity and endobenthic community structure did not occur apparently until the Middle Triassic (Schubert and Bottjer, 1995; Zonneveld et al., 1998; Twitchett, 1999; Pruss and Bottjer, 2004; Twitchett and Barras, 2004; Pruss et al., 2005). A close link between the severity and duration of Early Triassic marine anoxia and endobenthic ecosystem recovery has been demonstrated (Twitchett and Wignall, 1996; Twitchett, 1999; Twitchett and Barras, 2004); at localities where anoxic conditions ceased earlier, benthic epifaunal recoveries were apparently more rapid (Twitchett et al., 2004). Further, palaeolatitude may have played a role in the timing of post-extinction recovery, as higher latitude endobenthic ecosystems recovered significantly earlier than those at lower latitudes (Wignall et al., 1998; MacNaughton and Zonneveld, 2003). The overall pattern of endobenthic ecosystem response during and after the end-Permian mass extinction was that of a protracted negative feedback interval (Tables 36.1 and 36.2). Ichnodiversity, ichnofabric index, burrow depth, burrow size, and tiering were all reduced significantly during the extinction, survival, and early recovery stages, which extended from the Permian–Triassic boundary into the midEarly Triassic (Dienerian to Smithian) at most sites. At several localities, early Early Triassic (Griesbachian) endobenthic ecosystems were characterized by relatively high abundance, low-diversity faunas, e.g., dominated by Planolites or Arenicolites, that represent examples of opportunistic, short-term positive feedback response. This scenario of opportunistic radiation in the late survival to early postextinction recovery intervals is interesting in that both domichnia (Planolites) and fodinichnia (Arenicolites) are represented, indicating a potentially complex pattern of survival and favored feeding behaviors or lifestyles.

587


TABLE 36.2 Reference Bottjer et al.

Summary of Documented Marine Ichnodiversity Changes and Ecosystem Responses, End-Permian Mass Extinction Location South China

(1988)

Interval or Age(s)a Studied Permian-Triassic boundary beds

Ichnodiversity Chondrites

Responseb 3

Planolites

Western U.S.A.

Dienerian–

Bottjer

Smithian

(1995) Twitchett &

Northern Italy

Spathian Griesbachian

Multiple shallow-

beds 2

ii 2-5; burrow depths

2

Burrow depths < 10 cm ii 1-2

infaunal taxa Arenicolites Catenichnus

Wignall

Cochlichnus

(1996)

Palaeochorda

ii 5–6; alternating burrowed & laminated

Mineralized burrows Schubert &

Comments

< 10 cm

Palaeophycus Planolites Dienerian– Smithian

Asteriacites

2, 3

Catenichnus

ii 2–5; burrow depths few cm; burrow

Cochlichnus Dendrotichnium

diameters < 1 cm Lag in post-extinction

Diplocraterion

infaunal & epifaunal

Lockeia

recovery, Dienerian to

Palaeophycus

mid-Smithian

Phycodes Planolites Rhizocorallium Skolithos Indet. small burrows Spathian

Asteriacites

ii 5; burrow depths

Diplocraterion

few cm; burrow

Lockeia

diameters < 1 cm

Palaeophycus Planolites Rhizocorallium Skolithos Indet. small burrows Wignall et al.

Spitsbergen

Latest Permian

(1998)

Chondrites

2

Multiple tiers, deepest

Diplocraterion

burrow depths 30–50

Planolites

cm; decreasing

Zoophycus

ichnodiversity at top

Pyritic threads Permian–Triassic boundary & Griesbachian Late Griesbachian– Dienerian

Planolites Pyritic threads Arenicolites

2

Abrupt ichnodiversity decrease within anoxic, pyritic, finely laminated shale Relatively early,

Catenichnus

stepped ichnodiversity

Diplocraterion

increase within

Gyrochorte

offshore, shoreface, &

Monocraterion

foreshore facies

Palaeophycus Planolites Rhizocorallium Skolithos Thalassinoides (no Zoophycus) (continued)

588


TABLE 36.2 (Continued) Reference

Location

Zonneveld

Western Canada

Interval or Age(s)a Studied Early Triassic

et al. (1998) Middle Triassic

Ichnodiversity Thalassinoides

Responseb 2

Comments Intertidal, shoreface,

Trichophycus

offshore-transition, &

Cruziana

offshore deposits;

Didymaulichnus Isopodichnus

malacostracan body fossils occurring with

Ophiomorpha

arthropod trace fossils

Palaeophycus Rusophycus Spongeliomorpha Thalassinoides Twitchett (1999)

Northern Italy

Latest Permian

Diplocraterion

2

ii 2–5, decreasing

Planolites Rhizocorallium

upwards to extinction level; max. burrow

Skolithos

diameter = 18 mm

Zoophycus Early–late Griesbachian

Planolites

1

ii 1–2; burrow depths 1.5 cm; max. burrow diameter = 3 mm

Late Griesbachian– Dienerian

Arenicolites

2

Increasing ii; burrow

Diplocraterion Lockeia

depths 8–10 cm; max. burrow

Planolites

diameter = 17 mm

Skolithos Smithian

Spathian

Asteriacites

3

ii 1–2; burrow depths

Cochlichnus

1 cm; max. burrow

Diplocraterion

diameter = 5 mm; trace

Palaeophycus

fossils rare

Planolites Pre-extinction

ii at pre-extinction

ichnodiversity

levels; burrow depths

reached (except

10 cm; max. burrow

Zoophycus)

diameter = 24 mm; recovery interval as defined by Kauffman & Harries (1996)

Fraiser & Bottjer (2000)

Western U.S.A.

Dienerian–Smithian

Arenicolites

1, 2 (overall)

Low ichnodiversity; high density; ave. burrow diameter < 1 cm

Twitchett et al. (2001)

East Greenland

Late Permian– Early Triassic

Loss of diverse assemblage incl.

2

Decreasing ii (5 to 1) & ave. burrow

Palaeophycus,

diameter over 50-cm-

Planolites, &

thick extinction

Rhizocorallium

interval (continued)

589


TABLE 36.2 Reference MacNaughton &

Location NW Canada

Interval or Age(s)a Studied Early Griesbachian

(Continued)

Ichnodiversity

Responseb

Cruziana

2

Comments Bioturbation absent or

Zonneveld

Palaeophycus

weakly developed

(2003)

Planolites

only, all facies

Spongeliomorpha Teichichnus Thalassinoides Late Griesbachian–

11 ichnogenera

In upper-shoreface beds, small Skolithos present only

Early Dienerian Pruss &

Western U.S.A.

Spathian

Arenicolites

2

ii 1-3, except

Bottjer (2004);

Asteriacites

limestones (ii = 4–5);

Pruss et al.

Gyrochorte

reduced bedding plane

(2005)

Laevicyclus Planolites

coverage & tiering; max. burrow diameters

Rhizocorallium

rarely > 12 mm; tiers

Thalassinoides

do not reach preextinction depths; strong facies control of ichnofauna

Twitchett & Barras (2004)

Multiple

Latest Permian

Chondrites

2

Diplocraterion Palaeophycus

Localities

Decreasing ii (6 to 2) & burrow diameters

Planolites Rhizocorallium Skolithos Thalassinoides Zoophycus Earliest Griesbachian

Planolites

1

Burrow depths < 1 cm; small burrow sizes (1–5 mm)

Late Griesbachian

Arenicolites

2

Skolithos

Burrow depths 1–2 cm; burrow diameters 1–2 mm

Late Griesbachian–

Catenichnus

Early Dienerian

Cochlichnus

depths, diameters, &

Diplocraterion

density

2

Increasing burrow

Lockeia Palaeophycus Dienerian

Increasing

ii 3–5; increasing

ichnodiversity Smithian

Ichnodiversity remains relatively

burrow sizes 3

ii 1–2; small burrow sizes

high; monotaxic Asteriacites Spathian

assemblages common Pre-extinction ichnodiversity

ii 3–6; increasing burrow depths & sizes

(except Thalassinoides) a

Early Triassic geologic Ages, from oldest to youngest, are the Griesbachian, Dienerian, Smithian, and Spathian. bResponse column refers to predicted feedback/response hypotheses discussed in text: 1—positive feedback/response; 2—negative feedback/response; 3—no feedback/response. Ichnofabric index (ii) values are discussed in text.

590


Following an initial episode of partial endobenthic ecosystem recovery in the late Griesbachian to Dienerian, ichnodiversity, ichnofabric index, burrow depth, and burrow size reached a plateau or were slightly reduced during the late Dienerian to Smithian at several localities (Twitchett and Wignall, 1996; Twitchett, 1999; Twitchett and Barras, 2004). This pattern of little or no feedback/response may have been caused by protracted anoxic conditions that characterize the Early Triassic, post-extinction interval in many localities or by facies types that were less favorable to endobenthic colonization (Wignall and Twitchett, 2002a; Twitchett and Barras, 2004). By the end of the Early Triassic (Spathian), most endobenthic ecosystems had achieved substantial recovery based on the proxies of ichnodiversity, ichnofabric index, burrow depth, and burrow size (Table 36.2), although the reentry of such key ichnotaxon as Zoophycus was delayed until the Middle Triassic at several sites (Twitchett, 1999; Twitchett and Barras, 2004).

End-Triassic Mass Extinction Detailed studies of the Triassic–Jurassic boundary and of the concurrent end-Triassic mass-extinction event have been hampered by a paucity of suitable, complete stratigraphic boundary sections yielding abundant, diagnostic fossil material (Walliser, 1996a; Hallam and Wignall, 1997; Hallam, 2002). Regardless, the end-Triassic interval clearly represents a major biotic turning point in both the marine (Walliser, 1996a; Hallam and Wignall, 1997) and continental (Olsen et al., 2002a) realms. A calculated 53% of marine genera and 22% of marine families went extinct during the event, making it comparable in magnitude to both the Late Devonian and endCretaceous mass extinctions (Fig. 36.1; Sepkoski, 1996). With the exception of works by Olsen et al. (2002a) on terrestrial tetrapod trackways and by Hallam and Wignall (2000), Hankins and Bottjer (2001), and Twitchett and Barras (2004) on marine ichnofossils, there has been little detailed research on trace-fossil response across the end-Triassic extinction interval. Although major biotic turnover is recorded in multiple tetrapod (Olsen et al., 2002a), palynomorph (Fowell and Olsen, 1993), and marine invertebrate groups (Hallam and Wignall, 1997), a catastrophic tempo for the end-Triassic event is not well documented (Hallam and Wignall, 1997; Hallam, 2002). Further detailed research is required to verify the signature of the event. Proposed causes for the mass extinction include volcanism, anoxia, increased

mantle plume activity and epeirogenesis, and extraterrestrial impact (Hallam and Wignall, 1997; Hallam, 2002; Olsen et al., 2002a). Hallam and Wignall (2000) conducted a study of the Triassic–Jurassic boundary, including analyses of trace fossils and ichnofabrics, at a proposed global boundary stratotype in west-central Nevada (Taylor et al., 1983). Late Triassic ichnofaunas comprise Chondrites, Helminthoida, Planolites, and other unidentified bioturbation that display ichnofabric indices of 2–5. In latest Triassic and earliest Jurassic, ichnodiversity and ichnofabric indices remain low, with the exception of rare Jurassic beds containing deeply penetrating Arenicolites and bored hardgrounds. Twitchett and Barras (2004) provided a compilation of marine endobenthic response across the endTriassic mass-extinction interval based on three localities—southern England, central Austria, and west-central Nevada, which was a re-examination of the proposed global stratotype interval studied by Hallam and Wignall (2000). Pre-extinction, Late Triassic (Rhaetian) endobenthic ecosystems were diverse, comprising Arenicolites, Diplocraterion, Planolites, Rhizocorallium, Skolithos, Thalassinoides, and Zoophycus. By the latest Triassic (latest Rhaetian), ichnodiversity, burrow depth, burrow size, and ichnofabric index all appear to be reduced, probably in response to the onset of widespread low-oxygen conditions (Twitchett and Barras, 2004). After an ichnodiversity minimum in the earliest Jurassic, endobenthic ecosystems recover relatively rapidly and Early Jurassic (mid-Hettangian) tracefossil assemblages include Arenicolites, Chondrites, Diplocraterion, Palaeophycus, Planolites, Rhizocorallium, and Thalassinoides. Concurrent with this post-extinction ichnodiversity recovery, ichnofabric index, burrow depth, and burrow size all increase. Endobenthic ecosystems clearly displayed a negative response pattern across the end-Triassic event (Table 36.1), although the magnitude of ichnodiversity loss, severity of ecosystem disruption, and duration of the post-extinction survival and early recovery phases were all apparently less than that documented for the end-Permian event.

End-Cretaceous Mass Extinction The end-Cretaceous mass extinction has received more intense study than any other biotic crisis, due in part to the strong correlation between the event and one or more major bolide impacts (e.g., Hart, 1996; Ryder et al., 1996; Walliser, 1996a; Hallam and Wignall, 1997; Koeberl and MacLeod, 2002;


Keller et al., 2003; Kenkmann et al., 2005). Despite many years of ongoing studies attempting to link causally large extraterrestrial impacts with the other four of the ‘big five’ mass extinctions, the endCretaceous remains the best-documented example of impact-related extinction, which has endured numerous cross-disciplinary scientific tests since the hypothesis was proposed over 25 years ago (Alvarez et al., 1980). The extinction of several important fossil groups such as the rudistid and inoceramid bivalves prior to the Cretaceous–Tertiary boundary has led many researchers to hypothesize that other, earth-bound extinction mechanisms must have also been operating in concert with extraterrestrial impact to explain the observed patterns of biodiversity loss (e.g., Hallam and Wignall, 1997). In the case of many other taxonomic groups including low-latitude planktonic foraminifera, ammonites, microfloras, macrofloras (e.g., see references cited in Walliser, 1996a; Hallam and Wignall, 1997), and dinosaurs (Fastovsky and Sheehan, 2005), high-resolution sampling and increasingly more robust datasets have eliminated earlier sampling bias effects, demonstrating that major biodiversity loss occurred abruptly at the end of the Cretaceous. A defining characteristic of the end-Cretaceous mass extinction was its selectivity—both in the fossil groups and ecosystems that suffered the heaviest losses and in the extinction and early post-extinction feeding strategies that imparted the greatest advantages for survival (Sheehan and Hansen, 1986; Sheehan et al., 1996; Robertson et al., 2004). Overall, an estimated 47% of genera and 16% of families were lost during the extinction (Fig. 36.1; Sepkoski, 1996). Most hard hit were: (a) groups tied to trophic food webs based on primary productivity, including marine and continental photosynthetic plants, herbivores, and non-scavenging carnivores (Sheehan et al., 1996); (b) large, continental vertebrates that were unable to find shelter (e.g., in burrows, caves, crevices, water, dense aquatic vegetation) during the first few hours following the end-Cretaceous Chicxulub impact event (Robertson et al., 2004); and (c) groups that could not assure their post-extinction survival by possessing resilient spores, seeds, roots, eggs, or pupae (Robertson et al., 2004). In contrast, groups that could live in detritus-based trophic food webs such as some protozoans, annelids, molluscs, insects, lizards, amphibians, and other freshwater aquatic vertebrates were able to survive and possibly thrive during the extinction and early post-extinction interval when primary plant productivity was recovering but still low (Sheehan et al., 1996). This

591

survival signal is potentially preserved also within Cretaceous–Tertiary boundary endobenthic ecosystems, as discussed below. Despite the intense study that the Cretaceous–Tertiary boundary body-fossil record has received, detailed, systematic studies of trace-fossil assemblages across the mass-extinction interval are relatively few. Several studies analyzed and compared Cretaceous and Palaeogene endobenthic biodiversity and ecosystems, but did not address specifically the endobenthic responses at the end-Cretaceous massextinction interval (e.g., Leszczynski, 1991; Miller, 2000). In several other studies, trace fossils at the Cretaceous–Tertiary boundary were used to evaluate the depositional environment, sedimentation rates, and stratigraphic completeness of the boundary strata, including postulated impact-generated tsunami beds (e.g., Savrda, 1993; Stinnesbeck et al., 1993; Ekdale and Stinnesbeck, 1998; Rodrı´guez-Tovar et al., 2004). Ekdale and Bromley (1984) provided detailed ichnodiversity data across the Cretaceous–Tertiary boundary within chalk-dominated depositional settings in Denmark. In deeper water areas, uppermost Cretaceous beds are characterized by a diverse ichnofauna including Chondrites, Thalassinoides, and Zoophycus. At the Cretaceous–Tertiary boundary, Chondrites and Zoophycus abruptly disappear, and the overlying lowermost Tertiary units are dominated by Thalassinoides. This ichnological change is attributed primarily to sea-level fall and to a change in substrate type across the boundary. In shallower water localities, Ekdale and Bromley (1984) recorded a similar decline in ichnodiversity within uppermost Cretaceous chalk beds, which are overlain by dark, organic-rich, dysoxic to anoxic sediments of the lowermost Tertiary (lower Danian) Fish Clay beds. Qualitative data indicate that ichnodiversity, ichnofabric index, and burrow size all remain low in the Fish Clay interval, increasing only in the overlying Danian chalks above. Ward and Montanari (1997) summarized the tracefossil record across the Cretaceous–Tertiary boundary from several sections in France, Spain, and Italy. Abundant Chondrites, Planolites, Thalassinoides, and Zoophycus occur in uppermost Cretaceous strata, with very low ichnodiversity evident within the overlying 1 m of the lowest Tertiary (Danian) strata. Based on the sedimentology of the boundary layers, endobenthic activity may have remained high into the very earliest Tertiary, with endobenthic organisms mining down into the underlying uppermost Cretaceous beds. The marked decrease of ichnodiversity seen in the overlying, 1-m-thick lowest Tertiary interval is attributed to starvation, which persisted

592


until trophic webs had recovered later in the Danian. Above, in higher Danian rocks, ichnodiversity recovers to Cretaceous levels. More recently, Rodrı´guez-Tovar (2005) described a significant Cretaceous–Palaeogene (Cretaceous–Tertiary) boundary section in southeastern Spain, where uppermost Cretaceous Thalassinoides burrows are passively infilled by abundant Fe-oxide (goethite) grains, determined to be altered, glassy impact ejecta spherules characteristic of the Cretaceous–Tertiary boundary at many localities. Based on the sedimentology and field relationships of these burrows, this author concluded that there was near-contemporaneous endobenthic colonization by Thalassinoides tracemakers immediately prior to, or at, the Cretaceous–Tertiary boundary impact event. These data suggest that active ichnofauna were present until the very end of the Cretaceous, indicating the abrupt nature of the event within the endobenthic realm. Ichnofaunal ecosystem changes across the endCretaceous mass-extinction event may indicate a short-term, positive feedback response immediately after the impact event and extinction, based on available data. This situation would have likely favored detritus-feeding tracemakers such as crustaceans, polychaete worms, and deposit-feeding echinoids, gastropods, and bivalves, followed later by a more prolonged, negative feedback response in the post-extinction survival interval, as detrital food sources became scarcer (Table 36.1). Endobenthic ecosystems apparently remained vital and active up until the time of the end-Cretaceous impact; during the post-extinction interval, endobenthic ecosystem recovery was probably more rapid than ecosystem recoveries following the other Phanerozoic mass extinctions. These observations suggest that there were fundamental differences in the way that endobenthic ecosystems responded during the endCretaceous event when compared to the other ‘big five’ events, in agreement with the conclusions reached by Sheehan et al. (1996) in an analysis of the latest Ordovician and end-Cretaceous extinctions.

DISCUSSION—HYPOTHESIZED AND EMPIRICAL ENDOBENTHIC ECOSYSTEM RESPONSES COMPARED More than one hypothesized, end-member endobenthic ecosystem response can be displayed during a mass-extinction interval, especially where detailed, high-resolution data are available. The more

complicated patterns apparent within endobenthic ecosystems represent varied possible behaviors to the environmental crisis, based on oxygen-depletion tolerance, feeding strategies, and many other evolutionary and environmental factors affecting survival through extinction episodes (Harries et al., 1996; Hart, 1996; Kauffman and Harries, 1996). Tracemakers with higher tolerances for oxygen-depleted water masses clearly had an advantage over other less tolerant epi- and endobenthic groups during the crises. The Late Devonian, end-Permian, and end-Triassic crises were associated with widespread, severe, and prolonged anoxia in relatively shallow-marine settings. Endobenthic groups able to exploit detrital food sources, such as would be present briefly in greater abundance during and directly following collapse of trophic food webs, may have experienced short-term periods of opportunistic expansion during the massextinction survival phase (cf. Sheehan and Hansen, 1986; Sheehan et al., 1996). During the protracted recovery phase of the end-Permian mass extinction, ichnodiversity numbers did not rebound consistently or uniformly, as studies noted trends of slowed, or even reversed, endobenthic biodiversity increase during the Early Triassic (Table 36.2). Although due in part to such changing environmental factors such as facies type and relative sea level, this trend is likely a signature of the prolonged and severe nature of the end-Permian event, including strong marine anoxic conditions that persisted well after the main episode of extinction (Wignall and Twitchett, 2002a). Overall, the ‘big five’ mass-extinction episodes clearly had a lasting, negative effect on endobenthic ecosystems that paralleled trends observed in epifaunal groups and epifaunal trophic food webs. Where examined, ichnodiversity, ichnofabric index, maximum burrow depth, burrow size, and tiering structure all show major reductions across each of the mass-extinction intervals (Fig. 36.8). Based on what first-order correlations are available, biodiversity loss and recovery within endobenthic ecosystems appear to have been in phase with similar changes within the epifaunal realm. A significant difference, however, emerges where high-resolution endobenthic data are available: the observed length and severity of the negative ichnological response interval through any given mass extinction. These data on observed endobenthic responses may have important implications for understanding and identifying correctly the mechanisms that drove the extinctions. Endobenthic response during the end-Cretaceous seems unique when compared with the other ‘big five’ events (e.g., Sheehan et al., 1996). Evidently, active burrowing continued up to the impact event that

DISCUSSION—HYPOTHESIZED AND EMPIRICAL ENDOBENTHIC ECOSYSTEM RESPONSES COMPARED

593

FIGURE 36.8 Generalized late Precambrian through Phanerozoic tiering history for softsubstrate, suspension-feeding ecosystems, showing inferred negative effects of major massextinction episodes on epifaunal construction height and endobenthic penetration depth. Only maximum levels of epifaunal and endobenthic tiering are shown. Vertical axis indicates distance in centimeters from the sediment–water interface (SWI). Dotted lines are inferred levels. Arrows denote the ‘big five’ mass-extinction events, as shown in Fig. 36.1. Depicted deep-endobenthic penetration, up to 100 cm beneath the SWI, during the Cambrian and Ordovician are documented by Hasiotis et al. (2003) and Sheehan and Schiefelbein (1984), respectively. Modified from Ausich and Bottjer (2001).

marked the end of the Cretaceous (Rodrı´guez-Tovar, 2005) and endobenthic ecosystems appeared to recover relatively fast following that event. In contrast, the other episodes displayed a relatively prolonged, complex episode of endobenthic recovery in the post-extinction interval (e.g., latest Ordovician, Late Devonian, and end-Permian). More detailed analyses of the end-Triassic interval are needed, but it appears that this event displays an endobenthic loss and recovery pattern more similar to the latest Ordovician, Late Devonian, and endPermian. Although several studies (e.g., Olsen et al., 2002a; Simms, 2003) have discussed the potential that the end-Triassic mass extinction was coincident with a major bolide impact event, the temporal and geological evidence linking impact and extinction during this crisis are less substantial than that for the end-Cretaceous. Ongoing investigations of iridium concentrations at several continental Triassic–Jurassic boundary sections in central Pangaea have identified only modest enrichment of iridium (up to 285 ppt) in one region (Olsen et al., 2002b). Furthermore, documented Late Triassic (Norian) impact structures (e.g., Spray et al., 1998) predate the Triassic–Jurassic boundary by nearly 14 million years, and were unlikely mechanisms of the end-Triassic extinction. As a result, many researchers still consider the

possibility of an Earth-bound mechanism for the end-Triassic event. Thus, endobenthic ecosystems may record faithfully the duration and magnitude of the crisis interval associated with mass-extinction events. Ichnological responses during stepped or graded extinctions, which are expected to span longer relative durations, may include short-lived success of opportunistic detritus-feeding infauna during the extinction and survival phases (hypothesized response #1, Table 36.1; cf. Sheehan and Hansen, 1986; Sheehan et al., 1996). This initial success is followed by a much longer period of low or suppressed ichnodiversity during the early and late recovery phases (hypothesized response #2, Table 36.1). In the case where the driving mechanism or mechanisms were especially severe and long lasting (e.g., end-Permian event and subsequent Early Triassic recovery interval), infauna may reach a temporarily stable, low plateau of ichnodiversity and ecosystem robustness below pre-extinction levels, which could endure for a significant time period during the more protracted recovery interval (hypothesized response #3, Table 36.1). In contrast, during catastrophic extinction events such as those driven by an extraterrestrial impact, endobenthic diversity and ecosystem collapse are expected to be extremely abrupt, and the post-event

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recovery would occur much more quickly, assuming that no other, longer term environmental perturbations were operating in concert with the impact (e.g., the postulated coincidence between impact and large igneous provinces; Wignall, 2001). In fact, when compared to Earth-bound crisis intervals that may have lasted 105–106 years or more, the hypothesized survival window for organisms experiencing a Chicxulub-size impact is relatively short, a period of perhaps hours to several years (Toon et al., 1997; Robertson et al., 2004). The shielding affect of an endobenthic mode of life, coupled with the pre-adapted ability to tolerate a wider range of physicochemical substrate conditions and to possibly exploit a brief influx of detrital food sources, would make these groups less vulnerable to extinction, especially to the relatively short but intense environmental shock associated with an extraterrestrial impact.

DIRECTIONS FOR FUTURE RESEARCH The use of ichnological records as a tool to further characterize and understand mass-extinction episodes is in its infancy (e.g., Twitchett and Barras, 2004). Detailed, comprehensive endobenthic records across these crisis intervals have the potential for providing critical new data to evaluate the driving mechanisms proposed for extinction events. There are numerous, fruitful directions that integrated studies of endobenthic ecosystems and mass extinctions could explore in the future, including: (1) More comprehensive, quantitative analyses of ichnological records across mass-extinction intervals. Such high-resolution studies should document not only ichnodiversity trends, but also variations in ichnofabric index, maximum burrow depth, burrow size, and tiering structure. These important groundwork studies will comprise the datasets necessary for future evaluation of mass-extinction intervals. (2) Studies linked where possible to existing detailed biostratigraphy and records of coeval biotic response in the epifaunal realm, in order to further test and evaluate the synchroniety of ecosystem responses. Improved integration of in- and epifaunal records is essential. (3) More studies that cross palaeoenvironmental boundaries to compare endobenthic ecosystem responses in a variety of co-existing settings such as deep to shallow marine, marine to continental, and aquatic to terrestrial continental. Limitations

currently exist in our ability to biocorrelate from the marine to continental realm. Future improvements in correlation tools such as sequence stratigraphy, chemostratigraphy, numerical-age dating, and magnetic susceptibility, however, promise to provide a more robust framework for correlating across marine and continental palaeoenvironmental gradients. (4) Further critical evaluation of the sedimentology and depositional settings of mass-extinctionevent beds based on what ichnofossils reveal about depositional rates, timing of colonization, and relative time between depositional events, such as that conducted for the end-Cretaceous interval (Savrda, 1993; Ekdale and Stinnesbeck, 1998). Trace fossils contain an extremely important, in situ record of depositional history and biotic response that has been largely undervalued in most previous mass-extinction studies. (5) Additional detailed geochemical analyses of trace fossils across mass-extinction intervals (cf. Rodrı´guez-Tovar et al., 2004) that may provide important new data on the timing of endobenthic colonization relative to geochemical signals or anomalies that characterize the massextinction event. (6) Further testing of the hypothesized, predictive models proposed herein not only against additional trace-fossil datasets from the ‘big five’ mass extinctions, but also against data from other, lower order Phanerozoic extinctions. A key test of the conclusions from this review will be to examine, in detail, possible endobenthic ecosystem responses to other relatively large, Phanerozoic extraterrestrial impact events where the impact record is recorded in proximal, coeval sedimentary sequences, like the Late Devonian Alamo impact (cf. Tapanila and Ekdale, 2004).

ACKNOWLEDGEMENTS We thank William Miller III for inviting our contribution to this book and for his patience with our progress. We also thank Don Eicher, Roger Kaesler, Erle Kauffman, and Charles Sandberg for their comments and suggestions on the initial ideas expressed in this chapter. Paul Wignall and John Warren Huntley provided thorough and helpful reviews of the manuscript. We thank Brian Platt and Jon Smith for their help in preparing the chapter for publication.

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Index

A Aardvark burrows, 208 Abandoned channels, 287, 290, 298, 308, 315 Abbreviated tail traces, 200 Abiotic components, 579 controls, 273 Above-ground biodiversity, 179, 180 biota, 269 Absence of ichnotaxa, 160 Abyssal, 58, 59, 65, 68 Accessory boring organ, 329, 331 Accidental fauna, 276 Acetabularia, 369, 372, Acidic saliva, 337 Acripes, 22, 55, 56 Action cartoons, 463 Active channels, 289, 291, 309, 311, 315 Activity, 276 Actual evapotranspiration, 176 Actuogeology, 4 Actuoichnology, 415 Adaptations, 463 Adaptative behavior, 474 Adhered preservation, 104 Adhesive meniscate burrows (AMB), 282, 283 Aeotosaurs, 211 Aestivation, 56, 205, 206 Africa, 179, 180 African bullfrog burrows, 206 Age of fucoids, 3 Agrichnia, 54, 68 Agronomic revolution, 395, 397, 402 Alabama, 479 Alfisols, 176, 189–192 Alga Ostreobium quekettii, 368–370, 372, 378 Algae, 368–370, 372, 378, 570 Algeria, 180 Algorithm, 460

Allocyclic, 110, 113, 119, 120, 121, 128, 130 Allostratigraphy, 110 Alluvial, 177 environments, 272, 273 ichnodiversity, 274 plains, 287, 288 Amalgamated sequence boundaries and flooding surfaces (FS/SB), 123, 127–129 Ameghinichnus, 142 Amensalism, 165 Amherst College, 38, 39, 45 Amphibians, 196, 199, 202, 205 Amphisbaenian burrows, 207 Anatomic extensions, 460 Ancient humans, 547 water table, 279 Andisols, 175 Angle of divarication, 199 Animal-bone assemblages, 559 Animal–sediment interaction, 199 Animals, 196, 478, 480–482, 486–488 Anisian, 503 Annelids, 502, 514, 515 Anomoepus, 142 Anoxia, 65, 417 Ant nests, 184, 281 Antelope carcass, 554 Antiperistalsis, 451, 452 Ants, 181 Anurans, 206 Apatopus, 142 Aphotic, 376, 378 Apparent foot width, 200 track depth, 200 Appelton Cabinet, 38, 39 Aquatic, 269 anuran cocoons, 206 environments, 196 tetrapods, 203

599

Arachnids, 568, 569, 572 Arboreal, 278, 279 Archaeological, 545, 546 context, 546 record, 555 Archaeologists, 545 Archeozoon (Eozoon) acadiences, 385 Archetypal, 52, 59, 63, 69, 74 Architectural morphology, 199, 205, 547 Archosaurs, 203 Arenicola, 8 Arenicolites, 61, 62, 64, 70, 71, 101–103, 562, 564, 566, 568, 570–572, 586, 587 ichnofacies, 99 Argentina, 185 Aridisols, 175, 176, 188 Arkansas, 362 Arthropod trackway, 507, 510 Arthopoda, 478–481, 483, 486–488 Arthropods, 502, 514, 515 Artifacts, 214, 546 Artiodactyls, 203 Asteriacites, 100 Asterosoma, 63, 64, 66 Atdabanian, 395, 403 Attaichus, 58 Australia, 185, 186 Autocyclic, 113, 119–121, 128 Automaton, 443 Axis of coiling, 199

B Backfilled burrows, 282 horizontal burrows, 182 Bagrid catfish, 208 Bahamas, 164, 166 (Table 10.1), 232–234, 236–246, 372, 375, 376, 378 Balanced fill lakes, 313, 314 Balanoglossites triadicus, 505, 510, 514

600 Bangia, 369, 372, 378 Bangialean rhodophytes, 369, 378 Barnacles, 360, 361 Barnum Brown, 42, 43 Bateig Fantasia, 166 (Fig. 10.5A) Bathymetric zonation, 368, 375–378 Bay line flooding surface, 128, 129 Beaconites, 55, 56, 566 Bear dog dens, 211 Bed-junction preservation, 94, 95, 97, 104 Bees, 181 Beetles (supratidal), 8, 181 Behavior, 97, 474, 476, 478, 479, 482, 485, 486, 488 Behavioral ecology, 463, 464 evolution, 135, 136, 147 proxies, 279 tokens, 461, 463 Below-ground biodiversity, 179, 180 biota, 269 Beni-Abbes, 180 Benthic, 278, 511, 514 fauna, 535 Bergaueria, 61, 70, 71, 429 Bichordites, 164, 166 (Fig. 10.5A), 168 Big five mass extinctions, 575, 576 Billings, 19, 20, 21 Bioclastic, 503, 505 Bioclaustration, 146, 345–354 Biodiversity, 177, 178, 270, 324, 325 loss, 591 Bioerode, 278 Bioerosion, 104, 105, 324–357, 363–365, 368–370, 376, 392, 395, 397 Biofacts, 214 Bioimmuration, 346, 349 Biolaminates, 276 Biomechanical, 456 Biostratigraphy of trace fossils (palichnostratigraphy) advantages of, 135, 136 applications, current, 136–145 Cambrian–Ordovician Cruziana biostratigraphy, 138 Ediacaran–Cambrian trace-fossil biozones, 136, 143–145 Oldhamia biostratigraphy, Cambrian, 137 Paleozoic ’Cruziana’ biostratigraphy, 137, 138, 140, 143 vertebrate coprolites, Mesozoic (coprostratigraphy), 142 vertebrate track assemblages, Mesozoic, 141 applications, potential, 145, 146 bioclaustrations, 146 borings, 146 graphoglyptids, 145 insect-produced traces, 146

INDEX

ensuring reliable results, 144–147 limitations of, 135, 136 Biota, 270 Biotic components, 579 crisis, 576 crisis episode, 576 crisis intervals, 575 turnover, 587 Bioturbation, 306, 307, 309, 315, 391–393, 395–398, 400, 402, 403, 413–417, 419–423, 442, 443, 445, 453–455, 483, 493, 500 density, 580 depth, 151, 154 indices, 156 Bipedal trackways, 199 Bird, 32, 41–46, 48, 49 nests, 208 trackways, 202 Birds, 197, 203, 205 Bison, 549 astragalus, 548, 553, 555, 558 bones, 545, 546 calcaneus, 551, 553, 556, 558 centroquatro, 556 femur, 548 metacarpal, 548, 551, 558 metapodial, 551 metatarsal, 548, 551, 553 phalanx, 548, 551, 556 radius, 548 scapula, 551 Bivalve burrow, 280 Bivalves, 357, 358, 361, 362 Body fossils, 461, 462 motion, 198 Bolide impact, 587 Bones, 197 Boring, 82, 85–90, 104, 105, 111, 114, 116, 117, 146, 269, 278, 345–349, 351–353, 357–365, 518–521, 523–527 Bouma cycles, 59, 68 Box model, 420, 421 Brachychirotherium, 142 Brachydectes elongatus, 210 Brackish, 64, 74 Brackish-water environments, 391–403 Braided fluvial, 287, 290, 291, 292, 294, 295, 296, 297 Branching grooves, 555 Brasilichnium, 568 Brecciation, 507, 514 Breeding, 197 Bridge Creek Limestone, 153–155 Brinell Hardness Test, 119 Brissopsis lyrifera, 165 Broken bones, 557 Bromalites, 212 Brontopodus, 45 Brown, 44, 45

Bryozoans, 357, 359, 360, 361 Bubble, 444, 445, 447, 451, 453 Buccinidae, 325, 326, 332, 333, 339 Buildings, 214 Burial preservation, 99 Burrinjuckia, 348, 351, 352 Burrows, 82, 85–90, 175, 196–198, 269, 505–508, 510–512, 515, 564–570, 572, description, 205 diameter, 153–156 evolution of, 447 mammals, 207 mechanics, 449, 454 morphology, 450 network, 198 penetration depth, 155 selective mineralization, 96 snakes, 207 stratigraphy, 93, 94, 98, 149–151, 580 systems, 278, 476 traces, 456 Butchering, 545

C Caddisflies, 181 Caddisfly cases, 281 traces, 182 Calcaneous, 547 Calcaneum, 546 Calcarenite della Casarana, Italy, 167 Calcite seas, 357, 361 Calcretes, 188, 507–509 Calichnia, 56, 197 Calichurus major, 161 Callianassa subterranean, 163, 165 Camborygma, 55–57, 281 eumekenomos, 183 litonomos, 183 symplokonomos, 183 Cambrian, 368, 374, 428, 438, 439 Early, 137 explosion, 391–399, 401, 403 Late, 136, 138–140, 143 Middle, 136, 137, 143 Canadian School, 14, 15, 28 Cancellophycus, 220, 221 Cancellous tissues, 554 Carbonates, 232, 233, 234, 246, 502, 503, 515 cycles, 153 platform, 502, 514 Carboniferous, 137, 138, 141, 202, 374, 375, 479, 480 conodonts, 375, 379 tracks, 203 Carcasses, 545 Cardioichnus, 164 Carmelopodus, 142 Carnivores, 278 gnawing, 559 scavenging, 547

601

INDEX

Carving, 197 Case histories, 166 (Table 10.1) Catastrophic extinction events, 593 Catastrophist, 34 Catellocaula, 348, 351, 352 Caulostrepsis, 357, 358, 365 Caunopore, 346, 349, 350 Cave drawings, 197 Cavernula coccidia, 374 pediculata, 374 zancobola, 374 Celliforma, 56–58 Cenozoic, 474, 476 Centrichnus, 358 Ceramics, 214 Chaetosalpinx, 348, 349, 351–353 Chalk, 94, 103, 104, 111, 112, 119, 127 Chamber, 183 Changes in diversity, 160 Channel-overbank environment, 183 Channels, 287, 289, 290, 291, 298, 308, 309, 311, 315, 547, 555 Charles Darwin, 18 Chelonians, 211 Chemoreception, 428, 432, 436, 437 Chemotropism, 387 Chicxulub impact event, 591 Chimney, 183 Chinle formation, 280 Chirotheres, 141 Chlorophyta, 369, 372, 374, 377 Chondrites, 63–67, 70, 71, 94, 95, 152, 155, 416–419, 583, 587, 591 Chop marks, 555, 557, 558 Chubutolithes, 58 Cicada backfilled burrow, 280 Cicatricula, 358, 364 Cichlids, 208 Cincinnati School, 14, 23, 28 Circolites, 358 Circulichnus, 55 Clam traces, 182 Classification, 82, 458, 461 Clastitropism, 387 Clavate, 116, 129 Claw impression, 200 Clayton formation, 96, 106 Cleavage relief, 99, 101 Climactichnes, 429 Climactichnites, 17, 28 wilsoni, 136 Climate, 176, 177, 179, 180, 270, 283 change, 191 indicators, 181 Clinoform, 119 Clionoides, 358 Clionolithes, 358, 518, 519, 527, 528 Closed lakes, 299, 306 Cochlichnus, 55–57 anguineus, 511 Cocoons, 197 Coiled, 466–469

Coiling, 468, 469, 471 Coleoptera, 559, 568 Collateral mineralization, 96 Cololites, 212, 213 Colonization, 391, 394, 396, 398, 399, 402, 403 window, 102, 104, 105, 160 Commensalism, 346 Complex burrows, 278 trace fossils, 458–465 Complexity, 205, 458–460 Composite ichnofabrics, 127 ichnofossil, 492, 493, 498–500 material, 443 surface, 128, 127, 129 trace fossils, 458, 459 Compositional complexity, 459 Compound trace fossils, 458, 461, 559 Computer modeling, 463 tomography, 414 Concealed bed-junction preservation, 101, 102, 104 Concentration lagersta¨tten, 106, 107 Concentric fractures, 200 Conchocelis, 369, 372, 374, 377 Conchyliastrum enderi, 369, 373 Concretions, 94, 96, 97, 106 Condensed section, 111, 113, 126, 127 Conichnus, 61, 62, 70, 71, 102 Connecticut Valley, U.S.A., 33, 35, 37, 49, 142 Conservation lagersta¨tten, 106 traps, 106, 107 Constraints, 442–444, 451 Construction, 458–460, 462–464 Contemporaneous composites, 461, 462 Continental, 53, 55–57, 61, 65, 74, 268 biota, 193, 268 deposits, 282 environments, 286–288, 310, 316, 391–403 ichnocoenoses, 279 ichnofossil climate indicators, 182 ichnology, 268 organisms, 179, 180, 283 realm, 270, 275, 560 tiering, 279 trace fossils, 172 Contour currents, 119, 120 Conveyor-belt species, 452 Coplanar surface, 127 Coprinisphaera, 54–58, 61, 182 ichnofacies, 55–58, 61, 192, 285–287, 289, 315, 570 Coprolites, 142, 196, 212 Corals, 357 Core scanner, 414, 419 Correlative conformity (CC), 121, 123, 126

Cosmic factors, 578 Cosmorhaphe, 59, 64–68, 459 Coyote Buttes, 563–572 Knolls, 585 Cracking, 442, 558 Craneflies, 181 Cranefly tubes, 182 Crayfish, 181, 184 burrows, 182, 183, 280, 281 Creep, 446, 449, 453, 454, 456 Cretaceous, 141, 145, 146, 153, 372–377, 466, 468, 470, 474, 475, 476 mammal tracks, 203 sea turtle nest, 211 Cretaceous–Tertiary boundary, 591 Cretoxyrhina mantelli, 212 Crocodiles, 203 Crustaceans, 197, 510, 511, 513–515, 578 Cruziana, 53, 54, 56, 58, 59, 61–65, 69, 75, 100, 169, 438, 584 breadstoni, 138 furcifera, 138, 139 goldfussi, 138–140 ichnofacies, 65, 69, 75, 94, 99, 106 pectinata, 140 rugosa, 138–140 semiplicata, 138–140, 147 tenella, 143–145 tortworthi, 138 Cryptozoon proliferum, 385, 386 Crystallaria, 505, 507, 508 Cyanobacteria, 368, 369, 371, 373, 374, 377, 378, 569 Cylindrichnus, 61, 64, 162 Cylindricum, 55, 182, 564 Cynomys, 198

D Daimonelix, 211 Darwin, 25 Davenport Ranch, 48 Dawson, 17–19, 28, 34 Deane, 35, 36, 39–41 Decoupling hypothesis, 395 Deep geologic time, 192 Deep-sea, 413–415, 418, 422, 423 omission, 126 Defecation, 197 Deliberate biogenic structures, 460 Deltaic, 69, 74 Demopolis Chalk, 95, 97 Dendrina, 369, 373, 374, 518, 520, 527, 528 orbiculata, 369, 373, 374 Dendritic groove patterns, 555 Denver, Colorado, 459 Deposit feeding, 282, 444, 448, 452, 454, 455 Depositional hiatus, 111, 115 Depressions, 552 Depth of bioturbation, 160

602 Dermestids, 547, 559 borings, 550 damage, 554 infestation, 549 life cycle, 547 pupation chambers, 546, 550 Description and measurement of terrestrial locomotion traces, 198 Desert, 180 Desiccation, 502, 506, 508, 514 Desmograpton, 459 Detritivores, 278 Developmental complexity, 460 Devonian, 138, 196, 374, 375, 466, 470, 474, 476 tracks, 203 Diagenesis, 95, 502, 503, 513, 516 Diagenetic controls, 95 mineralization, 95, 97, 105–107 preservation, 96–98, 103 processes, 101 Diagnosis, 84 Dictyodora, 146 Dicynodonts, 141, 142 burrows, 210 Diet polymorphisms, 324 Diffusion coefficient, biological, 442 Digesta, mixing and movement, 451 Digestion, 197 Digestive, 444, 450–452, 455 Digit, 200 Digital axis, 200 image analysis, 418 pad, 200 Digitichnus, 562, 568, 569, 571, 572 Digitigrade, 199 Dilution cycles, 153 Dinantian, UK, 169 Dinehichnus, 142 Dinosaur speed, 45 Dinosauriforms, 141 Dinosaurs, 141, 142, 203 Diorygma, 351, 352 Diplocraterion, 61, 62, 64, 68–71, 102, 159, 168, 587 Diptera, 568 Direct precipitation, 272 Discoidal cracks, 447, 453, 454 Discontinuities, 53, 58, 69 Discontinuity, 110–113, 115, 117, 118, 120, 121, 123, 126–130 Disrupted bedding, 182 Distal, 200 Diversification, 391, 395, 396, 402, 403 Dodgella priscus, 369, 373 Domichnia, 569, 586 Dominican Republic, 362 Doomed pioneers, 154 Downlap surface, 112, 113 Drag mark, 200 Dragonflies, 278

INDEX

Drill holes, 325, 327, 329–332, 339 Drilling predators, 325, 339 Dry climate, 188 Dual anchor, 447 nomenclature, 519, 520 Dune, 564 Duripans, 188 Durophagous behavior, 554 Dwelling, 197, 269 Dysaerobic, 502, 510, 514 Dysoxia, 417–419 Dysphotic, 378

E Early Paleolithic age, 215 Earth-bound driving mechanisms, 576 Eatonichnus, 57, 58 Echinocardium, 161, 164, 165, 167, 168 cordatum, 162 (Fig. 10.1A), 165 Echinoids, 358, 362 Echiurids, 357 Ecospace, 181, 391, 394, 397, 400, 402, 403 Ecosystem deterioration, 582 Ecuador, 463, 464 Edge-drilling, 330, 331 Ediacaran, 136, 137, 143–145, 147, 391–395, 398, 400, 403, 438 ecosystems, 391–398, 400, 402, 403 Effective precipitation, 179, 270 Effects on sediments, 278 Egernia, 207 Egestion, 442, 443, 452, 454 Eggs, 197 Egypt, 185 Ejecta, 200 Elastic, 442–446, 449, 450, 453, 454 Elephant bones, 546 tracks, 202 Elite trace fossil, 93, 102 traces, 160 Ellipsoideichnus, 58 Embedment, 345–348 Encrustation, 345–349 End Triassic, 575, 576, 581, 592 End-Cretaceous, 575, 576, 581 impact, 592 mass extinction, 587 Endobenthic, 55, 64, 69, 577–579, 586 ecosystems, 577, 578 mass extinctions, 577 Endolithos, 69 Endoliths, 346, 368–370, 373, 375–379 End-Permian, 388, 575, 576, 581, 592 mass extinction, 586 End-Triassic mass extinction, 587 Entisols, 175, 188–191 Entobia, 55, 73, 74, 104, 358, 361, 365 ichnofacies, 73 subichnofacies, 104

Entradichnus, 562, 566, 568, 572 ichnofacies, 562, 570–573 Environmental perturbations, 581, 594 stress, 463 Eodiorygma, 351, 352 Eohyella campbellii, 371, 373, 374 dichotoma, 371, 373, 374 elongata, 371, 373, 374 rectoclada, 371, 373, 374 Eolian, 177, 184, 187–189, 270, 287, 288, 562–564, 567–570, 572, 573 environments, 272, 273 ichnodiversity, 275 Eolianite, 562–564, 568, 571 Eophyton, 21 Eozoon, 18 Epeiric 59, 65 basin, 156 Epibenthic, 64 Epicontinental, 502, 503, 513–515 Epifaunal biological signals, 583 Epigeal, 278, 279 Epigeon, 276, 278 Epireliefs, 98–100 Episodic, 56, 68 Epiterraphilic, 174, 188–191, 271, 279 Erg, 562, 563, 569, 570, 573 Erosion structures, 505 Erosional contact, 423 Escalation, 324, 329 Escaping, 26 Estuaries, 316 Estuarine, 120, 128–130 E–T surface, 129 Ethologic controls, 97 identification, Ethology, 52, 466 Eubrontes, 142 Euendolithic micro-organisms, 368, 370–373, 378, 379 Euphotic, 376, 378 Europe, 503 Eurygonum nodosum, 371, 374 Eustasy, 119 Eutaw formation, 102, 103 Evaporation, 178 Evapotranspiration, 176, 178, 270, 283 Event beds, 98–101, 165 deposits, 503 Event-bed integrity, 100 Ever-dry climate,179–182, 188 palaeoclimates, 184 Ever-wet climate, 179–182 palaeoclimates, 191 Evolution, 324, 325, 329, 331, 339, 340, 466, 474

603

INDEX

Evolutionary importance, 325, 340 paleoecology, 147, 391, 392, 403 theory, 464 Excavation, 449 Excavators, 278 Exhumation, 113, 115, 117 Exposure, 508, 509, 514 Expulsion rims, 200, 201 External trackway width, 199 Extinction, 576 interval, 584 magnitude, 576 models, 576 selectivity, 582 Extraterrestrial driving mechanisms, 576 impact, 594

F Fabrication analysis, 462 Facies, 52, 53, 61, 64, 74, 75 controlled, 110 model, 74, 75 Facultatively bipedal, 199 quadrapedal, 199 Fair-weather bioturbation, 101, 102 tracemakers, 99 wave base, 121, 123, 126 Fascichnus asinosus, 371, 372, 374, 378 dactylus, 371, 372, 374, 378 frutex, 371, 372, 374, 378 grandis, 371, 372, 374, 378 parvus, 371, 372, 374, 378 rogus, 371, 372, 374, 378 Faunal turnovers, 391, 392, 403 Features, 214 Fecal pellets, 464 Feces, 198 Feedbacks, 579, 581 Feeding, 197, 269, 276, 278, 552 behavior, 492, 499, 500 strategies, 582 techniques, 338, 339 Feet, 198 Femora, 558 F–F boundary interval, 585 Filuroda, 358 Firmgrounds, 68–71, 74, 103, 104, 106, 110–113, 115–122, 124–130, 310, 311, 510, 514 bypass, 113 traces, 103, 104 Fish, 196, 205 nests, 207 trails, 203 Fitness, 461, 464 Fjords, 316 Flake tools, 546 Flakes, 546

Floating preservation, 104 Flooding surface, 113, 114, 123, 127, 128, 129 Floodplains, 287, 288, 298, 299 Florence, 221 Florida, 232–234, 236, 237, 239, 245, 246, 361 Fluvial, 285, 287–290, 292, 294, 296, 298, 307–311, 315, 316 Fly pupae, 546 Flysch-Molasse, 65 Fodichnia, 197 Fodinichnia, 462, 586 Folsom, 545 Folsom-type dart points, 546 Fontanai, 58 Foot shape, 198 Footprint length, 200 Footprints, 197, 199 Foraging, 428–434, 438, 439 Foraminifera, 369, 374 Foraminiferans, 502, 511, 513–515, 518–520, 523–525, 527 Force arches, 446, 447, 449, 450 Forced regression, 120, 121, 123, 126 regressive shoreface, 120, 121, 122 Forces, 443–446, 449, 450, 452, 454, 455 Forensic anthropology, 546 Form, definition, 382, 383 Fortune Head, Newfoundland, Canada, 144, 145 Fossil feces, 212 plants 224 record of vertebrate burrows, 208 Fossile Kunst, 14 Fossilisation, 502 Fossil-lagersta¨tte, 502, 513, 514 Fossorial, 278, 279 habitats, 208 insects, 283 Fractures, 445, 446, 448, 449, 453, 454, 505–507, 509 France, 221, 466, 468–472, 475 Freshwater, 268 bivalves, 181, 184 environments, 285, 287, 297, 298, 306, 307, 309, 310, 314–316 organisms, 191 Friction, 445, 449, 450, 454 Frog tracks, 203 Frogs, 206 Fucoides, 25, 220–222, 227, 228 Fucoids, 3, 14, 19, 24, 25, 27 Full reliefs, 98 Fungi, 368–370, 374, 376, 378, 569 Fustiglyphus, 67, 68

G Galleries, 281 Gas escape pore, 200

Gastrochaenolites, 70, 71, 74, 85, 88, 103–105, 358, 362, 364, 365 Gastrolith, 196, 213 Gastropod, 181, 324–340, 359, 362 Gelisols, 175 Genetic stratigraphic sequences, 110 stratigraphy, 110, 112, 119, 120, 130 Geobionts, 276, 278 Geographic gradient, 339 Geophiles, 276, 278 Georgia, 478, 482–488 coast, 164, 165 Germanic basin, 502, 503, 513, 515 Germany, 503, 514 Glacial, 270 Glen Rose, 44, 47–49 Globodendrina monile, 374, 519, 520, 524, 527, 528 Glossifungites ichnofacies, 68–71, 74, 103, 110–118, 120–122, 124–130 Glottidia, 163 (Fig. 10.3) Glyphichnus, 163 (Fig. 10.4B) Gnathichnus, 55, 73, 74, 104, 358, 362, 363 ichnofacies, 73 subichnofacies, 104–106 Gnathorhiza, 208 Gnaw marks, 198 Gnawed, 552 Gnawing, 545, 554 Gobie fish, 206 Gondwana, 135, 138, 140, 141 Gordia, 55–57 Grallator, 568 Granular mechanics, 446, 447 Graphoglypid traces, 274 Graphoglyptids, 135, 145, 147, 459, 461 Graves, 214 Gravity, 442, 450–453, 455 core, 413, 419, 422 Grazing behavior, 554 Great Barrier Reef, 375, 376, 378, 379 Green sea turtle nests, 208 Grizzly dens, 207 Grooves, 547, 555, 556, 560 Groundwater flow, 177, 178 profile, 271, 275 zone, 178 Group, definition, 386 Gulf of Gaeta,165 Gut structure and orientation, 450 Gutter casts, 505 Gwyneddichnium, 142 Gypcretes, 188 Gyrochorte, 64 Gyrolithes, 61, 96, 161, 162 (Fig. 10.2C)

H Habitat engineering, 460 preference, 278

604 Hands, 198 Hardgrounds, 53, 55, 69, 73, 104, 105, 110–114, 119, 127, 129, 357, 358, 363, 364 omission, 113, 119 Harlaniella podolica, 144 Hartselle Sandstone, 100, 479 Heinrich-event, 417–419 Helical shafts, 211 Helicosalpinx, 346, 348, 351–353 Helicotaphrichnus, 358 Heliotropism, 387 Helminthoida, 587 Helminthoides, 429, 438 Helminthoidichnites, 55–57, 143, 513 Helminthopsis, 63–67, 219, 513 Helminthorhaphe, 67, 68 Herbivory, 197 Heterogeneity, 428, 434, 437–439 Heterogeneous materials, 443, 456 Heterolithic successions, 98 Heterotrophic, 369, 376, 378 Hexapodichnus, 55 Hiatal surface, 111, 119 Hibernation, 205, 206 Hicetes, 347, 348, 351–353 Hidden biodiversity, 283 Hierarchical complexity, 460 Histerids, 568 Historical layer, 150–153 Histosols, 175 Hitchcock, 32–35, 38–41, 49 Holes, 560 Holocene, 219 Holotype, 84, 85, 90, 219, 226 Hominid artifacts, 215 footprints, 215 trace fossils, 197, 214 Hominids, 196 roadways, 197 Homo sapiens, 460 Homogeneous layer, 420, 421 Honeycomb structures, 508 Human behavior, 547 butchering, 557 disturbance, 546 drilling, 558 modifications, 560 traces, 559 Human–medium interactions, 545 Humans, 196 Humeri, 558 Humid, 180 Hummocky cross stratification, 503 Hunting, 559 Hydrocarbon-source rocks, 149, 154 Hydrology, 314 Hydrophilic, 174, 188–190, 191, 279 Hyella balani, 371, 373, 374, 378

INDEX

caespitosa, 371, 373, 374, 378 stella, 371, 373, 374, 378 Hyellomorpha, 519, 526–528 microdendritica, 374 Hyena den, 208 Hygrophilic, 174, 188–190, 191, 271, 279 Hyla faber, 208 Hyporeliefs, 98–100

I Ice rafted debris, 417–420 Ichnoclade, 569 Ichnocoenoses, 52, 53, 69, 74, 174, 119, 122, 127, 129, 149–155, 232, 234–246, 239, 241, 245, 246 Ichnodiversity, 180, 181, 274, 288, 298, 299, 309, 314, 396–398, 400, 402, 403, 503, 510, 511, 584, 586, 587 Ichnofabric, 112, 113, 127, 149, 152, 232, 233, 245, 246, 307–310, 315, 395, 414, 416–419 index, 577, 586, 587 Ichnofacies, 93, 94, 232–234, 236, 241, 245, 246, 282, 285–289, 298, 299, 306, 307, 310–312, 314–316, 395, 397, 400 paradigm, 74, 75 Ichnofamily Dendrinidae, 527, 528 Ichnofaunas, 502, 587, 591, 592 Ichnofossil-lagersta¨tten, 106, 107 Ichnofossils, 547, 576 Ichnogenus, 219, 222, 225, 227, 228, 230, 564, 571, 572 Ichnoguild, 391, 568, 572 Ichnologic fidelity, 92, 93, 99–103, 105–107 patterns, 578 studies, 584 succession, 110 Ichnological nomenclature, 518, 519, 527 Ichnologists, 196 Ichnology, 196 Ichnology of Annandale, 41 Ichnology of New England, 41 Ichnopedologic associations, 177, 181, 184, 188–191, 193 characters, 189–192 Ichnoreticulina elegans, 372, 375, 377 Ichnospecies, 219, 222, 224–226, 230, 564, 568, 572 Ichnostratigraphic paradigm, 110 Ichnostratinomic, 92 Ichnotaxa, 127, 221, 368, 370, 371, 373, 374, 376–378 Ichnotaxobases, 86–88, 81, 83–90 Ichnotaxonomy, 25, 81, 83, 84, 86–90, 135, 138, 142, 146, 147, 219, 502, 511, 518, 527 ICZN, 82, 83, 90 Inceptisols, 175, 188–191

Incidental biogenic structures, 460 Incised shoreface, 121–123, 126 valley, 120, 128, 129, 130 Inclined Heterolithic Stratification (IHS), 119 India, 180 Infauna, 579, 581 Infiltration, 177, 178 Ingesters, 278 Ingestion mechanics, 450 Insect feeding behavior, 545 pupation behavior, 545 Insects, 282, 510, 514, 547, 559, 562, 568–570, 572, 573 Interactions, 458, 462–464 Interdigital webbing, 200 Interfluve, 112, 113, 128, 129 Intergrowth, 346, 348–350, 354 Intermediate zone, 178 Internal trackway width, 199 Interpedes, 201 Interstitial, 502 Intertidal, 503, 509, 510, 514, 516 environment, 480 Intraclasts, 503 Intracratonic basin, 503 Invertebrates, 173, 197, 559 ichnology, 3 trace fossils, 545 traces, 560 Involutinidae, 511 Iridium concentrations, 593 Isotope, 416, 419–422 Isotopic excursion, 586 Israel, 362, 363 Italy, 219, 221, 222, 227, 228, 462

J Jade Busen, 7 Jardine, 41 Joseph James, 24–26, 28 Jurassic, 368, 371, 373–377, 562, 563, 567–573 Early Jurassic mammal burrows, 210 Middle Jurassic, 142 Late Jurassic, 142

K Kastengreifer (= boxcorer), 7 Kellwasser, 583 Kentucky, 361 Kenyan sand boa, 207 Key stratal surfaces, 112, 113 Khartoum, 180 Kingfisher nests, 208 Klemmatoica, 351, 352 Klinotaxis, 432 Knives, 546

INDEX

Ko¨ppen climatic classification, 177 Kristineberg, 4 K–T boundary, 104

L Labral spine, 333, 335 Lacustrine, 177, 531, 532, 534, 536–542 environments, 273 ichnodiversity, 274 Ladinian, 503 Laetoli footprints, 215 Lakes, 288, 299, 306–308, 310, 312–315 Lamellae, 466–473, 476 Lamina, 466–471, 473–476 Laminar crusts, 508 Lamination, 505 Laminites, 151–153 Landscape, 175, 270, 271 Lanice conchilega, 8, 9 Lapispecus, 359 Large pits, 547 Larva, 550 Late Devonian, 575, 576, 581, 592 mass extinction, 582 Lateral, 200 Latest Ordovician, 575, 576, 581, 582, 592 Latitude zones, 165 Laurentia, 135, 140 Lectotype, 226–229 Lee stocking island, 372, 376 Lepodactylus, 208 Leptichnus, 359, 361 Life cycle, 278 Light, 368, 369, 371, 376, 378 Limbed tetrapods, 198 Limestone, 503, 505, 506, 516 Limiting factor, 179 Limonite, 506, 509, 513, 514 Limulid, 478–488 Limulidae, 555 Limulus polyphemus, 478, 480, 481, 483, 488 Linear elastic fracture mechanics, 445 Lingula, 163 (Fig. 10.3) Lingulichnus, 61, 168 (Fig. 10.6A), 169 Lip, 200 Lipscomb, 545, 546, 560 Liquefaction, 447 Lithics, 214 Lithification, 101 Lithified materials, 196 Lithographic limestone, 224 Livorno, 227, 228 Lizards, 181 Lobed, 474, 476 Lockeia, 24, 56, 60, 64 siliquaria, 507, 510 Locomotion, 197, 269, 276, 479, 482–488 Logan, 15, 16 Log-grounds, 71, 105–107, 112–114, 127, 130

Long axis, 200 bones, 546 Looseground, 113 Lorenzinia, 67, 68 Los Angeles, 180 Lowstand shoreface, 120–123 systems tract, 121, 129 Lubricants, 450 Lungfish burrows, 206, 208 Lyon, 221 Lysorophid burrows, 210 Lysorophidae, 210

M Macanopsis, 55–57, 60 Macaronichnus, 61, 103 isp, 492–494, 497–500 Mackenzie Mountains, Canada, 143–145 Macrobiota, 278 Macroborings, 356, 361, 363, 364, 365 Macrofauna, 276 Maculichna, 56 Maeandropolydora, 357, 359 Maintenance, 458, 462 Maladioidella (trilobite), 147 Malay Peninsula, 179, 180 Mammal tracks, 202 Mammals, 197, 203, 205 Man tracks, 48 Manus, 198, 201 Maretia, 166 Marginal ridge, 200 thrust, 200 tube, 466–469, 471–475 Marine biosphere, 583 flooding surface (MFS), 113, 114, 123, 125, 126, 127, 129 ichnodiversity, 588 vertebrate coprolite, 213 Marks, 545 Marl, 127 Marlstone, 503, 505, 506, 510, 516 Marrow, 546, 558 Marsupials, 203 Mass extinction, 575 Massalongo, 219, 221, 222, 224–228, 230, 466–476 Massdeath site, 549 extinction episodes, 592 extinction-event beds, 594 extinction intervals, 576, 578 Mastigocoleus testarum, 371 Mat encrusters, 392 scratchers, 392 stickers, 392 Matgrounds, 107, 395

605 Matthew, 21–23 Maximum flooding surface, 127, 503, 516 Mayan Ranch, 47 Mayflies, 181, 278 Mayfly traces, 182 Meandering fluvial, 287–291, 293–297, 299 Measurements and descriptions of fish trails, 201 Measures of distances and angles of vertebrate trackways, 201 Meat ant nest, 281 Mechanical, 442–444, 447, 448, 450–454 Mechanics, solid, 445 Medial, 200 condyle, 548 Mediterranean climate, 179, 180 outflow water, 418 Medium, 196, 278 Megalosauripus, 142 Meiobenthic trace fossils, 502, 503, 505–515 Meiofauna, 502, 503, 506, 511 Meniscate, 55, 57 backfill, 564, 568 Meridian sand, 103 Mermia, 55–57 ichnofacies 55–57, 99, 106, 192, 287–289, 299, 306, 307, 310–312, 314–316, 570 Merostomichnites, 510 Mesofauna, 276 Mesozoic, 135, 136, 141, 172, 181, 503 marine revolution, 356, 357, 361, 363–365 Metals, 214 Metapodial-phalangeal axis, 200 Meyeria, 162 Mice, 208 Micrite, 505, 506, 508–510, 513, 514 Microbes, 276, 278 Microbial binding,104 mats, 107, 392–395 Microbialite definition, 382–385, 387, 388 Microborings, 368, 369, 372–376, 378, 379 Microfaults, 200 Microfauna, 276 Microhabitats, 278 Microphytic feeders, 278 Middens, 214 Middle Jurassic, 468–472, 474 Middle Paleolithic age, 215 Middle Paleozoic Marine Revolution, 356–358, 361, 363–365 Milankovitch cycles, 119, 127, 154 Miller, 26–28 Millimeter ripples, 506 Millimeter-scale voids, 506 Mineralization, 513

606

INDEX

Minifaults, 507 Miocene, 186 Patagonia, 167, 169 Spain, 166 Mistaken predation, 330 Mixed layer, 93, 94, 97, 101, 104, 106, 149–154, 413, 415, 419–421, 424 traces, 97, 99, 101 Mixgrounds, 395 Mixing, 419–421 Mobility, 452 Model of stromatolite formation, 382–388 Modern continental environments, 269 humans, 547 Moira, 165 Mole crickets, 510, 514 Moles, 208 Mollisols, 176 Molluscs, 324, 325, 329, 332, 334–340 Monesichnus, 58 Monodactyl, 198 Monsoon, 562, 569, 570, 573 Monte Bolca, 221, 222, 224 Mooreville Chalk, 106 Morphological features and measurements of vertebrate-tail traces, 200 Morphology, 86–90, 458, 459, 462, 463, 466, 474, 476 Morphotypes, 382, 383, 388, 575 Morrill Paleontological Collection, 546 Morrison formation, 280, 282 Moth larvae, 546 Mucopolymers, 443 Mud cracks, 506 flat, 502, 510, 514 shrimp, 460 Mudskippers, 206, 208 Mukkara, 175 Multituberculates, 203 Mummified bone, 547 skin, 547 Muricidae, 325, 327, 329, 339 Muschelkalk, 502, 503, 505, 506, 511, 514–516 Mutualism, 346 Mycellia, 416, 419, 423

N Namibia, 144, 184 Nanotechnology, 443 Naticidae, 325, 327, 329, 339 Natural History Museum, 222, 224, 226–228, 230 Navajo Sandstone, 562–573 Nemakit-Daldynian, 393–395, 403, Nematodes, 502, 511, 512, 514, 515 Nemerteans, 502, 513–515

Neogene, 371, 372, 374–376 Neoichnological, 111, 129 Neoichnology, 429 Neoproterozoic, 135, 136, 142–144 Nereites, 53, 58, 59, 64, 67, 68, 429, 438, 478–480, 483, 485–488 ichnofacies, 58, 59, 65–68, 93, 99, 106 missouriensis, 479 Neritic, 121 Nesting, 197 Nests, 196, 197, 278 Net primary productivity (NPP), 172, 173, 179, 180, 184, 188–191 Neurotoxins, 337 Newark group, 32, 33 Nile River, 184 Noah’s Raven, 39, 40 Nododendrina, 519, 527, 528 Nodules, 508 Nomenclature, 81–85, 90, 518–520, 527 North–South Carolina, USA, 161 North Carolina, 357, 361 North Sea, 164, 165, 269 Notches, 547, 552, 554 Nutrient cycling, 270 Nutrients, 368, 375, 376, 576

O Oblate, 444, 445 Obrution deposits, 106 Occupation of structures, 460, 461 Ocean anoxia, 583 Oceanic currents, 119 Ocypode, 162 Ocypodidae, 58 Odor plumes, 439 Office building analogy, 459 Ohio, 363 Oichnus, 325, 359, 362, 364 Oldhamia curvata, 136 Oligocene New Zealand, 166 South Australia, 166 (Fig. 10.5B) Omission suite, 53, 110–112, 119–121, 125, 126, 129 surface, 69, 73, 110, 112, 114, 119, 126, 127 Omnivores, 278 Ontogenetic switching, 331 Oolitic, 503 Open lakes, 306, 312 Operation, 458–460, 462, 463 Operational complexity, 460 Operculae, 325–327, 331, 332 Ophiomorpha, 7, 59, 61, 62, 64, 68, 96, 100, 101, 103, 107, 161, 162 (Figs. 10.1B, 10.2A,B), 163, 578 nodosa, 163 (Fig. 10.4A), 166, 167 Ophiomorpha–Planolites ichnofabric, 162 (Fig. 10.1B) Opportunism, 65 Opportunistic, 476

Optimal foraging theory, 430 Ordovician 368, 370, 373, 374 Arenig–Llanvirn, 138, 139 Gondwana, 169 radiation, 391, 396, 403 Tremadoc, 138 bioerosion revolution, 356–365 Organic carbon preservation, 154 Organics, 214 Organism activity, 277 behavior, 196, 271, 276 response, 576 size, 276, 277 Organism-media interactions, 283 Organism-substrate interactions, 577 Organisms, 181 Organizational complexity, 459 Orinithichnites, 37 Ornithopod tracks, 202 Ornithopods, 203 Orra White, 34 Orthogonum appendiculatum, 369, 373, 374 fusiferum, 369, 373, 374 giganteum, 369, 373, 374 lineare, 369, 373, 374 spinosum, 369, 373, 374 tripartitum, 369, 373, 374 tubulare, 369, 373, 374 Otozoum, 142 Overbank, 289, 294–299, 308–311, 315 Overfilled lakes, 310 overbank, 298, 299, 311, 313, 314 Overland flow, 178, 272 Overtraces, 200 Ovoid pit, 548 Oxisols, 176, 189–191 Oxygen, 576 minimum zone, 154, 156, 415 Oxygenation, 100, 106, 149–156 curve, 152–155 Oxygen-related ichnocoenoses, 149–155 Oxygen-restricted ichnocoenoses, 127

P Pace angulation, 199 length, 199 width, 201 Palaeobiology, 502 Palaeocastor, 211 Palaeoclimate, 172, 179, 191 criteria, 160, 161 proxies, 181 Palaeoclimatic, 268 indicators, 187, 193 interpretations, 177 Palaeoconchocelis starmachii, 372, 374, 377, 378 Palaeoecologic, 268

INDEX

Palaeoenvironment, 502, 506, 514 Palaeohydrologic, 268 Palaeohydrology, 576 Palaeoichnocoenose, 503 Palaeopascichnus, 143, 144 Palaeophycus, 55–57, 61, 63, 64, 70, 71, 102, 136, 143, 562, 568, 569, 571, 572, 587 Palaeosabella, 357, 359, 361, 364, Palaeosols, 172, 175, 280, 282 Palaeozoic, 219 Paleobathymetric, 53, 368, 376, 378 Paleoceanography, 413 Paleocene, 461 Paleoclimate, 562 Paleocoene–Eocene Claron Formation, 186 Paleocontinental reconstructions, 141 Paleodictyon, 59, 67, 68, 459, 463 Paleoecology, 135, 147 Paleoenvironment, 52, 53, 74, 75, 562, 571, 573 Paleoenvironmental analysis, 135, 146 Paleoethologic blueprint, 458, 463, 464 Paleogene, 374–376 Paleoindian hunters, 546 Paleoindian kill site, 545 Paleolithic, 546 Paleomeandron, 68, 438 Paleontologist, 559 Paleo-oxygenation, 149 Paleo-redox, 149 Paleosols, 55, 56, 58, 112, 128, 129, 275 Paleozoic, 135, 137, 138, 140, 143, 349–353 Palimpsest, 53, 58, 68, 69 softground suite, 111, 122 Pallichnus, 56, 58 Palm, 200 Palmiraichnus, 58 Palustrine, 177, 272 Paluxy River, 41, 43, 47 Paralectotype, 226–228, 230 Parasequences, 503, 506 Parasitism, 346, 351 Paria Canyons, 562, 563 Parowanichnus, 58 Partial divarication of digits, 199 Partially digested bone, 213 Peatground, 113 Pedogenesis, 175 Pedogenic characteristics, 189, 191, 192 Pedogenic processes, 560 Pentadactyl, 198, 202, 203 Pelagic, 59, 68, 127, 278 Pelleted, 282 Pellets, 452, 456 Pennsylvanian tracks, 203 Periaquatic, 272 Periodic fauna, 276 organisms, 279 Periosteum, 554 Perissodactyls, 203

Peristalsis, 449, 451, 452 Peritidal, 502, 515 Peritrophic membrane, 452 Permanent fauna, 276 organisms, 279 Permian, 374–376, 503 amphibians, 210 tracks, 203 Perturbations, 282 Pes, 198, 201 Petroxestes, 359, 362–364 Phalanges, 199 Phanerozoic, 502 biodiversity, 577 extinctions, 594 mass extinctions, 576 Phenotype, 461, 462 Phenotypic extensions, 458, 464 Pheophila dendroids, 372 Philippines, 180 Phobotaxis, 437 Phoebichnus, 64 Pholeus, 161, 502 Phoronids, 357 Phragmosalpinx, 348, 352 Phreatic zone, 174, 177, 183, 184, 270 Phrixichnus, 359 Phycodes, 64, 583, 585 circinatus, 135, 136 Phycosiphon, 59, 63–66, 94, 95, 97 Phymatoderma, 463, 464 Physico-chemical, 52, 75 attributes, 269 Physiologic projections, 458, 460, 464 Phytosaurs, 211 Pilot basin, 575, 583 Pipe rock, 6 Piped zone, 150–153 Piscichnus, 61 waitemata, 492–497, 499, 500 Piston core, 413, 423–426 Pits, 550, 552, 560 Planobola cebolla, 374 macrogota, 374 radicatus, 374 Planolites, 55–57, 60, 63–67, 97, 136, 143, 153, 155, 562, 564, 568, 569, 571, 572, 583, 585, 586, 591 Plantigrade, 199 Plants, 196, 197 Plastic deformation, 446, 447 Platydendrina, 519, 527, 528 Platypus nesting burrow, 208 Pleistocene, 545, 560 Washington State, USA, 167 Plinthic textures, 176 Pliny Moody, 39, 40 Pliocene–Pleistocene, southern Italy, 167 Pliocene, 463, 464 Mediterannean, 161, 166 Washington State, USA, 167

607 Plio–Pleistocene fish nests, 211 Pockmarked surfaces, 557 Podichnus, 359 Polyactina araneola, 369, 373, 374 fastigata, 369, 373, 374 Polychaetes, 357, 358 that fracture, 448 Polychresichnia, 197 Porphyra, 369, 372 nereocystis, 369, 372 Posidonienschiefer, 95 Post-depositional traces, 98–101 Postelsia palmaeformis, 224 Postelsiopsis, 224 Post-extinction interval, 578 Postlithification borings, 111, 127 Postomission suite, 111 Post-turbidite suite, 68 Posture, 197, 444, 450–453, 455 Pot casts, 505 Potential evapotranspiration, 176, 179, 270 Potential of preservation (or preservation potential), 492, 493, 499, 500 Pottsville formation, 100 Prairie dog, 198, 208 Precipitation, 178 Precipitation and temperature, 173, 175, 179 Predation, 197, 325, 329, 330, 331, 333–340, 428–432, 438 intensity, 329, 330, 331, 339 marks, 197 Predator–prey dynamics, 324 Predepositional traces, 98, 99, 101 Predictive models, 579 Prehistoric human-food processing, 545 Prelithification omission burrows, 111 suite, 103 Preomission suite, 111 Presence in media, 276, 277 Preservation, 86–88, 90 Pre-turbidite suite, 68 Primary lamella, 467–471, 473, 476 Primary stratum, 151 Primates, 203 Primitive tools, 197 Producer, 82, 84–89 Progradation, 121, 123, 126 Prosauropod dinosaurs, 203 Proterozoic, 371, 373, 374, 382–384, 386, 388 Protopterus annectens, 206 Protovirgularia, 510, 514 Protracted tail traces, 199 Protrusive burrows, 226 Protrusive spreiten, 117 Proxies, 577 Proximal, 200 causes, 576

608

INDEX

Proxy, 270 Proxy record, 413, 419, 422, 423 Psammichnites, 429 Pseudoanticlines, 175 Pseudo-borings, 117, 356 Pseudotetrasauropus, 142 Psilonichnus, 53, 58–61, 70, 71, 75, 161, 164 ichnofacies, 53, 58–61, 75 latimuratus, 167 Pterosaur tracks, 202 Pterosaurs, 203 Punctures in bone, 212 Punturas formation, Argentina, 167 Pupation chambers, 547 Pushers, 278 Pyrite, 502, 506, 513, 514 Pyxicephalus, 206

Q Quadrupedal trackways, 199 Quaternary, 232–234, 236, 239, 374, 413–415, 417, 426

R Rabbits, 208 Radial fractures, 200 Radula trace, 326, 336 Radulichnus, 104, 359, 362 Raipur, 180 Ramodendrina, 519, 527, 528 Ramosulcichnus, 359 Ramp angle, 199 Rauisuchians, 211 Ravatichnus, 142 Ray(s), 492, 493, 499 Reading formation, UK, 163 Recharge, 177–179 Recovery, 576 Redox cycles, 153 Redox cyclicity, 153 Reduced oxygen, 127 Reef, 324, 325, 329, 331, 332, 334, 335, 337–340 Reference cylinder, 199 diameter, 199 Refugia, 56 Regressive Surfaces of Erosion (RSE), 113, 120–123, 126, 129 Regurgitalites, 196, 212, 213 Regurgitation, 197 Relief casts, 8 Renichnus, 168 (Fig. 10.6B), 169, 359, 362 Repaired shells, 340 Reproduction, 276 Reproductive behavior, 552 Reptile, 196, 199, 202, 205 Resource polymorphisms, 324 Rest interval, 442 Rheotaxis, 432 Rhizocorallium, 59, 63, 64, 69–71, 86, 583, 585 irregulare, 510, 514 Rhizoliths, 56–58, 60, 178, 184, 188

Rhodes formation, Rhodes, Greece, 167, 168 Rhodophyta, 369, 374, 377, Rhopalia catenata, 372, 374, 378 Ripley formation, 96 Ripple bedding, 503 Rivers, 296, 304 Roads, 214 Rock art, 197 Rockgrounds, 104, 113, 127 Rodent gnawing, 557 Rodents, 181, 203, 547 Rogerella, 74, 360–362, 365 Rome formation, 100 Root etching, 545, 547, 555, 556 Root patterns, 173, 269, 278 Rootlet etching, 548, 554 Roots, 182 Ropalonaria, 361, 362, 364 Rosellichnus, 58 Rosselia, 61–64 Rugosity, 449 Runoff, 177, 178, 272 Rusophycus, 17, 19, 56, 64, 100, 438, 583–585 avalonensis, 143–145

S Saccomorpha clava,369, 373, 374 sphaerula, 369, 373, 374 terminalis, 369, 373, 374 Sahara, 179, 180, 184 Salamanders, 206 Salinity, 299, 306, 310, 314–316, 368, 375, 398 Sanctum, 360, 364, Sand-swimming behavior, 207 Sapelo island, 478, 482–486, 488 Sauropod tracks, 46, 47, 49 Sauropods, 32, 41, 42, 202, 203 Scalar hierarchy, 460 Scallops, 547, 548, 552–555, 560 Scaphichnium, 182 Scarabaeids, 568 Scavengers, 545 Scavenging, 197 behavior, 555 marks, 197 Schaubcylindrichnus, 61, 64 Schizaster, 162 (Fig. 10.1A) Scolecia filosa, 374, 378 maeandria, 374, 378 Scolecocoprus, 572 Scolicia, 65–68, 166 (Fig. 10.5B), 583, 585 Scolithus, 24 Scoyenia, 53, 55–57, 61, 182 ichnofacies, 55–57, 286, 287, 289, 298, 299, 306, 307, 311, 312, 314–316, 570 Scraped, 552 Scrapers, 546 Scratches, 199, 552, 554, 555, 560

Seafloor, 468, 473, 476 Sea-level, 416 Season, 177 of death, 546 Secondary lamellae, 469–473 Sediment bypass, 119, 121, 129, 130 deformation, 423, 424 ingesting, 282 Sediment-gravity flow, 121 Sedimentology, 502, 503, 505 Sediments, 196 Segmentation, 451 Semiarid steppe, 180 Semidendrina pulchra, 518–520, 522–524, 527, 528 Semiplantigrade, 199 Semireliefs, 101, 102 Senckenberg am Meer, 8 Senckenberg Museum, 4 Sequence Boundary (SB), 104, 112, 113, 120–124, 126–129 Sequence stratigraphic surfaces, 103 Sequence stratigraphy, 110, 112, 113, 119, 144, 146, 285, 310, 313, 502, 503, 515, 516 Shaft, 183, 199, 200 fill, 200 wall, 200 Shallow-marine, 502, 503, 515 Shark bite marks, 212 Sharp-based shoreface, 121 Shear strength, 119 Shell abrasion, 327, 333, 334, 340 blisters, 325, 326, 336, 337, 340 breakage, 333, 335 Shell-breaking, 325 Shell-chipping, 325, 331, 333, 335, 336, 340 Shellground, 113 Shielding affect, 594 Siderite, 125, 126, 129 Silcretes, 188 Silesian, UK, USA, 169 Silurian, 368, 372, 374–378 Simple burrows, 278 Sinclair oil, 45 Singapore, 180 Sinusichnus, 161, 162 (Fig. 10.2D) Siphonichnus, 61, 64 Sipunculid, 357, 466, 472, 476 Size, 87, 88 Skalling laboratory, 8 Skeletal hardparts, 324 Skin impression digit, 200 Skink burrows, 207 Skolithos, 4, 6, 16, 26, 53, 55–59, 61, 62, 64, 65, 68, 70, 71, 74, 75, 99, 102, 103, 136, 159, 165, 455, 458, 459, 461, 562, 564, 568, 569, 571, 572, 591 ichnofacies, 58, 59, 61, 62, 64, 68, 74, 75, 99, 102, 103

INDEX

Slope, 413–419, 422, 423 Small pits, 547 Soft tissues, 511, 513 Soft-bodied, 502, 503, 505, 506, 513–515 Softgrounds, 55, 58, 59, 68, 69, 71, 74, 93, 110–113, 117–122, 127, 130, 299, 308–315, 510, 514 Soil, 196, 270, 272, 275 bugs, 181 formation, 175, 180, 270, 275, 283 moisture zones, 279 orders, 176 type, 177 Soil-forming factors, 274 Soil–water balance, 176, 270 belt, 177, 178 budget, 179, 180 cycle, 179, 180 shortage, 177, 178 surplus, 177, 178 zone, 177, 178 Solar radiation, 176 Sole, 200 Soupground, 113 Soupy substrate, 156 South Africa, 185 America, 179, 180 Spadefoot toad burrows, 206 Spain, 186 Spatangus, 164 Spatial patterns, 576 Specialized, 476 Speciation, 324 Spheroid, 444, 445, 452, 453 Sphincter, 451–453 Spider burrow, 281 Spirichnus, 360 Spirophycus, 67, 68 Spirophyton, 65–67, 220, 221 Spirorhaphe, 67, 68 Spodosols, 176, 189–191 Spongeliomorpha, 71, 161, 162, 578 Sponges, 357, 358, 361 Spreite, 226, 227, 466, 467, 469, 471, 473 Spreiten, 59, 61, 65, 69 Squirrel nests, 208 Stagnation deposits, 106 Steinichnus, 182 Step length, 442, 454 Sticklebacks, 208 Stiffground, 54, 113, 119, 120 Stomach and intestinal contents, 212 Stoneflies, 278 Storage withdrawl, 178 Storm beds, 102, 104, 106, 503, 505 wave base, 121 Storm-related ichnofabrics, 102 Storms, 98, 99 Stratinomic classification, 98 Streptindytes, 349, 352 Stress intensity, critical, KIc, 445, 456

Striae, 200 Stride length, 199, 201 Stromatolite biostratigraphy, 382–388 definition, 382–388 ethology, 382–388 ichnofacies, 382–388 macrostructure, 382–388 taxonomy, 382–388 Stromatolite tropism, 382–388 Stromatolites, 276 Strophotaxis, 437 Stumps, 182 Subenvironments, 270, 272 Subfossils, 197 Subhumid, 180 Submarine canyon, 111, 117, 120–122, 124 Substrate, 81, 82, 85–90, 474, 476, 576 consistency, 154, 156, 502, 507, 508, 510, 515 Substrate-controlled, 53, 68, 69, 111–113, 116, 117, 119, 120, 126, 127, 129, 130 Subtidal, 502, 503, 509, 514–516 Sudan, 180 Sulfide minerals, 513 Superficial scratches, 547 striations, 557 Supratidal, 502, 503, 509, 514–516 Surficial morphologic characters, 197 morphology, 199, 205, 547 Surplus, 177 Survival, 460, 461, 464, 576 strategies, 576 Swimming sauropods, 47 Swirls, 547 Symbiosis, 156, 345, 346, 348, 350, 352–354 Syntermesichnus, 58 Systematics, 81–83, 90

T Tacuruichnus, 58 Taenidium, 55, 61, 64, 70, 71, 107, 153, 155, 282, 562, 568, 569, 571, 572 Tail motion, 198 movement, 199 Tallahatta formation, 96, 100 Talpina, 360, 365 Taonurus, 220, 227, 228 Taphofacies, 93, 287 Taphonomic filters, 105 pathways, 287, 299, 310–312 Taphonomy, 92, 93, 146, 502 Taxobases, 519, 527 Taxonomy, 219, 518, 527 Tectonism, 113, 119, 120, 121 Teichichnus, 63, 64, 95, 103, 153, 155, 583

609 Teisseirei, 57, 58 Tektonargus, 281 Telluric factors, 578 Temperature, 368, 375 Tempestites, 64, 99, 100, 154, 503, 505 Temporal patterns, 576 variability, 272 Temporary fauna, 276 organisms, 279 Tenebrionids, 568 Teredolites, 53, 68, 69, 71–73, 360, 362, 105–107 ichnofacies, 53, 69, 71–73, 105, 110–114, 116, 117, 129, 130 Terminal chamber, 199 Termite, 184 damage, 554 nests, 184, 185, 461, 463 Termitichnus, 55–58, 282 ichnofacies, 55, 192 Terraphilic, 174, 188–191, 271, 279 Terrestrial, 268, 269, 272 beaver, 211 environments, 196 locomotion traces, 199, 204 organisms, 192 subenvironments, 270 Terrestrialization, 400 Tethys, 503 Tetradactyl, 198 Tetrapods, 141, 142 tail traces, 199 tracks, 202 Texas, 44, 48, 49, 363, 545 Texas: attack scenario, 47 Texel, 8 Thalassinoides, 58, 63–67, 70–72, 86, 94–97, 102, 104, 152, 155, 161, 162, 418, 421–424, 578, 583–585, 589, 591 Thalassinoides-Phycodes burrow systems, 462 Thanatocoenosis, 513 The Sandstone Bird, 37 Therangospodus, 142 Therapsids burrows, 210 Theropods, 203 Thornthwaite and Mather, 176 Thuringia, 503 Tidal flats, 478, 506, 509, 514, 515 laminites, 99–101 rhythmites, 316 scour ravinement, 113, 125, 129 Tidality, 515 Tier, 415–417, 422–425 Tiering of burrows, 160 Tiering, 93, 94, 99, 102, 174, 189–191, 279, 283, 417, 422–424, 577, 578, 593 Tiers, 127 Timber wolves, 208

610 Time-averaging, 154 Tipulids, 568 Tithonian, 164, 168 Toads, 206 Tommotian, 395, 403 Toponomic classification, 98 Torquaysalpinx, 348, 352 Torrowangea, 511 Tortuosity, 205 Total divarication of digits, 199 Trace fossils, 81–90, 197, 232, 234, 236, 238, 239–242, 245, 246, 324–326, 328, 329, 332–340, 345–354 diversity, 153, 155 preservation, 92–94, 98, 106, 154 tiering, 181, 580 visibility, 92, 94, 95, 100, 102–104, 106, 107 Trace-fossil associations, 279 record, 581 Tracemaker behavior, 97 Trace-maker, 53, 56, 58, 61, 64, 65, 71, 466, 470, 472–474, 476, 478–480, 483, 485–488 Tracemakers, 546 Traces, 181, 545 Track length, 199 Trackmakers, 199 Tracks, 196, 197, 269 Tracksite(s), 198, 202 Trackway midline, 199, 201 Trackways, 197, 198 Trails, 196, 197, 269, 503, 506, 508, 509, 511–513 Transgression, 121, 123, 126, 127, 129, 130 Transgressive ravinement, 113, 118, 123, 126, 129 Transgressive surface, 104 Transgressive Surface of Erosion (TSE), 111, 112, 118, 123, 125–127, 129 Transgressive systems tract, 112 Transgressively incised shoreface, 113, 123, 126, 129 Transient fauna, 276 organisms, 279 Transition layer, 93, 94, 98, 99, 106, 149–153 Transpiration, 178 Transverse axis, 200 Treatise on Invertebrate Paleontology, 145 Tree roots, 182 Tremichnus, 351, 352 Treptichnus, 55–57 (Phycodes) pedum, 143 Trirachodon, 209 Triassic, 374–376, 502, 503, 513, 515 France, UK, Canada, 163, 169

INDEX

tracks, 203 vertebrate burrows, 210 vertebrate nests, 211 Twyford formation, UK, 163 Triassic Carnian, 141 early Triassic, 141 Induan, 141 Ladinian, 141 late Triassic, 141, 142 middle Triassic, 141 Olenikian, 141 Rhaetian, 141 Triassic–Jurassic boundary, 587 Trichichnus, 415, 416, 419, 423–425 Tridactyl, 198 Trilobites, 136–138, 140, 142–144, 147 Trophic polymorphisms, 324, 332, 339 Tropical, 324, 325, 329, 331–339 monsoonal climate, 179, 180 wet-dry climate, 179, 180 True foot width, 200 track depth, 200 Truncated beds, 200 Trypanites, 53, 68, 69, 73, 74, 357, 359–361, 364, 502 ichnofacies, 53, 69, 73, 74, 104, 110–114, 116, 117, 126, 127, 130 Tubular tempestites, 100–102 Tunnel, 183, 199, 547, 550–552, 554 Turbellarians, 357 Turbidites, 59, 61, 65, 68, 99, 121, 123, 154, 474, 475 Turbidity currents, 98, 99 currents unconformity, 119 Tylosaurus kansasensis, 212 Type specimen, 219, 222, 224, 230

University of Nebraska State Museum, 546 Unlobed, 476 Upogebia, 58 Upper Jurassic Morrison Formation, 183, 186 Upper Paleocene Fort Union Formation, 183 Upper Paleolithic age, 215 Upper Triassic Chinle Formation, 183 Uriah James, 23, 24 Urohelminthoida, 67, 68 Uruguay, 56, 58 U-shaped Burrows, 61, 69 Utah, 186, 562, 563, 565, 566, 567, 569, 571, 583 Utilization, 177, 178

V Vadose zone, 174, 177, 178, 183, 270, 282 Venom, 336, 338 Vermiforichnus, 359, 360 Verona, 221, 222, 224, 226–228, 230 Vertebrate burrows, 197 feeding traces, 211, 212 footprints, 32 ichnology, 197 nests, 205 trace fossils, 196 track common measurements, 200 tracks, 200 Vertebrate-media interactions, 215 Vertebrates, 175, 196, 197 Vertisols, 175 Virgil’s Aeneid, 459 Viscoelastic, 446, 453, 454 deformation, 446 Vogel, 368, 370–372, 375, 376, 378 Volcaniclastic, 177, 270 Vomit, 212 V-shaped grooves, 555

U Ubiglobites, 74 U-burrow, 469 Ultimate causes, 576 Ultisols, 176, 189–191 Umfolozia, 55, 56 Unconformity, 73 Underfilled lakes, 313, 315 overbank, 310, 315 Undermat miners, 392 Undertrace, 200 Undertracks, 99, 101 Undichna, 55–57, 203 Unguligrade, 199

W Wadden Sea, 3 Walther’s Law, 52, 53, 112, 130 Warren, 35–37 Water, 168 availability, 173 gain, 178 loss, 178 surplus, 178 table, 178, 183, 270 Wave ravinement, 113, 125, 129, 130 Weathering, 97, 547 Wedge, 442, 445, 447–449, 455 Wedging, 325

611

INDEX

Western interior, 153 Weston-super-Mare, UK, 168 (Fig. 10.6A) Wet, 180 climate, 179–182 palaeoclimates, 190 to ever-wet climates, 191 Wet-dry climate, 179–182, 189, 190 Whorl height, 199 Whorls, 469, 470 Wilhelmshaven, 3, 269 Woodground, 69, 71, 72, 105, 106, 110, 113, 114, 129, 130 Woodpecker nests, 208 Worm-like animals, 502, 510, 513–515

Wrinkle marks (’Runzelmarken’), 505, 506, 514 Wyoming, 183

X Xiphosura, 478, 480, 482, 487, 488 Xylic substrate, 69

Y Yakataga formation, Alaska, USA, 167 Yelovichnus, 143, 144 Yonaguni formation, 492–495, 499, 500 Young’s modulus, E, 445

Z Zooarchaeologist, 559 Zoophycos, 53, 58, 59, 63–68, 70, 71, 73, 94, 95, 97, 152, 155, 165, 219–222, 224–228, 230, 429, 458, 459, 461, 462, 467–476, 587, 591 brianteus, 222, 224, 230 caput-medusae, 221, 230 group, 461 ichnofacies, 58, 59, 65, 66, 68, 75 scarabelli, 222 villae, 222, 224, 226, 230

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