Tyrannosaurus rex. The Tyrant King

TYRANIVOSAURUS REX, THE TYRANT KING Life of the Past James O. Farlow editor TYRANNOSAURUS REX, THE TYRANT KING Ed...

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TYRANIVOSAURUS REX, THE TYRANT KING

Life of the Past

James O. Farlow editor

TYRANNOSAURUS REX, THE TYRANT KING

Edited by Peter Larson and Kenneth Carpenter

Indiana Unit ersity Press B Io

omin gton

6 lndi an ap oli s

This book is a publication of lndiana University Press 601 North Morton Streel Bloomington, lN 47404-3797 USA

http: / / i u press. i nd ia n a.ed u Telep h o n e orders : 800 - 842- 679 6 Fax orders:

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2-855-793

1

Orders by e-mail: [email protected] @

2008 by lndiana University

Press

All rights reserved No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and recording, or by any information storage and retrieval system, without permission in writing from the publisher. The Association of American tJniversity Presses' Resolution on Permissions constitutes the only exception to this prohibition The paper used in this publication meets the minimum requirements of American National Standard for lnformation Sciences-Permanence of Paper for Printed Library Mateild1 ANSI 239.48-1984.

Manufactured in the United States of Ameilca Library of Congress Cataloging-in-Publication Data Tyrannosaurus rex, the tyrant king / edited by Peter Larson and Kenneth Carpenter. (Life of the past) p cm.

-

lncludes index. ISBN-13: 978-0-253-35087-9 (cloth: alk. pape) 1. Tyrannosaurus rex-Research. L Larson, Peter L. Il. Carpenter, Kenneth, date QE862.S3T977 2008

567.912'9-dc22 2007045376

12345131211100908

CO NTE NTS

ix

SUPPLEMENTAL CD-ROM CONTENTS

xi

CONTRIBUTORS

xiii

PREFAC

E

xv

INSTITUTIONAL ABBREVIATIONS

'f

On" Hundred Years of Tyrannosaurus rex:The Skeletons

1

NEAI L. LARSON

A Z

Wyoming's Dynamosaurus imperiosus and Other Early Discoveries of Tyrannosaurus rex in the Rocky Mountain West

57

BRENT H. BREITHAUPT, ELIZABETH H, SOUTHWELL, AND NEFFRA

3

How Old ls T. rex? Challenges with the Dating of Terrestrial Strata Deposited during the Maastrichtian Stage of the Cretaceous Period

63

KIRK JOHNSON

+

A

Preliminary Account of the Tyrannosaurid Pete from the Lance Formation of Wyoming

67

KRAIG DERSTLER AND JOHN M. IVYERS

r)

Taphonomy of the Tyrannosaurus rex Peck's Rex from the Hell Creek Formation of Montana

75

KRAIG DERSTLER AND JOHN N/. N/YERS

A.

IVATTHEWS

O

Taphonomy and Environment of Deposition of a Juvenile Tvrannosaurid Skeleton from the Hell Creek Formation (Latest Maastrichtian) of Southeastern Montana

33

'.1

lF

1

a-ai- D IENDERSON

/

One Pretty AmazingT. rex

93

fvlARY NIGBY SCHWEITZER, JENNIFER L, WITTMEYER, AND JOHN R. HORNER

6

Variation and Sexual Dimorphism in Tyrannosaurus rex

103

_ Y A

131

10 167 4.1

PETER LARSON

Why Tyrannosaurus rex Had Puny Arms:An Integral Morphodynamic Solution to a Simple Puzzle in Theropod Paleobiology MARTIN LOCKLEY, REIJI KUKIHARA, AND LAURA MITCHELL

Looking Again at the Forelimb of Tyrannosaurus rex CHRISTINE LIPKIN AND KENNETH CARPENTER

||

Rex, Sit:

193

KENT

.l 't I

Z

205 |

5

233 ltA

l+ 245

.lr I

AND WlLLlAl\4 H. HARRlSON

)

255 vi

il

Digital Modeling of Tyrannosaurus rexat Rest

A. STEVENS,

PETER LARSON, ERIC D. WILL5,

AND ART ANDERSON

rex Speed Trap

PHILLIP L. MANNING

Atlas of the Skull Bones of Tvrannosaurus rex PETER LARSON

Palatal Kinesis of Tvrannosaurus rex HANS C, E, LARSSON

Reconstruction of the Jaw Musculature of Tyrannosaurus rex RALPH E, I\4OLNAR

Contents

lO

Vestigialism in a Dinosaur

283

WILLIAM L, ABLER

4a II

287

18 307

_ 19 355

_ 20 371 14

ZI

Tyrannosaurid Pathologies as Clues to Nature and Nurture in the Cretaceous BRUCE IV, ROTHSCHILD AND RALPH E. MOLNAR

The Extreme Lifestyles and Habits of the Gigantic Tyrannosaurid Superpredators of the Late Cretaceous of North America and Asia GREGORY S. PAUL

An Analysis of Predator-Prey Behavior in a Head-to-Head Encountlr between Tyrannosaurus rex and Triceratops JOHN HAPP

A Critical Reappraisal of the Obligate Scavenging Hypothesis for Tyrannosaurus rex and other Tyrant Dinosaurs THOIMAS R, HOLTZ

Tyrannosaurus rex: A Century of Celebrity

399

DONALD F. GLUT

429

IN DEX

vii

JR.

Contents

CONTRIBUTORS

William L. Abler, 1200 Warren Creek

Rd.,

Arcata, CA 95521, USA.

Art Anderson, Virtual Rd., Suite 16,

Surfaces lnc., 832 E Rand Mt. Prospect, lL 60056, USA.

Brent H. Breithaupt, Geological Museum, University

of Wyoming, Laramie, WY 82071,

USA.

Kenneth Carpenter, Department of Earth Sciencet Denver Museum

of

Nature and Science, 2001 Colorado Blvd., Denver, CO 80206, USA.

Kraig Derstler, Department of Earth and Environmental

Sciences,

University of New Orleans, New Orleans, LA 70148, USA.

Donald F. Glut,2805 N Keystone

lohn Happ, 3889 Chestnut

St., Burbank, CA 91504-1604, USA

Hill Rd., Harpers Ferry, WV 25425, USA.

William H. Harrison, Department of Geology and Environmental Geosciencet Northern lllinois University, Dekalb, lL 60115, USA Michael D. Henderson, Burpee Museum of Natural History, 737 N Main St., Rockford, lL 61103, USA.

Thomas R. Holtz Jr., Department of Geology, university of Maryland, College Park, MD 20742, USA. John R. Horner, Museum of the Rockies, Montana State University, Bozeman, MT 59717, USA

Kirk lohnson, Denver Museum of Nature and Science, 2001 Colorado Blvd., Denver, CO 80206, USA. Reiji Kukihara, Dinosaur Tracks Museum, University of Colorado at Denver, P.O. Box 173364, Denver, CO 80217, USA. Neal L. Larson, Black Hills lnstitute of Geological Research lnc., P.O. Box 643, Hill City, SD 57745, USA.

Peter Larson, Black Hills lnstitute of Geological Research lnc., P.O. Box 643, Hill City, SD 57745, USA. Hans C. E. Larsson, Redpath Museum, McGill University, 859 Sherbrooke St. W, Montreal, Quebec H3A 2K6, Canada. Christine Lipkin, University of Chicago, Chicago, lL 60637, USA.

Martin Lockley, Dinosaur

Tracks Museum,

Univertty of Colorado

at Denver, P.O. Box 173364, Denver, CO 80217, USA

Phillip L, Manning, Tne Manchester t,4useum, lJniversity of

r,1arc.:s::'. Ot'crs ?cad,

l',4anchester, M13 9PL UK.

Neffra A. Matthews, Geological Museum, lJniversity of Wyoming, Laramre, WY 82071, USA. Laura Mitchell, Dinosaur Tracks Museum, University of Colorado at Denver, P.O. Box 173364, Denver, CO 80217, USA. Ralph E. Molnar, Museum of Northern Arizona, 3101 N Fort Valley Rd., Flagstaff, AZ 86001, USA.

lohn M. Myers, Department of Geology,

108 Thompson Hall, Kansas State University, Manhattan, KS 66506, USA

Gregory S. Paul,3109 N Calvert

St., Side,

Baltimore MD 21218, USA

Bruce M. Rothschild, Arthritis Center of Northeast Ohio, 5500 Market, Youngstown, OH 44512, USA

Elizabeth H. Southwell, Geological Museum, University of Wyoming, Laramie, WY, 82071, USA.

Mary Higby Schweitzer, Department of Mailne, Earth and Atmospheric Sciencet North Carolina Stafe University, Raleigh NC 27695, USA. Kent

A. Stevens, Department of Computer and Information

Science, University of Oregon, Eugene, OR 97403, USA

Eric D. Wills, Department of Computer and lnformation \rionra I tnivar2= r^ a!@ -OOr

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\oomLn.loJ= NNNrnove the base of the Lance, or 460 m belor.v the top of the forrnation (fig. a.2). At the site, approrimately J m of Lance are exposed. All but the upper 30 cm consist of light bror,r'n, friable, n-rediurn-grained sanclstor-re, with 10-80 cm crossbed sets and scattered pieces of carbonizecl nood. LDP 977-2 occurrecl ir-r the upper 50 crn of this sancl. T'he outcrop u'as capped bv a l0-cm-thick laver of dark bro*'n, nell-cemented, n.reclium- to fine-grained sandstone that had 5-10-cm crossbe ds arranged as clinbing ripples. This sandstor-re bodr,' u'as elongate nortir-soutli and, despite the r.veathering, thinned noticeablv to the east and rr e st. Thc contact betrveen the underlving light-colored sanclstone and the d.rrk one above is obscured

Occurrence

ihe fact that the dark sand u'as concreted and the zone of heavv cement exiended dorvn into the fossiliferous sandstone. The tops of nany of the bones r,vere cemented witl-rin this concreiecl zorre. The bone-bearing sandstone is interpreted as point bar and meandering channel deposits. The hard cap rock is interpreted as a surviving segrnent of a braided stream deposit forrr-red during the dry season on the rnuch larger rneandering charlnel sands. This is not to say that the rocks necessarilv represent a sir-igle wet-drv seasonal cor-rplet. One of us (K.D.) has observed similar concreted, braided-strearn segments thror-rghout the thicker meandering channel sands of the Lance and contemporaneolls Hell Creek deposits of \Vvorning, the Dakotas, and Montana. When thev $'eather out, thev are frequentlv rnisidentified as petrifiecl logs bv nongeologists. Occasionalli', a bit of the original anastomosing pattern of a braided stream is preserved. The outcrop contained too little information to deterrnine u,hether the bones specificallv accumulated on a point bar or came to rest u'ithir-r the channel of the meanderir-is stream. b,v

Description

The exca'n'ation covered roughlv 150 m: (Fig. a.3). The entire set of in situ bones came fron-r the north-central l0 m2. A huge debris field extended from the exposed edge ofthe outcrop and continued for at least 100 n'r into a deep canvon east of the or-rtcrop. Tens of thousar-rcls of bones scraps were

recovered, but onh'a snall percentage rvas osteologicallf identifiable.'l'he bones are sliglitly,' perrnineralized ivith calcite and traces of pvrite, which is tvpical ofbones from the Lance. As shon'n in Figure 4.1, the fossil includes 2 short segrnents of serri-

articulated cervical ancl dorsal vertebrae contair-ring 5 vertebrae each. An llth isolated vertebra was also recovered. T'he outcrop also produced at le:rst I cervical rib, 10 dorsal ribs, and 4 gastralia. In the field, crew memFigure 4.3. Bone map of LDP 977-2. Only the upper portion of the

debris field is shown.

l..!'.."!'^l..,......*

Kraig Derstler and John M. Meyers

bers identified fragn-rents of numerous dorsal ribs and gastralia, at least 2

Figure 4.4. Distribu-

proxirral caudal vertebrae, i distal caudal vertebra, dorsal/cervical r.'ertebrae, the shaft of a l-rind limb long bone, and several heavy pieces of the

tion of bones found

pectoral girdles. No skull elements or teeth r,vere ider-rtified. The distribution of identified bones is shorvn in Figr-rre 4.4. Interestingly, all of the ribs appear to have their ventral ends broken before final burial. 'fhe dorsoventral height of the last cer','ical is 72 cm, whereas the anteroposterior thickness of the second dorsal centrun-r is Il cm. 'l'hese measLlrements are three-fourths the size of those corresponding to FMNH PRZOBI (Sue). Thr-rs, Pete was probabl.v an anirnai 9.4 n (ll feet) long. Until LDP 977-) is prepared, the fossil will be difficult to identify beyond noting that it is alarge tvrannosaurid. The bones cliffer in no significant n'ay from those of defir-ritive specirn ens of Tyrannosdurus rex (e.g., CM 9380, MOR 555, and MOR 980, BHI 3033). As sr-rcl.r, the specimen is tentatively identifiecl asT. rex.

Drawing modified from Derstler (1 994), scaled to an animal with a

LDP 977-7 n as found in a region of the Lance Creek area knorvn to have been examined by several early paleontologi expeditions. Hatcher collected in the region for O. C. Marsh in the late lB00s and for the Carnegre Musenm in the earlv 1900s. Although he did not keep notes on the areas

with

31

ot

Hatcher's niap rFrs.

J.i

-foot length; 80-cm1

tall human for scale.

istorical Consideration H

he prospected dr,rring the initial exploratior-rs of the Lance dinosaur fields, it is possible to reconstruct this infonnation fbr each vear (lBB8-1892) by noting the 1,'ear of collectior-i for each of the ercavation sites he placed on his hand-drawn map (Hatcher et al. 1907). -\lthough these rnaps cannot be compleiely reconciled n'ith nore recent utaps. it is possible to approxi-

mately locate LDP 977-2

Pete (LDP 977-2).

. Fron-r this, Hatcher

69

N

t

ie Cr.

1

891 Greasewood Cr.

DP# 97V{2

1892

I'

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Figure 4.5. Hatcher's Lance fieldwork for Yale Peabody Museum,

reconstructed from museum records by year. Base map modified from an unpublished handdrawn map in Hatcher's

handwriting found in Yale Peabody Museum

files. Shaded polygons oneln<e parent that N1OR 980 n'as concentrated in the cleepest part of tire oxbon'.

Bone

n-raps

for pre-2004 ercar,atior-ts are sketchv at best. For exanrple,

lr'e are not arvare of any maps that il'ere proclttcecl cluring the 1997 looting or the follon-up salvage excavatiott. In 2002, Bill \Vagner reconstrttctecl a bone map for all of the areas excavated up to tliat tinre using old pl-rotographs, sketch maps, preparation maps for several largc bone-bearing concretions, and personal recollections. He proi'ided K.D. lrith this rnap, Kraig Derstler and John M. Meyers

N

-.,,r/!,j:_l

'"/t..

i

"it4

i

'1,.

'!'rt.

cst lor stradgraphi( sect;on pre2004 backfill

.n

1'-+!d--r-_r 10

meter!

Figure 5.3. The 2004 quarry map. Ltghter gray

-

areas are portions of the exposed Rex Sand that were left in place. P indicates old plaster on the side wall of previous excavation. Edge of

-.,,--iou,11"r_-_.

outcrop and edge of old excavauon are mapped only where observed. The 1997 talus was rden-

tified by Duane Sibley and others present during that year's excava-

tion. The area includes debris produced by all 3 excavations that year. O.iginal

Figure 5.4. Bone map for 2004 excavation of MOR 980. Unexcavated portions of the Rex Sand are /ess than 5 cm thick and judged unlikely to contai n add itional bones.

€xcavation

.,/

t

J

'P !L:r

i-- -!-'_ -

_

I rlr

-"

C i nd i cates bo

n e-

bea ri ng

meston e co ncretio ns; +, survey grid points.

Ii

Taphonomy

of

Peck's Rex

77

Frgure

::

map c:

:':

lontour

case of the Small dots

Rex 5a-J -*^ ql//:): ^t^,^*;^^ I >Ld. :tcvdLrut

/

tlor,s Contour rnterval

is

m fsrhanizod lan< v,.,iihin the Rex Sand are 1A

e

shovtn in solid black.

copies of his original clata, ancl another field rnap produced during the 2003 season. We combined all of this ir-iformation onto a single, pre-2004 bone rnap, but trnfortunatelr,, n,e coulcl not correlate this ll,ith the 2004 nap. This correlation n'as macle possiblc bv uncol'ering about 9 rn of the old excar':rtion to usc as a datum for linkir-rg the old and ne*,maps. Plaster splatters or-r the exhurned excavations also helpecl align tl-re tw,o. The resulting composite map is shon'n in Figure 5.6.

Bratded channel sands

Fossils

from the

Rex Sand within the underlying BBQ Sand are shown as

ray areas. O rientation and flow direction of asymmetrical ri pples i n g

a basal layer of the Rex Sand are shown by bear-

ing symbol attached to a directional arrow. Other information taken from Figures 5.3 and 5.4.

The or1r,prorninent vertebrate fossils in the Rex Sand are Peck's Rex and a partialli' articulated hadrosaur. The l:rtter apparentlr' lav several rneters southn'est of N{oR 980 on a higher part of the sarne depositioral surface. We are not alr,arc, hol.,'ever, of anv maps or other written records for the condition of this hadrosaur or its precise location. A fer,r, bones and tendor-rs from the haclrosaur r'vashed clou'n into the deeper area and *,ere r'ixed rrr with Peck's Rex. Understandabh'. none of the Tj.rarntorarrrrs bones i,vashed upn'ard to commingie lvitl-r tl-re hadrosaur.

Onli' rare

scraps of other anirnals \\'ere recovered fron the Rex Sand. ir-rclude a feu'intemal molcls of nondescript snails, ser,eral sl-tedLeidosuchus teeth, a large shed tootl-r frorn a large drornaeosanrid, some gar and

'fhei

other fish debris, one baer-rid turtle fragment, ancl ror-rndecl fragrnents of Kraig Derstler and .lohn M. Meyers

.,u& tN

Triceratops bones and teeth. Unusuallv; the Rex Sand contained no soft-shel1

turtle ren'iains. Although animal fossils are sparse, plant ren-rair-rs are abundant and often rvell preserveci. 'l'het'include carbonizecl wood, seeds, arnber droplets, and foliage representing a diverse assernblage of dicots, palms, ancl conifers. The Rex Sand cont:rins no obr,ious trace fossiis other than tlie dinosaur tracks at the contact ri'ith the overlving Dnane Clar' (see belou).

The Rex Sand is ir-rterpreted as an oxbor.v lake filling. It occr,rpies a channel tl-rai u as cut into the underlving BBQ Sand, and it grades uprvard into overbank siltv clavstone (dubbed the Dr,rane Cial'). The upper surface of the Rex Sand is pianar and subhorizonal. The thickness of the Rex Sar-rcl corresponds to the depth of tl-re underh,ing depositional surface. Interr-rallr, the Rex Sancl can be dil'ided into I subunits. The lorvest is a several-certimeter-thick series of thin-bedded, r'ellorv-green, siltr.', fine-grained sandstones. Each lai,'er contains asvmmetrical ripples thai indicate current

flo"ving tolvard the south-southeast. 'l'he second unit contains the bones of Peck's Rex. It is a 5-70-cn-r-thick, orange-broun, siltl,sand, n'ith small shale chips, rranr, pieces of carbonized u'ood, otl-rer plant debris, small linestor-re nodules, and occasional p-vritic or sideritic concretions. Some Taphonomy

of

Peck's Rex

Depositional Model Finrrra ( 6 Cnmnncifa

bone map. Pre-2004 maps and information compiled by Bill Wagner. Dashed figures on old beari ng concretions. Note

the articulated stilng of caudal vertebrae near the eastern edge of the map.

79

of the sideritic concretions l-rave a linrestone core.'l'he unit is massive bui poorlv ccrnented. occasional inbricated pebbles inclicate current flo'',tou'ard the south-southeast. Hori'ever, tl-re lack of obvious bone orientation

that the currents rvere r.r'eak. 'fhe uppermost subur-rit is a 60-100crr-tl-rick, mecliun-beclcled orange sand, n'ith rnultiple lavers of sideritic concretions ancl occasiorral large pieces of carbor-rized rvood. It contains fen' other fossils ancl no internal sedirnentar-v structures. Ir-r general, it is bellcr cerrrcrrted tlrrrr tlre bone-bearirrg lar er. 'fhe i:r-rderlving BBQ Sand is a neanclering channel-and-point-bar unit deposited bv a sizable rneandering streant. Reflecting wet-drv seasonalitv in the regior, tlie BBQ Sa'd co.tains a fe*'braided cha'nel sands depositeci cluring tlie dr1' seaso.. These braidecl cha.nels, their internal sr.rggests

crossbeds, and crossbeds rvitl-rin the meandering portions of the BBQ Sand east (Fig. 5.5).

ali inclicate n'atcr flon,ing to the

In contrast, the Rex Sand has consistent indicators sholr'ins that the r,vater) noving to the sor-rth-southeast. N,'Iost reasonablr', this infilling is not related to the deposition of the r:rderlving BBQ Sar-rd. Insteacl, it mar., be tied to the sane stream that cut and oxbon'filled rvith sedirnent (and

then abandoned the oxbow channel. Despite the presence of flo',r' indicators u,ithin the Rex Sand, several pieces of evidence indicate that the oxbon, lr'as generall_v stagnar-rt. The lack of aquatic fauna, particularli'soft-sheil ttrrtles, sr.rggests hosiile aquatic conclitions. Preservation of plar-rt rraterial (particuiarlv abr-rndant, diverse, n'ell-preserved foliage in the base ofthe bone-bearing part ofthe Rex Sand) indicates that a.oxia pre'ertecl the leaves fron deca'ing. Final\,, the siclerite four-rd

tl-rroqghout the Rex Sand strggests that the bottom of the lake was chen.ricallv reclucing, again consistent u'ith the ar-roxia and stagnant water hypotheses. Presun-rablr', orvge'ated *ater and sediment reached the oxboq'episodicallr', durir-rg floods. Betu'een floods, tl-re oxbow rvaters were inhospitable to life. Peck's Rer entered the fossil record through this setting.

Taphonomy

There is presentll' no rneaningful informatioii on the cause of death for NIOR 980 or hori' it entered the Rex Saird oxbor.r,. Hon'ever, it seems reasonable to suggest tl-rat it er-rtcred as a relativelv intact carcass. The high degree ofskeletal cornpleteness, the articulatecl caudals, anci the presence

of the bones th:rt usr,ralh' disappear earh' ir-r postn.rorten l-ristory (nanus, distal caudals, gastralia) all support this hvpothesis. The prepared portions of the skeleton do uot shor'r,anv solid e'ide'rce of postmortem scavenging marks. This is cor-rsistent ri'ith the nearly con-rplete absence of shed teeth of poter-rtial scavengers ir-r the Rex Sand.

'l.he

bor-res are concentrated in the deepest portion of the oxborv rvhere ll'atcr u'as at least 1.5 rr deep (based on the thickness of sedin-rents). The lack of bor-res on the oxbolr, sheif to the n'est indicates that this area r,r,as tor-r shallori for the carcass. Thereforc, the skeleton arrived as a bloated carcass in the dcepest part clf the oxbou, and rvas nnable to move into shallolv areas, or it rias actuallv grourdecl there. In either case, tl-re bones dropped from the carcass to the lake bottom as thev rotted free.

Kraig Derstler and lohn M. Meyers

N'Iani of the bones are broken, n,ith the pieces found rreters apart. Sr-rch

broken edges are ne.,'er sharp, and ther,'usuallr'frave rnatrix injected

into thc trabecr-rlae. Strch bones had to be softer.r before breakage so that thel'simpll'fell apart. In short, manv of the bones u'ere rottecl before thel fell frorn the carcass. Consistent u ith this hvpothesis are hundreds of theropod bone shards scattered throughout the rridclle portion of the Rex Sar-rcl. 'fhese represent bones that rotted to the point u'here ttiev sin-rpl1, disintegrated. The nissing 15% of the skeleton cannot be explained as loss due to rnoclern rveathering because none of the skeleton r,r,as exposed at tl're tinre of discoverv. Ratl-rer, the specimen u,as accidentall,v cliscor,ered in the course of excai.,ation of a hadrosaur skeleton. 'fhere are fel,r' alternatives to explain the missing portions. Perhaps a feil'smaller bones rer-nain in the thin. unexcavated areas of the Rex Sand. Possibl1.a fel'n'are hidden li,ithin the unprepared concretions, or a fen srnallcr bones rrav have rotted cornpleteh' before buriai. Finallv, sorne of tl-ie bones corild hal'e bcen clestroved or othern'ise lost during looting and the salr'age erc:rvation. Whatever the explanation, \\,e are surprised that N{OR 980 is uot more complete because there seems to be no 6b1,is11s 11'21' to clispose of the missing bones.

We thank the staff and volunteers at FPPI and their counterp:irts at the tJ.S. Arrm' Corps of Er-rginee rs, particularh Dtrane Siblcl, l,oLr Tren-rbler', and Bill Wagner. \\''e also ackr-rou,ledge the erceptior-ral field assistance of Douglas and Arcl'r Var-r Belle., Dorv Tr-rrnipseed, Teresa Logudice , Steven Luton, Dana Hensler,, and Ruth Ebert. Bob Richter arranged for and dclir. ered :r great deal of field equipment. Nat \{urphv and Bill Wagner provicled infonnation on the occurrence and historl of N,IOR 980. Peter I-arson \\:as an enclless sorlrce of inforrnation ancl enthusiasm concerning'I't-ran-

Acknowledgments

nos(ilfius rer. Finalli, Larrv and Jovce'l-uss, \\/ir-rifred, N{'l , hosted us u'hile preparing this cl-rapter in the extencled aftern-rath of Hurricar-re Katrina.

Rigbv, j. K., l,inford, C. B., and Rigbv, j. K., Jr. 2001. Geologr,of the McRae Springs Quaclrangle, NIcCone Countr', northeastern N{ontana. Geologl, Studies, Brigham Young Unirersity 16: l5-91.

Taphonomy of Peck's

Reference Cited

Rex

81

Fiarra A 1 RA/lP

P20A2.4.1 (Jane) on dis-,t;

tt f ha Rt trnaa A,4t t:c n nf l\lzft trzl LJictnrtt ll -^ ^ 'ztarr'l

Michael

D

Henderson and William H. Harilson

TAPHONOMY AND ENVIRONMENT OF DEPOSITION OF A JUVENILE TYRANNOSAURID SKELETON FROM THE HELL CREEK FORMATION (LATEST MAASTRTCHTTAN) OF SOUTH EASTERN

MONTANA Michael D. Henderson and William H. Harrison

Extensir,'e outcrops of the Hell Creek Forniation (uppermost Maastrichtian) occur in eastern N{or-itana. Tl-re formation is r.videlv regarded as har.

ing been deposited in a low'lar-rd flr,rviolacustrine sl'stem; these sections consist of a stacked series of fining-uprvard seclimentarr,seqllences forn-red by cl-ranneis rneandering across a lowland floodplain (Kirk fohnson, personal comrnunication). The soft texture of the Hell Creek strata, conbined with the sporadic rainfall in the nortl-rern Great Plains, has resulted in the developrnent of extensive bacllands throughor,rt its outcrop area. These badlands contain an abundant and diverse fossil flora and fauna, including clinosaurs.

In 2001, an expeditior-r frorr the Btrrpee Nllnseum of Natural History, with perrnission from the Br,rrear-r of Land Management (BLM) to survey, for vertebrate fossils, discoi,'ered several foot and lou'er limb elenents of a theropod dinosaur lveathering from an exposure of the Hell Creek Formation in Carter Cotrnt\,, N'IT. After initial evaluation, the site was u'interized and an application made to the BLM to open a quarry the follor.ving year. In the summer of 2002, a field creu' returned to excavate tl-re specimen. During the course of the excavation, a sizable quarry i.r,as created, which yielded rrajor portions of the skeleton of a tvrannosaur (BN4R P2002.4.1), nickr-iamed fane, approximatell'7 n'r in length (Fig 6.1). In addition to Jane, manv associated plant, invertebrate, and vertebrate fossils rvere recovered from the quarrv.

Lack of fusion of the r-reurai arches to their respective centra in the vertebral column indicates that Iane is a iuvenile animal. Examir-ration of histoiogical sections from a rib, fibula, ancl metatarsal indicates that at death, fane l1 years old and stillin a phase of rapid gror,vth (G. Erick"vas son, personal comrnunication 2003). Recovered skull bones and teeth of fane (BMR P2002.4.1) bear a close resemblance to those of CN{NH 7541, a controversial tr''rannosaurid skull that has been interpreted as belonging to eitlrer a juveniie Tyrannosaurus rex (Carr 1999; Carr and Williamson 2004) or a separate taxon, Nanotyrannus lancensis (Bakker et al. 19BB;

J

u ve n

iI

e

Ty ra n

n osa u r i d Ske/eton

Introduction

Cnrrie 2003a,20003b; Cr-rrrie et al. 2003). Research is currentlr'ongoing into tiie s1'stematic position of both specimens. h-r spite of manv taxa of dinosaurs knon'n fiom the Hcll Creek Formation, most finds consist of isolated bones (Pearson et al. 2002). 'l'he discor. err.'of a substantial portion of a jur,er-rile tvrannosauricl skeleton in the formation is so unusual that the circumstances of its burial and preserr,ation nerit careful ar-ral1'sis so that like environrnents can be erplorecl.

Stratigraphy

Extensive exposrlres of the Hell Creek Formation occur in southeastern \Videll' regarded as a prograding, clastic ri,edge associated n,ith the retreat of the \\'estern Interior Sea, the Hell Creek prinrarilr corrsists of poorll'cemented channel ancl crer.'asse splar,'sandstones, overbank rrrrdstones and siltstones, paleosols, carbonaceous clavstoncs, and thin and N,'Iontana.

sparse lignite becls deposited dr-rring the iast l'ears of the Cretaceor-rs Periocl

':,,e 5.2. Jane Quarry ' :^: re/i Creek Forma: r- ,iesi l\/laastrichtian) ' 'a.:n'lvestern carter . ?:-^ty,

MT.

(Nlurphv et al. 2002; fohnson this i'olunre). Near its tvpe section in Garfield Countr', north-central N'{ontana, the Hell Creek Forrnatiolr is I70 m thick (lohnsor-r et al. 2002). Its thickncss in soutlieastern N{ontar-ra is estir-r-ratecl to be 150 n; hon,ever, no conrplete sections of tl-re forrnation are erposecl. 'l'he nearest complete scctions are in south',r'estern North Dakota (aboLrt 100 km frorn the qtrarrrJ, n'here the formation is approrimatell' 100 m thick (N,h,rrphr ct al. 2002). Unfortunatelr', no identifiable marker beds occtrr in thc Hell Creek, r,r'ith the exception of the top and bottor.r-r contacts. Within tl-re formation, there is little lateral continuitr of beds and bentonitic snrface iieatherinq obscures

,t":-.-

rhi

lth

,".

Figure 6.3. Stratigraphic section of the Hell Creek Formation exposed in the lane Quarry, Carter County, MT.

sandy mudstone-contains yertically orienled root casls

f-

rop otquarry sandslone laminaled siltslone

tano$one

siltstone sandslone sillstone cross bedded $andslone laminaled siltstme wilh abundant Prslia conuoata Clayball snglomerale (Tf rannosaur beanng unit) n{as$ive $andstare wilh weak cross beds

bedding (Jol-rnson et al. 2002). Consequentlv, the exact stratigraphic placernent of Jane t,ithin the formation is con-rplicated. Pollen and plant rnegafossils from the fane Quarrv correlate u,itli a stratigraphic level in southll'estern North Dakota that is 28 to 35 m below' the top of the forr rratiorr.

The Jane Qtrarn' is located on the northern side of an elongate eastr,vest-trending ridge in northwestern Carter Countr; M f (Fig. 6.2); the exact localiiy is ar,ailable fiom us. 'fhe tr,rannosallr \\'as discovered r,r'eathering or,rt near the base of the butte. The far.re Quarn'section exposes a fining-upward sequence of clastic sedirnents approximateh'8 m thick (F'ig. 6.3).

At the base of the section is nrassive, poorh' cerrented, clirty; tanbron'n, crossbecided sanclstore. Its total thickness is unknorvn because it is inconpletelr'exposed. Abundant ivood and coniferous and deciduous leaf impressions are present on or near the upper strrface of the sandstone. Decidncrus leaves recove recl fron-r this unit are identified as belonging to Dryophyllum nLblalcatum and "l'ltls" stantoni. The onlv vertebrate fossil encountered in the ur-rit u'as a single midseries cervical vertebrae of a large azhdarchid pterosaur (Henclerson and Peterson ir-r press). A clav-ball conglomerate cornposed of poorlv sorted sand, silt, ar-rcl rounded greenish-colored clar,clasts overlies the sandstone (Fig. 6.4). This unit is lentictrlar, shoi,ving rapid lateral variation ir-r thickness (12-40 cm). The tvrannosaur skeleton u'as discovered in the lori er part of this conglornerate, at its contact r.iith the ur-rclerl_ving s:rnclstone. Diageneticallv proL

-. ?nite Tyrannosaurid Skeleton

B5

: o-.e

6 4. Thin section

o' ine clay-ball conglomo,- L|dt lul/Lol//gu = +,,--^^^--,,t 11ir Lyt dtu tv)qur jQVf ^^;/^ ( B l\4

R P2002.4.1 ).

(t/c /-^^ Jdt tc

Arrows

indicate siderite and a clay ball. Scale bar = 1 cm.

cluced siderite nodules occur n'ithir-r the conglomerate and partly'encased several bones of B\"IR P2002.4.1. Plant fossils recovered frorn this unit include n'ood and bark irrpressions, conifer cones and ueeclies, and numerous srnall, roturd to oval seeds, preserved as internal casts. In addition, an abunclant, cliverse, :rnd r,r'e11-preserved palynoflora occurs in siderite noduies and clai'balls ri'itlrin the conglor-r-rerate. To clate, 5l genera of pollen, spores? and cr,sts hai'e been recor,ered. These indicate the presence of a diverse flora of flori'ering plants, conifers, ferns, c1'cads, and pahns. Poller-r of Cunnera, a herbaccous plant, is especiallv common. Recovered poller-r and spores are tvpical ol the Aquilapollenites pall'nofloral province, rvhich is found in Upper Cretaceous rocks from rvestern North America westward into r-rorihe astern China. hn'ertebrates are representecl b1'poorly preserved inten'ial casts of unionid bivalr,es (2 species) and high-spired gastropods (l species). Remains of r,ertebrates (clinosatrrs, lizards, freshwater fish, croco-

dilians, champsosaurs, turtles) are common and represented bv disarticulated skeletal elernents randornh,distribr-rted lvithin the r-rnit. Preserv:rtion of these bones and teeih range from pristine to significantll, won-r. A 2- to 4-cnr-thick lal'er of siderite caps the conglomerate. Above tl-rc siclcrite cap is a siltstone. The basal l0 to 35 cm of the siltstor-re is finelv larninated ancl contains extremel,v abundant fossils of aquatic monocots, prirrcipallr,a kind of u'ater lettuce, Pistia corrugafrz, many preservecl as u'hole plants (F ig. 6.5). A seconcl 2- to 4-cn-r stratum of siderite caps the Plstiabearing lavers. Higher in the unit, sporadic sandstone lenses (up to 1.5 rn thick) occrrr. Crossbeciclir-rg u.'ithin the sand units indicates water floiv from

Michael D. Henderson and William H. Harrison

sorltli to north.'fhe top 0.5 nr of the qLlarrv is sandl siitstone, ri,hich is not laminated, :utcl iontains verticalh' oriented root casts.

Tl-rc Jane Quarrv section appears to be a tvpical floodplain seqllence. We interpret the nrassive, crossbeddecl sandstone on lvhich the tlrannosaur lal as

point bar sancl. The clar.ball conglomerate that contained the juvenile t1. r:rnnosallr records a nuclflot'from a flood event, or a bank collapse. Abor,e fane, the lan-rinated siltstone containing reecls ancl Pisfla inclicate a strear-rr avuision ancl tfre strbsequeirt do'elopnent of an oxboli'lake on the site, lvhile

Environment of Deposition

:r

sandstone lenses higher in tl-ie section are thought to have been prodr-rced bv

rundern'ater dunes nrigrating througfr the lake during times of high w'ater n'hen the abandonecl channel uas ternporarilr,reconnected to the rir,er svs-

of

terr. Verticallr oriented root casts present at the top of the cprarrf indicate

Figure 6.5. Leaves

er,entuallr siltcd up and vegetation w'as established. Fossils of plants and animals associated n'ith Janc (BN,IR P2002.4.1) corresponcl closelt'u'ith those collected in association w'ith a TlrrunrlosdLLrus rex (Peck's Rex) fron-r the upper Hell Cre ek Formation of N,lcCone Countl; NIT

laminated siltstones above the tyrannosaurbearing unit.

tl-rat the lake

(Derstler and N'lvers this a'cl aroiher T rex (knou n as Scottr) fro.r 'ol'rne), the contemporaneoLls Ftenchrnar-r Fbrnration of southw'estern Saskatcher,al, Canada ('lbkarlli and Brl'ant 2004). The eni'ironment of cleposition of all these specimens inclicates burial took place on a \\,arm, net, lor,r,land floodplain.

All t'u.rannosarir skele tal elcments recovereci fron the Jane Quarrv are consis- Taphonomy tent rvith deri'ation from a single indi'iclual. 'l-he 1-15 bones, representirrg approxirrratel

"'57%

of the skeleton, ilere collecte d trom

i L',, e rt

i

I

a

e

4 m: area (Fig. 6.6).

Tyra n nosa u rid S keleton

Pis-

tia corrugata from the

q12

\\

-n ,-7'

/c>

ri

in\

0$

s

Ag

Figure 6.6. Quarry map showing distribution of skeletal elements of BMR

P2002.4.1 (Jane). Dotted lines indicate field jackets. Sca/e bar = 1 m.

'fl-re ty'rannosaur 1a1'on its rigl-rt side u'hen buried. Portions of the right foot remained in articr-rlation. Skull bones r,vere disarticulated but concentrated in a lin-rited area over the hips. A segrnent of 16 proxirnal caudal vertebrae, rvith their associated hernal arches, u'as found arcing over the back.'l'his drs-

tribution of bones ir-idicates that after death, shrinkage of rntrscle

s ar-rcl

liga-

rnents along tl-re vertebral column contortecl tl-re carcass into the classic dinosaur-avian death pose. Loose teeth from the right dentary'u'ere found north

of it in a pattern consistent with rnovement b."' u'ater or nrud from south to nortl'r. Manr,of fane's ribs and presacral vertebrae n'ere scattered or rtissing. This could be the result of movement bi, lr'ater or mucl, bloating then bursting of the carcass, or scavengir-rg of the carcass. The right hurnerus n'as found about a rreter from the main bone concentr:rtion, ttpstream from inferred paleocurrent direction and in direct contact with a shed tvrannosatir tooth. The context suggests scar,'enging, but the cornpleteness of the skeleton and concentration of bones indicate scavenging rvas not extensive . No tooth rrarks t'ere observecl on oresen'ed bones. BB

Michael D. Henderson and William H. Harrison

The bone preseru'ation of Jane is excellent, u,ith no signs of postrnortern weatherir-rg. 'l'l-ris ir-rdicates that tl-re skeleton ll,as not erposed on the point bar for an exter-rded period of tine. Rapid burial of fane's skeleton b1' a mudflow appears to be the kel' event responsible for its completeness. The finelv laminated siltstones of the orbon' lake deposited on top of the remains pior.'ided furtl-rer protectior-r fror-n d isturbance.

'fhe seqtrence of events leading to burial

1.

2. 3.

4.

5.

6.

ma-v be

surnmarized as follorvs:

Summary

A juvenile tvrannosaur died. At the time of death, or shortlr thereafter, its bodv can're to rest on the point bar of a cl-rannel on a forested, lou'land fl ooclplain. Shrinking rnuscles and ligarnents contorted the tvrannosaur s corpse into the classic dinosaur-avian death pose concurrent n ith, or soolr after, n-rinor scavenging of the corpse occllrred. As decav proceeded, disarticr-rlation of the skeleton reached an advanced stage. Ligaments rerr-iaining aiong the hips, base of the tail, arrd feet kept these eleurents in place. Burial ri'as accornplisfred bv a viscous mudflou'composed of poorl,v sorted sand, silt, and clal'balls. Entrained in these sediments u,ere pieces of r,','ood, seeds, leai.'es, and a varietv of .n'ertebrate bones ar-id teeth. Possiblv, burial r',,as related to a cutbank failure triggered by a flood event. Sorre skeletal elements rvere mor,ed by tl-re mudflolv. After depositior-r, diager-retic siderite nodr-rles forn.red around some of tl-re clinosaur's bones and in tl-re conglornerate. The meancler channel r.r'as abandoned and becarne a deep oxborv lake. Under qr-riet water conditions, aquatic plants flourished and larninated silts n'ere deposited.

Peter Larson (Black

Hills Institute) generouslv provided advice and assistance Jol-rr-rsor-r (Denver Museum of Natr-rre & Science) r'isitecl the tvrannosaur qllarrv site and provided assistance in inierpreting tl-re strata exposed there and helped identifi.,plant remains. Doug Nichols (USGS Denver) provided assistance in identifying the palvnoflora associated u'ith the tvrannosaur. Reed Scherer and f . N{ichael Parrish (Northerr-r Illinois Universitr,) read ancl comrnented on a draft of this chapier. John Warnock (Nortl-rern Illinois University) prepared the stratigraphic column

in collecting the tyrannosaur. Kirk

and Molll'Holman (Burpee Museum) produced the skeietal drarving of Jane. A number of staff and volunteers frorn Burpee N{useum assisted ir-r the excavation ancl preparation of Jane's skeleton, including: Melissa Birks, Dave

Carlson, Ler,l Crampton, foseph De La Morte, Shannon Farley-Maconaghli Chris Garnhart, Jill and Richard Hertzing, Lisa Johnson, Jim Keller, Cl-rrissy \'{ajero',visz, N{irian-r Michaelis, Deborah Nloar-rro, Brian Ostberg, Holli Pahner, )oseph E. Peterson, Sheila, Richard, and \anci,Ran'lings, Scott Santoyo, N'lelissa Sciirock, Ernie and Sue Srnith, \like Spiachello, Mindy Thornpson, Katie Tremaine, Carol and Hazen Tirck. and Scott Wiiliarns. .

,.-'

te Tyrannosaurid Skeleton

Acknowledgments

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Bakker, R. T..

--"-

r:orn lr-!5rr11 r\ LdTILLUJLTLUT rl

r

Michael D. Henderson and Wrlliam H. Harrison

Figure 7.1 . Medullary bone in extant laying hen. (A) Gross cross section of femur of actively Iaying hen shows extensive medullary bone formation. New bone is ranr'lamltt arianfad

a

nr'l

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tion of the medullary bone from cortical bone is seen as sectionrng artifae | | aroo m, tlfint trla^+^) dteu

^.+^^-l--+uJteuL/d)()

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ane Pretty Amazrng f . rex

during egglaving in Japanese ql:ail. American lournal of Anatonq, 162: 35-4). \liller, S. C., and Bou'man, B. N'I. 1981. Medullart'bone osteogenesis follou'ing estrogen aclnriristration to mature n-rale Japanese qvail. Detelopmental Biolog,t 87: 52-63. N{ueller, W J., Brubaker, R. 1,., and Caplan, N'I. D. 1969. Eggshell fornation and bone resorpiion il eggJaf ing hens. Federation of the American Societt, of Experimental Biclogists 28: 18il-1855. Pelligrino, E. D., and Blitz, R. M. 1970. Calciurn carbonate in nedullarr,bone.

Calcified Tissue Research 6: 168-171. Relnolds, S. ]. 2003. N{ineral retention, rnedullarl'bone formation and reprodtrction in the rvhite-tailed ptarn.rigan (Lagopus leucurusl): a critique of Larson et al. (2001). Auft 120(I):724-278. Robel', P. C. 1996. Vertebrate mineralized rnatrix proteins: stntctttre and function. Connective Tissue Research l5(1*4): 18t-190. Schraer, H., and Hunter, S. J. 1985. T'he development of medullart'bone: a n-rodel for osteogenesis. Comparative Biochemistrt and Bioplrysiologl,

EZA(l): ll-17. Schrveitzer, N'I. H., Wittmever, J. L., and Horner, J. R., and Toporski. J. 2005a. Soft tissue vessels and cellular preser"'ation i:nTtrannosaLtrus rex. Science

307 1957-1955. 2005b Gender specific reproductive tissue

ir-r

ratites ancl Tt'rannosaurus

rex. Science 308: 1456-l'160.

-. Sereno,

P C. 1997. The origin and er"olution of dinosaurs. Annual Reviews of Earth and Planetary Science 2i:435-489 I99i Sirnkiss, K. 1961. Calciurn metabolism and avian reproductiotr. Biological Re,-iew 36: 321-367.

Snith, D. K.

1998.

A rrorphor.netric anal', sis of AllosatLrus. lotLrnal of Yertebrate

Paleontolog,t, l8( I ):

1

26-i42.

Sugivama, T., and Kusuhara, S. 200i. Avian calciun metabolism ar-rd bone function. Asian-Australian lournal of Animal Science 14: 82-90. Tar4or, T. G., Sirrkiss, K., and Stringer, p. ,1 l9;1. The skeleton: its structure and metabolism. P. 621-640 in Freeman, B. NI. (ed.). Physiolo$ and Bioclrcmistry of tlrc Domestic Fou'/. Vol. 2. Acadelr.ric Press, Ner.v York. Teresclrenko, V. S., and Alifanor,, \1 R. 2003. Bainoceratops efrenrovi,2r ne\l protoceratopsid dinosaur (Protoceratopiclae, Neoceratopsia) fronr the BainDzak local itr, (south Nlon golia). Paleoriolo gt, I ournal 37 : 793 -707.. Van Neer, \tr'., Noven, K., ar.rd DeCupere, B. 2002. On the use of endosteal lar. ers ancl medull:rrv bone frorn domestic forvl in archaeozoological studies. lountal of Archeological Science 79: 123-134. Wang, X., Ford, B. C., Praul, C. A., and Leach, R. \1. 2005. Characterization of the non-collagenous proteins in avian cortical and medullari'bone. Conzpdrdtit)e Biochemistr,t and Physiolog,t B I+0: 66i->72. Weishan.rpel, D. B., and Chaprnan, R. E. 1990. Nlorphorretric stuclv of P/aleosaurus from Trossingen (Baden-Wurttemberg, Federal Republic of Gerrnanv). P. 4l-51 ir-r Carpenter, K., and Currie, P J. (ecls.). Dinosaur Systematics: Approaches and Perspectites. Canbridge Universitt Press, Cambridge. Whitehead, C. C. 2004. Overvieri.'of bone biologv in the egg-lavir.rg hen. Poriltr,t Science 83:193-199.

Wilson, S., and Thorp, B. H. 1998. Estrogen and cancellous bone ioss in the fou,l.

100

C alc ifi ed T i ssue

Mary Higby Schweitzer et al

Internati onal 62: 506-5 I ..

tti

t:eue W *, ,ei*

tl:

VARIATION AND SEXUAL DIMORPHISM IN TYRANNOSAURUS REX Peter Larson

The science of paleontologl has often been accusecl of being more art than science. This assessn-re nt sterrs frorn the probler.r-rs e ncounterecl ri'hen dealing n,ith the patrcitl, and incorriplcteness of the fossii rccord. Not the least of the problems confronting paleontologists is the scarcitv of specirnens. To date, '{6 specimens (\. L. Larson this volurne) consistiirg of more than a fer." associated bor-res have been assigned to'I'yrannosaurus rex Osborn (1905, 1906). Although this is a robust representation for ertinct theropods, r.r'hen conrparecl n'ith extaut populations, this nLrnrber seems ertremcll inadequate. Fbr erample, BLrss (1990) reported a 1973 cor-rnt of 14,109 African clepharfis (Loxodonta ttfricana) in the 3840 kmr (1481 rnir) Kabalega Falls National Park in Uganda. On its face, 46 specimens scerrs a palrrv nurrber from q hich to de finc a specie s, lct alone :rtternpt to identifv males ar-rd females. Yet that is eractlr,t'hat this stuclv attenrpts. The use of modern taxonomic nrcthods rnav be used to identifi anomolons morphological characters and to remove qucstionable specinrens fiom a t:rron to u'hich thet,have been urrnaturallr joined (nrorc belon). Taken even further, rrorphometrics, phi'siologr, ar-rd pathologr,can be used to help separate ancl defi rtc scr rr rorpl rotr'pe:. For this studr', J,l specimens attributeci to'l\,rannosatLrus rex, including specimens listed as Ttrrrnnosriurus "x" lncl Nanotr-rannus (considerecl as specirnens ofT. rer br Carr 1999), li'ere examined. In addition, 2 specimens assigned to TarbosatLrtLs bdtdctr, one assigned to Corgosattnrs and another to Albertosauru.s, \\/ere eramined as or-rtgroups. These specirnens are listed in Table 8.1.

In arv pop.l:rtion, indi'idual n'ithin a species n,ill occur. This 'ariation variation is clue to ontogenr', nutrition, genetic variance, p:rthologr; and, of corlrse, sexual climorphisrr-r. Thus, it is inrperative that these factors be excluded n'hcn examining the cluestion: "Have rescarchers inclr-rded specimens w'ithir-r the species T rer, ri ith variation ber,ond that expected n,ithin a living population?" Extant phvlogenetic bracketing tecl-rniques (Witmer 1995) li'ere tlsed to evaluate the characters used in this studi for the purpose of isolating those :rttributable to ir.rtraspecific rariation.

Vanation and Sexual Dimorphsm

Introduction

Figure 8.1 . (Left) Tyran-

"x' (AMNH 5027). (Right) Tyra nnosaurus rex (BHl 3033). nosaurus

Figure 8.2. Medial view of right dentary of the type Tyrannosaurus rex CM 9380. Note the incisiform first dentary tooth. Figure 8.3. Left and ilght first dentary teeth of

Tyrannosaurus rex BHI 3033. (A) Lateralview, (B) Posterior view. Note that both serrations are exposed in the posterior view, creating the typical ty ra n n osa u ri d D -sh a ped cross section.

Variation

Table 8.1. Specimens I lcad in tha (.tt trh,

Tyrannosaurus CM 93BO

cM

rex

Tyrannosaurus

"x"

Nanotyrannus Outgroups

AMNH 5027

BMR P2002.4.1

MOR 008

CMNH 754,1

LACM 23844

SDSM 12047

BHt 6235

LACM 2345

Samson

LACM 28411

1400

Tarbosaurus BHt 6236

ZPAL-MgD-t/4

Gorgosaurus

MOR 009

TCM2001.89.1

MOR 1128

Albertosaurus

MOR 1125

BHt 6234

MOR 555 MOR 980 FMNH PR2OBl BHt 3033 BHt 4100 BHI 4182 BHI 6232 BHt 6231 BHt 6233 BHr 6230

BHt 6242

TCM2001.90.1 RTMP 81.12.1 RTMP 81.6

1

UCMP118742

BMNH R7994 NHN/ R8OO1 USNM V6183

LL.12823

Ontoger-ietic variation rna,v include aspects other tl'ran the ob',,ious increase in size. For example, it mav also include an increase in the nurrber of alveoli, or tooth positions (e.g., Edn'LontoEdurus annectens; personal obsenation). In certain groups (i.e ., namrnals), gron'th to ach,rlthood mav also inciude modi-

fication of tooth n-rorphologl', along with an increase in the number of tooth positions (Romer 1966). Iror manr.,r,'ertebrates, ontogeny' also includes an increase ilr bodv size at a faster rate than for the brain, e1,es, and skull (Locklel' et al. this volr-rrne). Nutritional variation mav rnanifest itself as smaller bodv size ar-id smaller body mass-differences that are not generally cor-rfused witl-r taxonoinic characters. Genetic variation mav be rronitored by' using extant populations as examples (Darrvin 1868). Pathologic specimens shoi,ving eviclence of disease or healed injurl are relativelv easily recognized, and are generall,v not reproducible from specimen to specimen in a form that lr'ould be noted as a taxonomic character. Finally, sexual dirnorphism lvill be discussed in depth near the end ofthis chapter. Peter Larson

More than 25 I'ears ago, Robert Bakker (personal cornmunication) made the case for dil'iding the North American genu,sTttrannosdurus into 2 species, T. rex ancl what he refers to asTyrannosaurus "x" (Fig. E.l). Bakker's reasoning',vas based on a peculiar variation in the anterior dentition of the dentary. The type of Tyrannosaurus rex (AMNHg71. = CM 9lB0) possesses a single incisiform tooth occupf ing the anterior position in the dentar1,. This tooth is morphologically reniiniscent of the teeth of the premaxilla, is D shaped in cross section, and is substantiallr,'smaller tl-ran those directly posterior to it (Figs. 8.2 and 8.3). Bakker also noted thatAMNH 5027 ap-

The Case for TyrannosauraJs

"x"

pears to possess 2 incisors ir-r each dentarv. For lack of specimens, his vier.vs were never published. Paul (1988) and Molnar (1991) have both also con-

sidered the possibilitv of a seconcl species of Tyrannosaurus. A quarter of a ceniurv later, there now' exist at least I5 reasonablv complete Tyrannosaurus skulls. Three of these specin-rens (MOR 008, SDSM 12047, and Samson) share certain characters, including the double lower incisors, with ANINH 5027 (Figs. 8.4 and 8.5). Because tl'rese "incisors" are ei-

ther missing or were restored on all 4 specimens, i,r'ithout cornputed tomographic scans to look at unerupted teeth, the D-shaped morphology of these "incisors" is in question. The apparent differences seem to be best expressed by con-rparing the size of the second dentarl'tooth rvith that of the third, ar-rd because the teetl-r then-rselves r.vere not alu'a)'s available to n-reasure, the length of the second ancl third alveoli were measured and compared. The results of these rreasurements are founcl in Tbble 8.2.

Although all 4 skulis seem short r,hen compared rvith fr,rll-grown ir-rdividuals (i.e., BHI 3033 and FMNH PRZ()BI = BHI 2033), ontogenetic variation mar,'be ruled or-rt becatrse other individuals of approxirnately the same skull length do not share this character. One of the specimer-rs, Sarnson, has a femur (length, 129 cm) of comparable length to Stan (BHI 3033; length, i11 cm), but r,r,hose skull is less tl'ran 80% as long (104 crn). A shorter skull and variation in lorver jaw clentition is unlikeli to be caused bl,differences in nutritior.r. Pathologv mal'be ruled out becar-rse of the lack of ar1' associated n'ranifestation of healed injr-rrl. Genetic variance also seems in-rprobable because no modern correlates exist. A case could be rnade for the differences in the dentition being attributable to sexual din'iorphisn.

Specimen T.

DT2-L

(mm)

DT3-L

(mm) Ratio of DT3 to DT2

rex.

CM 93BO

55

f\40R 555

52

56

1.1

MOR 980

51

51

1.0

BHt 3033

56

60

1.1

BHt 4182

33

2A

1.0

MOR 008

4B

64

1.3

SDSM12047

3s

55

16

33

EA

T.

1.0

Table 8.2. Comparison of Lengths of Second (DT2L) and Third Dentary Tooth or Alveolus (DT3-L)

*

From the holotype.

"x"

Samson

1.6

Variattan and Sexual Dimorphism

105

!qk_*,

R$ \E g E*3

w x

F

gure 8.4. Dorsal view of

the anterior portion of the left dentary of Tyran-

nosaurus rex CM 9380 preserving small first dentary tooth DTl and ls

ra a <aran r-l rl a nf

a rt

t

tooth DT2.

Although there arc moclern exarnples of semal dirriorphism in the canines of some prir-nates (Nlartin et al. 199'1) and in the canines or incisors of ri alrus, elepl-rants, bush pig, ar-rd hippopotan'rus (Lincohr 1994), serual dinrorpl-risrr expressed as differences in clentition ir-r extant tara seems to bc restricted to marrmals. Any dental e\pression of sexual cliurorphism remains ttndocumentecl for crocodilians, extinct tootl-recl birds (ertant plnlogenetrc brackcting), or other ertant reptiles. Can the differcnce in the teeth be attributable to speciation? Although stratigraphic information for the 4 specirnens is r-rr-rai'ailable, tiiere are gooci records available for Ti'rannosaurus rex. BHI 2031 n'as coliected l6 m belon' tl-re Kjl'boundarv in the Hell Creek Formation (the Hell Creek in the area, near Buffalo, SD, is approximatelr' 150 m thick). A second indisputable specinen of ?yran nosdurlLl rex (BHI 4182) ivas collected nearbr', frorn n ithin I0 rn of the base of the fornratiorr, and it represents perhaps the oldest knon'n recorcl of 'li'rannosaurus from Norih America (Kirk Johnson, personal cornrrunication). Geographic distribution is also not a factor, because 'f. rex cooccrlrs u'ith

106

Peter Larson

T

"x."

rt.ii.t

:"1|i.*:

i!l:r:r:

Dentarv and rnaxillan,tooth (alveoli) counts also seem to var)'between the 2 "species." Tl'ris is particularlv evident in the dentarl; lr'ith ll or 14 for 'fyrarLnosourus rex ancl 14

or

15 for

T 'r."

The distribution of all of these

characters, vithTarbosatLrus hataar as an outgroup, are listed in Tbble B.l. A fourth character separating the 2 forrrs is the relatir,e size of the lateral

pneumatic lachrvrnal foranien. Specimens referablc to T 'x" l-rave relatively snraller lateral pneumatic lachri.'rnal for:rrr-rina th:rn those of 'li,rannosaurus rex (Fig.8.6). when me'surecl .nd plottecl as lach^'mal forarnina length's. laclrrl,n-ral length (Fig. E.7),7\'ranrrcsd.urus "x" cl.sters separateli,, frontT. rex

iiiii

Figure 8.5. Dorsal view

of

the anterior portion of the left dentary of Tyran-

nosaurus "x" (Samson) preservi ng sm a I I a lveol i for DTI and DT2 and a large alveolus for the

third dentary tooth DT3.

(as do GorgosaunLs anclNanotyranntts). Ho*e'er, it should be notecl that the size of the lachrv'ral forarnira in Allosaurus is extre'rely and this 'ariable, difference betn'een 'I'. rex a''d T 'i" mar r-rot be statistically'significa't, espe-

cial\, gil en the sample size ( Kenneth

Skull Character

Car penter. p.rro,-r"L .o,-,-,rnunicationl.

Tyrannosaurus Tyrannosaurus Tarbosaurus rex

Lateral lachrymal pneumatic foramina

Small

Maxillary tooth count

11

or

12

Dentary tooth count

13

or

14

Dentary incisor count

1

L3DT/L2DT DT3-L/DT2-L

1.0-'1

1

Very small

Small

12

12

14

or

15

or

Table 8.3. Comparison Skull Characters

13

15

2

1

1.3-1.6

1.2

Var'arion and Sexual Dimorphism

t07

of

Figure 8.6. Lateral view

of the left lachrymals of (A) Tyrannosaurus "x" AMNH 5027 and (B) Tyrannosaurus rex BHI 3033. Note the larger lateral pneumatic foramen on T. rex.

B Are these 4 cranial characters enougl'r to erect a new species? (No significant postcranial characters r.vere noted.) Becanse r,ve are dealing with ar-t extinct group, cloir-rg so at this tirne rnight be premature. Although it is likell tlrat a second North Arnerican Latest Cretaceous species of Tyrannosaurus exisis, all of the specirnens in questions are in need of further preparation that rvill perrnit a more thorough conrparison ri'ith tl-re t1'pe (ANINH 973 =

CM

9380) and other referred specimens. Fortur-iateh', preparation of 2 of the specinrens (SDSM 12047 and Sarnson) is alreadv nnderrva\'. The ultimate disposition of Tyrarutosaurus "x" mav soon be resolied.

ls Nanotyrannus

lancensis a Juvenile Tyrannosaurus rex?

'fl-re genus Nanotrrannus r,vas erectecl bv Bakker et al. (1988) for the ti'pe specirnen (CN{NH 7541\ of Corgosaurus lancensis Gilmore (1946). This specirnen (fig. 8.8) consists of a relatir.,el,v cornplete skull preservecl with

the jau's

ir-r

occlusion, n'ith verl'little distortion and no associated postcra-

Lachrymal Length vs Lachrymal Foramina Length

Figure 8.7. Lachrymal

length vs. lachrymal foramina length.

lTcad2ool

-a

€9.r

15

Jo o4o '=

BHI 3033.

P35 L

o30

e

E.< o

tto*tta,,^....

aTMP 81.61

aBHt 4r@ MOR Ooe

Lachrymal Length

F;;-;t-la;;na t0B

Peter Larson

.

AMNI{ JO'.

nial rlaterial. Bakker et al. (i988) argtrecl tlrat certain derived cliaracters,

FinrrraRR

inciuding thc constnrction of the basicranium, the angle of the occipital

men of Nanotyrannus lancensis CMNH 7541 .

condvle, tlrc marillarl'tooth count, the over:r]l tootli morphologi,, tl-ie reiative narron,ness of tire snout,:rncl tl-re erpansion of the tenpor:il region of

the skull cleariv separatecl tl-ris specimen from other tvrannosaur clades (Gorgosaurtts, Albertosaurus, L) aspletosaurus, and Tl,rannosatLrus'). .\lthotrgh the characters discussecl bv Bakker et al. (1988) clearh., separated this specinren from its earlier assignnrent to ()orgosaurus, its distancc fron.r the T\,rannosaurtLs clacle seerned less clefined. Thev both "achieved the highest degree of potential stereoscopv kno\\'n among large theropods,"

and thel agree irr characters, inclucling the orientation of the occipital cor-rd11e (Bakkcr et al. 19EE, p. 25).'l.hev also acldress the question of the skull being that of a jur,enile : "The sutures betn'een the lachrl'n-ral and prefrontal have thoror-rghli.'coalesced inNanotyram?us,

as have

the sutures

beti,veen frontals and prefrontals. . . . Without question, the tvpe of Nano-

tyrannus ll'as fullr.aclult and had reached the urarirnilm size the individual rvould frave attainecl if it had lir ecl longer" (Bakker et al. I988, p. I7). Carpenter (1992, pp. 259, 260) disagreecl \\'ith Bakker et al. (l9BB) when he noted tl-rat "tl-rc coalescence of cranial bones is knoun to be r"ariable in dinosaurs" bringing ulrder suspicion "its Lrsabilitv to 'age"' dinosaurs. Carpenter furtlier noted that "the oval shape of the orbit" rnav rvell

\,ia.,aiion and Sexual Dimorphsm

109

Trrnacnaei-

be a juvenile character. He concluded that Nanof yrdnnus lancensis covld be a jur,'enile T. rer. Carr (1999) expanded this possibility. On the basis of 17 specirnens

referred to Albertosaurus libratus, Carr erected an ontogenetic series of (l-3). From bor-re texture, lack of fusion, shape of the orbit, and overall skull morphologr', Carr placed CMNH 7541 into his stage l, ihe voungest in his ontogenetic series. Carr then declared Nanotl,rannus Iancensis to be a juvenile T),rannosaurus rex.In later argurnents (Carr and Williamson 2004; Carr et al. 2005), this designation lr'as used io establisl-r gror'vth stages

a

grorvth series for

T

rex, establishing a sequence ofchanges

fron the srriall

juvenile LACN'I 28471, follorved b_v the juvenile CMNH 7541 (stage I), through sr-rbadults LACN{ 23845 and AMNH 5027, to the full1'grou'r-r adults LACNI 2)844 and FMNH PR208l (BHI 2013). Although Carr (1999) preser-rted a compelling and thoughtful argurnent, not ali paleontologists agree with his assessment. Currie (2003, p. 223) pointed out that "rnost of the characters used to demonstrate that Nanotyrannus and Tyrannosaurus are synonvmous are also characters of Tarbosaurus andDaspletosdurus." Bakker et al. (l9BB; personal comrnuuicatior-r) noted the discrepancl,' ir-r tooth cor-rnts- l5 maxillary teeth in Nanotyrannus and 1l or I2 ir-r TlrannosarLrus rex-and the lack of tooth recluction ontogeneticallt, in tire maxill:r of anv extant species. The primitive compressed n:rture of l\anotyrannus teeth (Bakker et al. 1988) as conpared u'ith the derived inflated teeth seen in T. rex and evidence of feeding behal'ior differences also argue for the ur-riqr,reness of CNIINH 7541 (Larson I999). Because the groli'th series argnment of Carr is rooted in the assumptior-r tlrat NanotyranntLs is a juvenil e T. rex, rnuch of Carr's concept of ontogenetic change and ontogenetic stages irt T\,rannosaurlts rex is in question (Jorn Humm, personal communication). I agree w'ith Carr and Williamson's (2004) assessment of LACN4 28471 (the so-callecl Jordan theropod)u,ith CN'INH 7541 (the tvpe of Ncnottrannus)), ar-rd u,ith the designation of the subadult LACM 2)845 asTyrannosaurtLs rer. Horvever, I disagree ',i'ith the subadult designation of AMNH 5027, which groups as a full adult r,r'ith TyrannosaurtLs "x" and rvith Nrcnotyrannus as a juvenile T rex. An isolated left lachrvn-ral (BHI 6235) comparable ir-r size and r-norphology to CMNH 7541 u,as found associated n'ith Sue (FNINH PRZOBI) and erroneously identified as a juvenile T. rex (L,arson 1997). It, too, should be referred to l\anotyrannus. Finall,v, the recent cliscoverv of a fourth specimen (BI,lR P2002.4.1) is clearl,v referable toNanotyrannus. Tl-ris specirnen, nicknarned Jane, in addition to many ur-rcnrshecl and w'ell-preserved skull elen-ients with a nearlv conplete der-rtition, also preserves much of the postcranial skeleton. Although this subject is discussed in cletail elsenl-rere (Cr-rrrie 2003; Currie et al. 2003; Larson in press), a list of characters separating Nanotyrannus fron'fyrannosaurus is presei'rted in Table 8.4. For pr,rrposes of comparison as outgroups, those characters are also listed for Tyrannosaurus " x," T arb ct s aur u s, C or go s auru s, a nd Alb e r to s aur u s.

110

Peter Larson

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stract of Papers, 58a. 2001 Paleopathologies in Tlrannos durus rex (in Japanese). Dino Press 5:

26-35. In press. 'fhe Case for Nanotlrannus. Black Hills InstiiLrte of Geological

Research. -. l,arson, P. L., and Donnan,

K. 2002. Rex Appeal: TIrc AmazingStort of Sue, the Dinosaur that Changed Science, the Law and NIt'Li/Z. Inr.'isible Cities Press, N4ontpelier, VT. Larson, P. L., and Frer', E. 1992. Sexual dinorphisrn in the abundant Lipper Cret:rceous theropod, Ty rannosaurus rer (abstract). l ourn al of \;ertebrate Paleontologt, Abstract of Papers, 38a. Lincoln, G. A. 1994.'l'eeth, horns and antlers: the rveapons of ser. P 131-159 in Short, R. \1, and Balaban, E. (eds.). The Differences between the Sexes. Can.rbridge Universitv Press, Cambridge. Lir.rder.rfors, P,'hrllberg, B. S., and Biu'"r', \1. 2002. Phr{ogenic analvses of sexual selection and semal size dimorphism in pir.rnipeds. Behavior, Ecology, Sociobiologr 52: 188-191. Lir.ezer', B. C., and Hurnphrev, P S. 1984. Sexual dimorphisrn in continental stearner-ducks. The Cooper Ornithological Societr'. Condor vezer..(86): 368_377.

N,lcGillivrav, \\l B., and Johnston, R. F. 1987. Differences in semal size dir.norphism, and bodv proportions betrveen adu]t ancl subadult house sparrous irr North Arlerica. 1987. Auft 104: 681-687. Macdonald, D. \\1. 1984. The Encwlopedia of Mamrnals. Facts on File, Nen York. N'lalonev, S. K., and Dauson, T. J. 1993. Sexual dirnorphism in basal rnetabolisrn and bodv temperatLrres of a large bird, the ernv. Condor (95): 1034-1037.

N{artin, L. A., Willner, L. A., and Dettling, A. 1991. The evolution of sexual size dinrorphisrn in primates. P. l;9-202, in Short, R. V., and Balaban, E. (eds.). The Differences between the Sexes. Canrbridge Unir,ersitv Press, Carnbridge.

Minasian, S. N,L, Balconib, K. C., III, ancl Foster, L. 1984.The \\/orlds \Yhales The Conplete lllustrated Gulde. Smithsonian Books, Wasl.rington, DC. N{olrrar, R. E. 1991.'l'he cranial rnorphologl ofTtrannosaurus rex. Palaeontographicia. Abteilutg A 217: 13,--176. 200; Selral selection and serual dirnorphisrn in theropods. P.27 /--283 in Carpenter, K. (cd.). The Carniyorous Dinosaurs.lndiana tlniversitv Press, - Bloornington. Norrnarr, N'I. D., Paul, l)., Finn, J., and Treger-r 2a,T. 2002. F irst encounter witir a live male blanket octopus: tlie u'orld's n-rost sexuallv size-dirrorphic large anirrral. New Zealand lournal of \,Iarine and Freshwater Research 36: i-33-736.

Osborn, H. F. 1905. Tt,rannosaurtrs rex and other Cretaceous carnir,orons dinosatrs. Arnerican Nluseun of Natural Histort, BtLlletin 21: 259-296. 1906. Tyrannosaurus ra.r, Upper Cretaceous camivores dinosaur (second cornmrrnication). Anrcrican Nluseum of Natural Histort, Bulletin 27:

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28t-296.

Parrl, G. S. 1988. Predatory- Dinosaurs of tlte\Yorld: .\Contplete Illustrated

Grrlde. Simon & Schuster. Neu,York.

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J. S. 1q9tt. Serual size dimorphisrn and parental care patterns in a rnononrorphic .rncl a clirnorphic Laricl. Aule 107: 760-271. Raath, NI. .\ 1990 \lorphological variation in snall theropods ancl it's n'reaning irr slstcnratics: eviclence fronr Slrzlarsu s rlndesiensis. P 91-105 in Carpenter, K., and Currie, P J. (eds.). Dinosaur Slsfenzcflcs: Approaclrcs and Per-

Quinn,

spectives. Canrbriclge LJniversitv Press, Canrbridge. Romer, A. S. 1966. \,'ertebrate Paleontologt. Universitl of Chicago Press, Chicago. Sanclercock, B. K. 1998. Assortive ruating ancl sexual size dimorphisrri in n'estern and semipalnratecl sanclpipers. Auft 11513): 786-791. Sato, 'll, Cheng, \'., \\11r, X.. Zelenitskv, D. K., ancl IIsiao, Y 200t. A pair of shelled eggs insicle a fenrale clinosaw. Science 308: 175. Schnell, G. D., Worthen. Cl. 1,., ancl Douglas. NI. E. 1985. Nlorphometric assessment of senral dinrorphisrn in skeletal elernents of California gulls. C'ondor 87:

484-491.

Schueitzer. \'1. H., Wittmerer. J. L.. ancl Horner, J. R. 2005. Gender-specific re prodtrctive tissue in ratites and Tt'rantrcsar-rus rex. Science 108:

1456-i+60. Schaaclt. C. P.. ancl Bird, D. NI. 1991. Ser-specific grou th in osprevs: the role of sexual size clirriorpirisrn. Auft 110: 900-910.

'lal'lor,'l-. G.

1970. Hon an egg shell is nrade. Scientific American 222(3): 88-95. Weltr,, T. C., ancl Baptista, L. 1988. The Life of Birds.4th ed. Saunders College Publications, F-ort \\/orth, 'fX. Winker, K., \/oelker, C. A., ancl Klicka, J. T. 1994. A morphometric exarnination of sexnal clinrorphisnr in the ll1/oplzilus,Xenops, ancl an Aulomolus fronr sotrtlrern \/eracruz, l\lexico. lotLrnttl of Field Ontitlrclog1,65(3): 307-323. Witrner, L. \,'1. 199t. 'l'he extant phrlogenetic bracket ancl the irnportance of reconstructing soft tissue in fossils. P l9-33 in Thonason, J. J. (ed.). Func tiotnl N'Iorphologl, in Yertebrate Paleorttologt. Canrbriclge LJniversitv Press,

Carrbridse.

128

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skull, which demonstrates a reciprocal relationship between cranium and jaw if one is peramorphic, the other is paedomorphic, and vice versa. Nofe that the main evolutionary trend is toward cranial enlargement (e ncepha I izati o n or a nten). After M cN a (1997). mara ri o ri zatio

130

Martin Lockley et al

WHY TYRANNOSAURUS REX HAD PUNY ARMS: AN INTEGRAL MORPHODYNAMIC SOLUTION TO A SIMPLE PUZZLE IN THEROPOD PALEOB IO LOGY Martin Lockley, Reiji Kukihara, and Laura Mitchell

Tl-re pnrpose of this chapter is to shorv that the reason Tyrannosaurus (and

lntroduction

Carnotaurus) had miniature arms may be surprisinglv simple as n'ell as consistent u'ith the broad rnorphological context of theropod and saurischian grorvth d\,namics ancl heterochrony. Inherent, or formal, morphodr,namic groli,th irends (sensu Gould 2002) lead to strong anteriorization (of the head) in derived, large (mainil' perarnorphic) members of varions theropod, saurischian, and dinosaur clades, as well as in other r,ertebrates. These seem to be of no obvious functional sigr-rificar-rce (sensu Gould 2002), ieading to il-re inference that we sl-roulcl pav more attention to these r-norphocll'narnic trends as part of the inherer-it structure of veriebrate organization. For example, in arnphibians (salarnanders ."'ersus frogs), pterosaurs (rhamphorvhnchoids \rersus pterodacty'loids), sauropodomorphs (pro-

sauropods versus brachiosar-rrs), orr-rithischians (primitive th-vreophorans versus derived ceratopsiar-rs), and primates (monkevs versus honirricl$, the latter (deril'ed) groups ahval's show more anteriorization (encephalization) than their prirritive relatir,es. There is also a compensatory reduction or loss

ofthe tail.

Liken'ise, in derived forms, tire inner (proximal) portions of the limb (fernora and hr,rmeri) are typicallv more developed than the distal portions. Tl-ris differentiation of proximal and distal limbs and feet or hands gives rise to diverse rnorphologies that have been interpreted as being of functional utilitl'-for exampie, grasping theropod hands or slashing raptor clarvs. However, such developrnental exaggeration or ernphasis in one organ or region of the bodv inevitabh,' results in underdevelopmer-rt in adjacent organs, as required bv the principle of corlpensation, also knou'n as heterocl-rronic trade-offs (sensu McNarnara 1997). Nlor,rnting er.,idence from evolution of development str-rdies (Carroll 2005)-populariy knorvn as evo-devo-suggests tirat organs must be looked at holistically (i.e., in the context of the rvhole bod,v) and that formal cler elopmental patterns and rr-rorphologies reiterate fractally and conr.ergelrih througl-rout the ',,ertebrate r'r,orld, and indeed in the biosphere in gene ral. T. rex is undoubtedlv one of tl-re most popular. iascinating, and controversial dinosar-rrs. Although iis iarge head and ferocious teeth have ob.",ious WhS

-.'=":saurus

rex Had Puny

Arms

lf grasping hands and long arms generally typify theropods, how does one explain the outrageously d i m i nutive forelimbs of Tyrannosaurus

andCarnotaurus....lt not at all clear why these animals indepen-

is

dently miniaturized their arms.

Fastovsky and Weishampel 2005, p. 283

131

ftrnctional rrse in fostering its repr-rtation as tlie king of the preclators (or an uncliscrinrinatirrg bone-crunching scavcnger or scavenger-predator), its tint' arn'rs star-rcl out as an Lrlrllsllal or anonalous rnorphological feature. Incleed, thc forelinbs are described as "outrageousll'climini-rtilc" bi'leading experts in the latest tertbooks (c.g., Iiastoi'skr.. ancl Weishantpel 200i, p 283). Cliven the prevalcnce offunctional explanations generatecl br,the Danvinian paradigrri (Goulcl 2002), it is not surprising that paleontologists have pondered the usc of such smali and apparentlv iestigial organs. A1though Darri inist-n tr.picallr, demands or at least prefe rs fur-rction:rl explanations, biologv gener:rllr' accepts that some organs arc llore functional than otl-iers, and the llsc of terms like vestigial acknonleclges the fact that function mav hal'e bccr.r lost or dimir-rished in some org:lns, as Paul (1988) inferred in the casc of tlrannosanrids. \\/e n'ill return to the specific case of T. rex forclinbs once \\'e iiave presented a broader contert in uLrich to develop our Llnderstanding of tl'reropod lirnbs. Functioniil argrlrncnts c:rn onh.take us so far because tl.rer,ignore inherent, intrinsic, or fornal grori'th ancl developn-rent. Hi'o-devo pronrises to gre:rtlr' subsrlrne and reorient the functional Daru inian paradignr. But evo-devo is not ne'"r,; it is rnerelv the rediscovert' of the sr-rbdisciplines of

heterochronl and rnorphocllnanics (Gould 1997; N{cNarrara I995, 1997) bi'biologists. This intrinsic, fomral approach has been knorvn for decacles, although undenrtilizecl, and can be traced as far back as Wolfgang Goethe ancl Ceoffror,Saint-IIilaire in the late 1700s ancl earlr'1800s (LeGLlader 2004). 'l'hese approaches are holistic and internallr'corrsistent, and, as current cxciterrent aboLrt evo-de\,o shon's, ther help denronstrate that n,e can reaci clevelopmental patten-rs in the fossil record, even though some biological (genetic :rnd nrolccular) er,'idence is not directli'available. We ner,'ertl-reless see the same patterns of rnorpliological erpression in :rncient and rnodern forms :rncl can thus unifr.,biologi'and paleontologv nore thoroughlr'. Incre:rsingll', it is possible to clemonstrate that these organizational trends or patterns repeat in manl groups in an ordered, lau.,ful n'av. 'l'he rnain thrust of this cliapter is therefore 2-fold. First, r,r,e rnakc the case that norpholog\,is not rrecess:.rri1r'cornpletelv or uholli erplicable ir-r terms of function because intrinsic growth clr,nanics, rihich Goulcl (2002) describes as forn'ral (and related to intrinsic generation of fonl), plav an irrportant role , as recclgnized bv stuclents of heterochronr' (NlcKinner.and \lcNarrara 1997; il.,lcNanrara 1997) and evo-clo,o (Carroll 2005). Second, an understancling of these formal dvnamics rer,eals that shifts in the tining or inorphological cler,elopment produces a cascade of cornpensating effects throughout the bodv so that if one organ gror.r's large, one or nrore adjacent organs u.,ill be reducecl in size and vice versa.

We arguc that T rer and other tvrannosar-rrids had srrall forclirnbs because thev had such large heacls-or nrorc accnr:rtelr', ne stress the nrorphodr,nan-ric cornpensation bet\\,een heacl ancl forelirr-rbs. 'l'hus, anterior grou th blpassecl other anterior orgalls :urd concentrate cl in the heac1. This is in contrast to the patterns observed in other relatecl theropod dinosaurs (cocluros:rurs), snch as tlic ornitliornirnicls, n'hich dereloped lorrg front

linbs and necks but hacl snrall 132

Martin Lockley et al.

heacls.

In such anirnals, anterior gron'th

concentrated in the forelimbs and neck (as n e ll as the anterior organs), but ner.'er becarne exaggerated in the head. Strpport for such a h1'potl-resis rs derived from an overvier,r,of recurrent morphological trends in the Theropoda as a rvl-role, and in the Saurischian clade to ri'hich thel'belong. Fractal or recursive trends mean that thev repeat at different le','els or scales of organization rvith similar br-rt not identical patterns (see Bird 2004 for definrtions). For example, as noted below, in manv tl-ieropods, includingT. rex, short forelin-ibs are associated lr'ith relaiively'long hind limbs. As poir-rted out bl'Locklel'and Kukihara (2005) and Locklev (in press), dimorphisrn in tl-re r,r'ell-knorvn dinosaur Coelophtsis reveals similar compensatior-rs (srnall forelimbs = large head, and large forelirnbs = small head) at the species level. (There is also a patten-i of compensation betrveen large forelirnbs and sn-rali hind limb, or vice versa, and corresponding cornpensations throughout the rvhole bod1,'.) 'fhese are larvful in the sense that the1, can be shown to recur fractallv at man.", differer-rt taxonornic levels ivithin the r,ertebrates, and so nust represent sone inherent pattern of biological organization. For exarnple, just as tl-rere is a polaritv betn'eer-r the 2 Coelopliysis dirrorphs or the primitive and derir"ed coehrrosaurs (ornithomirnids versus derived tvrannosaurs), so too there is a similar polaritv betneen prinritive and derived ceratosaurs (e.g., Coelophysis versus CantotatLrusi). In tlre latter case, the convergence betrveen Carnotaurus and T re.r in respect to forelirrb-head compensatior-rs is striking. We argtre that tl-re implications of this rnorphodl'namic approach are far-reaching. For exanple, it has long been knor.r'n that theropods had their hands free, trnlike other clinosaurs, and so rvere not o\rerspecialized or committed to qr,radrupedal locoi.r-rotion, like most other dinosaurs ancl the maiority of terrestrial vertebrates. How,ever, rve take this argument further b)'strggestir-rg that not onh' did the anterior limbs of tiieropods der.'elop phvsical fexibilitr., lrfiich in turn helps support a phvsical or bionechanical connectior-i lr'ith n'ing der,'elopment in birds, but also a close relationship existed betrveen the respiratorv svstent as an anterior organ and the anterior lirnbs. Thr-rs, it is inportant to think in terms of hor.v the aforernentioned morphod1'r-iamic der,elopment in lirrbs, neck, or head is closel,v integrated r,vith de-

velopment of ph1'siological svstel-ns like respiration. \\'e knori' that marn' theropods (coeiurosaurs and oviraptos:mrs) and birds hacl a fundarrentalli inportant relationship with the air (i.e., air sacs, feathers, wings, and fliglit), and we argue that this represents an emphasis on the anterior part of the middle s\,stem (pulmonarv svstem, anterior torso, and forelimbs). For example, Carrano and O'Connor (2005) describe the vertebrae and srnall ribs of the neck region of Ontitlrcmimus as being perforated bv the pulrnonarv svsteilr, although in larger, nrore peranlorphic theropods, like Tyrannosaurus ancl Carnotaurus, sor-natic grou'th eviclentlv bvpassecl the forelimbs and u,as concentrated in the head. These large forrns also frequentl,v developed extensive pneun-raticitr,-not just in the neck region, but often throughout the rl,hole bodv (Xu et al. 2004). The same pattern is seen rnost rnodern birds. Thus, small birds rra,v shon' less pneumaticitv than large ones. This is not directlv correlated \\'ith flight because some large birds, such as the ostrich, are flightless. Therefore, one n'iight argue that rn thc larger theropods, as rs Why T.lratr osaurus rex Had Puny

Arms

133

the case in large birds, the nfiole boclr hacl become like an enlargecl hu-rg. Feathers are also a llleans of incorporating air ri'ithin the boundaries of the phl,sical bodr. One rriight argr-re, therefore, that feathered forrrs n'ith little skeletal pnetrrnaticitv ha','e a nrore outnard relationstrip ilith the air than large forrris u,itl-r rvell-cler,elopecl internal pneum:rticitv but no feathers. Agairr. llris is arr erarrrple of corrrpcrrsrrliort. Before preser-rting the data that support these morphological comparrsons and inferences, it is necessarr,to outlirie the morphodl'nanic paradignr and its stronglv heterochronic flavor.

The

T\l'o generations before Darri,in introchrcecl the concept of natural selectior-r, u'ith all its functional inrplications, the German founders of moclern biologr', incluclir-rg Goetl-re, n'l'ro introduced the term morphologt, thought in terms of dvn:rnic processes. The recent introduction into the English langtrage of the verb to morph emphasizes both this dvnarnic connotation ancl tlre resLrrsence of strch process thinking. (fhe OxfordEnglishDictionary defines this verb as to "change srnoothlv and gracluallv from one image to another.") hrterestir-rglr', this trsage is intirnatel-v associatecl n'ith the drnanic field of anirnation. 'l'his clvn:rrnism contrasts n'ith the mincl-set of

Morphodynamic Paradigm

spatial coordinates, rneasurements, and discrete character attribr-ites associatecl

lr'ith n:rnr, tarononric, anatorrical, nrorphornetric, and cladistic

ap-

proaches that follon,ecl. Although these are ali useful to varving degrees, rnanr,of the contributior-rs of the carlv Gerrnan biologists (e.g., Coetl're and Ernest Haeckel) n'ere often oi'erlooked li'hiie attention r',,as directed to tl-re u'eli-established tradition of monographic description of anatoml' for clas-

sification purposes. In effect, our concept of rrorphologv becarre frozen, and species vn'ere mostl'n' described on the basis of adult forms that representccl tl-re final n-ranifestation of thc dvnamic proccss of ontogenr.. Such cataloging, althorrgh important, has sometines been characterized as rnere st:rmp collecting, ancl it shifts our mind-set au'ar,'from tlie dt,namic, org:rnic process. In the contert of the dvnamic nature of the gron'th process, this charge is r.rot n'l-rollv ur-rjustified. For exarnple, as notecl by Arthur (2006), onlr,a feri, 20th-centun,biologists r,r'orking betvn,een 1900 and 1975 u'ere realh' focused on thc cl1'namic relationships betr.r'een evolution and dei.'elopn-rent; among these u'ere Juliar-r Huxlel', Cavin de Beer (1940), and Dl{rct,Thorrpson, ri'hose classic On Crowth and Form (1917) has been cited as an exarrple of "the tlieorl of transforrnations" (Arthur 2006, p. 401) dealing u'ith the tvpes of macronrorphological clr,r-ran-rics n,e discnss here. Hori.'ever, despite the freezing of tire concept of morphologr.', lvhich ivas originallr,' closelv allied to the cll'namic concepts of rretamorphosis ancl transmutation (the latter:rn e arlr' 19th-centnrv svnonvm for evohrtion), Gernran biologists sucir as Hacckel (li,ho coined the term biology) \\'ere at the forefront of embri,ological rescarcir, thus maintaining a foctrs on cltnamic processes. Haeckel (1866) also coined the term heterochrony, and he developed the famous biogenetic lzrr','that "ontogenv rccapitulates phr. logenr." 'l'hus, an anteriorization trend (P-A) in ontogenv m:rv parallel one in phr logenr (as seen inTrrannosaunrs; see belou). Despite the shortcom1)/

Martin Lockley et al.

ings in this lan' if taken too literallr', its general relevance in linking indir,idual clevelopment and evolution has rrerit. hrdccd, the recent emergence of the evo-cievo field is in itself stror-rg validation of the rener,ed interest in this approach (Arthur 2006). There are even clairrs of a reverse biogenetic

law'(Suchantke 1995), u'hich can be characterized as er reverse rnorphodr nanic moverrient (i.e., an anterior-posterior [A-P] tiend in one organ mav be compensated for br,a P-A trend in another). What is of fr-rr-rdanental importar-ice here is to note tl-rat heterocl-rrorr-v is not some specialized branch of biologv. Indeed, a compelling case can be made that it is essentiallv a svnonym of the original dvnarric concept of morphological dei,elopment as process, which emphasizes the highil,' organic natllre of changing or morphing of anatorn, through time. Nloreover, the dir-ramic processes are driven b1, internal oniogenetic forces. Although such dvnamics nere recognized in the biometric sense b1' such concepts as allornetrl'or nonlinear gror.r'th, thev ha.,'e been overlooked bt,the Darrvinian notion that the organism is too rnuch under the spell of external influences tl-iat force it to passiveh,adapt to the environmer-rt. Gould (2002) clearl.,, recognized the difference betu'een the forn-rer intrinsrc

Coethean (or forrnal) perspectir,e of the Gern-ranic school and tl.re latter extrinsic Darr,r'iniar-r (or functional) perspective of the English school. It is onlv noli,'that the Darri'inian and neo-Darq,'inian (genetic) paradign-r l-ras been explored to the poini t'here deficiencies in ftrnctional explanatiorrs are evident that the intrinsic or formal paraclign-r is cornir-rg back intcr voglre arnong rnainstreanr biologists. Ccnetics, in its earlv davs, ain-red to support the selectionist Darwinian paradigm br,using mathematical populatior-r-base cl st:rtistical rnodels (harking back to l9th-centurv social Darn,inisn-r and Malthus's icleas of populations competir-rg for scare resources). Ironicallr, nrodern cleveloprrental genetics ancl er.o-devo nou. inforn ns that form and species dii,ersit)'is generated bi'ir-rternal processes tl'iat are most

d','nanic and complex in the verv earlv formative stages of ontoger-ry. Put sin'rplv, focus has shifted from the paracligm of a passi.,.e Darr,','inian organism, pushed around bv the erternal environrnent and competing to snrvive bl.functioning properll', to an active rrodel of clvnamic organisms generating form throtrgh complex internal or fornal organization. Despite tl-re prer,'ior,rs strong focus of nainstrearr biologl' and evolutionarv studies on Daru'inian selection paradigrrs, a number of norkers have kept alternative perspectives alive. Anorrg the rnost relevant studies are those that have explored the cl1'namics of heteroclironv (Goulcl 1977; N{cKinnev and il,IcNan-rara l99l; N{cNanara 1997). The latter studv introcluced the irnportant concept of l'reterochronic trade-offs that are, in fact, basicallv a st'nonvm of thc compensation principle ir-rtrocluced by Goethe (1795). This principle essentiailr' tells us that no organ can develop rvitl-rout a reciprocal effect on an adjacent organ. N'lcNanara (1997) gives the exceilent example of the tracle-off betrveen the large hunan craniurrr and srnall jari'ancl contrasts it rvith the opposite oi reciprocal case of the srrall craniurn and large jan', as seen in the chirrp or certain primitive honrinicls (Fig. 9.1). In such a case, the larger organ is peramorphic (exhibiting ntore grou'th) ancl the srraller one is paedomorphic (erhibiting less grori th). It seems that sucl'r Wht f\'a'.csaurus rex Had Puny

Arms

135

cornpensations are follnd universaill'throughout the organic w'orld and thai they are an integral factor in the evolutionarv process. In this regard, lve may r-rote the recent resnrgence of interest ir-r the work of Geoffrov Saint-Hilaire (l8ZZ). Endorserrents b1'Thoni (1975), Gould (1985), DeRobertis and Sasai (1996), and LeCuyader (2004), among others, ciearly demonstrate Saint-Hilaire's profound understanding of ir-rtegrated organization in organic s1'stems as early as the 1790s. Thus, Saint-Hilarre recognized and endorsed Goethe's compensation principle, which he called tl-re "lau' of balancement of organs," and tried to encourage French anatomists such as George Cuvier to understand its fr-rndamental in-iportance and pa,v more attention to the higher level of biological tl-rinking going on rn Cermanv (Lenoir 1987). Despite ihe rejection of ihis svstem of thinking bi, Cuvier and later by n-rost Darr.vinians, rvl-io labeled the school "transcendenial Nature Philosophv," Saint-Hilaire has been proved right in his thesis that ail organisn-rs displav a fundanental unitv of compositiorr and unitv of organization. Thus, he realized that clifferences in rnorphologl'between organisms r,vere only superficial and the result of different ernphasis of organs durir-rg cleielopment. 'fhis is essentiall,v the central message of heterochrony; whicl-r is still paid too little attention todav. Saint-Hilaire give explicit examples of differential development, noting ihat if a bone did not del'elop in one species, it could be shorvn to l-rave been arrested at an earlv stage, when it r,vas

still tissue or cartilage. N{ore pertinent to the present stucll; Saint-Hiiaire noted that bod1, plans repeat again and again in what todav rve u'ould call a recursive or fractal pattern, lvhich he variouslv called "r-rnity of organization," "unit,v of plan," and "unitv of cornposition." Thus, rvhen "der.elopmer-rtal genetics . . . arrived on the scene like a thunderbolt" (LeGu1'ader 2004, p.244), it became clear that horneotic genes (Hox genes) of the homeobox shorved the same A-P or-

ganization as the macrornorphologl'-exactly as Sair-rt-Hilaire frequentl,v noted in his principle of connections (or theorv of analogues). This is norv call,ed colinearily (Duboule and N{orata i994). It is outside the scope of this chapter to delve further into Saint-Hilaire's prescient observations, except to note that his claim that arthropods lvere organized like upside-down vertebrates, although long scornecl bv Cuvier and many subsequent generations

of ar-ratornists, has been shoun to be genetically correct: that is, "tu'o major

directions . . . the that r.vith dorsal expression in the vertebrate and vice versa!" (LeGuvader 2004, p. 252). The r-nessage is tl-rat it is dangerous to dismiss prescient holistic thinkers because their ideas are perceived to be too general, too complex, not obviouslv applicable to specific cases' or otheni,'ise hard to follow. Sair-it-Hilaire, like his contemgenes have been discovered rvhich intervene in antagonistic

insectt gene ivith ventrai expression is the

san-re as

porarv Goethe, lvould have been quite at hon-re discussing the compensation principle, antagor-iistic genes, and tl-re balancernent of orgar-rs n'itl-r an1'or-re versed in modern heterochronic and developmental studies. Like modern students of heterochrony (McNaniara, personal communication), Goethe and Saint-Hilaire n'ould likely have been surprised to learn that developmental genetics claims that rnar-n'of these insights are new in prir-rciple, r.vhen in fact such insights were around at tl-re birth of biologr', and since then, devel-

136

Martin Lackley et al.

opmental genetics has beer-r n-rostly concerned n'ith rediscoverv of these principles and explar-ration of details and mechanrsms. 'i'he fuller potential of such approaches is brilliantll'realized in tl're lr,ork of Schad (1977) on Man and Mammals, n,hich u,as brieflv strmmarized bv Riegr-rer (1985, l99B) ar-rd Locklev (1999a) and applied to dinosaurs (Lockley 1999a, 1999b,2001, in press). In these and a few other related str-rdies, the tern morphodttnamics has been introduced partly as a rreans of redvnarnizing the concept of morphology so as to reflect its original process meaning, but also as a convenient n'ay of stressing that there are morphodi/namic trends in the evolution of varior-rs clades, such as increasing anterior or posterior developnental emphasis. These cephalo-caudal or caudo-cephalic trends have been known for many years, and a substantial literature on the topic exists, especiail,v in the field of phvsical anthropology (Kingsbun' 1924; Verhulst 2003). In recent years, developrnental microbiologl'has been ror-rtinelv preoccupied with horv A-P axes and polarities develop (e.g., Wallenfarrd and Se1dorrr 20007. Possibl-v the best-known and most obvior:s example of a recursive anteriorization trend is that referred to as cephalizctiorz, lvhich is seen in vertebrate clades and in vertebrates ir-r general (Fig. 9.1). Other examples include the polaritv betneen prirnitive arnphibian organization, as seen in tl-re salamander morphotvpe (characterized by a long tail and small head), and frog morphology (large head and no tail). Everl'schoolchild knows the stori' of tadpole-frog metamorphosis. Liker,vise, we see the same trends u-i prirnates (from monkevs to hominids). The sarne trend is also obvious ir-r many dinosaur clades such as ceratopsians, and here \ve point to the reiteration of the trend in theropods. Such anteriorization trends can generalll' be classed as correlated progressions, i,vhich refer to the reiteration of directional trends in evolution that follorv repeated or fractal variations on a theme (sensu Kemp 1999). This concept is essentially sirnilar to the concept of colinearitl, (LeGuvader 2004). Schad's genius u,as to recognize that the expression of ph1,'sical exaggera-

tion of anterior or posterior organs in anr animal (man-rrnals in his

1977

studv) rnust be seen as onl,v one side of a compensatorv relationship w'ith phvsiological processes. Phr.'siologically, for example, r-rngulates (r,vhich are predominar-rtlr,'large, placid, longJived, derived, and evoiutionarilv specialized) have rvell-developed posterior digestive (or metabolic) slstems (rnultrcharnbered stomacir) ancl iimbs designed for sustained (long distance) loco-

rrotor efficienc\,. Horvever, the main ph1'sical exaggeration is seen in the anterior regions (horns, shoulders, manes, bearcls, front limbs ofter-r larger than hir-rcl). In striking contrast, the predominantly small and evoh,rtionarill unspecializecl rodents shou'tl-ie opposite, or reciprocal phvsical and phvsiological organizatior-r. They are phl'siologicallv dominated (anteriorly) b1' overactive sensorv and nervous svstems (sense-ne1,e en'iphasis) ancl are behavior-

allv frenetic and shortlived, u'ith u'eak, lon.endurance lirnbs, but

they

express their rnaxirnurn or exaggerated ph1'sical clevelopment in the posierior part of the body (long tail and hind limbs longer than front limbs). The carnivores represent a middle or central gror-rp (trpicalh intermediate in size),

in

r,r4rich the anterior and posterior physical and phrsiological svsterns are

Why fyra^rcsaurus rex Had Puny

Arms

137

Ftgure 9.2. A holistic viev. of 3 major groups of placental mammals (after Schad 1997; Lockley t999a). The rodents, carnivores, and ungulates express d if fe re nt e m p h a sis of the physiological organ systems, i.e., uPr alvr d^^1,-)/ )L//

,

coideus intermedius; sl, M. su p racoracoid eus I on gus, tbi, M. triceps brevis

intermedius; tll, M. triceps longus lateralis; tm, M. terres major. Termi-

nology adapted from Meers (2003).

182

Christine ..pL :n

2nj

Kenneth Carpenter

In this sectior-r, rve do a reanalvsis of Carpenter and Sn-rith (2001)

ar-rd an extensiorr of the biornechanical properties of the forelimb tn TyrarLnosaurus rex based rnostll'on FMNH PR208l. hr order to rvork out the forces

acting on the forelirnb, rve start by n-rodeling the forelirnb as a third-class lever (Fig. I0.16). In a tl-rird-class lever, the effort force (N{. biceps rnuscle) is applied betu'eer-i the fulcrr-im (elborv foint) and the resistance force. The elbor,l' joint is a hinge rvhere the humerus, ulna, ancl radius articulate. Of all of the nuscles coordinating and controlling the rrol'ement of the elbolr,, the M. biceps is the rnost powerful flexor of the elbou' joint (Ozkar,a and Nordin 1999). Our moclel assumes tl-rat the M. biceps is the rnajor ffexor ar-rd tl-rat the line of action (the tension) at the biceps is vertical. Anatomical ineasurements were used to derir,e the motive force arn (MFA) and the resistive force arn-i (RFA) (Table 10.1). For the ulna, the N{FA was r-neasured from the signoid notch to the rnidscar of the insertion pornt for the M. biceps (n'rotive force, MF), and the RFA lr'as derived from rneasuring the ulna frorn the sigmoicl r-rotch to the clistal end (F-ig. 10.16). To obtain ihe MIrA of the radius. we measured from the radial head to the rridscar of the insertion point for the M. biceps and frorr-i the radiai head to the distal end to determine the RFA. A tenclor-r ter-rsile strength of I00 MPa, the global n-rear-r across all species, was used to estimate the tendon tensile strengtl1inTl,Tannssaurus (Nigg and

Herzog 1999). The safetv factors in tire values of bird tendons range from i.19 to 4.10 (Van Snik et al. 1994;Alexander 19Bl). A safetv factor of 3 n,ill be used ir-r this studl'. The normal working range (NWR) is one-third the safetv factor (Carpenter and Smith 2001). Although the size, sl-rape, ar-rd tl-re biomechanical behavior of each tendon differs, the basic structure of tendons and tl-reir rnechanical properties are sin-rilar (Jdzsa and Kannus 1997). The size of the cross-sectional area ofa tendon is clirectlv related io the size ofthe load that can be carried before failure (Butler ei al. 1978). 'fhe srrrface area of the scar for the insertion of the \,1. biceps rs 122.11 mn-rr on the radius and 192 nmz on the uh-ra. The conversion for the tendon strength, expressed as MPa, is I MPa = 1,000,000 Pa, u.'ith l Pa = I N/mr. Therefore, I NIPa = I N/rnmr. The maximum i,vorkir-rg range (N{WR) and the NWR are calculated from the tensile sirength of the tendon.'fhe formula for estirnated tendon tensile strength is as foliows:

tendon tensile strength/area2 x surface area of the scar for insertion of the M. biceps = estimated tendon tensile strength

Biomechanical Analysis of the Forelimb in Tyrannosaurus rex

Elbow

Figure 10.1 6. Free-body diagram (sinplified model) of the forelimb of FMNH PR2081. Abbreviations: MF, motive force; MFA, motive force arm,' RF, resistive force; RFA, resistive force arm.

(1)

Tendon tensile strengih for the radius is 100 N/mm2

x

122.11 mm2

where NIIWR is 12,211 N/3 = 4070 N, and

= 12,211 N

N\\'R

is 4070

N/l = 1357 N

Tenclon tensile strensth for the uina is:

100 N/mm2

x

192 mm2

= 19,200 t

N

ooking Agarn at the Foreltmb

183

Table 10.1 . Power Analysis

Measurements

Measurement

Radi us

Ulna

MFA

15.2 mm (0.0152 m)

45.8 mm (0.0458 m)

RFA

166 2 mm (0.166 m)

186.6 mm (0.187 m)

MANUS

177.6 mm (0.178 m)

171.6 mm (0.178 m)

343.8 mm (0.344 m)

364.2 mm (0.36a m)

Abbreviations.-MFA, motive force arm; RFA, resistive force arm.

RFA

including manus

rvhere N{WR is 19,200 N/3 = 6400 N, and NWR is 6400 N/3 = 2lll N. 'fhe values for the MWR and NWR represent the estimatecl strengtir of the iei-rdon at the insertion of the NI. biceps and are ttsecl as the NIF in the analvsis of the poiver of Ihe TyT6lnnosdurus forelirnbs. Tl-re follolving equations are nsed to estimate the amount of force the arrn of Tyrannosau' rus can resist (resistive force, or RF):

MFxMFA=T

(2)

RFxRFA=T

1?)

Measurement of the Inanlls (177.6 rnm) n'as taken front a cast of to tl're prorimal end 2081, from the proximal end of the "r'rist of the claws. It n,as then aclded to the RFA (166.2 nm).

FNINH PR

N{WR for the radius of

T

re.r is as follorvs:

4,010 N x 0.0152m= 61.86 Nm RFx0.1418m=61.86Nm RF = 179.91 N (or 18.36 kg) NWR for the radius of T. rex is as follo"vs: 1,357 N x 0.0152 m = 20.63 Nm

RFx0.3438m=20.63Nm RF

MWR for the uina of T

= 60.0'1 N (or 6.12

kg)

rex is as foliou's,

6,400 N x 0.0458 m = 293.12 Nm

RFx0.3642m=293.12Nm F = 804.83 N (or 82.13 kg) NWR for the ulna of T. rex is as follou,s: 2,133 N x 0.0458 m = 97.69 Nm

RFx0.3642m=97.69Nm RF

= 268.23 N (or 27.37 kg)

Adding the resistive forces of the radius and ulna results in 984.76 N \4WR (no safetv factor) ancl 318.24 N

(100.49 kg or 221.10 por-rnds) for the

Christine Lipkin and Kenneth Carpenter

(13.a9 kg or 77.70 pounds) for the NWR (u,ith safetv factor). The conversion factor for kilograrrs to ner,r'tons is 1 kg = 9.8 N.'l'hese results are sunrrarized

in Table 10.2. An a','erage strength of

5 kg/cm2 per cross-sectional area of muscle u'as deterrnine the cross-sectional area of the M. biceps in TNrannosaurus (Carpenter and Smith 2001). The NWR of the tendon tensile strength for the

rrsecl to

and ulna nere added together to get the MF: 1357 N + 2lll N = +490 'l'he formula used to determine the cross-sectional area of rruscle is N,{F (kg)Atrength (kg x cni t) = ctoss-sectional area (cnr). Thus, radir-rs

N

(356.12 kg).

the estirrated cross section of theT\,rannosduruE M. biceps is 356.12 kg/5 kg x cnr I = 71.224 crrf . 'fhis translate s into a diameter of 9.52 crn. Of course the N'1. biceps is r-rot the onh'arrn protractor. In fact, b\,r,rsing half the estirnated cross-sectional area of the upper arn-r (based on a diameter of 2j cni), the arriount offorce generated is estimated to have been around l l 50 kg, or I 1,270 N. Of this, the biceps generated aboti40%, and tl-ius'"r,as a major muscle.

A small lever arn'i requires greater nuscle tension to balance a load. Therefore, n'hile resistir-rg pre\,or holding prer; it is clisadvantageous to ha'u'e a rruscle attacl.rment close to tl-re elbon' joint. The advantage to having the rruscle attachment close to elborv joint is that it il,ill have a larger range of motion of

Mechanical Analysis of the Forelimb in Tyrannosaurus rex

tl're elbon flcxion-extension. and therefore the hand can nrove faster toward

the upper arm or sl'roulder (Ozkar,'a and Nordir 1999). 'I'he rnechanical advantage is the amount of force a given effort can procluce. It can be expressed as a ratio ofthe resistive force to the N{F, or as a ratio of tlie NIFA to the RFA (Kreighbaum and Barthels 1985). Both of the equatior-rs produce the sarr-ie result.

TheTtrannosrzurus forelimb is found to have a n-iechanical advantage of the 0.09 (RFA rneasurenrent including the hand) ar-rd 0.18 (RFA measurenent excluding the hand). The rlechanical advantage of a humarr forcarm is 0.07 (RFA n-reasurernent inclucling the hancl) ar-rd 0.13 (RFA measurement cxcluding the hand). Next n'e er,aluate the force at the elborv joint. The sum of the tr{Fs (NWR + \'l\\1R) at the radius (138.3 kg) and the ulna (217.5 kg) rninus the RF'at the rranus (33.5 kg) nust equal the force at the elbou'for a static con'|38.3 fiqrrratiort. I lrcrefore, T1'ranrtosaurus has a force of + 2l-.; - 33.; = joint liZ.lUgat the elbor.r, for the NWR. This cornpares with a force of about 128.25 kg at tl-ie elbo'nv joint of an average adult rnale human for the NWR.

RF

Table 10.2. Power Analy-

(kg)

sis

Range

Radius

U Ina

Combined

MWR

18.36

82.13

100.49

NWR

6.12

27.37

33.49

Summary

Abbreviations.-RF, resistive force; MWR, maximum workrng range; NWR, normal working range.

Lccking Again at the Foreltmb

185

Acceleration

Frorn the torcpre of the forearrn, the force that could be applied at the manus and the resultant force at the elbou joint ri'erc determined. Wc non estimate the acceleration that could be generated at the clan's using the nontent of irrertia. The fleshed-out versiorr of ihe arm olTl,rannosaurus (Figs. 10.1510.17) rvas converted to a closeh'packecl series of elliptical o'linclers.'l'he cross sections of each

elliptical o'linder nere deterrnined from Figure

10.15.

Assurnir-rg a clensitv of 1000 kg/n'r: for tissue, t}'re dat:r frorn these o'linders resr-rlt ir-r a mass of 1.8 kg for the fore arm plus nlanrls. The integral of the densitr'

times the perpendicular distance to thc pii'ot point results in a moment of inertia of 0.06 kg mr. Becar-rse the \\\rR torquc of thc forcarnr and I'rand to be 118.J Nm, the angular acceleration (torclr-re divided bv the morncnt of incrtia) is l98l s 2. Tl-re angular acceleration can be conr.'ertecl to a linear acceleratior-r bv rriultiplving it b1'the distance (0.154 m) frorn the pivot point to the clan's, n'hich results in a linear acceleration of 702 nis r. This is likeh' an ot'erestimate because the skin and the clat'sl-reatli are not factored in. Aiso, this onlv gives the initial acceieration. The force fiom uruscles is krton'n to rapidlv recluce at high speeds

Conclusions

(Hill

1938).

As rve have shou n, the forearm of Tvrannosaurus \\'as capable of resisting large forces and rnor,ing at high accelerations. These results strcr-igthen the hvpotl-resis that the forelimbs n'crc ttsed during predatior-r. Hon,cver, because of the small size of the forelimb relative to the bodi'size, it is unlikeh that the T\'rannosaurtLs lr'oulcl use the nranlls for striking pre\', as discussed in Carpenter (2002). Rather, thc forelimbs mar'have been usecl to cling to pre\,. Our results of finding large fcrrces at the elbou' joint and possible signs

of injr-rn at the furcula fr,rrther support tltis l-n'pothcsis. Fir-ralli', in contrast to the belief of l,ocklev et irl. ttl-ris volun-rc) that "no usefrrl ftrnction is plausible" to explain the forelirrb of 'It,rctnno"aurus, our results support the prer,'ious assertion tiiat tlie forclin-rb plavcd a functional role in predation. Bv iniplication, the short forelinrbs of other tl.rannosau-

Figure 10.17. A 3-D representation of the forearm and manus in the

Tyrannosaurus rex FMNH PR2081. In (A)

lateral, (B) anterior, and (C) reaching views.

186

Chilsilne Ltpktn and Kenneth Carpenter

100%

radius

90%

Figure 10.1 8. Compailson of forelimb length to

70%

hind limb length shows that a progressive reduction in forelimb length does not occur in the

6s%

Abbreviations; Gu,

humerus

80%

Tyrannosauridae.

Guanlong (basal 50%

tyrannosauroid); Go,

40o/o

Gorgosaurus; Da, Daspletosaurus; Ab,

Albertosaurus;

30%

T,

Tyrannosaurus.

20% 10% 0%

Gu age {mya)3 -156

Go

-75

Go

*75

Da

Ab

T

-75

-72

-66

rids had a similar function. In strpport of this, n,e note that a progressir,'e reduction in tl-re forelinb does not occur in tl're Ti'rannosauridae (Fig. 10.18), contrarv to Paul (1988; and l,ockler et al. (this l'olurre). In point of fact, once the shortened forelirrb of the tvrannosar-rrids ivas established, it remained proportionallr stable relative to hindlimb length.

We are honclred to contribute to this r.olume. and n'e thank Neal Larsorr and Peter Larson for the organization of the sl,rrposiurr that preceded it.

Acknowledgments

We are indebted to Bill Sin'ipson and Peter \'{akor,ickr.,for access to ITN4NH PR 2081. and C.L. rvotricl like to thank Paul Sereno for access to the cast of FN,{NII PR 2081, ar-rcl N{icl-rael Benton, Paul Sereno, Gordon, }iirgen Kriu,et, Simon Braddt', Lorrie NlcWhinner', ancl Don Henderson for helpful discussions. K.C. tlianks fohn Daggett, Bill Sirrpson, and Pcter Larson for loans of specin-rens or casts, and N{att Srriith for our previons joint r,r'ork

onT. rex forelinb analvsis. C'l'scans are br.Steven White, Kaiser Perrnanente, Denr,er.

Alerander, R. \{cN. 19E1. I,irctors of safetr,in the structLrre of anirnals. Science

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188

Christine Lipkin and Kenneth Carpenter

Jenkins, l'. A., Dial, K. P, and Goslou,, G. E. 193 .\ cineradiographic anallsis ofbird flight: the u,ishbone in starlings is a spring. Science 241: 1495-1498. Jizsa, L. G., and Kannus, P 1997. HurnanTendorts: Anatomy, Ph,-skiog1,, and Pathologt' Hur.uan Kinetics, Champaign, I1,. Kreighbarrm, E., and Barthels, K. \,1. 1985. Bictmechanics: AQualitative Approaclt for Stur/r,ing HtLman Moyernent. Burgess Publishing, Minneapolis, N,lN. Lar-rrbe, L. N'1. 1917. The Cretaceous Tlrcropodous Dinosaur Corgosaurus. Ceological Survev of Car.rada Nlemoir 100. I.,arson, P, arrcl Rigbr, J. K. 2005. Furcula of Tyrannosaurus rex. P.247*255 in Carpenter, K. (ed.). The Carnivorous Dinosaurs.lndiana Universitv Press, Bloonringtor-r.

l,ingham-Soliar, T. 1998. Guess uho's corring to dinner: a portrait of Ttrannosdu,"us as a predator. Ceology Today 14: L6-70. Lipkin, C., and Sereno, P. C. 2004. The furcula inTyrannosaurus rex. lounul of Vertebrate Pale ontolo 91, 2'l( Suppl. to 3) : 83A. Nlakovickr,, P, and Currie, P J. 1998. The presence of a furcula in tvrannosaurid theropods, and its phl,logenetic and functional irnplications. lournal ofYertebrate Paleontologv 18: 143-119. Meers, N{. B.2002. Nlaximnm bite force :rnd prev size ofTyrannosaunts rex and their relatiorrships io the inference of feeding behar.'ior. Historical Biology 16:

llz.

Crocodvlian forelin-rb nusculatnre and its relevance to Archosar.ria. Anatomical Record Part A. 274A: 891-916 -. \'{olnar, R. E. 1998. N'{echanical factors in the design of the skull ofT,rrannosar-Lrus rex (Osborn, 1905). P 193-218 in P6rez-N.'loreno, B. P., Holtz, T. J., Sanz, J. L., ar.rd N{oratalla, J. (eds.). Aspects of Theropod Paleobiology.

Caia: Ret,ista de

Ceociencias, Museu Nacictrtal de Historia Natural, Lishon, 15.

Nigg, B. N., and Herzog,

W

1999. Biomechanics of tlrc Nlusculo-Skeletal S1'slem.

Znd ed. J. \Viler,, Neu'York. Osborrr, tl. F. 1905. Tyrannosaurus and other Cretaceous carnivorous dinosaurs.

tsulletin of

th.e American MusetLnt of Natural History 2I: 2i9-265. 'lrucltodon. Irrlcgrrrnerrt oI llre igrranodorrl dinosrrrr \lemoirs. Attterican Nluseun of Natural Historl' l: 13-54. -. Ozkava, N., and Nordin, NI. 1999. Fundamentals of Biornechanics: Equilibritnn, Motion, and Defonnatlon. Springer, Neu York. Paul, G. S. 1987. Preclation in the meat eating dinosaurs. P 173-178 in Currie, P, attcl Koster, E. (eds.). For-LrthStmposiumonNlesozoicTerrestrialEcoststems, SlnrtPapers. Occasior.ral Papers of the'l\,rrell N'Iuseum of Palaeontologl 3. 1988 Predatort DirLosaurs of theWorld. Simon & Schuster. Neu York. Ra,vfield, E. J., Norrnalr, D. B., Horner, C. C., Horner, J. R., Smith, P. N{., -. 'l'honason, J. J., and Upchurch, P. 2001. Cranial design and fnnctron in:r large theropocl drnosaur. Nature 409: 1033-1017. Resnick, D. 2002. Diagnosis cf Bone and loint Disorders. W B. Saur.rders, Philadelphia. Rothschild, B. N{. 1988. Stress fracture in a ceratopsian p}ralanx. lotLrnal ofPale-

lqll.

ontologt 6l: ?02*?0-{. Rothschild, B. \'{., and Nlartin, L. D. 1991. Paleopathologt: Disease inthe Fossil Record. CRC Press, Boca Raton, F L. Rothschild, B. N{., ancl Tanke, D. H. 2005. Theropod paleopatl.rologr'. P. l5l-165 in Carpenter, K. (ed.). The Canivorous Dinc.tstturs.Incliana Llnilersitv Press, Bloornington. Ruxtorr, G. D., and Houston, D. C. 2001. Could Ji rannosdtrus rex have been a

Lcoking Again at the

Forelimb

189

scavenger rather than a predator? An energetics approach. Proceedings: Biological Sciences 270: i)I-733.

Dutheil, D. B., Iarochene, \,{., l,arsson, H. C. E., Lvon, G. H., Maguene, P N1., Siclor, C. A., Varricchio, D. J., and Wilson, J. A. (1996). Predaton'dinosaurs fron the Sahara and Late Cretaceous faunal differentiation. Sclenc e 2 r- 2: 986-99\. Stevens, N{. A., El-Khonrl', C. Y., Kathol, \'{. H., Branclser, E. A., and Chori', S 1999. Imaging features of avulsion injLrries. Radiographics 19:655-672. Tehranzadeh, I. 1987. The spectrum ofalulsion and avulsion-like injuries ofthe Sereno, P. C.,

rntrsctrloskeletal s1'stern. Radio graphics 7 : 9 45 '97 4. \\'. i961. On Growth and F'orm. Cambridge Llnir.ersitv Press, Cambridge. \/an Snik, G., Ohnos, N{., Casinos, A., ancl Planell, J. A. 199'1. Stresses in leg tendons of birds. Netlterlands loun'Lal of Zoologl: +1: l-11. Yasrrda, N{. 2002. The An:rtonl of CalltLs. Tokvo, Ur.riversitr,of Tokr"o Press. Thornpsor-r, DArcv

190

Chisilne Lipktn and Kenneth Carpenter

Figure 11.1 . Ray Wilhrte using an Immersion M icroscri

casts

of

be

d ig

itizer on

elements of the

pelvic glrdle of Tyrannosaurus rex specimen BHI 3433 6tan). Photo cour:-"s;, Ray Wilhite and Vir'

lual Surfaces lnc.

192

Kent

A. Slei,ens et al.

REX, 5lT: DIGITAL MODELING OF TYRANNOSAURUS REX AT REST

11

Kent A. Stevens, Peter Larson, Eric D. Wills, and Art Anderson

The great tl-reropod TrrannosaurtLs rex is usuallv depicted in an active, brpeclal pose, perhaps in purstrit of prei'or lacing off ar-r opponent. Some artists, e.g., Lau,rence Lan.rbe (19i7), Cregorl. S. Paul (1988), John Sibbick (Non-nan I991, p. 72), and N'Iichael Skrepnick (Currie et al. 2004), hale providecl vieri's of these animals in other, less active postures, includir-rg h-

Introduction

ing prone or squatting. Presurnabl',' the anirral ri'ould rest',vith a substan-

tial portion of its bodr n-rass supported bv the pronrinent pubic boot. Trace fossils of small crouching theropods shot' both tarsal and pubic-iscl-riatrc ir-rpressions (e.g., Cierliriski et al. 2005). In the great theropods, descending

from a standir-rg pose to a rest position \\'as presllmablv a straightforivard matter of squatting, a process cor-rsiderablr less involr,ed than the complex sequencing of folding movenents that sorre modern large quadrupeds, sttch as camelids (Cauthier-Pilters and Daag I981)ancl bovids, nse to lorver tlreir nrass to the ground . Tyrannosar-Lrus rer might sin-rpli' have settlecl vertrcalh' in one continuons flexiorr mor,enrent inr,olving the hip, knee, and ankles.

It is in risirig front a prone or sqtratting rest position that some concent for the mechanics of the tvrannosauricl frarre might present itself. Hou' could the center of mass (CO\I) be controlled so that the anirnal lr'as stable lr4rile rising? Was there strfficient rnechar-rical adr.'antage in the rnajor extensor rnnscles to provicle a clirect ascent tl-rat retraces the trajectorr, follor'ved in descending to the ground? Were the forelimbs uscful in stabilizing the boclv and in providing thmst cluring the initial stages of the ascent? To address sone of these questions, a fullr articulated digital rnodel of 7l'rdnnosaurLrs rex \\,as created ri'here limb nror,.ements are delirnited by ar-ratomicalll' based estirnates of achiei'able range of motiorr, and the position of the instar-rtaneous CON{ of the anin-ral can be visualized in order ro judge balance and stabiliti'. Extant bipeds that lnight serve as analogs for str-rdving the sitting and standing movenents ol'I'. rex, include members of the N,Iacropodoidea, notablr,' tlre large red kangaroo (Nlauopus rufus) and a varietv of birds, particularlv the large ratites sr-rch as the emu (Drontaius not,aehollandiae) and tlie ostricl-r (Struthio carnelus). As anin-ral rrass increases, muscular strategies cannot be erpected to scale indefinitelv (Alerander 1989); the effortless rise of a small passerine fron rest to a bipedal stance rnight require rnr.rltiple, nlore cleliberate stages of limb ertension in a bipecl of ser. eral orders greater seight. 'l'he biorrechanical principles governing tfre Rex. 5lt

193

choice oi:trategr', particularll as regards.cairi; nith bodv tnass, are not il'ell unde rstood. Nlotion stuclies have conc cnir.rte d on capturing relativelv steadr-state locornotion (e.g., N{ulbridge 159v; Jenkins etal. 19BB), notthe transient bociv rnovements associated n ith :ittinq or st:rnding. 'lb examine tlre potential movernents that take the anirnal frorli standing to sitting. and vice ',,ersa, it is important to begin il ith an estirnation of the tl picai stand and sit postures. N{or"enrents that srnoothlr,'transition betn'een tliese extrerres can then be proposed and analvzed. In their analysis, it is irnportant to r-rnderstand hoii'tlie CO\l translates during the rrovemer-rt. Longitudir-ral (caudai-cranial) pitcliing ntovements in particular lvould produce instabilitv tl-rat i,l'ould have to be correctccl at risk of injurr' to the great theropod. It is also irnportant to exauine range of motion issues tl-rroughout the sit-stand moventents and the rnechanical leverage of large mnscle groups for pror,iding the necessar\, rnor"ements. Proposals have beer-r offered for horv T. rar could sit dorvn on its pubic boot, then rise bv first using the forearms as props to help anchor the front of the bodl' u'hile the rear legs n'ere straightened. 'l'he r-rpper bodv would then be tiltecl back to regain an upright standing posture (Nervman I970). This idea is but one of the poteniial uses proposed for tl-re forelinibs (Osborn i906; Horner and Lessem l99S; Carpenter and Smith 200i; Carpenter 2002). In tl-ie follou'ing, an articulated, J-dimer-rsional cligital reconstruction is used to explore alte rnatir,'e hvpotheses regarding the sit-stand mot'ernents of this dinosaur. The process of descending and then ascencling is amena-

ble to quantitative modeling, taking into consideration the distribution of rnass in the anirnal and the flexibiliti' of those joints involved in the rnovernents, particularh'the ankle, knee, and hip ri ithin the hind iimb, and the potential role of the forelinbs in the process of rising. Qr,rickTirre video sholr'ing the action is available in the supplemental CD-RON{.

Creating an Articulated Digital Model

DinoNlorph softn'are

(Ster.'ens 2002) provides a frameu'ork lvitl-r u'l-ricl-r to create and pose a cligital nrodel of T1'rattlosdurus rex.'lhe softrvare can accept 3-dirrensional data representing bone rnorphologr' (e.g., from corn-

puted torriographic fCTl scan or hand cligitization), as n,ell as more schernatic and sinrplified representations. In this str-rdr', the Tlrannosaurus rex specimen BHI l03l (Stan) at the Black Hills N,{useun of Natural Histor-v u'as used as the source for the digital nroilel. Tl'ie articrilation of the apper-rdicular skeleton and tire morphologv of the peli'ic ancl pectoral girdles n'ere of particular importance, so thel' u,ere specificallv for this studi.' (Fig. 11.1). Digitization data of the liead r,ias provided from an earlier CT scan macle b1'Virtual Srirfaces Inc. and the Black Hiils Institute. 'f he ren-rainder of the axial skelcton',i'as nrodeled schematicalh', lvith centra, nettral spines, iateral processes, chevrons, and ribs in a dimensionallv accttrate br-rt simplifiecl forrri 1Fig. 11.2). 'l'he nert step n'as to estimate the relative placement of each bone ivithir-r the olerall skeletal framen'ork. -\long tire presacral axial skeleton, the interlertebral separations and oi'era11 crtrr';rture u'ere deterrnined frorr-i Kent A. 5t?,'ens et al.

measurements ar-rd photographs ir-r lateral vielv. Likeu,ise, the rib cage \\'as formed by' painstakingll, adjustir-ig each digitallv represented dorsal rib to match the curvature, dimensions, and placement of its counterpart in reference photographs that were unclerlaid ivithin DinoN4orph as background images (Fig ll.3). To refir-re the 3-dimensional skeletal n.rodel, tl-re trr-rnk was successivelv r,ie',r,ed in anterior, dorsal, and lateral orientations, and for

each vierv, the cun'ature and placement of the ribs q,ere adjusted so that the digital ribs superirnposecl precisely'over their phoiographic counterparts. The pelvic girclles, complete u'ith furcula, r.vere then placed or-r the

thev are rnounted on Stan (Larson and Rigby 2005). Next, those DinoMorph parameters governing the position and orientation of all appendicular joints r.vere adjusted to create a neutral standir-rg

rib cage

as

pose, the starting point for this study. Tl-ren, for the major apper-rdicular joints in-rportant to this stud\', a range of motioir rvas deternined on tl-re basis of an estimate of the tl-rickness and extent of the intervening cartiiage in modern avians and direct manipulation of the casis (Kennetl-r Carpenter and Yoshio Ito, personal connunication June 2005). Direct rnanipr-rlation assisted in deterrnining, for example, the axis of rotation of the femur head

ivithin the acetabulurn, and in the forelimb the orientation of the fully

ex-

Figure

BHI 3033 (Stan). The appendicular skeleton and hoarl rttara diaitizar'l ,^,4^.^^+A^ -,.;-l )^-1,î ' vvt tct cd) Lt tc d^tdl FT6h tlt2< ranraLd-

bilize the body during ascent, but the line of action of the ground reaction force would have placed the furcula under significant bending strest consEtent with commonly observed healed fractures. Forelimb range of motion estimated i n collabora -

tion with Kenneth Carpenter.

have precipitated such fractr-rres.

The great bulk of an aclult -fi)rdnnosduruE rex \\:as capable of being gracefully lor'r'erecl until it settlcd its weight on the elongate pubic boot, freeing the animal to adjr,rst its legs mnch as a sports spectator r.r'ould use a portable oneleggecl stool. When it carre to rising again to a bipedal stance, the options, particularll'for a sn-rall tvrannosaurid, would be a sprint start u'ith or u,ithout assistance fror-r.r the forelirnbs, or a more gradr,ral elevation usir-rg the hind limbs during u'hich the forelimbs plaved an essential role. 'l'he latter w,as en-

Conclusion

ergeticalh'rrore efficient and nright have been preferable for the adult. The forelimbs rvere literallv pii'otal in this operation, and mishaps rnight have resultecl in transmissiorr of enormous compressive forces on the pectoral girdies

and the delicate furcr-rla that spanned the :icromion processes. Although it was perl-raps ungainlr for the t1'rant king to rise rr.rmp first, its ascent u'as likeli' rnore elegant than th:rt of rrodern bor,ids rising irorl repose. Rex, Sit

201

Kent A. Stevens et al

We are gr:rteltrl b Rav Wilhite for digitization of T rer bones usecl ir-r tl-rrs studg ar-rd to the Black Hiils Instiiute of Geologic Research for hosting the 100Years ofTtrarntosctrLrusrex51 n.rposiurnandforprovidingaccesstospecimens. 'l'hanks also to Phillip \Ianning, Yoshio Ito, ar-rd Kenneth Carpenter for helpful sugge stiorrs regarcling range of motion and rnovements.

Acknowledgments

Alerander, R. N{cN. 1989. Dr.namics of Dinosaurs and Otlrcr Extinct Ciants. Colunrbia University Press, Neri \brk. Carpenter, K. 2002. Fbrelirlb biornechanics of nonavian theropocl dinosaurs in predation. S e ncke nb er giana Lethae a 82: 59 -7 6. Carpenter, K., and Smith, NI. 2001. Forelimb osteologr,and biorr.rechanics of T)'rannosatLrus rex. P.90-116 in Tanke, D., and Carpenter, K. (eds.). Mesczoic Yertebrate Life. Indiana Unir.ersitl Press, Indiana. Cr-rrrie, P. J., Koppelhus. E. B., Shugar, NI. A., and \\,tight, J. L. 200,1. Feathered D ragotts. Ind iana LIn iversrtl Press, Bloon-rin gton. Cauthier-Pilters, H., and Daag, A. I. 1981.T|rc CarneL ltsEcologt.Behayior and Relationship to I'Ian. Unir ersitv of Chicago Press, Chicago. Gierliriski, G., l,ockler; NI., ancl N1ilner, A. R.C. 2005. Traces of earlv Jurassic crotrchrng dinosaurs. P. l inTiackingDinosaur Origins: TlrcTriassicllurassic

References Cited

TerrestrialTransition Abstract\lolunte. Dirie State College, St. George, LIT. Estinating the masscs and centers of nrass of extinct arrinr:rls br' 3-D niathernaiical slicir.rg. Paleobiologt 25: 88-106. Horner, l. R., and Lessenr, D. 1991. The Complete T rsx. Simon & Schuster, Neu,York. Hutchinson, J. R., ancl Garci:r, NI. 2002. 'I\'rannosaunts u'as not:r fast runner. Nature 115:1018-1021. lenkins, F. A., Dial, K. P., and Goslou, G. E. 1988. A cineradiographic analr,sis of bird flight: the rr ishbone is a spring. Science 241: 1495-1.198. L:rnrbe, L. N4. 191;. The Cretttceous Theropodous Dinosaur Corgosaurus. Canacla Department of \lrnes, Ceologic Surver.of Canacla, Nlenioir 100. Larson, P L. 2001. Paleopathologies in Tlrannosdurus rex (in Jap:rnese). Dino Henclerson, D. N{. 1999.

Press

i: 26-1i.

Larsorr, P. L., and Donnan, K. 2002. Rex Appeal: The Amazing Stort of Sue, the DinosatLr that Changed Scierrce, the Law artd NLt,Life. Invisible Cities Press,

Nlontpelier, \/T. L,:rrson, P L., and Rigbr', K., Jr. 2005. Tfre fr-rrcula of'firarntosaurus rex. P.24 t-255 in Carpenter, K. (ecl.l. Caniyorous DinosatLrs. Lrdiana L.lniversitr.Press, Bloonrir-rgton.

Nltrlbridge , E. 1899. Arimals in \.Iotiott. London: Chapman & Hall. Dover re-

print,

1957.

Nervnran, B. H. 1970. Stance ancl gait in the flesh-eating dinosaur Ttrannosaurus. Bioktgical lounnl of tlrc Linnean Societt 2: Il9-123. Norm:rn, D. 1991. Dinosar-Lr! Prentice Hall Cleneral Reference. Nen York. Osborn, H. F. 1906. Ti,rannosaurus, Upper Cretaceorrs carnil'orons dinosaur. Bulletin of the Anrcrican N[ttsetLnt of Natural Histort 22:281-296. Paul, Cl. S. 1988. Predatorr Dinosaurs of the \\rorld. Ncri \brk Acaclernv of Sciences. Ne\\,York. Steverts, K. A. 2002. L)inoNlorph: parametric modcling of skeletal structures. Senckenbersiana Letl'Laea 82( l): 23-34.

Rex, Sit

Figure 1 1 .10 Ele tar o' the posteriar whtle archoring the anrer,o. cc:.. by the forelimb1 creatrng a pose much like a sprtnt

-'

start. The mechantcal advantage of a secondclass lever is provided during extension of the hind ilmbs in raising the COM. With sufficient elevation ach ieved, the animal could push back and regain bipedal balance, and complete its -+-^J;^^t9 o)LEr /( (u a- )Ldtluil

pose.

Fiat

ra 1) 1

Crn to 138" to the gror-rnd. Variatior-r in the step cvcle limb position angles r,r'as greatest in birds, ranging frorn 56o-> to 63" at heel-dow'n to 106'-> to IJ8'at toe-off phase of the step o'cle. 'I'he relative position of an aninal's center of mass to the angle of the action of force acting on the foot results in variation in the distribtrtion of pressure over the sole of the foot during a step o'cle. Can this variation in pressure possibll'be one of the kevs to alk-ni the kinernatic information stored rvitl-rin a track to be unlocked?

T. rex Speed Irap

213

A Critical Eye for Walking

Experin-rental i.r,ork on tracklr,ays, coupled ivith considerations of

linb ki-

nematics and substrate conditions, permits the rnost robust inferences abor,rt track maker's and fossil footprint data (Padian and Oisen 1984, 1989; Manning 1999, 2004). It is logical that similar trackrval,s indicaie analogous kinernatics in rnany large theropods (Padian and Olsen l989). Horvever, Gatesv (199i) questioned the resoiution at r,vhich details of limb-segrner-rt orientation, kinematics, rnuscuiar anatom,v, and neuromuscular control cor-rld be addressed by means of Padian and Olsens (1989) techr-rique. He suggested that footprints coulcl not be equallv inforrlatir,e about all locornotor categories, even iftrackrvavs have helped confirm that birds retair-red the obligaiorv, digitigrade bipeclalism and l-righly addr,rcted limb postrire of their tl-reropod ancestors. Cates,v (1995) concluded that rt u'as quite possible that such bipeds could make alrnost identicai footprints even if thev differed in several locorrotor categories. He rnaintained tl-iat trackwai,'s could not provide enough detail to discrin-rir-rate betrveer-r l-ripbased (primitive theropod) and knee-based (avian theropod) limb-retraction mechanisnis. The track rnorphologv of tl-re iargest living ground birds (ratites), such as eu-u-r (Padiar-r and Oisen 1989; Nlanning 1999; N'lildn 2003; Milin et al. 2004) and ostricl-res (Farlorv 1989), allou, comparison of track morphologv generated by either avian knee-based or hip-based (primitive theropod and hr-rrnan) retraction mechanisrns b-v using laborator,v-simulaied and fossil tracks (Nlar-rning i999, 2004). Observations on the distribution of pressure across ratite feet wl-rer-r walking, inferred frorli track morpl'rologi' (Thulborn and Wade I9B9; F'arlorv 1989; Mar-rning 1999, 2004), indicate the presstrre distribution across the foot of a knee-basecl retraction nechanisir differs from a track ger-rerated bl'a hip-based retractor rrechanism. The distinct heel-dor'vn phase in laboratorv-simulated tracks aiid fossil tracks is almost abser-rt from emu and ostrich tracks (Farlow I9B9; N,{annin g1999). 'I'he l-reeldorvn phase is replaced by what can be described as a contact phase. In the contact phase, an avian theropod tests the groulrd to assisi motor control for the cornpleted step cycle (Gatesv and Biewener l99l). This enables an animal to accommodate for substratun-r heteroger-reitv during locornotion in a natural environment (Clark I9BB; Gaiesv and Bien'ener l99l), rvithout committing its u'hole mass over the foot, as with a heel-dor,vn phase of a hip-based retractor r-nechanisrn. The knee-based retraction mechanisrn appears to combine the heel-dorvn phase and rotation phase of the step o,cle (contact phase), r'i'ith the greatest force exerted at ti-re distal end of digits at the pushoff phase of the step cvcle. The variation in the distributior-r of pressr-ue across

the foot is essentiallv a bl.product of the relative positior-r of tl.re animal's center of rlass dr-rring a step cycie, as the bodl'moves over each foot and step, respectively. Tl-ris suggests, contrary to Gaiesr' (199i), that it is possible to differentiate betrveen hip- and knee-based retractor s1'sten-is from track geometrl', given that track relief (sr-rrface and subsurface) is a function of the distribution of pressure. The center of mass of a theropod dinosaur is also reflected ir-r the distribution of the animal's u,'eight on its 2 limbs. If the center of rlass is directly over the limbs of a biped, each iirrb will support an equal amount of 214

Phillip L. Mannino

r,ieight (u'her-r the animal stands stiil). Tl-re posture of a theropod clinosaur had to account for the rclative position of the center of mass to be stable, or, il4ren

ivalking, to be dy-ramicalli unstable (see Stel,ens et al. this volun're). The difference in the position of the center of rnass u,ould certainl','have had an effect on all theropod loconiotion, inclucling sitting, standing, n'alking, running, ancl junping. 'l'he distribution ofprcssure exerted across the sole ofa foot can vary with subtle directional changes in the load applied during a step cvcle (N,'lanning 1999). Laboratori track sirnulations ar-rd force-plate (optical pedobaragraph) experirrents can vield useful informaiion on the substirface rr-rorphologv of tracks ancl tl-re clistribution of pressures across the sole of a foot (N,f annin g 1999,2004). 1'he varving degree to n'l-rich a digit or cligrts n'ere transnritted to deeper successil e lavers correlates lr'itfr the distribution and rnagnitude of pressure acting on the sole of a foot. Experimer-rtal pressure plate svstens have been used to track the r,ariation in the center of pressrlre during a step cvcle, rnaking it possible to correlate r.'ariatior-r in load rn'ith the restrltant distribution of pressures over time throLrgh a step cvcle (N'lanning 1999, 2004). 'l'he inplication of beir-rg able to infer the kinenatics of a step ci'cle frorn a fossil track, coupled r,r'ith the size of the anirnal and speed at rihich it n'as trar.cling, could i'icld important ir-rformation on the locomotion of all dinosaurs. The lD subsurface track record of the relatii'e magnitucle ancl distribution of pressr-rre across a foot can assist in assigning theropod tracks to a primiiive (hip-based) or derived (knee-based) locomotor s),sterr. This coulcl provicie usefr-rl data on el olutiolarl trends in theropod locomotion in the fossil track record, thus supporting the evider-rce from the bodv fossil record (Catesr 1990, 1991, 1995). It mav no\\'be possible to differentiate from L,ate Cretaceons avian theropod and bipeclal ornithopod tracks on the b:rsis of subsurface deforrnation bv the presence or absence of a heel-dori n phase di-rring locomotion. A N,Iiddle furassic theropod track frorn the Scalbl' F'ornation, Yorkshire, UK, provides an ex:rmple of a 3-phase track ('l'hulborn and \Vade I989) (Fig. 12.7), u'ith features ti'picall1'erpectecl for a hip-based limb retractior-r mechanisrr (Nfanning 2004). The cross section along the meclian 1ir-rc of digit III shon's a region of clot,nriarped sediment ir-r the heel area (A), r'vhich delineates the clefomration carrsed at the l-reel-donn phase of the step o'cle (Fig. 12.7). 'fhe briclge of the foot (B) of the section of digit III delineates the seconcl forw'ard rotation phase of the step cycle (Frg. 12.7). 'l-he third and n-rost distinct point of the step cl'cle, the toe-off phase (C), is clearlv deiineatcd b1'a severelr,dou'n'nr,arped area of sedirnent larrrnae, couplcd u'ith liquefaction failure (Fig. I2.7).'fhe track displavs all 3 pl-rases of a step o,'cle (Tl'rulborn ancl \\'ade 1989) that n'ould be expected for a hip-based retractor rrechanisrr, tvpical of a N{iddle Jurassic theropod clinosaur (N,'lanning 1999, 2004). 'lb test tlris h1'pothesis further ivoulcl require the sectior-ring of manl' coniplete fossii tracks from the Jurassic and Cretaceous, to compare and contrast the distribution ofpressure across the foot in relation to subsurface featr-rres, n4rich n,ill (curators n'illine) be the subject of future rvork.

T. rex Speed Trap

215

Figure 12.7. Cross section along medial line of digit lll from a Middle Jurassic theropod track, Scalby Formation, Burniston, lll( Araa< A f^ a ranro<enf nh:cp< nf fha +:

:ot t3g

{l){U €;nt

Track layer depth {mm} posterior point of the tr:rck, measured parallel to the long axis of the track (Leonardi 19E7; Thulborn and Wade l9E4). The eristing definition r-rnfortr-rnatelv has the greatest l'ariation in its pararneters with deptli because the N,IZD represents the maxinum erter-rt of a track. Hon'ei'er, if theropod FL r,vere defined as the length of digit III (Nlanning 1999, 2004), a closer approxirnation can be made of the true length of digit III, and in turn, a calcr-rlation of the total FL can be made. Hou'ever, this relies on an individual recorcling FL frorr surface tracks that displar,a clearly definable middle digit

(digit III) or clear skin inipressions (Currie et al. 1990), or can be defined bv the relative position of the track's force bulb (as discussed earlier). Laboraton'track sirnr-rlations have demonstratecl that FL variation is as much a ftrnction of sedin.rent as it is of the track rnaker's foot morphology ancl size (N{anning 1999, 200'+). For example, the Tbble l2.l charts the resuits from 11 laboratorr-gencrated tracks (N'Ianning 1999). The actual length of foot (template) is a knon'n quantitr', as are the sediment characteristics and condition at tlie time of track forrration. The same amount of force \\ras applied to the foot on each track run in the sarrie step cl'cle. The percentage variation from actual foot (template) length r'"'as calculated for the maximum and ninirriun track size recovered frorn strrlace and subsurface tracks. Tl're i'ariation in track paraneters n'ith depth lr,as dependeni on the noisture content and sedinent used. Track Il (Table 12.2) and Track 10 (Table 12.3) u'ere generatcd br the same experinrental setup and sedirrent, i,vith the onl1'r,ariation being moisture content. The fine-grained sand used for both experiments il'as inclented drv (n.roisturc content 1%1 and saturated

Figure'12.10.

track (' fossi I vol u me" ). Trark< a-h r-d

botto m s u r f a ces, respectively, of 3 layers that combtne to create a

single track volume. The

plotted track outlines (af) show variation in FL with depth. The gray line (tracks a and f) marks the posteriormost point of the track, with the arrow (track f) indicating the degree of anterior travel of the track feature with increasing depth.

Track ll (satnrated sediment) shon'ed a large variation in FL frorr surface laver I to basal laver 11 (Table 12.21. ftorn 17.5 to 9.0 crn, respectivelv, a r,ariation of some I9+.4%. The length iFl,) of track l1 rl,as then usecl to calculate fi. Accordinq to Alexander 19-6t. h was 36-65.2 cm, Irap

snd a-f

represent the top and

lnroistrrre corrterrt 1071.

T. rex Speed

Ornitho-

pus g raci I io r transmitted

221

MZD

Track

Digit lll

FL

Maximum Minimum Variation Comoared Maximum Minimum Variation Compared (cm)

(cm)

with Actual

1

19

12.3

152-98.4

1

I

19

4.7

152-37.6

1

j

2A

7.4

160-59.2

-

15.4

12.4

131.2-99.2

5

16.4

10

'r

6

17.8

7

1

Simulation

(%)

(cm)

(cm)

with Actual

6.5

9.5

137-78.9

5.5

10.2

128.7-84.7

13.5

9.7

112.1-80.5

14.8

12.5

122.8-103.8

2-80

13 5

10

112.1-83

4.5

132.4-36

15.2

12.5

126.2-103.8

8.5

14.8

148-118.4

15.3

13.4

127-111.2

8

24.7

14.5

197.6-116

18.2

11

1

9

23.6

6.3

188.8-50.4

16.4

9.2

136.12-76.4

10

21.5

7.5

172-60

16.3

10.2

135.3-84.7

11

17.6

9

140.8-72

14.3

11.9

118.7-98.8

Table 12.1. Variation in

Maximum Zone of Deformation (MZD) Track Length (FL) and Digit III Compared with True Track Length (Length of Foot Template) from lndivi d u a I Track 5i m u lations

Note.-The actual length of the foot template was 12.5 cm. The actual

length of digit lll was

12.1

cm.

31

.

51

(%)

.1-91 .3

Tl-rnlborn (1990) gives h as 405-99.97 ctn, and Locklev et al. (1983) give fi as 45-105 cr-n-a poteniial variation of 291.6%, depending on nhich track layer was used. 'l'his poter-rtial variation is clearly not restricted to laboratorv-generated tracks but is present in fossil tracks (Fig. 12.10). Track l0 (drv sediment) also exhibited a large variation in FL frorr surface layer 1to basal layer II ('fable 12.3), from 21.5 to 7.5 cm, respec, tivelv, a variation of sorne 286.6%. 'l'he length (FL) of track l0 n,as tlen used to calculate fi. Accorcling to Alexancler 0976), h ranged 30-81.6 crri, Thulborn (1990) gives h as ]3.7-122.i cm, and Lockler,et al. (1983) givc h as ]7.5-129 cm-a potential variation of $0%, r,vhich clepends or-r ri.hich track laver and h estirnate method are used. If a fossil trackivav erposed relativelv deep, transrnitted tracks, equir.'alent to la-ver II of track sirnulation l0 (Table 12.3), and the FL n,as usecl to calculate /i and in turn the speed at ivhich the ar-iinal was traveling (h1,-pothetical stride length of 2 m), then the follou,ing results are obtained:

L 2.

Using lon,er linrit estination of hip height (Alexander 1976) of 30 cm, Equation 2 gives a speed of 10.29 rn/s. Using the upper limit estimatior-r of hip height (Locklev et al. 1983) of 45 cm, Equaiion 2 gir,es a speed of 6.,1 rn/s.

if the fossil trackrval exposed tl-re equivalent of lar.er 5 of track sin.rulation l0 ('lbble l2.l) and the FL n,as used to calculate /z ancl il Hower,er,

tum the

spe ed at u'hich the animal u'as tra',,eling, the hvpothetical striclc length of Z m nou, reduces to 1.86 rn as a result of tl-re increased foot length encroaching into the stride length (Fig. l2.ll) nould gir.e the follori'ing

results:

222

Phillip

L Manning

Track

'11,

Dry Fine-Grained Sand

h in Relation to

FL

(E)

65.2

73.35-92.91

81.5-97.8

14.3

57.2

64.35-81.51

71.5-85.8

17.5

70

78.75-99.97

87.

12.7

50.8

57.15-72.39

63.5-76.2

-6.3

10.6

42.4

47.7-60.42

53-63.6

-8

q

36

40.5-51

45-54

FL (cm)

h (cm) =

1

0

16.3

3

-1.6

5

?a

7

-4.9

9

l. 2.

(1990)

Lockley et al. (1983) h (cm) = FL5-6

Depth (cm)

11

('1976) Thulborn

h (cm) = FL4 5*5.7

Alexander

Layer

FL4

3

Using lou'er linit estimation of hip height (Alexander 1976) of 86 cn, Equation 2 gives a speed of 2.65 mA. Using the upper limit estimation of hip height (Locklev et al. 1983) of 129 cm, Equation 2 gives a speed of 1.65 m/s.

A fossil trackrl,al', with tracks sirrilar to those transrnitted in track simulation 10 (Fig. 12.11), creates the potential difference in speed from varl'ing track laver depths from 1.65 m/s to 10.29 n-r/s, depending on r'vhich layer and hip height values are applied. 81'comparir-rg the NIZD foot length data frorn laboratorv track simtrlations (Manning 1999, 2004), there is significant variation in track geometrv between surface ai'rd transmitted tracks. Tiack sin'rulation 10 l-ras a','ariation of up to 286.6% and simulation li a variation of up to 194.4%. 'I'he onlv paraneter altered betu,een tl-re Z r','as rroisture content; sedirnent, foot morphology, force, etc., remained constant. The higli rnoisture content 01.2%) of track simuiation I1 ir-rclicates that the MZD is reduced with higher rnois-

ture contents; effectivelr,', the sediment's bulk densit_v is higher as a result of the increased rnoisture filling the pore spaces, increasing the shear strength. It is clear that a controlling factor in the forn-ration of track features is the re-

Track 10, Dry Fine-Grained Sand (E)

Depth

(cm)

h in Relation to Alexander (1976)

FL (cm)

(cm)=fr+

h

Thulborn

5-]

05

Table 12.2. Vailailon rn Hip Height (h) Due to

Depth and Method Chosen for Estimating Hip Height (h) for Laboratory Track Simulation 11

Abbreviation.-FL, foot length.

Table 12 3. Variation in

Hip Height (h) Due to Depth and Method Chosen for Estimating h for La bo ratory Track Si m u I a -

tion

1A

Abbreviation.-FL, foot length.

FL

(1990)

Lockley et al. (1983)

h(cm)=FL4.5-5.7 h(cm)=frS-O

1

0

20.4

81.6

91.8-116.3

102-122.4

3

-1.7

20.1

804

90.45-114.6

100.5-120.6

5

)1

21.5

86

96.75-122.5

107.5-129

7

-5.3

16.5

66

74.25-94

82.5-99

9

-6.87

11.5

46

51.7-65.5

57.5-69

11

-8.43

7.5

30

33.7-42.7

37.5-45

T. rex Speed

lrap

223

4.7 cms

Figure 12.1 1. Cross sec-

tion of trackway showing variation of FL and stride length with depth. Data from track simulation 10 (Table 72.3).

lationship betweer-r moisture ar-rcl density'that prevails in a volurne of sedinrent at the time of inclentation. FW car-r also be r,rsecl to calculate hip height (Thulborn and Wacle 1984; Lockle-v et al. 1986; Thulborn 1990). Horvever, FW also varies il.'ithin indirelation to the relative position to the trr-re track sr.rrface. Anall' sis of dinosaur tracks also indicated FL rvas more variable than IiW (Thulborrr and Wade 1984), and that FL i',as the least reliable indicator of foot size. FL and FW data (N,Ianning 1999) agreed rvith that of Tliuiborn and

l'idr,ral tracks

ir-r

Wade (1984), thus sr,rpporting sinallelu'ariation in FW n'hen compared u'ith FL ('l'able i2.'f). It is clear that FW rather than FL could be r-rsed q'hen calculating the speed of a clinosaur oIr the basis of measttred paraneters from tracku'avs. The use of F-W can be fi-rrther justified if a clear relationship betrveen FW ar-rcl hip height can be established. 'l'hulbonr and Wade (1984) proposed an index of footprint size (SI), r.r,hich thev calculated bv r-rsing the FW and F L of a fossil track (expressed in the sarne units of measurernell: 5l = (FL x FW)o

s

Thulborn and Wacle (l984t applied their index of footprint size to 57 fossil trackr,r'ays (Wintonopus) frorn tl'ie Middle Cretaceotts, Winton Formatiorr, Qr,reer-rs1and, Australia. Thev concluded that the footprir-rt size index (SI), based or-r tl-ie sarnple the sanplc of 5 t- \Yhionoprrs tracki.r'avs, \\:as the rnost reliable guide to estimating the size of track niaker. 'l'he data frorn laborator]-simulatecl tracks provides the ttt-tttsual situation il'here both the track size frorr eaci'r laver of a single track volttme and the actual foot length (ten-rplate length) of the track rnaker lr'ere knorl'n 224

Phillip

L Manning

MZD TW

MZD TL

Track

Maximum

Simulation

(cm)

(cm)

1

19

12.3

2

19

3

20

4

1E

5

Minimum

Variation Compared with

Variation

Maximum Minimum Compared with

(cm)

(cm)

Actual

152-98.4

19.4

to

157.1-129.6

4.7

152-37.6

to

12.3

129.6-99.6

7.4

160-59

17

5.5

137.7-44.6

12.4

131.2-99.2

15.9

14

128.8-113.4

16.4

10

1

.2-80

19.7

8.6

159.6-69.7

6

17.8

4.5

132.4-36

16.6

3.2

134.5-25.9

7

18.5

14.8

148-118.4

16.3

136

132-110.2

B

24.7

14.5

197.6-116

18.3

14

148.2-113.4

9

23.6

6.3

188.8-50 4

18.4

6

149-48.6

10

21.5

75

172-60

19.2

12

155.5-97.2

11

17.6

9

140.8-72

20.2

1

A

Actual

3

1

FL (%)

2

naker-ir-r tl-ris case, a prosthetic theropod dinosaur foot. The inclex of footprint size (SI) u'as applied to both the maximun'r (SI.l) and minimum (SI.2) N,IZD FL and N4ZD FW data frorn N{anning (1999) (Table I2.4). The SI ri'as calcr-rlated usinq the follou,ing equations:

= (maximum MZD FL x maximum MZD FW)0s $l.l = (mininlrrn N,{ZD FL x minin'rum N,IZD lrwli'; Sl 1

The SI results for the maximnm (SI.1) and rrinimum (SI.2) were not as close to actual SI foot size as predicted bv Thulborn and Wade (1984) (Table 12.5). Horvever, if the SI.l and SI.2 l'alues n'ere treated as maxirnum and mininum 'u.alues from a trackli av ar-rd fed back thror,rgh the SI formr-rlae, a different picture emergecl. SI.l and SI.2 in effect prol,ide an index of footprint size (SI) for ar-r inclividual track (SI.3): Sl.3 = (S1.1 x Sl.2)o

163.6-85.1

0.5

qtrantities (N{anning 1999). 1'his makes it possible to test u'hether the ir-idex of footprint size (SI) rnore closelv reflects the foot geometrv of the track

Table 12.4. Vailation in

Maximum Zone of Deformation (MZD)Track Length (TL) and Track Width (TW)Compared with the True Track Length within lndividual Track Simulations

Note.-The actual foot length template T8 is 12.5 cm, The actual foot width TAmnl2TA tXt< t/ 4am

s

The estirnated value of SI.3 provided a closer estimate to the original track maker's foot size (Table I2.5). Because the true foot length and foot lvidth rvere knorvn for the terrplate that il'ere used in the laboratorv simulations, it rl'as also possible to calculate tl're true index of footprint size SI (true SI), for comparison lr,ith SI.l, SI.2, and SI.3 (Table 12.5). SI.3 represented tlre footprint size index for a]l track lavers from an individual track and could be used to estirnate hip height fron a multitiered fossil or laboratorr,.5i-.rirt.d tracku,ar,' (if all track la1'ers u'ere recor,erable).

T. rex Speed Trap

FL (%)

225

Table 12.5. lndex of Footprint Size for Laboratory-

Track Simulation (cm)

Template*

Simulated Tracks Based on Data from Table 12.4

sr.1r

sr.2 +

st.3 s

1

19.2

14.03

16.41

2

17.45

7.6

| |.)L

3

18.44

6.38

'10.85

4

15.65

13.18

14.36

5

19.97

9.27

12.9

6

17.19

3.79

8.07

7

17.37

14.19

15.7

B

21.26

14.25

17.41

9

20.84

6.15

11.32

10

20.32

o i40

13.9

11

18.86

9.72

Abbreviations,-FL, track length; FW, track width. - FL = t2,5 cm; FW = 12.4 cm.

t

True Sl of T8 = (12.5 x 12.4)0.5 = 12.45 cm. f True Sl of TB = (12.5 x 12.4)0.5 = 12.45 cm. 5 True Sl of T8 = (12.5 x 12.4)0.5 = 12.45 cm.

t

J. )z+

The index of footprint size for the MZD fL (SI.1) shou,ed a percentage variation from the irr.re foot length of ITi.Z%-fi1.I7o, conparcdwith 76%197.6% variation in FL. The index of footprint size for the minirrr-rm MZD FL (SL2) shou,ed a percentage variation from the tnre foot length of 10.6%1I4.9%, con-rpared ,xith25.8%-162.9% variation in FL. However, the revised inethod for index of footprint size SL3, usir-rg the i,'alues for SI.l and SI.2, gave a percentage variation of only 64.8%-179.8% compared u'ith the tnre foot iength. The application of the index of footprint size (Tliulborr-r and Wade l9B4) to tl-re data from this studv suggests that it provicles an estimate for the percentage variation in track size in a sequence oftracks. Ifthe tracku'al'is a series of transmitted track features, u,ith tracks represented by the maximum size of the MZD, the /z generated u,ill be too high and the speed calculated fron-r the tracku'ai' too loll'. Hon ever, if the tracks are from a horizon that represents the minimum developrnent of the NIZD, it is possible that h u'ill be underestimated, and the speed calcr-rlaied ivould be too high. Bv cornbining the laboratorv-simr,rlated track data from SI.l and SI.2 to calculate SI.l (Table 12.5), a closer estin'rate of the track size can be made, allorving nearer estimates of /r. The FL generated using SLI (Table 12.5) gave an average of 18.6 cm, and for SI.2, tl-re average FL u,as 9.8 cn; horver.'er, SI.3 ga\re an average FL of ll.Z7 cm, the closest to the true SI FL (12.45 crn). The index of footprint size (SI) is onlv acclrrate if the tracks fron-r u,hich the rneasurements are taken closelv resernbie in size and proportion the original track rnaker's foot size parameters. Hou'ever, bv using the revised iechnique of SL3 (Table 12.i), it mav be possible to estirnate h frorn transrnitted tracks and sr:bseqr,rentlv calcr-rlate the speed from a trackr"'ay more accurately. The speed at r,vhich a dinosaur u'as traveling is an inportant variabie to assess ifthe potential ofthe 3D preservation oftracks is to be fully'utriized. The speed at nhich an anirnai travels directli" affects the tin-re a foot

226

Phillip

L Manning

remains on the grollnd (dr-rty factor) and the intensiil'and distribution of the load transrnitted in that gil,en time. 'l'hulborn (1990) suggested it u'as irrpossibie to calculate the duty factor for a dinosaur directly from its trackwa1'; hou,ever, a 3D approach to track subsurface cleformation cor-rld possiblv alter tl-ris. The anterior displacement of track features 'uvith increasing depth (F ig. 12.1 1) is a result of the phvsical properties of sedinent and the

dvnanic load encour-itered during track formation. The distribution of presslrre (load) over the sole of a foot correlates with the resultant subsurface track relief. If the track and associated features allow an estin-rate of

the cor-rditions prevailing at the tirne of track forn-ration, the subsurface deforn'iation could be coupled r,r'ith the calculated speed of a trackwar,- to enable an estimate of the dutv factor. 'l'he subsurface relief (contours) of the fossil track could provide a means to reconstruct the dynamic pressure distribution or,er the sole of a dinosaur's foot. This, coupled n ith a knor,vn speed, might provide insight into the amount of tine a dinosar:r's foot remainecl on the qronnd (dutv factor) dr-rring locon'rotion.

It

is clear that the use of

FL in calcr-rlations of speed frorn

a trackrva,v (Al-

Summary

erander 1976) should account for transmitted track features because ihey' can potei'rtiallv r,an'speed estimates bv I0-fold. The use of dinosaur tracks in corlparative mtrltivariate studies should be restricted to surface track features for comparisor-r ',vith otl'rer surface track features. f'he inclusion of transrnitted tracks in such studies invaliclates anv taxorrorric or osteological reiationships inferred as a result of the ciisparitv beti'"'een surface and subsurface track rnorphologi. Anv multivariate studv based on n'rorphological variabilitv in tracks and tracku'ay,s can onh'be viable if the lD variabilitv

of track rnorphologv is ur-iderstoocl. Iir:ture multivariate studies must approach the task of ur-rderstanding the 3D cornponents of a track before valid comparison can be n-rade u,ith other tracks li'itl-rin a JD franervork.

This chapter has opened a possible ichnotaxonornic can of rvorms. The shifting sands of time har.e disguised so rnuch of the process of track formation and preseru'ation tliat potentiallv verv little of a track rnakers foot norphologv might be faithfuliv locked in stone (Mar-rning 2004). Vertebrate ichr-rotaxa shor,rld reflect the n'iorphological differences resulting from behal'ior, not the affiniil,of an alleged track rnaker or artifacts of track forrnation and presenation (Nlanning 2004). What is clear is that the interpretation of fossil tracks requires the application of more robust quantitatir,e methodologies. I hope tl-iat if an illusive tracku'av of a trotting or rlrnning 7. rer is for-rnd in the future, its documentation and interpretation will r-rot fall into the potential traps disci-rssed in this chapter. Who knorvs-the ichnospecies could even be narred after a haclrosaur!

I thank Peter f,arson, Neal Larson, and Bob Farrar of tl-re Black Hills Institute of Ceologic Research (BHIGR) for organizing the 100 Years ofTyrantlosdltLls rex Si'rriposiurn in Hill Citv (2005). l'he BHIGR personnel u'ere perfect hosts and providecl access to their rionderfirl collections. A speciai T. rex Speed

Irap

Acknowledgments

227

thanks to Chris Ott, rvho

the instigator of tlie il{-role rex s'n'rrpositrm. Many thanks to Whitel' Hagadorn (Anrherst Coilege) for access to the Hitchcock fossil track collection (Pratt N{useun-r). Also rnanv t}ianks to ri,'as

Amherst College for their generous grant from the General Eastn-ian Fr-rnd to assist in mv research trip to the Pratt N{useum. I thank the Unir,'ersitv of Sheffield for a Hor-ne/EC Bursari'that made the research possible, and aiso N4ike Romano ancl Nlartin Whr,te. N'lan-v tfranks to Ernma Schachner for permissior-r to use the line drau.'ing of T. rex and to Richard Hartlel'for redrar,i'ing Figure 12.11. Thanks to Emma Finch for squeezing and rnanipulatir-rg data into Petrel. N4anr,'thanks to rn1 n'ife ancl clzrr-rghters, r.i'ho perrnit me the tin're to undertake this research. F inalli', a special thanks to N4arion Zenker (BHIGR), rvho kept chasing this chapter and finallr'fotrnd a strategic place to insert a rocket for rne to get it finished.

References Cited

Alexander, R. N'I. 1976. Estin-rates of speeds rn clinosaurs. NatLLre 261: 129-130. 1996. Ty,rannosatLrus on the run. Nature 3 i-9: I2I. Alexander, R. Ntl., Din.ren', N. J., ancl Kerr, R. F-. 1985. Elastic structures in the back and their role in galloping in sornc rnamnrals. lounnl of Zoologl, 187:

-.

r25-r+6. Allen, J. R. L. 1989. Short paper: fossil r'ertebrate tracks and indenter nrechanics. lournal ofthe Ceological Society, London 1'+6: 600-602. 1997. Subfossil manrmalian tracks (Flandrian) in the Severn Estuarr,, S. \\l Britain: mechanics of forrnation, prcservation and distribution. Philo-. sophicalTransactiotts of tlrc Rot'al Societl', London B 152: 381-ilE. Baird, D. T. 1957. Triassic reptile faLrnales fron N,lilford, Neu'Jerser'. Bulletin of the Nluseum of Comparative Zoologl, Il7: 449-5?'.0. Biewener, A. A. 2002. Biornechanics: ualking uith tr.rannosaurs. Natrzre 415:

97r-973. J. 1883. Application des potentials a l'dtude de ment des solides dlastioues. GaLrthier-Villars. Paris.

Bor-rssines
In ihe liF ing crocodilians, tliis muscle originates frorn around and wiihin the sr-rpraternporal fenestra, r,vhereas anong the lil'ing lizards, it originates frorn the region of the posttemporal fenestra (Lakler 1926; Oelricl-i I956; Fisher and Thrrner 1970; Nash and Tanner 1970; Avert'and Tanner 1971). In Tyrannosaurt$ re\ the snpratemporal fenestra is surrounded br'' a ror-rgl-rl1' bowl\,I. ADDUCTOR N,IANDIBULAE F,X'|ERNUS PROFUNDUS (rrC. r5.5):

shaped, smooth-surfaced supraternporal fossa, and the posttemporal fenestra

This is sirnilar to the condition in crocodilians, shallower ancl less borvllike in forrn. InT. rex, the suprateniporal fossa is deepest over the parietals, shallowing abruptlf in the frontal region. The parietal portion of the supratemporal fossa, as rvell as the snooth anterior face of the supraoccipitai crest, presurnabll'forrned the area of origin of the N,l. :rdd. rrancl. ext. prof. No clear delirniting rnark for ihis muscle could be found on the supraoccipital crest, although the rugose texis almost completely closed.

although there, the fossa

is

Figure 15.5. Sketch of the

left squamosal in dorsal view, based on BHI 4100. The proposed area of origin of the M. adductor ma nd i bu I ae extern us p ro fundus, based on BHI 3033 and 8H14100, is to the right of the dashed line. Anterior is to the right, Iateral to the top.

Scalebar=5cm.

ture along the dorsal margin strggests that this r,r'as not part of the area of flesl-rv origin. In ml'dissertation, I suggested that this muscle rnav also have taken origin from a flat surface on the dorsr-rm of the squarnosal. This seems to be correct, but not in the ser-rse intended in the dissertation, lr'here I had believed that the entire dorsal face n'right har.e given attachrnent to the muscle. N{ost of the dorsum appe ars to be too rough in texture for a muscle scar. Hoil'ever, Tom Carr (personal comnlunication) observed a crescentic smooth surface mediallv adjacent to the rnargin of the supratemporal fenestra on tl-ie squarnosals of BHI 3033 (and less clearlv on BHI 4100) that appears to have been a muscle attachrnent. Thr-rs, it seerris likelv that a portion of the M. add. nand. ext. prof. took origin frorn the dorsum of the sqtramosal.

N4ediallr', the parietals rise to forrn a sagittal crest that is mr-rch lou,er than the supraoccipitai crest. Hence, it rvoulcl seem that the antimeres of

this n-ruscle probabii'rnet across this crest.'l'he lateral surface of the parretal is sr-r-rootl-i all the riav to its ventral margin. This smooth surface continues dolvn across rnost of the posterodorsal portion of tl-ie lateral surface of the laterospher-roid and the anterodorsal corner of tl-re lateral surface of the prootic 1Fig. I i.71. The supratemporal fossa consists of 2 parts: first, the shallor'r'er frontal excavation anterior1.",, and second, a deeper posterior excavation bounded bi the parietal, the supraoccipital crest, and the arch

Jaw

Musculature

263

:

-. ,' ,'E "

' t:

:

' '::

: !:';1

11,.:;. .

":.::-"-

;.:

::!

$#"iir"....:*fu'.' ; '.: *srffiF.;.: .

Figure 15.6. Oblique anteroventrolateral view of the braincase of Tyran-

nosaurus rex, AMNH 51 17. Most of the lateral

r,:,,lir;;r:

ffi;ii

-,,,{^-^ ^l +1,^ ^^.;^+-l )ur /o!E ut LI lc yat IcLat

K

(labeled "Pa." on the

*

8 m 1or-rg) Corgosaurus (TN{P94.12.602) rvith fractured ar-rd healed right fibula ar-rd u'ell-healed dorsal ribs, as did Russell (1970) in G.Iibratus ancl as seen inT. rex (IrN'{NH PR2081, F ig. U.3). Roughened and thicker-red bone near the distal end of the left fibtrla of a Corgosaurus (Lal-rbe 1917) sr-rggests a healed bone fracture. Heaied midshaft fracture of the right fibula rvith good alignment r'r'as also r-roted ir-r TNIP91.36.500 (G.Iibratus). A possiblc r'i'ellhealed ur-tilateral clentari'fracture and a fractr,rred and rvell-l-realed right fibr-rla u'ere

Cnrrie (1997) reported a

Bruce M. Rothschild and Ralph

E Molnar

I

I

I

also founcl in that specimen (Keiran 1999; Tanke I996a). The freqtienci,' of fibular fr:rctures suggests that these are not fron-r falls, unless the anrmals n,ere less coordinated than at least one of use (R.NI.). More likelr',

the fractures resulted from conspecific interactions, but are less likelv frorr tail impacts. Tr,'rannosauricl tails are too high off the grour-rd, althougl-r possible injurl,from a prev nnimal (e.g., sauropod tail u,hip) could

Figure 17.3. Oblique ante-

rior view of leg of Tyrannosaurus (FMNH PR2081). Partially healed

fracture with possible infection.

be cor-rsiderccl. INTERAC'I'IoNs: Dingus (1996), Brochu (2002), and Rega and Brochr-r (2003) reported rib fractures in TyrannoscLuruE (Fig I7.4) and by Molnar (2001) in an urdescribecl t'n'rannosanrid (r'hich also had a humeral fracture). Fractnres har.e been reported ir-r gastraiia by Larnbe (1917) in Gorgosaurus ancl b-v Grierson (1998) in an unspeciated tl'rannosaur (TNIP97.12.229) frolr

Dinosaur Provencial Park, Alberta. Although fractures are br, definition tranura rclatecl, the specific source of the trarun:r in F-IVINH PRz08l ('l'. rer)

in an injured rib of a tooth fragrrent from a conspecific (Larson 2001a, 2001b). Fracture healing rnav result in limb element shortening r','ith malpositioning of eler-r-rents, as exenplified bv shortening in Albertosaurus (NIOR 3079) u'as revealecl b1'the presence

ar.rd

the specimen reported bv N{oh-rar (2001) nientioned abor,e. Pseudoarthro-

Tyra n

nosau ri d Pat holog ies

291

Figure 17.4. Lateral view

of Tyrannosaurus (FMNH PR2081)thorax. Rib fractures.

irerein the fracture components do not fuse but rather form a false joint, rvas noted in a Corgosaurus gastraiiun-r (RTN'IP 91.36.500; Keiran 1999). sis, n

Other evidence of injury incltrdes exostoses (Fig. 17.5), wherein a portion of the bone is spalled free at one end. Growth frorn the retained base produces an external bony overgrou'th, the exostosis. Rothschild and Tirnke (2005) reported hr:meral exostosis on FMNH PR20B1. The dan'iage has been variously attributed to avulsion of the teres rnajor or triceps humeraiis (Larson 2001a, 200lb; Carpenter and Smith 2001). Exostoses are found rn the scapulocoracoid FMNH PR208l (Larson 2001a, 2001b). Although

they'rvere originally attributed to osteoarthritis, ihese have been reclassrfied as exostoses because they are not at the joint surface. Rather, thev are at sites of rnuscle attachment. Molnar (2001) described exostosis in rretatarsal IV ofA. sarcophagus. Russell (1970) reported a distal humeral pathol-

in Daspletosourus torus. The roughened surface of the left metatarsal IV in Gorgosdurus (RTMP 91.16.500) suggests trautna, perhaps prey interaction fronr an event similar to that which restrlted in a srlall, mtrshroomlike hvperostosis on a right pes, amorphouslv shaped, digit III r,rngual (Larnbe 19l7). 'I'his pathologv, referred to as an osteocl-rondroma, was aiso found in a Corgosaurus pedal phalanx (RTMP 91.36.500, Rothschild and Tanke 2005). Rothschild og1,

292

Bruce M. Rothschild and Ralph E. Molnar

Figure 17.5. En face view

of Tyrannosaurus (FMNH PR2081 ) humerus. Surface disruption with bone spur.

Tyra n

nosa u rid Patholog ies

gure '17.6. Anteilor oblique vrew of Tyrannosaurus rex proximal pedal phalanx. Bump F

.^,,^^l- J/tc -+.^--:+^ u/ ^{ JLtE)) /Evudl)

fracture.

and Tanke (2005) described pe sagittal plane

-l

sagittal plane

Figure 19.3. Left supraorbital horn of Triceratops (A) Left lateral view caudal direction to the right. Questions marks sig nify possible tooth marks. (B) Caudal view of cross section of horn showing displacement of tooth marks in different transverse planes.

sen 1995), and their morphologv is consistent rvitl-r the peglike shape of stout tvrannosauricl tccth (Farlou'et al. l99l; Abler 1992). In Figure 19.lB, the second depressior-r cornpares to the apical portion of the crou,n of a nrarillarr'lateral tooth of an aclult T rex (Erickson and Olsen 1996, fig. 3). Thc svnrmctricalh,opposing positions of the depressions on ihe dorsal and r.'entral surfaces of the horn that pass through a comnlon sagittal plane through the nicllinc of the horn and clisparate directions of tooth penetration (Fig. 19.1B) stronglf impll'that the punctures resttlt frorn a single bite. Because the horn core is composed of a thick outer iaver of cornpact bone at thc points of penetration, tl-re clarnage requires a bite of ttnusttal force. Analvsis of cranial design and function in tvrannosatrrids indicates that the jan's are capablc of ger-rerating crushirg bites (Hurur-n artd Currie 2000; N,{eers 2002; Rar'field 200'1; Ral.field et al. 2001). In fact, Erickson et al. (1996) estimatecl tl-rat'I'. rexhar bv carnivorous dinosaurs. P 135-144 in P6rez-N{oreno, B. P., Iloltz,'l-. ]., Sanz. J. L., and \{oratalla, J.

Predator-Prey Behavtor in T. rex and Triceratops

References Cited

(ecls.). Aspecfs

oiTlrcropod Prtleobiologt'. (]aia: Reyista de ()eociencias, \,ht-

seu Nacional de Historia Natural, Lisbon,

Chir, K.,'[c-rkarvk,'Il ]'., Erickson,

Ii.

L. C. 1998. A king-sizecl iheropocl coprolite. Nalure 39J: 68tl-682. Clurrie, P J., ancl jacobsen, '\. R. 199;. An azhclarcl-ricl pterosarrr eaten bv a velo^; ""+^' :'' ^ rl' ^-"'- ^'l C anad i an I cnLnn I of E ar th S cience 32: 972 -92i. l)odson, P. 1971. Seclirnentologv and t:rphonornv of the Oldnan Forrnation (Canrpanian). Dinosaur Provincial Park, Alberta (Canada). PalaeogeograCl. 14., ancl Calk.

o c I innto I o gt. I' a I a e o e c o Io 91, 1 0 : 2 I -7'1. 1996 The []r-trnedDinosattrs. PrincetonLlnilersitvPress,Princeton,NJ. Dodson, P, Forster. C. A., and Saurpsorr, S. D. 2004. Ceratopsiclae. P. 194-5It -. in Weishampel, D., Dodson, P., and Osm6lska, H. (eds.). Tlrc DinosatLria. t-lniversitv of Califomia Press, Berkelev. Erickson, C. \1., ancl Olson, K. H. 1996. Bite narks attributable toTyranrutsatLrus rer: prelirninarv description and iLuplic atrons. lountal of\lertebrate Paleontr;logt' 16: 1Ii-178. Erickson. C. \1., \ran Kirk. S. D.. SLr, 1.. Levenstoir, Nl. E.. Caler, \\r. E., and Carter, D. R. 1996. Bite-tbrce estination for Trrarntosaurus rex frorn toothnrarkecl bones. Ndlure 182: 706-708. Estcs, R. D. 1991. 'l'|rc Beharior GtLide to African X,Iarnmals. LJniversitv of Clalifnrrtir Press. B.rkeler. Farlon, J. O. 1990. Dvnarnic clinosaurs. Paleobiolc4,t 16: ?.11-241. Farlou, J. O., ancl Brirrkman, D. L. 1994. \\'ear surfaces on the teeth of tvrannosatrrs. P 165-17t in Rosenberg, C. D., and \\blberg, D. L. (ecls.). Dino F'est. Paleontological Societv Special Publicatron 7. Farlon, i. O., Brinkrnan, D. L., Abler, \\i L., Currie, P J. 1991. Size, shape, ancl serration clensitv of theropocl clinosaur lateral teeth. Nlodern Ceologt, 16

p h1'. P al ae

t6l-19E. F-arlou. J. O., and Holtz, T. R., ]r.2002. The fossil record of predation in dinosarrrs. P. 2;I-265 in Kou:rleriski, NI.. ancl Keller, P H. (eds.). TlteFossilRecord ofPredatior. Paleontological Societv Papers

D.

E.

1987. Paleoertvironrrents ofvertebrate-bearing strata

during the Cretaceous-Paleogcne transition, Eastern N,lontan:r and Western r-orth Dakota. Palaios 2: 282-29;. IIapp, J. \\'.. 2003. Pcriosteal reactiorr to injr.rries ofthe supraorbital horn and sqrranosal of an aclult'Iriceratops (Dinosauria: Ceratopsiclae). lotLrnal of \lertebrate Paleontologt 2 3 i 3. Suppleruent): 59A I1app, ) \\''., and Nlorrou', C. N,l. 1991. Bone rnoclification of sub:rdultlriceratops (L)inosauria: Ceratopsidae) bv crocodr'lian and theropocl dining. IorLrnal of \''ertehrate Paleontologt 17(Suppl. l): 51A. . 2000. Evidencc ofsoft tissue associated u'ith nasal and srrpraorbit:rl horn cores, rostr:rl ancl eroccipital o{ Tr icerato p s. l ournal of \te rtel:rate PaleontolFastovskv,

ogr' 20tSrppl. 3): '17,\

Hatc}rer. J. B., Nlarsh, O. C., and Lull. R. S. 1907. The Ceratopsia. Uritcd States Geological Surr,er' -\'lonograph 49. Halncs, Cl. 1980. Er,idence of carrnivore gnau'ing on Pleistocene and recent nrarrrnr:rlian bones. P ale obiolo gt 6 t 3+1 -3 t 1. 19E1 Prey borres and predators: potential ecologic informatiorr frorn analvsis of bole sites. Ossa 7:i5-91. -. Holnres, R. B.. F'orster, C., Rr,an, NI., ancl Shcphercl.

K. l\'1.2001. Aneu species

of Ch.asntosatLrus (l)inosaruria: Ceratopsia) from tl-re l)inosaur Park Forrratior of southern Alberia. Ccnndian lottrnal of Eartlt Science 38: 1423-l'f 18.

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florner, J. R., and Lessern, D. 1993. The Conplete T rel. Sinon & Schr-rster, Ner.i'York.

Huether, S. E., and l"4cCance, K. L. 2000. L)nderstandingPatlnpht,siolog,t. N'losbr', St. Louis. J. H., ancl Currie, P j.2000. The crLrshingbite of tr.rannosaLrrids. /ournal of \lertebrate PaleontologT- 20: 619-621. Jacobser-r, A. R. 1995. Predatorv Behavior of Carnir,orons Dinosaurs: Ecological Interpretations Based on'Iooth Marked Dinosaur Bones and \Vear Patterns of Theropod Teeth. N,I.Sc. thesis, Universitv of Copenhagen. 1998 F-eediDg beh:rvior of carnir.'orous dinosaurs as determined bt'tooth marks on dinosaur bor.res. His/oric aI Bictlog,t 11: 17-26. -. 2001. Tooth-marked small theropod bone: an ertremell rare trace. P. 5863 irr Tanke, D., and Carpenter, K. (eds.). NlesozoicYertebrate Life. Indiana -. lJniversity Press, Bloomington Krurrk, Ii. 19 ,-2. The Spotted Htena: A Studl of Predation and Social Behat,ior. Lhiversitr, of Chicago Press, Chicago. Lull, R. S. 1933. A Reyision of the Ceratopsia, or Horned Dinosaurs. lnlernoirs of the Peabodl, N{useum of Natural I{istorl' 3. Nlech, L. D. 1970. The Wolf: The E,cologt, turd Behavior of an Endangered Specles. Natural Historr,Press, Garden Cit\', NY. N'lech, L. D., and Pcterson. R. O. 2001. Wolf-prev relertiorrs. P. 111-160 in N,{cch, D., and Boitani, t,. (eds.). Vlolyes: Behaykr, Ecolog,t,, and Conservation. LIniversitr' of Chicago Press, Chicago. N{eers, Ntl. B. 2002. N{arimuni bite force ancl prel stze olTt,rannosaurus rex and their relationships to the infe rence of feecling behavior. Historical Biologl,

Hurun,

i6:

1-12.

N{olnar, R. E. 1998. Nlechanical factors in the design ofthe skull ofTyrannosarrrrrs rex (Osborn, 1905). P 193-218 in P6rez-\'{oreno, B. P, Holtz, T. J.,

L., and Nlloratalla, ). (eds.). Aspects of Tlrcropod Paleobiologt'. Caia: Revista de Geociencias, NIuseu Nacional de Historia Natural, Lisbon, l,i. 2001. Theropod pathologr': a literatLrre survc\'. P )i7-363 in Tanke, D., and Carpenter, K. (eds.). Nlesozctic\lertebrate Llfa. Indiana t.inir,ersitr.Press, Sar.rz, J.

-.

Bloornington

Ostrom, J. H., ancl Wellnhofer, P 1986. The NlLrnich specirnen of Triceratops nith a rer.'ision of the genus. Zitteliana 14: 111-158. Paul, G. S. 1988. Predatort, Dinosaurs of the World. Sin.ron & Schuster, Neu,

\brk. Rar'field, E. j. 2004. Cranial rrechanics and feeding inTtrarutosaurus rex. Proceedings ofthe Rolal Societt ofLondon B 771: I4j1-1159. Ravfield, E. J., Nomran, D. B.. Ilorner, C. C., Horner. J. R., Smith, P N4., Thomason, l. J., and Upchurch, P. 2001. Cranial design and function in a large theropod dinosaur. Natttre 409: 10ll-1017. Rogers, R. R. 1990. 1-aphononl of tfrree dinosaur bone beds in the Llpper Cretaceous T\lo N{edicine Formation of Nort}nvestern Nlontan:r: eviclence for dronght-related mortalitv. Palaios 5: 39+-413. Rothschild, B. N{., and Tanke, D. H. 1992. Paleoscene 13. Paleopathologv of vertebrates: ir.rsights to lifestr,le ancl health in the geological record. Geoscience

Canada 19: 7l-82.

Sampson, S. D., Rvan,

\'{.

J.,

and'lhnke, D. H.

1997.

Craniofacial ontogen}'in

centrosaurine clinosaurs (Ornithischia: Ceratopsidae): taxonornic and beha'n'ioral irnplications. Zoological lountal of the l,itntean Society 12I: anf

))-

Predator-Prey Behavtor ln T. rex and

Triceratops

367

Schaller, G. B. 1972. The Serengeti Lirn: AStud1,of ltredator-Pre1'Relations. Llniversitv of Chicago Pre ss, Ciricago.

Sereno,P.,andNov:rs,F.tr. 1993.'l.heskullandneckofthebasaltheropoclHerrerds(lurus iscltigtLalastensis. |ounnl of Vertebrate Paleontologt, 13: 4tI-I t-6. Tankc, D., :rnd Currie, P. 1998. Heacl-biting behavior in theropocl clinosaurs: palcopathological er.'idence. P. 167-lE4 in P6rez-N'loreno, B. P, Iloltz, T. 1., Sarrz, J. L., and Nloratalla, J. (ecls.). Aspects of'I'heropod Paleobiologl,. ()aia: Reyista de Ceociencias, A4usau Nacional de Historia Natural, Lisbon, 15. Toots, H. 1965. Sequence of clisarticulation in rnarnrrialian skeletons . Llniversitt of Wl,orning Contributions to Geolog1- 4: 37-39. Van Valkenburgh. B., and N,lolnar, R. tr. 2002. Dinosattrian irud mammalian predators conpared. Paleobiolog,t 28 57 t--543. Williamson, T. U. 1996. ?Brachycharnpsd sedler-i, sp. nov. (Crococlvlia, Alligatoroidea), fron ihe Upper Cretaceous (Lou'er Canpanian) Nlenefee Fortlertiorr, Northwestern Neu,Nlerico. lournal of Yertebrate Paleontolog,t 16: 42r-443.

368

John Happ

B

A 7

:-'t

20't. l,4orphomet-

r c c,nensions measured for this analysrs. (A) Skull of juven i le Go rg osau rus

libratus, after Carr (1999). BL, skull base

length, QL, skull quadrate length. (B) Dentary tooth of Tarbosaurus bataar, after Maleev (1

974). Abb reviatio

FABL,

fore-aft

ns :

base

length; BW, base width,' CH, crown height. See text for discussion.

370

Thomas R. Holtz

Jr.

A CRITICAL REAPPRAISAL OF THE

20

OBLIGATE SCAVENGING HYPOTH ESIS FOR TYRANNOSAURUS REX AND OTH ER TYRANT DINOSAU RS Thomas R. Holtz Jr.

The biologt' of tl-ie giant latest Cretaceous coeluros:r:rr Tyrannosaurus rex and its kin, the Ti'rannosauridae, i-ras been of great intercst to botl-r paleontologists and the general public. Of particular interest is the ecological behavior of these dinosaurs: specificallr', nere tr,rant dinosaurs predators or

Introduction

scar,engers?

Arrong modern camir,ores (that is, anirnals tliat derive the majoritv of their food requirements in the forrn of flesh), both scar.er-rging (obtaining food fron animals alreacll.dead b1'other means) and predation (killing other anirrials for food) are founcl. Indeed, large-bodied animals thai obtarn their foocl solell,fron one or the clther behavior seem to be vanishinglv rare (DeVault et al. 2003). Crocuta crocuta (the spotted hvena) \\'as once thought to be primariiv a scar.'enger (e.g., Walker 1964), btrt direct fielci observatior-rs rer.'ealed that thev obtair-r much of their food br,' preclation (KruLrk 1972;

Holekarnp et al. 1997), although the srnaller Hyaena hl,aena and H. brr.utnea (th.e striped and brown hvena, respectii'elr') do obtain more food br, scaverrging than bv killing (Krr-ruk 1976; On'ens and On'ens 1978). Panthera leo (the lion), the archetvpal nan-rrnalian predator, obtains approxrrnatelr, l0% ol its food bv scar,enging (N4ills and Biggs 1993). It is therefore difficult to define a scavenger \.ersus a predator. It might be rlore accurate to sa1'that there erists an ecologic:rl categorv called carnivore, and that carnivores var."' in terrns of the clegree of scavenging ar-icl preclation behar. iors bv u'hich they obtain foocl. Deternrining thc relative frequeno'of scavenging versus predation is extraordinarilv difficult er,en for rrodern preclators. Of several clifferent field techniques (stonach ana11'sis, fecal anali,'sis, tracking spoor, opportur.tistic encoulrter, radio location, ancl direct observation), the least biasecl nethod, and the one in n'hich such factors as prev selection, kill frequencies, ar-rd consurrption rates c:rn be nieasured, is direct obsen'ation (N{ills 1996; Radloff ancl Drflbit 2004). Of corlrse, direct fielcl observation of t'r' rannosauricl food acquisition behal'ior is impossible for paleontologists. Frrrllrermore. recogrizirrga scavenqirrgeventfrorn a srrccessfrrl pre

Tyrannosaurus rex. The Tyrant King

King of the Bosporus (Tyrant 4)

J. F. Rivkin - Age of Dinosaurs 01 - Tyrannosaurus Rex

Barnum Brown: The Man Who Discovered Tyrannosaurus Rex

Tyrant

Tyrant Moon

Rex

Tyrannosaurus Sue: The Extraordinary Saga of the Largest, Most Fought over T-Rex Ever Found

Tyrant Moon

Tyrant Moon

Milosevic: The People's Tyrant

Tyrant Moon

Dear Tyrant

A Tyrant Abdicates

Tyrant Il Distruttore

Anonymus Rex

Tyrant?s Blood

There Came a Tyrant

Solus Rex

Theodore Rex

Anonymus Rex

Z. Rex

Parasitus Rex

Rattus Rex

Anonymus Rex

Z Rex

Theodore Rex

L.A. Rex

Rattus Rex

Tyrant Storm of Arrows

The Mask Of The Rex

Tyrannosaurus rex. The Tyrant King

King of the Bosporus (Tyrant 4)

J. F. Rivkin - Age of Dinosaurs 01 - Tyrannosaurus Rex

Barnum Brown: The Man Who Discovered Tyrannosaurus Rex

Tyrant

Tyrant Moon

Rex

Tyrannosaurus Sue: The Extraordinary Saga of the Largest, Most Fought over T-Rex Ever Found

Tyrant Moon

Tyrant Moon

Milosevic: The People's Tyrant

Tyrant Moon

Dear Tyrant

A Tyrant Abdicates

Tyrant Il Distruttore

Anonymus Rex

Tyrant?s Blood

There Came a Tyrant

Solus Rex

Theodore Rex

Anonymus Rex

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