Daniel J. Chure, Observation on the Morphology and Pathology of the Gastral Basket of Allosaurus, Based

ORYCTOS,Vol. 3 : 29 - 37,Décembre 2000

OBSERVATIONSONTHE MORPHOLOGYAND PATHOTOGY OF THE GASTRAL BASKET OF ALLOSAURUS,BASED ON A NE\rySPECIMEN FROM DINOSAUR NATIONAL MONT]MENT

Daniel J. CHURE

DinosaurNational Monument, Box 128,Jensen UT 84035,USA [email protected]

Abstract: A well preservedand complete gastral basket of Allosaurus(DINO 11541)corrects a numberof earlier misinterpretationsof this structurein Allosaurus.The basket consists of eighteenrows of gastralia.The first row has only oneelement per sideand these do not overlapmedially but ratherform a craniallyfacing notch. All otherrows havetwo elementsper side,the medialone being the longer.The right andleft medianelements overlap at the midline of the basket.Allosaurus has only four elementsper gastralrow. Previousinterpretations for Allosaurushave been as high asnine elementsper row. The supposedfused, V-shaped mediangastral element is now knownto be a furcula.The supposedfour lateralelements in USNM 4734are actual- ly all part of a singlemedian element injured during life andhealed as a seriesof pseudoarthroses.The presenceof pseudoarthrosesand calluses in othermedian gastral elements of USNM 4734 furrhersupport this interpretation. The presenceof similarpathologies in the gastraliaof anotherspecimen of Allosaurus(USNM 8367)as well asin the dorsalribs of a specimenof Acrocanthosaurusatokensis (SMU 74646)suggests that suchinjuries were not uncommonin allosauroidtheropods. These injuries may be the resultof eitherstruggles with prey or intraspecific behavior,such as kicking or head-flankbutting.

Key words:Dinosauria, Theropoda, Osteology, Allosaurus, Gastralia, Jurassic, Morrison, Pathology

Observationssur la morphologieet les pathologiesde la cagegastrale d'Allosaurus basées sur un nouveauspécimen daDinosaur National Monurnent,Etats-Unis d'Amérique

Résumé: Unecage gastrale complète en bon état de préserv ation d'Allosaurus permet de corrigerd'anciennes inter- prétationsde cettestructure chez ce dinosaure.Le cageen questionconsiste en 18 rangéesde gasfralia.La premiè- re rangéeprésente un seulélément par côté; les deuxéléments de cettepaire ne serecoupent pas médialement mais formentune encoche dirigée cranialement. Les auffesrangées possèdent deux éléments par côté,le médianétant le plus long. Les élémentsmédians gauches et droitesse recoupent sur I'axe de symétrie.Allosaurus ne possèdeque quaffeéléments par rangéegasfrale. Les anciennesinterprétations pour A/Iosaurus ont proposéjusqu'à 9 élémentspar rangée.L élémentgastral suppo- séfusionné en formede V s'estrévélé être une furcula. Les quaffeéléments latéraux supposés de USNM 4734sont enfait lesfragments d'un uniqueélément central fracturé durant la vie de I'animalet cicatrisésous forme d'une série depseudarthroses. La présencede pseudarthroseset de calssur d'autres éléments de la sériegastrale de USNM 4734 soutientcette interprétation. La présencede pathologiessimilaires sur les gasfraliad'un autrespécimen d'Allosaurus (USNM 8367)et sur les côtesd'un spécimend'Acrocanthosaurus atokensis (SMU 74646)indique que de tellesblessures n'étaient pas rares chezles théropodesallosauroides. Ces blessures peuvent être le résultatde luttesavec des proies ou de comporte- mentsintraspécifiques tels quedes ruades ou descoups de têtecontre les flancs.

Mots clés: Dinosaurta,Theropoda, Ostéologie, Allosaurus, Gastralia, Jurassique, Morrison, Pathologie 29 ORYCTOS.Vo1.3.2000

INTRODUCTION of a furcula, the compositionand morphology of the wrist, and the gastralbasket. Both the wrist and the Allosaurus is the most abundanttheropod in the furcula have already been described (Chure & Late JurassicMorrison Formation (Foster & Chure, Madsen,1996; Chure, 1999,and in press).The pre- 1998,2000 ; Chureet a1.,2000).As a resultof this sentreport focuseson the gastralbasket. rich fossil record it is one of the best known thero- podsand has been the subjectof severalmonographic INSTITUTIONAL ABBREVIATIONS studies(Gilmore, 1920; Madsen,1976; Chure, 2000). AMNH = AmericanMuseum of NaturalHistory NY. Becauseof this Allosaurus is a critical taxon in many BYU = EarthSciences Museum, Brigham Young University, UT. phylogeneticanalyses of the Theropoda. CMNH = CarnegieMuseum of NaturalHistory PA However, the discovery of a spectacularlycom- DINO = DinosaurNational Monument, UT. plete and articulated specimen of Allosaurus in MOR = Museumof Therockies,MT. Dinosaur National Monument has clarified several SMU = SouthernMethodist University, TX. aspectsof Allosaurusmorphology; namely the presence USNM = UnitedStates National Museum, Washington, D.C.

Figure 1. Gastral basket of Allosaurus (DINO 11541) in dorsal view. A. Position of basket between pectoral and pelvic girdles. B. Close up of median and lateral elements.Scale bar in cm.

30 CHURE - OBSERVATIONSON TIIE MORPHOLOGYANDPATHOLOGY OF TIIE GASTRALBASKET OF ALLOSAURUS

'Weigert, DESCRIPTION (Gradzinski, 1969; 1927), which probably explainshow the skeletonremained articulated in the The specimen(DINO 11541)is a new speciesof high energyriver environment.Part of the right (stra- Allosaurus, currently under description (Chure, tigraphically up) forelimb and hindlimb and the right 2000). It was found in the upper portion of a 60 cm. side of the skull is missing, along with the middle layer of conglomerateat the base of a 1.4 m deep part of the tail. The right side of the gastral basket paleochannelin the Salt Wash Member of the was damagedbefore discovery and many of the late- Morrison Formation of Dinosaur National ral elementsare missing or incomplete.However, the Monument (Hubert & Chure, 1992). The skeleton gastralbasket was in-placebetween the pectoralgird- was in the hyperdorsoflexedattitude strongly sugges- le andpelvis (fig. 1). tive of desiccation of the body before burial

l2 .,," :.-

15 Si1'':'", t7 t6,e

-:!:-' t t' l8 t7 t5

EI:I:n l3 B t2 &

Figure 2. 18 Gastral basket of Allosaurus 18 (DrNO 11541) in ventral view. A. View showing narrowing of basket towards caudal end. B. Closeup showing t7 displacementof contact between median elements. Numbers refer to gastral row, 16 numbered from front of basket. Scale bar in cm.

31 ORYCTOS,Vol.3,2000

right pubis left pubis The basket is rn a large block of sandstone along with the vertebral column, left dorsal ribs, the left scapula, and the left femur. As a result. the cranialhalf of the basketis exposed in dorsal view and the caudalhalf in ventral view. The cranial half of the cuirassis broad and flat (possiblydue in part to postmortem dorsoventral flattening), with a gentle dorsal curvature.The caudal part is narrower and Figure 3. Medial view of left lateral elements of gastral basket in DINO 11541. Note their position more V-shaped in cross- lateral to distal end of left pubis. Numbers refer to gastral row, numbered from front of basket. section(figs. 1, 2) and on the better preserved left side the caudalpart of the basket can be seen to be lateral to the pubic boot (fie.3). The basket contains eighteenrows of gastralia. The first row is different than the rest of the cuirass in severalways (fig. 4). In the flrst row there is only one elementon each side, ratherthan two. Theseele- ments do not overlap medially. Instead, the medial end of each is a vertical, oval surface and the right and left gastralia meet such that their medial faces form a cra- nially facing right angle notch (fig. 44, C). There are no grooveson the cranial margin of these elements for contact with lateral gastralia, further confirming that the first row consists only of the medianelements (fig. aB).

32 CHURE - OBSERVATIONSON THE MORPHOLOGYAND PATHOLOGYOF TFM GASTRAL BASKET OF ALLOSAURUS

In gastral rows two through eighteenthere are four gastraliaper row, two median and two lateral (fig. 5). There is no median V-shapedelement like the one reported by Gilmore (1920) in USNM 4734. The median elementsare longer and more robustthan the lateral ones and slightly sinuous in dorsalor ventralview (fig. 1). The medialend is cau- dally curved and expan- ded (fig. 2). The medial ends overlap such that in ventral view the right median gastraliumis ventral to the left. The ventral surfaceof the medial end of the left gastralium is convex and this fits into a concavity on the dorsal surfaceof the medial end of the right gastralium (fig. 2B). Laterally the medianelements taper to a point (fig. 5B). A groove on the cranial face of the median gastraliais for the contact with the lateral element(figs. 58, 6). There has been postmortem separation between the medianelements of the cuirass(fig. 5).

The ventral overlappingof the right medianele- gastralia(figs. 1A, B, 5B). This is typical for thero- mentsis bestseen in mediangastral pm I7. Therehas pods, although the condition is reversed in some been slight disarticulationof this contactin segments maniraptorans (Norell & Makovicky, 1997). Each 18 and 16.In segments13,14, and 15 therehas been lateral elementhas a wide, truncatedlateral edgeand considerablecranial shifting of the left median ele- tapersmedially (fig. 5B). Each lateral elementhas a ments,to the extentthat, for example,the medial end groove and fits in a groove on the craniodorsaledge of left mediangastralium 15 overlapsthe shaftof right the medial element (fig. 6). This overlap between median gastralium 14. This offset continues, to a median and lateral elementswas not strong,as there varying degree,through gastralsegment 2. is some separationalong this contact in all gastral The lateral elementsare shorterthan the median rows in DINO lI54l.

33 ORYCTOS,Vol.3,2000

However,the V-shapedelement in USNM 4734, of which only one was found, is now known to be a furcula, basedon the in-situ furcula found in DINO I754I (Chure & Madsen, 1996). This drops Gilmore's count to six or possiblyeight. Examination of the row which Gilmore thought to preserve four lateral gastralia shows that the three proximal segments are likely to be parts of a single, medial gastralium, which was damagedduring life and healed pathologically. The gastraliaof USNM 4734 show a number of Figure 6. Crosssection of medianand lateral pairs of right gastralia breaksand pathologies. Some are greenbreaks which in rows 16 and l7 of DINO 11541.drawn from a brokensurface. occurredat the time of deathor post-mortem(frg.7) Crosssection of row 16 at about 185 mm lateralfrom midline of bas- and need not concernus any further. Other patholo- ket. Crosssection of row 17 at about160 mm lateralfrom midlineof gies are the result of injuries life basket.Spacing between rows 16and 17reduced for illustrativepur- sustainedduring poses.le = lateralelement, me = medianelement Scale bar = 1 cm. which subsequentlyhealed. These are of two types. The first are healed fractures indicated by calluses (fig. 8C, D, E). The second are pseudoarthroses, DISCUSSION breakswhich during healing formed moveablejoints (fig. 84, B). Several of thesepseudoarthroses have The gastral cuirassof DINO lI54l is the most well formed ball and socket articulations.In all the- completeand best preservedfor any non-coelurosau- ropods the contactsbetween medial and lateral gas- rian theropod.Gastralia inAllosaurus areusually iso- tralia arelong, overlapping,sliding contacts.Ball and lated and incomplete (Cleveland-Lloyd Dinosaur socketjoints are unknown in gastralbaskets, further Quarry collections in the University of Utah, MOR supportingthe interpretationthat theseare pseudoar- 693,AMNH 5753,CMNH 33903,USNM 9367).An throses. exceptionis a partial basketin USNM 4734 desci- Thus, anomaliesin the gastralbasket of USNM bed by Gilmore (1920). However, in light of DINO 4734 canbest be interpretedas being the result of an 7154I several enors of interpretation can now be injury during life to the mediangashal elements.The identified in that work. subsequentregular movement of the gastral basket The gastral basket of USNM 4734 is still in during breathingand locomotion resulted in the deve- matrix, in threeblocks which fit together.It has been lopment of a number of pseudoarthroses.This inter- dorsoventrallyflattened and retainsnone of its origi- pretation, coupled with the recognition that nal curvature.The basketis exposedin ventral view, Gilmore's median element as a furcula, reducesthe although some of the elements have been rotated count in USNM 4734 to four elementsper row, a along their long axis and someare displaced.Most of median and lateral element on each side. This is the elements preserved are median and lateral ele- consistentwith what is now known basedon DINO ments of the right side, although there are a few scat- I754I and is typical for theropods(Claessons, 1996). tered left median elementspresent. There is a growing interest in how broad patterns Based on his study of USNM 4734 and 8367 of pathologies may provide insight into vertebrate Gilmore (1920) estimated that there were at least paleobiologyat varioustaxonomic levels (Rothschild seven,and possibly nine, gasûalia per row (at least & Martin, 1993; Rothschild & Tanke, 1992).Among tlree, and possibly four, laterals and a V-shaped dinosaurssuch analyseshave been done for ornthis- medianelement). This is an exceptionallyhigh count, chians but not yet undertaken on the same scale for the highest for any theropod.Gilmore (1920: p. 54) theropods.Nevertheless, it may be significant that found support for this high count in one gastral row callusesand pseudoarthrosesin the gastralialike those in USNM 4734 whtchhe thought preservedfour late- in USNM 4734 are also are present in the scattered rals on one side(figs. 7, 8A, B). gastralia of another Allosaurus fragilis specimen, 34 CHURE - OBSERVATIONSON THE MORPHOLOGYAND PATHOLOGYOF THE GASTRALBASKET OF ALLOSAURUS

,(,

Figule 7. Gastlalbasket in Allo.;uurus.fizrgllls(USNM 4734).A. Photographof basketin ventralview. B. Explanatoryline drawing.cl, c2, c3 = ciilluseson nredialsastral elements, g = greenbreaks, p = peudoarthlosealsurfaces on mediangastral elements, 1,2,3,4 = 4lateral gastral elementsas identifiedby Gihnore( 1920).Scale bar in cm.

USNM 8367(Gilmore,1920: fig. 38).This suggests morphologicalvariation betweengenera, including that injuries to the flanks and belly region may not the presenceof V-shapedmedian elements. have been uncommonin Allosaurusand that those The gastralbasket in Acro c antho s aurus atoken- injurieswere not alwaysfatal. These injuries may be sis hasat leastfour V-shapedmedian elements in the the result of intraspecificbehaviors, such as head- caudal region but only paired overlappingmedian flank butting or kicking (Paul, 1988), or possibly elementsare presentin the cranial region (Harris, from struggles during the subduing of prey, 1998). These V-shapedelements are clearly fused although we have no direct knowledge of what median gastraliaas they have groovesalong their Allosaurus preyed on or even if it was a predator. cranial marginsfor contactwith the medial part of Flank injuries may be of broad behavioralsignifi- the the lateral gastralia. Thus Acrocanthosaurus cance,at leastamong allosauroids, as Harris (1998) retainsthe generaltheropod pattern of four elements has reported a series of calluses and pseudoar- per row. throseson the dorsalrib shaftsof Acrocanthosaurus In Poekilopleuron bucklandi (Eudes- atokensis. Deslongchamps,1838) there are at leastseven V-sha- Finally, the discovery of an in-place furcula in ped median elements but, in contrast to DINO I154I led to the identification of a furcula in a Acrocanthosanrlts,they are in the cranial half of the numberof specimensof A/losantrus,both described basket and are more sinuous than in andundescribed (Chure & Madsen,1996).Alcober er Acrocanthosaurus.The only known specimenof P al. (1998) reported a furcula in an unnamedcarcha- bucklandi, including the gastralia,was destroyedin rodontosauridallosauroid from Argentina. However, an Allied bombing raid on Caen in 1944 (Taquet one can not jump to the conclusionthat any V-sha- 1998). Fortunately,a cast of the baskethas recently ped element is a furcula, becausethe few gastral been rediscoveredin Paris (Ronan Allian, pers. basketsknown in basaltetanurines show sienificant comm. 2000), and is currently inder study.

35 ORYCTOS.Vol. 3.2000

Finally, two V-shapedmedian gastral elements the spinosauroid Tbrvosaurus tanneri are known havebeen collected from the Dry Mesa Quarry in the from the site (Britt, l99l). This suggeststhat median Morrison Formationof Colorado(fig. 9). While these V-shapedgastral elements may have a wide distribu- elementsare not referableto Allosaurus, large speci- tion in basaltetanurines. mens of the neoceratosaurianceratosaurus sp. and

Iateral element

medial element

.l ll C D

Fi_cure8. Pathologiesin the the gastraliaof Allosuurus.frugilis (USNM 4134).A. Close up of rhe elementinterpreted by Gilmore ( I 920) as showing fbur gastraliaon one side of basket.as u'ell as severalsegments of medianelements with pseudoarthrosealsur- fàces.B. Explanatorydrawing of A. C. Closeup of callus(c I in fig. 7B). D. Closeup of pairedcalluses (c2 in fig. 7B). E. Closeup of callus(c3 in fi-e.'lB). 1,2,3,4,= Gilmore'sinterpretation of foulelementson one sideof basket.Lateral element, median element = identificationin this work of Gilmore'selements.

Figure 9. Likely V-shapedmedian gastral elements from the Dry Mesa Quarry in the Morrison Formation of CO. Ventral view. A. BYU 5115 B. BYU 12926.Scale bar in cm.

36 CHIJRE - OBSERVATIONSON T}IE MORPHOLOGYAND PATHOLOGYOF TIIE GASTRALBASKET OFALLOSAURUS

ACKNOWLEDGEMENTS Paleontology16 (3): 573-577. CLAESSONS,L.P.A.M. 1996.Dinosaur gastralia and their function This paper is an outgrowth of a Ph.D. in respiration.Joumal of VertebratePaleontology 16 (supplementto no.3): 284. Dissertationat Columbia University on the systema- EUDES-DESLONGCHAMPS,J.A. 1838. Mémoire sur le tics of the theropodfamily Allosauridae.I thank Drs. Poekilopleuronbucklandi, grand saurien fossile, intermédiaire Malcom McKenna and Eugene Gaffney for their entreles crocodileset les lézards;découvert dans la carrièrede encouragementand supportof that study.Thanks also la Maladrerie,près Caen, au moisde juillet L835.Mémoire de la go to Dr. Mark Norell (AMNH), Drs. Bob Purdy and sociétélinnéenne de Normandie6:37-146. Michael Brett-Surman (USNM), Dr. Jacques FOSTER,J.R. & CHURE,D.J. 1998.Pattems of theropoddiversity and distributionin the Late JurassicMorrison Formation, wes- Gauthier (YPM), Dr. Richard Stucky (DMNH), Mr. tern USA. Abstractsand Programfor the Fifih International Ken Stadtman(BYU), Dr. Jack Horner (MOR), Dr. Symposiurnon the Jurassic System,Intemational Union of Richard Cifelli (OMNH), Dr. Dave Berman Geological Science s, Subcommission on JurassicStratigraphy, (CMNH), Mr. Chuck Schaff (INf:CZ),and Ms. Laurel Vancouver,British Columbia,Canada: 30-31. Casjen (UU) for allowing me to study specimens in 2000.An ilium of a juve- (Dinosauria, under their care. My thanks to Ann Elder and Scott rrl.leStokesosaarus Theropoda)from the Morrison Formation (Upper Jurassic,Kimmeridgian), Meade County, Madsen (Dinosaur National Monument) and their SouthDakota. BrigharnYoung University Geology Studies 45:5-10 volunteer crews who labored long and skillfully for GILMORE,C.W. 1920.Osteology of the carnivorousDinosauria in many yearsin excavatingDINO Ll54l and skillfully theUnited States National Museum, with specialreference to the preparedthe gashal basketof the specimen.Support generaAntrodemus (Allosauras) and Ceratosaurus.United for this project camefrom the National Park Service StatesNational Museum Bulletin 110:159 pp. and DinosaurNational Monument. GRADZINSKI, R. 1969.Sedimentation of dinosaur-bearingUpper Cretaceousdeposits of the Nemegt Basin, Gobi desert. PalaeontologicaPolonica 2l: 148-229+ platesXXXVU - XLU. REFERENCES HARRIS,J.D. I 998.A reanalysisof Acro c antho s aurus atokensis, its ALCOBER,O.; SERENO,P.C.; LARSSON, H.C.E;, MARTINEZ, phylogeneticstatus, and paleobiogeographic implications, based R.N. & VARRICCHIO,D.J. 1998.ALate Cretaceouscarcharo- on a new specimenfrom Texas.New Mexico Museumof Natural dontosaurid(Theropoda: Allosauroidea) from Argentina. Joumal Historyand Science,Bulletin 13 75 pp. ofVertebratePaleontology l8 (supplementto no. 3): 23A. HLIBERT,J.F. & CHURE,D.J.1992.Taphonomy of. anAllosaurus BRITT, B.B. 1991.Theropods of the Dry Mesa Quarry(Morrison quarry in the depositsof a Late Jurassicbraided river with a gra- Formation,Late Jurassic), Colorado, with emphasison theosteo- vel-sand bedload, Salt Wash Membeq Dinosaur National logy of Tonosaurustanneri. Bigham YoungUniversity Geology Monument, Utah. /n.' WLSON, J.R. (ed.) Field Guide to Studies37: l-72. Geologic Excursions in Utah and Adjacent Areas of Nevada, CHLJRE,D.J. 2000. A New Speciesof. Allosaurus from theMorrison Idaho, and llloming. Utah Geological Survey, Miscellaneous Formation, Dinosaur National Monument (UT-CO) and a Publication92-3: 37 5-381. Revision of the Theropod Family Allosauridae. Ph.D. MADSEN, J.H. 1976.Allosaurus fragilis: A RevisedOsteology. Dissertation,Department of Earthand Environmental Sciences, UtahGeological and Mineral SurveyBulletin 109:163 pp. ColumbiaUniversity, N.Y.C., N.Y.: 1200pp. NORELL, M.A. & MAKOVICKI P.J.1997. knportant features of 1999.The wrist of Allosaurusand the evolution of the the dromaeosaurskeleton: information from a new specimen. semilunatecarpal. Joumal of VertebratePaleontology 19 (sup- AmericanMuseum Novitates no.3215:28 pp. plementto no.3): 384. PALIL, G.S. 1988.Predatory Dinosaurs of the World.Simon and n press. The wrist of Allosaurus (Saurischia: Schuster,N.Y.: 464 pp. Theropoda),with observationson the carpusin theropods..ln ROTHSCHILD, B.M. & MARTIN, L.D. 1993.Paleopathology: GALIHIER, J.A. (ed.) New Perspectiveson the Origin and Diseasein theFossil Record. CRC Press, Ann Arbor: 386pp. Evolution of Birds. PeabodyMuseum of Natural History Special ROTHSCHILD,B.M. & TANKE,D.1992.Paleopathology of verte- Publicationno. 5: brates:insights into lifestyle and healthin the geologicalrecord. _____BRITT, B.B.; FOSTER, J.R.; MADSEN, J.H. & GeoscienceCanada 19: 73-82. MILES, C.A. 2000,New recordsof Ceratosaurus,Torvosaurus, TAQUET, P. 1998. Dinosaur Impressions.Postcards from a Coelurus,arrd Stokesosaurus artd their implication for theropod Paleontologist CambridgeUniversity Press:244 pp. community structureand biozonationin the Late Jurassicof the WEIGELI, J. Dn. RezenteWrbeltierleichen und ihrepaliiobiolo- WesternInterior. Joumal of VertebratePaleontology 20 (supple- gischeBedeunng. l-nipzig: 277 pp. @nglishtranslation published mentto no.3) : 354. in 1989as Recent Vertebrate Carcasses and TheirPaleobiological & MADSEN, J.H. 1996.On the presenceof furculae Implications.University of ChicagoPress: 188. pp.). in somenon-maniraptoran Theropoda. foumal of Vertebrate