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lNTRODVCfION Marc R.GaDup
8816lOth Avenue,Inglewood;Caü!omiJl90305
Figure.1.Recoostruetionofthelell pesofP/eU/'DCDe/Ju$p,indeL,(PR
m
,
Fidd MuseumofNalural History)fmm theLowerCrCQceousPaluxyFormationofTexas.Mewarsal V,shownonthelatrigh~is20 cm
lon&.
GeologîcaJSociety ofAmerica SpecialPap..-238
1989
ABSTRACf
Functional morphology of the hindfoot of the
Texas sauropod Pleurocoelus sp. indet.
Studies of a.cornplele Ieft pes of the Texas Lowet' Cretaceous sauropod, ~sp.Iodet.,show~nthebasisof the fonn and size of .he elements, partteularty theclaws-someadap'alions for 5Cralcb-digging.Four distinddwwsare associaled with thepedalslleletoa,supporting theviewth.t'hisspecies wasat least one of .heGlenRose lracllmakers. Evidence presented herealliesPleurtH:«1uswith the bnodûosaurids.
TexasLower Cretaceoussauropodpedal prînts and!racle. waysor impressionsan: nOleworthy becausemany showevi.
dence of 6ve digits.At presenl, however.few sauropod skeletaJ elementsbave beeo discovered,and these are presentlybeing described (Gallup, 19&9) or prepared(Langston,persortal com. munication,19&6). Regretlably,as)'etnoskulls or evenmajor cranialelementsbave been found.Amoogthevariousposterao.iaJ materialsisa complete left bindfool,whichisbrieflydesaibed hen:; tbismateriaJwill be desaibed indetailelsewhen:.[nteres t-ingly, itbasfour claws.Thischapler focuses onthefunctiortal morphology of the [ool
The specimen(PR 977)ispartof a Field Museum ofNa tu-raiHistory collectionof Comancltean vertebra.especimens
ob-tainedin theearly 19505,and nolfd mainlyfor mammalian material.ItwasfoundiDavertical position in aligbtgraypack sand,a poorlycoosolidatedand cemented line·grained sandstone representing frequentlysaturatedolterbanledepositsofthePaluxy Fonnalion in Wise County,Texas.Similarsediments on the TexascoastaIplain Ioday becomethixotropicwhen wet,catehing deer and otheranimais.Vntil1973,whentheauthor studiedand describedit (Gallup,[974).thedioosaur portiono[thiscollection was largelyUnknOWD.
OSTEOLOGY
metatarsal and bas a broad,Qatproximalsurface. Melalarsal Il (20 cm loog)isincompleœbutwasapparendy longer and mon: s1ender!banthefirsl MeralarsallII(preservedlengtb,16,5cm) is plObablythe longestandlIIosts1enderof tbe 6ve.[ts upperdolSlll swfaœ bears a large ritlge, whœe probableideotityisdiscussed Themajor osteologicalfeaturesofthebindfoot incJude a beJow.Theiru:ompletely preservedmetatamJIV bearsawide dislal swelling of tbeti~iaand 6bula~ndno evideoeeofa calca- groove-likemidlatenlldepn:ssionprobablyfor the lastmetalarsa~ neum. Metatarsal1 (F'8'1;[2 cm)IStheshortest and sloulest whicbisa longbone withabluntdislalend. The melalarsafswen:
Gallup.M.R.1989,Fu ' -I morpholOgy oClbcb" - o f lbeTeus sauropodPIntooo<IJa-ÎIldd UrFarlo J0 cd.p.'-~ ...~.-di
Boulder,Colorado,GcoIocîcalSocielYofAmericaSpecialPape,238. ~ . w, . • •~o....,'"l.~ nooa.rs:
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71
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FuncliONJlfIff)rphology ofthe hiluJf(}()( of P1eurocoelus 73..
.
,...
..
':"".-10sorne degree interlocked,at least proximally, forrninga rather
-nug unit or bridge, witb a wide proximal articular surface for
support of the astragalus and the load of the posterior portion of
the trunk and tail. Ali ofthedistal articular surfaces indicate
welt-fo rmedjoints, suggesling considerable rnobility (Gallup,
1989).
The phalanges(pbalangeal formula2-3-4-2-0)also indicate well-fonnedjoints. Of special note is Il-l, whichbearsan
en-iarged lip on its proximal surfacetoenclosemetatarsalIl more
closely.Jn addilion, the anterior sideofthe first phalanx of digit 1 oossessesa wide triangulargroove,possibly for the passage of ~law levator muscles,and on the posteriorsidea triangular con-.avity pinches out against a ridge that is probably the site of
nsertionfor digital flelor muscles.
It appears that only the bottom two-thirds of each c1aw
.rniculated with a pbalanx at an oblique angle to the long axis of
he claw. The c1aws are largeand,in life, were probably covered
'Ylarge, horny sheaths!hat would have made them appear even
urger,
'ŒLATlONSHIPS
Ail the Texassauropod materialso far accumulateddoes not
.mtradict placement in the genusPleurocoelus;as suggesled by
angston (1974) and reaffirrned by Gallup (1974,1989).
lang-ton felt justified in referring ail the postdental malerial to this
Hon and placingonly the teetb into tbe genusAstrodo«:
Asœr-.ining whether the Texas speciesis conspecificwith the Arundel
, al/usrequiresfurther study.
As to familial reJalionships, the Texas hind foot presents a
·,osaic of features,each of wbich couldpIaœit in oneofseveral
.roupings. Several charaetClS of thepessuggestCamarasaunu,
'lit an even larger number appearlnplace the genus c10serln
IrachiasGliTUS. These latter characters are the largedegreeof
'pansion of tbe distal ends of the tibia and libula and the form of
·,etatarsals Il,111, and V.lnaddition, the TexasPleurocoelushas
,horter rnetatarsal1 comparedtametatarsal V,whichisop~
'teIhecondition inCof1l4TQSQUrus-acondition peculiarenougb
1Canuz1'QSQJlTUS to be a marker for tbat genus (John Mclntosb,
".-sona! communication, 197&). This charac1er therefore argues
~ainst pJacement in CanuzrasGliTUS. Finally, evidence cornes
,,'m ichnites,provided it can be supposed !bat tbis four-cLawed
IUropod made the {our-clawed pedal!raCksin the Glen Rose
mestone: FarlowandoIbelS(1989) suggestthatthe foreprintof leTexas sauropod more cIosely RSCIIIblestheforefoot ofBra·
'I/osaurus,basedpartly on the absence of the first claw.
There-'re,although the pes is a poor taxonomie too\, it nevertheless
1pports the work of the above-mentionedauthors who would lace the TexasPIeurocoeI/lSinto a familyBrachiœauridae.
UNcnONAL MORPHOLOGY
The fool of a large animal such asPleurocoeiJlJcontains a
"jelYof functional adaptalions,not the \east of which is lhe
Figure2.MedialviewofIdtpesofPleurocoe/ussp. indel.
rawrœ
10 show positions of heelcaIlus padand pbalangealpad (boIh cross-hau:bed),asweUasdaw levalor muscle altaehÙlg10tbeanterior faceof theme<allrsalandtheDexor ontheundelsideattaebin& totheposterior faceoflbeproximal pbalanxand mewarsal (bothstriped).usual "graviportal" suite:the relativelylarge and free fibula, the retention of ail live digits, sbort metatarsalswbose proximal eods are expandedtaaccommodate a blocldike astragalus, and a rather broad foot wbosetoesradiate around a central axis (see Coombs,1975).
ln stark contrastta these
predictablemorphologicaleharac-teristies,evidence exists in the Texas material for a form of dig-gingcaUedscratch-digging, describedby Hildebrand (1985).The enlarged distal ends of several of the phalanges, particularly the
lirst,and 1ip-likeextensionsof the proximal ends, wbich would have formed ralber secure hingejoints, demonstratestrengthening of the phalangealjoints and stronglyarguefor considerablemobil· ity (Gallup, 1989).A prediction tbat is borne out in fact and providesaootber certain indieatoristbe extremerelative lengtbof the third metatarsaI. Furthermore, the lalllenumber of phalanges for this digit suggeststhat tbe middledigitsalsohad an important
functionaf rolein scrateh-<ligging. This bellavior could bave
te-sultcd in excavatingor piling upmateriaIsfor...nestor even.
pushing somethingover. FinaUy,the metatarsopha\angealjoints,
again particularly exemplified by the lirst digit, are open, and therefore, must bave permitted a great deal of motion in the vertical plane, sometbing that would be p.-edictab\e for the scratch-<ligging hypothesis.Atleast two possiblereasonscome to mind for this suggested bigb degree of motioo:to permit motioo oftheindividual c1aws, especially the fust; and to dissipatethe
weightload,COIICOIJIÏtant withthegraviportaJ appendicular adap-tations. These possibmtiesneed not be mutually exclusive. For example,thissauropod's Iocomotorstylewas probably digiti-grade (Fig.2),which would have creatcdtherequired fn:edomof motion for the phalanges, includiDgthec1aws, and also allowed tbe cushioningprovidedbythe beel andtoecallus patis.
SliIl more evidence supports tbe suggestionofuogual mo-tion.Largemuscular insertion aress on the proximal portions of the metal8rsals and grooves in sorne pbalanges indicate !batthe
Figure 3.Restored lell pesof1'IeJuocotIlIssp.indel.inanlaiorview showing theetaws levaled and implanted intoa subslraœ. DraWÙll also shows phaiangeal <:alluspads,even underthefirth digit
animal had well-developed c1awlevators insertingon the superior portion of the proximal articular surfacesof the claws. This and the presenceofflexorsiteson the posterior surfacesof the prox-imal phalanges imply that motion of the claws was signifocant The oblique orientationofthe pllalangeal articulation with the claw suggestssorne horizontal as weil as vertical motion, imply-ing a pryimply-ing or twistimply-ing elfeet. This pryimply-ing motion seerns to be confinned by studying the position of the muscle scars on the metatarsals.Levation would have resulted in turning the tips
Figure4.RestoredIdtfOOIofPIeu_tussp.inde!. showingsoleand
pbalang..1pads.AIlclaws except thelargest(Iherom)00the leftare lewledand therefore implanted (coming ouIoftheplaneof~plie). Claw 1islumed morelatendlnemplwizeilsprobable greater
indr>-pendencefrom lhe0lI1ers.Ilesed"Ige/yon footprint piduredin
Lmg-5\On (1974; Plate3, no.3). Notice morphology offifthdigit.
ofthec1aws laterad andpermiuingthe tips of theb1adesto be embedded petpendiculartothesauropod's directionoftrave!. This bebavior would have provided a "snowsboe" effect, un
-doubtedly improvingthe anima!"s footing.Interestingly, the distal tipsofthe c1aws were curved mediad, whichwould meantbat even during levatioo the tips of the c1aws would bedirected almost straight downward(Fig.3) IDprovide verygood support.
Thisiscoofirmedfromexamination of various tracks(Figs.4and
5), whicb show the lateral orientation of the c1awb1adesaswell as the downward penetration of the claw tips.One mightsuspect tllatsuchdeep penetration by the c1aws meant a slow,sequential plodding or a sort of "slide and lift" Therefore,lhis author views calculationsofwaIkingspeedsofPleurocoelusoveramuddy substrate with sorne skepticism:they may be too high. Once implantcd, the c1aws must bavehelpedto stop forward motion, causing the animalIDprogressin a start-and-stopfashion.The animal appears to havebeenchoosingcarefully wheretaput its
nextSlep,
Turning of the claws and a pushing backwards of the hind foot in digging would requiresorne degreeof ankle rotation as weil, at \east in an anteroposteriordirection.The blocklikeastra-galus with a gently convex ventral surface does not cootradict this.Even though the entire astragalus as well as the adjacenl surfaces of the metatarsals and libia and fibula were heavily covered oy cartilage, as evidenced by the dense pitting in thèse areas,theextremely loose nature of the ankle joint does seem10
support a degreeof rotation.
Examination of what must he judged as undefonned tracks shows the presence of phalangeal callus pads even around the fifth digit, whicb lacked any phalangeal e1ements whatsoever.
Figure S, Restored leftfootofPleurocoelMJsp.indet,basedon trad<in Farlow (1987:FJg. 16,no.A).Notice difference from Flllure 4.
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-M.R.Gallup
Alamosaurus
and the sauropod hiatus in the Cretaceous
of the North American Western Interior
SpencerG,Lucas
NewMexico Museum of NalUral His/ory,P.O. Box 7010, Alblillu.erque, NewMexico 87194
AdrianP. Hunt
Depanmem
of Geo/ogy. UnilfeT5'iJy of NewMexico, Albu.querque. NewMaie<> 87131G<oIogicat Societyof America.
SpecialPape.238
1989
ABSTRAcr
Sauropod dinosaurs haveatemporally disjunet distnlJUlion ln the North Americ:an Western mlerior during Creta ccoustime. herereferredtoas thesauropodhiatus. Sauropod body and ichnofossils are presenl in lnlandbasioaIandcoastal deposils of Aplian-Albian age in Wyoming,Texas, Oklahoma. and Arkansas. Body fossils of
sau-ropods (the litanosauridAlamosaurus) oœurin inlandhasinaldeposils of
Maastrich.
tianagein Texas,New Mexico, Utah. and Wyoming. No sauropods of Cenornanian.
CampIDlian age are known from a Western fnlerîor sedimentaryrecord domittaled by
eoastal deposils and essentially devoidoflnland basinal deposils. Dlnosaur ichnofaunas
fromIateA1bian ooastaldeposilsinNewMe:r:lc:o,Oklahoma.andColorado lack
S3U-ropod footprints, and thus suggest sauS3U-ropod disappearanœ from Western Interior coastal environments by the endofEarJy Cretaceous lime.
Theseobsenalionssuggest twoscenarios:(1)sauropodsabandonedWestern Inte-rior co35taI environmenls atthe endoftheAIbian,bot persistediDWestern Interior inland basinal environmenls throughout Cretaceous lime. or (2) sauropods became e:ltinclinthe Western Inlerior attheendnf theA1bianand reîovaded during the
~chtian.0Ml0singbetweentbesescenarios depends on an eY8Iuationof negative evidetK:e. However,theclose phylogenetic relationsbip ofAIamosQUl'uslaSoullt Amer-icanlitanosaurids, the absence of sauropod fossils iniDlaoddepoàlsofthe CampllOian
Two Medicine and Judith River Format1011S. and the availability ofadispersal route between NlII1h and South America near theendof Cretaœous lime supportthesecond scenario. Thus,sauropodsapparendybecameexliDctiD theWestern mterior near the end of the AIbian. then reinvaded from South America during the Maaslrichtian but were onlyabletoeslabli$h themselvesiDlnlandbasioal eavironmenls. Theextinctionof
lIlIuropod$intheWestern Interiorattheend ofEar'lyCretaceouslime mayreDeetan
unrerognizedterrutrlal extinctioncoincldentwitlt die weJl-lmownseveremarine
ex-tinctioncausedbyamajorIateAlbian regression.
INTRODVcnON lagierangeinto the Upper Cretaœous,as indicatedby the present discoveJY, is of thegreatestinterest" (Gilmore, 1921b, p. 274).
ln 1921, Charles W.Gilmore announced the discoveJY of The sauropod foundinthe San Juan Basin,A/omosalU'1l$
san-sauropod dinosaur fossils in the Upper Cretaœous of the San jlJa1U!JlSis(Gilmore, 1922), remainsessenlially the ooly sauropod Juan Basin,.New Mexico, noting tbat wsinœthe remainsof sau- known from the Upper CrelaceousofNorth America, and the ropodousdmosau~ have nol been.koown beforeabove the carly North American Cretaœous record of sauropods remains tern-Lower Crelaceousln North Amenca, the extensionof theirgeo- ponDy disjunct. Sauropods are known from bodyfossilsand
Lucas,S.G., andH.n~ A P..19119,AIamt=wvsand the ..uropodhio....in theCl'ClWlOlI$of "'"North
Amen....
WcsœmInteriori.Far! J 0 cd.PoIeobioJocy
or
thedillOU.lllS:Boulder,Colorado,GeoIoeicolSociety ofAmericaSpecioI Papet238. ' OW, . • •The author thanksJames O.Farlow, John S.Mclntosh,and an anonymous reviewerfor their help in improvinglhis paper,ln addition,specialthanks go to Wann langston,Jr.,who bas pro-videdso much belp over the last 17years,
ACKNOWLEDGMENTS
Ccombs,W.P.,Jr.•1975.Sauropodhabit>andbabitats:~aphy.Pa·
IacocliD1atoJ"llY,Palaeoc:ol"llY.v.17,p.1
-33-Fartcw,J.O.,19117.Lowe< Crccaœoll$ dinosaurtraeks,PaI""Y Ri.., Villey,
Somavell CounlY.Teus;GeoIogical
Socio'y or
America South-CentralScaionmeetingguidebook:Waoo,Texas,Baytor Uoiversily,70Po
F.tlow,J.O.Piuman,J.G. and Hawthome, J.M.,19119,Bron"'fJOdus birm.
LowerCrew:eoussa.ropoclfootprinlSrromlbe
U.s
.
G.lf CoastalPlain,i.GilIedA:,D.andLoeldey. M.G.aIs.,Dinosaurtraeksand
'raa:s:
NewYocl<,CambridgeUniversityp... p.371-394.
G.II.p,M.R., 1974,Lo_ Crcraoeous dinosa....andassociated Y<I1dJr.a""from
nonh<entralTexas intheField M....m ofNaluralH~lOJ)'(MAlh""):
Austin, University orTe.... 159p.
- , 1989,Thefo.,-d.wedl.owerCmooeousdi"""'.'PI&_buMorsh
fromthePaI••y Formation of north-<mtrlltT....:JournalofPalronfd"llY
(in ,"",,).
Hildeb<ond, M. 19115,Dicgineof quodrupeds,UrHildebwld, M.,Brambl<,
D. M., L,- K. F.,and Wake,D.B.,eds.. Funaiollll1_ a l e
mo.phol"llY: Cambridec. M....ch...l1S, Harvard University Press,
p.89-I09.
Langstoo,W..Je.,1974,NORmammalienComancheanlCU'apods::Gcoscicnce and
Mao,v.8,Po 77-102.
PrintedinU.S.A.
REFERENCES CITED
M"NUSCRIPT ACCfYIW HVTHE SOCt'ETVlANUARY18~1989
they are small or seemingly nondescript,The behaviora!reper -toire of sauropods may simply have permitted them10
sucœss-fully exploit theresources of the intertidalecolagicalcommunity from time10time, perhapsduringdrougbt,reproduction,or
pre-datory stress
The restored foot (Figs.3and 4) would have lcft an unal-tered print of approximate1y 45to50cm-haIf that of the largest lracks----iuggesting that thisindividua1 was a juvenileor subadult.
Basee!upon tbe interpretatïon that the sediments enctosing the foot represent a thixotropic sand environment, 1 conctude thal this individual did not recognize quicksand wben it needed10, sank in at least up to ils knees, and died in a vertical position.
Death may not have come quickly.The presenceof broken teeth anributabletoDeinonychus cf.D.anlirrhopus, foundstratigraph-ically less than a meter from the specimen in the field,suggesl
il
gruesome death from long-term predation by small carnivores and exposure.
74
What is also observedisan extremelylarge beel pad (restoredin Fig.4).This may suggest weight-loading or preferential useof tbe heelin locomotion.No one doubtsthat thedifferencesbetween the many tracks inthe Glen Rose sogges;quitean ambulalory repertoire, probablyrelatedto wha! this authorsuspectswas often anunsurenessoffootingwhitemoving overslippery limemud
Pedallevation couldhave beena solutionfor the animal.Another
solution, seen in many of the trackways, would have beento reposita greatdeaIof weightto the inner or medialportionofthe foot10reduce or at least control slippage. This strategy would have driven the Iargest(first)c1aw deeply into themudand j'lrovided frictionfrom the largestofthefootpads.Severalof the
iracksdo show their media!portion10be deepestand noly faintly
showthe fourthclaw(Farlow, 1987), as thougb the foot were rotatedor tilted mediad.
Still another hehavior apparentlyinvolvedslidingthe heela short distance before engagingthe claws.Although 1 now
con-cede that the heel regionmay have been longer!hanindicatedin Figure4, as pointedout to me by James Farlow (persoaal com
-munication, 1988),1stillsee a great difference betweenthe tracks
represented by Figures4 and 5. One suspectsthal the difference
between Figure4(basedon an undeformedtrack) andFigure 5
(probablybased on a disturbed track)isthal in the latter the
animal may haveslid its heel forward beforebendingthe anterior portion of thepesinto themud,
Usuallythe animais walked with the toes pointedoutward
and with a greaterdistancebetweeo the legs,atleast in the front
quarters,thanin Mostother sauropods(Farlow, personal
corn-munication,1987). If tbe forelegs of thisspecieswere longerthan the hindl~,asinBrachiosaurus.thenbendingthem or
inereas-ing intermanualdistance would have lowered the cenler of grav-ity.This aIso may havebeenan antislip strategy,augmented by ùirecl c1aw levation and certainly predietable from ankle mor· j'lhology. However,Jeffrey Pittman bas observed(persona! corn· munication, 1987), on the basisof his reœntly collected postcranialmaterials,tbat the fore and hind limbs were nol
g,eatiy differentin length.If50,thenperhaps the sauropod was orehestrating ils walkand thereforeambulatiDg moredeliberately and slowly than the spacingmightindicate.
One can speculate whether the seemingly largenumberof adaptations for a slick, muddy substrate migbt indicate that the .<auropod was speciallyadaptedfor the intertidal region.The
aulhor thinks not.Exceptfor the presenceoffour c1aws, there is
,cally nolhingextraordinary about the foot of the Texas sau· ropo<!.Even the four elaws may not be unique.AsWann Lang·
'ton, Jr.(persona! communication, 1987) points out, peelal dementsmay often he lost or disregarded in collecting because
75
the hindl~,asinBrachiosaurus.then bendingthem ori
nereas-ing intermanualdistance would have lowered the cenler of grav -"'1"'\...._ _1 LA4'_ L .:~,: ....- . . .... ._ ... ...:1 ....w.
a ow, " . fC ~
Somavell CounlY.Teus;GeoIogical
Socio'y or
America South-CentralScaionmeetingguidebook:Waoo,!exas,~~~r ~~~v:~y,70Po, ••••
lionssuggest twoscenarios:(1)sauropodsabandonedWestern
Inte-rior co35taI environmenls atthe endof theAIbian,bot persistediDWestern Interior
