Giants and Bizarres Body Size of Some Southern South American Cretaceous Dinosaurs GERARDO - PDF document

GiantsandBizarres:BodySizeofSomeSouthernSouthAmericanCretaceousDinosaursGERARDOV.MAZZETTA*,PERCHRISTIANSENandRICHARDA.FARINDepartamentodePaleontologõa,FacultaddeCiencias,UniversidaddelaRepublica,Igua4225,11400Montevideo,Uruguay;DepartmentofVertebrates,ZoologicalMuseum,Universitetsparken15,DK-2100Copenhagen¯,Denmark *E-mail:mazzetta@fcien.edu.uyE-mail:p2christiansen@zmuc.ku.dkCorrespondingauthor.E-mail:faria@fcien.edu.uyHistoricalBiology,2004, spines,commonintheneckandanteriordorsalregionsofdiplodocoids,toextremes,astheyresemblelargespikes.AmongthemostinterestingformsoftitanosauriansauropodsknowntodateareArgentinosaurushuinculensis,widelyregardedasthelargestdinosaurhithertoknown(BonaparteandCoria,1993;Appenzeller,1994;Paul,1994,1997),andAntarctosaurusgiganteus,whichappearstohavebeennearlyaslarge.Aspectsofthepalaeobiologyofthesegiantshavenotbeeninvestigated,norhaverigorousbodymassestimatesbeenattempted.TworecenttheropoddiscoveriesonGondwana,althoughincompleteorfragmentary,appeartohaveequalledorevenexceededinsizetothelargestandcompleteTyrannosaurusrex,thespecimenFMNHPR2081informallyknownas“Sue”(HornerandLessem,1993).OneofthemisthepredatorydinosaurCarcharodontosaurussaharicus,aspeciesrstrecognisedin1927andrepresentedbynewmaterial(askull)discoveredintheearliestLateCretaceous(Cenomanian)oftheKemKemregionofMorocco(Serenoetal.,1996).Theother,andprobablythelargestterrestrialesh-eatereverfound,isGiganotosauruscarolinii,fromthemid-Cretaceous(Albian-Cenomanian)ofnorth-westernPatagonia,Argentina(CoriaandSalgado,1995;CalvoandCoria,1998).PalaeobiologicalstudiesofSouthAmericandino-saursarescarce(Casamiquela,1978;Mazzettaetal.1998;BlancoandMazzetta,2001;MazzettaandBlanco,2001).Fromabiologicalpointofview,manydinosauriantaxaofsouthernSouthAmericaareinterestingandinneedofpalaeobiologicalanalysis,particularlytheabove-mentionedhugetitanosauriansauropodsandthelarge-bodiedtheropod,astheyappeartorepresentsizemaximaindinosaurevolution.Inthispaper,weaddresstheestimationoftheirbodysizetoprovideabasisforfurtherpalaeobiologicalstudiesrelatedtolocomotionandotherpalaeoecologicalissues.Additionally,somebizarrePatagoniandinosaurslikethesmallsauro-A.cazauiandthemoderately-sizedtheropodCarnotaurussastreiarealsoincludedastheyarespecimensconstitutedbynearlycompleteskeletons.MATERIALSANDMETHODSIncludedTaxaAnincompletefemurattributedtoA.huinculensis(labelledMLP-DP46-VIII-21-3),andskeletalmaterialbelongingtoitsholotype(PVPH-1)andalsototheholotypeofanothertitanosauriansauropod,A.giganteus(MLP23-316),wereusedforthisstudy.ThementionedmaterialishousedattheexhibitionoftheMuseodeLaPlata,Argentina,exceptfortheholotypeofA.huinculensis,whichisexhibitedattheMuseoMunicipal“CarmenFunes”ofPlazaHuincul,Neuquen,Argentina.Additionally,theprincipalhindlimbbonesofAntarctosauruswichmannianuswereincluded.ThelattermaterialwascollectedinChubut,Argentina(Huene,1929),butpresentlyishousedattheFieldMuseumofNaturalHistoryinChicago.AtpresentitappearsuncertainA.wichmannianusisadifferentspeciesfromA.giganteus,butinthispapertheyaretreatedastwospecies(theimpressivesizedifferencemaybeconsideredanotherindicationthattheyrepresenttwospecies).Thefemur(FMNHP13019)andassociatedtibia(FMNHP13020)arenotfromthesamehindlimb(thefemurisarightsidebone,unlikethetibia)butwerefoundtogether,indicatingthattheymusthavebelongedtothesameanimal.Thisisfurthercorroboratedbythefactthatthesizeandproportionsappearrightforoneindividual,andsincethetextureandcolourofthetwobonesisidentical.AlthoughthebonesareofgiganticdimensionstheyclearlybelongtoanindividualdistinctlysmallerthanthecolossalA.giganteus(thelengthofthefemurinMLP23-316is2350mmcomparedto1855mminFMNHP13019).TheskeletalcastofA.cazaui,mountedattheexhibitionoftheMuseoArgentinodeCienciasNaturales“BernardinoRivadavia”,BuenosAires,Argentina,andadditionalmaterialhousedatthesameinstitution,labelledMACN-N15(holotype),werealsousedintheanalyses.Additionally,limbbonemeasurementsoftheholotypespecimenofC.sastrei(MACN-CH894)publishedbyBonaparteetal.(1990),andmeasurementsonappendicularbonesofthedisarticulatedholotypespecimenofG.carolinii(MUCPv-CH-1),werealsoconsidered.AllthespeciesstudiedherewerefoundinPatagonia,Argentina.A.giganteusisfromtheRNeuquenFormation,EarlyCenomanian,NeuqueProvince(north-westernPatagonia)(Huene,1929),A.cazaui(Fig.1)isfromtheLaAmargaFormation,LateNeocomian,NeuquenProvince(SalgadoandBonaparte,1991).A.huinculensisG.caroliniiarebothfromtheRoLimayFormation,mid-Cretaceous(Albian-Cenomanian),NeuqueProvince(BonaparteandCoria,1993;CoriaandSalgado,1995),whiletheothertheropodincludedinthestudy,C.sastrei(Fig.2),wascollected Institutionalabbreviations:CN,ZoologyMuseum,CopenhagenUniversity;FMNH,FieldMuseumofNaturalHistory,Chicago,USA;HMN,MuseumfurNaturkundederHumboldtUniversitat,Berlin,Germany;MACN,MuseoArgentinodeCienciasNaturales“BernardinoRivadavia”,BuenosAires,Argentina;MLP-DP(andalsoMLP),DepartamentoCientcodePaleontologadeVertebradosoftheMuseodeLaPlata,LaPlata,Argentina;MUCPv-CH,MuseodeGeologayPaleontologadelaUniversidadNacionaldelComahue,PaleontologadeVertebrados,ElChoconcollection,Neuquen,Argentina;PVPH,MuseoMunicipal“CarmenFunes”,PlazaHuincul,Neuquen,Argentina.G.V.MAZZETTAetal. fromnorthernChubutProvince(Bonaparte,1985;Bonaparteetal.,1990).ItwasformerlybelievedtobefromtheAlbian-CenomanianGorroFrigioFormationbutlaterwasreferredtothelowersectionofLaColoniaFormation,LateCretaceous(Campanian-Maastrichtian)ofPatagonia(ArdolinoandDelpino,1987).EstimationofBodyMassThebodymassofthesauropodA.cazauiestimatedby3-Dmathematicalslicing(Henderson,1999).Forthispurposethewidthandheightofitsbody(takingasreferenceitslife-sizedskeletalcast)wasmeasuredatregularintervalsfromthesnouttothetipofthetail.Eachpairofmeasurementswassubsequentlytreatedasthelargerandlesserdiametersofanellipse.Theoutersurfacesbetweensuccessiveellipsesweresmoothedtohaveacontinuousoutlineofthebody.Limbmasseswerecalculatedseparately,andlimbswereassumedtobecylinders.FollowingAlexander(1985),anoveralldensityof1000kgmwasassumedforthebody.Littledifferenceisobtainedconsideringabodydensityof950kgm,asforthesauropodsinTableI.Unfortunately,theavailableskeletalmaterialofthesauropodsA.huinculensisandAntarctosaurusspp.(andtheG.carolinii)istoofragmentaryforareliablemodelreconstructiontobemade.Thosesauropodsaretitanosaurs(e.g.Novas,1997b;Salgadoetal.,1997a),whichwerethedominantsauropodsintheLateCretaceous(Upchurch,1995).Althoughthedetailedanatomyofthetitanosaursincludesagreatnumberofapomorphiescomparedtomorearchaicsauropods(Salgadoetal.,1997a,b),theoverallbodyoutlineappearsratherplesiomorphicforasauropod,withratherlong,butrobustlimbs(e.g.Borsuk-Bialynicka,1977;Salgadoetal.,1997a;WilsonandSereno,1998),forelimbsnotapomorphicallyshortenedrelativetothehindlimbsasinthediplodocoids,andlackingtheapomorphicallyelongatedneckandveryelongatedtailofthesetaxawithupto82caudalvertebrae(Christiansen,1996).Thefewknownfairlycompletetitanosaurs(e.g.Saltasaurusloricatus)appeartohavebeenratherstoutlybuiltwithmoderatelylongnecksandtails,whichhasinuencedpopularreconstruc-tionsofArgentinosaurus(e.g.Appenzeller,1994;Bonaparte,1996b:p.142).Giganotosaurusisabasaltetanurinetheropodandmostanalysesindicatethatitisacarnosaur(sensuGauthier,1986).Itismostfrequentlyplacedalongsidethealmostequally FIGURE1Amargasauruscazaui.Reconstructionoftheskeleton.FromSalgadoandBonaparte(1991). FIGURE2Carnotaurussastrei.Reconstructionoftheskeleton.FromBonaparteetal.SOUTHAMERICANDINOSAURS3 massiveAfricanCarcharodontosaurusintheCarcharo-dontosauridae(Serenoetal.,1996),ataxonwidelyregardedasthesistertaxontotheAllosauridae(Serenoetal.,1996;HutchinsonandPadian,1997;Novas,1997b).AnumberofModelII,ReducedMajorAxis(RMA)orgeometricmeanregressionanalyseswereper-formed(seeRicker,1984,andSokalandRohlf,1995forcomputationalbackground)inordertopredictthebodymassesofAntarctosaurusfrommeasurementstakenontheirratherscarceskeletalremains(Fig.3).Thoseanalyseswereperformedonalog-transformed(base-10)databaseconsistingofmodel-basedbodymassestimatesandmeasurementsofbonedimensions(suchaslengthsofthefemur,tibia,andbula,distalwidthofthefemuracrossthecondyles,midshaftperimeterofthetibia,andcross-sectionalareaofthecentrumoftheseconddorsalvertebra)inanarrayof13othersauropodslistedinTableI.Clearly,bothkindsofvariables(thatis,bodymassandbonedimensions)aresubjecttomeasure-menterroraswellasinherent,biologicalvariability,thusrequiringaModelIIregressionanalysis(SokalandRohlf,1995).Moreover,ageometricmeanregressionlineisjustiableforpredictionpurposeswhen,asinthiscase,thesample(data)waswithdrawnfromabivariatepopulationwhosefrequencydistributionisunknown.Thegoodnessoftofthelinearregressionanalysiswasevaluatedconsideringthecorrelationcoefcient.Asimpleaverage(arithmeticmean)was TABLEIOveralllengths,model-basedbodymasses,andbonedimensionsforasetofselectedsauropodsBonedimensionsSpeciesOveralllength(m)Bodymass(kg)tllfwfptpvaAmargasauruscazaui9.126001050640640284440–11,651Apatosauruslouisae22.820,60017851115117553683253164,128Brachiosaurusbrancai21.839,500202811201190590945518148,597Camarasaurussupremus13.89300134182481842354240444,748Cetiosaurusoxoniensis16.515,9001660974–471715416–Dicraeosaurushansemanni14.25700122076075031352133514,833Diplodocuscarnegiei25.616,00015401010105041258935643,004Euhelopuszdanskyi10.5380095560261826140026412,441Haplocanthosauruspriscus14.812,8001275––309531–20,548Mamenchisaurushochuanensis20.415,100127586086538062133161,850Omeisaurustianfuensis20.298001215855860331526432–Opisthocoelicaudiaskarzynskii11.38400139581083043064442426,507Shunosauruslii9.93600865660655–393291–ThebodymassvaluesshownwererecalculatedfromChristiansen(1997),exceptforthecasesofEuhelopusHaplocanthosaurusOpisthocoelicaudia(datatakenfromPaul,1997),and(datumcalculatedforthispaper).Abbreviations:,lengthofthefemur;tl,lengthofthetibia;l,lengthofthebula;fw,distalwidthofthefemuracrossthecondyles;fp,midshaftperimeterofthefemur;tp,midshaftperimeterofthetibia;andva,cross-sectionalareaofthecentrumoftheseconddorsalvertebra.Allbonedimensionsareinmm,exceptva(inmm FIGURE3Twosamplegraphs(A,logbodymassvs.logfemurlengthandB,logbodymassvs.logfemurlengthcrosssectionalareaofposteriorarticulatingfaceofseconddorsalvertebra),eachshowingthescatterofpointsonwhicharegressioninTableIIisbased,thecalculatedregressionline,andthepredictedbodymassesofArgentinosaurushuinculensisAntarctosauruswichmannianusG.V.MAZZETTAetal. computedtoestimatethebodymassofthePatagoniansauropodstakingintoaccountthedifferentbodymassespredictedbyeachequation.The13sauropodspeciesincludedinTableIrepresentawidephylogeneticspectrumandtheirbodymasseshadbeenfoundbyweighingscalemodelsinairandwaterinthecaseofApatosaurusBrachiosaurusCamarasaurusDicraeosaurusDiplodocusMamenchisaurusOmeisaurusandShunosaurus(datafromChristiansen,1997).Commerciallyavailablemodels(see,e.g.Alexander,1985,1989)wereavoided,astheyareproportionallyincorrect(Paul,1997;Christiansen,1997,2000).However,thevaluesfromChristiansen(1997)wererecalculatedusingaslightlyhigheroveralldensity(950kgm),asthe900kgmusedinthatpapermaybeslightlytoolow.Mostneosauropodshaveextensivelypneumatisedvertebrae,particularlythecervicals,whichwouldtendtoloweroveralldensity.However,theseanimalsarealsoverylarge,implyingaproportionallygreateramountofskeletaltissue(Christiansen,2002),particu-larlyappendicularskeletaltissue,andconsequently,theyshouldhavehadahigheroveralldensity.ThebodymassesofEuhelopusHaplocanthosaurusandOpisthocoelicaudiaweretakenfromPaul(1997).Thesewereobtainedfromplasticinescalemodels,followingaskeletalrestoration.ThebodymassofAmargasauruswasalsoincludedinthedatabase(seeTableI)anditscorrespondingvaluewascalculatedby3-Dmathematicalslicing(Henderson,1999),asnotedabove.TherightfemuroftheskeletalmountofBrachiosaurusbrancai(HMNSII)consistsoftheoriginalmaterialproximallyanddistally(Janensch,1950).Consequently,onlythemeasurementcorrespondingtothedistalpartofthefemurwasincludedinthedatabase.Thediaphysisislacking,andthus,thebonelengthisnotavailable.Instead,thelengthofthefemurofB.altithorax(FMNH25107)wasused,thoughthisspecimenappearstohavebeensubequalinsizetoHMNSII(Paul,1988;Christiansen,1997).SeveralofthedorsalvertebraeincludedintheholotypeofArgentinosaurusappearratherwellpreserved(BonaparteandCoria,1993),whichallowedtheestimationofitsbodymassfromregressionsonthecross-sectionalareaofthecentrumoftheseconddorsalvertebra.AtpresentonlythefemoraldiaphysisofArgentinosaurusisavailable(fromthespecimenMLP-DP46-VIII-21-3),althoughacolossalfemur(topotype)hasalsobeenreferredtothisspecies(Bonaparte,1996b).Unfortunately,thelatterspecimen,whichisexhibitedattheMuseoMunicipal“CarmenFunes”,hasbeenanteroposteriorlycompressedinfossilization,makingitratherunreliableforbodymassestimationbasedonitscross-sectionalgeometry.The“tibia”oftheholotype(BonaparteandCoria,1993)isclearlynotatibiabutabula.Itlacksboththeproportionsandanatomicalcharactersofatibia.Thepurported“cnemialcrest”ismerelytheantero-proximalexpansioncommontosauropodbulae,andtheentirebonebearsresemblancetothebulaeofothersauropods.Hence,thebodymassofArgentinosauruscanalsoberegressedonitsbularlength.Addition-ally,thebularlength(1550mm),aswellasthefemoralmidshaftperimeterofthespecimenMLP-DP46-VIII-21-3(1180mm),wereusedforpredictionoffemorallengthinArgentinosaurus.Thisprocedurewasusedtochecktheutilityoftheparatypematerialtopredictthebodymassoftheholotypespecimen.Accordingly,femorallengthwasregressedonbularlengthandalsoonfemoralmidshaftperimeterconsideringthemeasurementstakenonthe13sauropodspeciesmentionedinTableIplusA.wichmannianus(TableIII).TheextrameasurementtakeninA.wichmannianuswasitsfemoralmidshaftperimeter(873mm).Finally,multivariateregressionanalysesforpre-dictionofsauropodbodymasswereperformedonseveral“independent”variableswiththeaimofestablishingifthistechniquewouldresultinabetterpredictionofbodymassthanwouldbepossiblebyanysingle“independent”variable.However,whenabiologicalsampleisconsidered,multivariateregressionanalysisofa“dependent”variableonaseriesof“independent”variableswillinevitablyleadtointercorrelationofthelatterones.Clearly,theproportionsofananimal’sbackbonecannotbeuncorrelatedwiththeproportionsofitslimbs.Hence,tolerancevalues,eigenvaluesandconditionindicesoftheequationwerecomputedtoevaluatetheintercorrelationofthe“independent”variables.Alldatavalueswerelog-transformed(base10)priortostatistical(bivariateormultivariate)analyses.Thelengthsofthefemora,tibiaeandbulae,aswellasthemidshaftperimetersofthefemoraandtibiae,weremeasuredwithameasuringtape.Thedistalwidthsofthefemoraacrossthecondylesweremeasuredwithalargecaliper.Thecross-sectionalareasofthecentraoftheseconddorsalvertebraewereestimatedfromtheirdiameters(dorsoventralandlateromedial)usingthestandardformulafortheareaofanellipse.ThebodymassesofthetheropodsCarnotaurusGiganotosauruswereestimatedafterthebivariateandmultivariateregressionequationsinChristiansenandFarina(2004).Thoseequationswereobtainedusingadatabaseof16theropodspecies,ranginginsizefrom16.5-kgOrnitholestesto6300-kgT.rexcomprisingawidephylogeneticsample.RESULTSSauropodsTheestimatedbodymassforA.cazauiwas2600kg,whenanormalvertebratedensityof1000kgmused.TheconsiderationofsuchadensityvalueisSOUTHAMERICANDINOSAURS5 suggestedbyitsstoutlybuiltbody,whichdoesnotshowthecommonexcavations(pleurocoels)foundinthedorsalvertebraeofothersauropods.Thatgureisonlyslightlyloweredto2460kgifthedensityassumedfortherestofthesauropods(950kgm)isused.Therestofthesauropodspeciesstudiedhereareofverylargedimensions.Indisputably,thelargestdinosaur(andalsothelargestlandanimal)thatisknownfromareasonablycompleteskeletonB.brancai.TheskeletonofthespecimenHMNSIIismountedattheMuseumfurNaturkundeinBerlin,andmajorportionsofthisskeletoncanalsobeviewed(ascasts)inthecompositemountofB.altithoraxattheFieldMuseumofNaturalHistoryinChicago.ThebodymassofBrachiosaurusbeengreatlyexaggeratedinmanypublications(e.g.Colbert,1962;Norman,1985;Benton,1988;etal.,1995;Christianetal.,1999).ThefragmentaryskeletalremainsofArgentinosaurus(seeFigs.4and5)aredistinctlylargerthanthecorrespondingpartsofBrachiosaurus.Forinstance,someofitsdorsalvertebraearemorethanameterandahalftall(159cmforthereconstructedrst?dorsal)andthebulais155cmlong(describedasatibiabyBonaparteandCoria,1993:Fig.1),comparedto119cminHMNSII.Moreover,thefragmentaryfemoraldiaphysisattributedtoArgentinosaurusmeasuresnolessthan118cminitsnarrowestcross-sectionalperimeter,comparedto94cminBrachiosaurusaltithoraxFMNH25107(203cmlong),and82cmintheratherslenderspecimenHMNXVIofB.brancai(211cmlong).Evidently,thebodymassofArgentinosauruswasimpressive.Someresearchershaveguesseditsmassatcloseto100tonnes(Appenzeller,1994),andPaul(1997)estimateditsmasstobe90tonnes.WhenusingasimplegeometricscalingwithbularlengthinHMNSII(119cm),whichphylogeneticallyistheclosesttointhedatabase(TableI)(Salgadoetal.,1997a;WilsonandSereno,1998),avalueof87287kgisobtained.istheoutgrouptotheTitanosauriformes(BrachiosaurusTitanosauria)(Salgadoetal.,1997a;WilsonandSereno,1998)anditsoverallbodyshapebearscloserresemblanceto FIGURE4CastofavertebraofthegiantsauropodArgentinosaurushuinculensis,asexhibitedintheMuseoMunicipaldelChocon,Argentina(PhotographtakenbyL.Quagliotto).G.V.MAZZETTAetal. thoseofknowntitanosaurs.AsimplebularscalingwiththepresentspecimenofCamarasaurussupremus(81.8cmlong)predictsamassof63273kgforMorereliableestimatesshouldbeobtainedwiththeregressionequationsincludedinTableII.Accordingtotheircorrelationcoefcientsandtheregressionscomputedonlengthofthefemur(inarestrictedsamplewithoutMamenchisaurus),lengthofthetibia,lengthofthebula,andcross-sectionalareaofthecentrumoftheseconddorsalvertebra(inarestrictedsamplewithoutHaplocanthosaurus)constitutethemostreliableequationsforbodymasspredictionofalltheequations.Itshouldbemadeclearthat,inthecasesofArgentinosaurus,wehadtoextrapolatebeyondtherangeofourobservationaldatatoestimatethebodymassesofthesehugesauropods.ThefemorallengthofArgentinosauruswiththeregressionsonfemoralmidshaftperimeterandalsobularlengthare2525,2486,and2659mm,fromequations1,2,and3,respectively(TableIII).Whenitsaverageiscomputed,thenallengthestimateis2557mm.Alloftheabovepredictedlengthsarehighlysimilar,andarealsonearlyidenticaltoBonaparte’s(1996b)lengthmeasurementforthecompletefemurreferredto(250cm).Thus,thosevaluesarewithin2%ofthelengthmeasuredonthatfemur,whichisconsideredavalidationofthereliabilityofsuchpredictions.Ontheotherhand,thosepredictionsindicatethatthefemoralfragmentMLP-DP46-VIII-21-3andthecompletefemurbelongstoindividualsofthesamesizethantheholotype.Consequently,thefemoralmidshaftperimetermeasuredintheformerspeci-menandthefemorallengthmeasuredinthelatterwerealsousedtoestimatethebodymassofUnfortunately,thelengthofthetibiaandthedistalwidthofthefemurcannotbeusedtopredictthebodymassof(itstibiaewerenotfoundandthefemurassignedtothisspeciesisdistorted,asmentionedearlier).Hence,thebodymassofhasbeencomputedfromsixregressionequations,wherethepredictedvaluesrangefrom60to88tonnes(TableIV).Whentheaveragebodymassiscalculated,theresultobtainedisapproximately71tonnes.Themultivariateregressionequationofbodymassonthelengthofthebulaandthecross-sectionalareaofthecentrumofthesecond FIGURE5FragmentofahugefemurofArgentinosaurushuinculensis,asexhibitedintheMuseodeLaPlata. TABLEIIBivariate(geometricmean)regressionequationsoflog-transformed(base-10)dataforpredictionofbodymassinsauropods95%CI95%CI(1)132.7803.1950.8910.90751.268**(2)*112.1202.8380.6770.94980.826**(3)fw122.8822.9311.1160.84224.274**(4)fw2.5933.0301.0000.89937.964**(5)fp132.2912.9550.8300.90650.388**(6)tl122.2853.8760.7820.958111.994**(7)tp113.8293.2881.4830.80116.157***(8)l112.2553.5940.7710.959102.008**(9)va101.3710.9800.3040.92547.303**(10)va1.0090.9940.2220.968104.657**aretheslopeandantilogoftheinterceptintheregressionequations,aslog(bodymassInallcases,bodymassesarecalculatedinkilogramsandbonedimensionsareconsideredinmillimetres.AbbreviationsasinTableI.(**,001;***,0ExcludingoutliersMamenchisaurus.†ExcludingoutlierHaplocanthosaurusSOUTHAMERICANDINOSAURS7 dorsalvertebrais:bodymasslogfibularlengthlogvertebralareawherebodymassiscalculatedinkilograms,andthebonemeasures,bularlengthandvertebralarea,areexpressedinmmandmm,respectively(358;001).Asexpectedthetolerancevalues,eigenvaluesandconditionindexindicatedsubstantialintercorrelationofthe“independent”variables(conditionindexupto142andtolerancevaluesof0.201),butthisisprobablyunavoidableinabiologicalsamplewheremultiplemeasuresaretakenonthesameanimal.However,thepartialregressioncoefcientsaresignicant(two-tailed-testsyieldvaluesof0.029and0.009,forthecoefcientsofbularlengthandvertebralarea,respectively),soredundancyoftheselectedpredictorvariablescanberuledout.Themultivariateequationmentionedabovepre-dictsabodymassof72936kgforAsthemultivariateregressionanalysisnotonlyhasahighercorrelationcoefcientthananyofthebivariateanalyses,butalsoincorporatesmoreanatomicaldimensions(i.e.moreinformation),weconsiderthelattervalueof73tonnesasthemostlikelyandwillusethisgureinfurtherdiscussion.wasalsoanenormoussauropod(Fig.6).Twocompletefemoraofthelargestspecies,A.giganteus,areknown.Itseems,however,tohavebeensmallerthanArgentinosaurus,clearlylargerthanBrachiosaurus.AsimplegeometricscalingoffemoralandtibiallengthsofthesmallerspeciesA.wichmannianus(measurementstakenonspecimensFMNHP13019andFMNHP13020,respectively)tothespecimenofC.supremus(TableI)yieldsbodymassvaluesof24617and33410kg,respectively.ThisisroughlycomparabletothevaluesobtainedwiththeregressionequationsfromTableII.Inthosecases,thebodymassesrangefromabout26toalmost48tonnes(TableIV).Regressionequationsrelatedtofemorallengthyieldedbodymassesofnearly29tonnes(equation1)andalmost26tonnes(equation2)for TABLEIIIBivariate(geometricmean)regressionequationsoflog-transformed(base-10)dataforpredictionoffemorallengthinArgentinosaurus95%CI95%CI(1)fp140.6160.3780.9070.1360.971197.937***(2)fp*130.6400.3050.8970.1100.983310.375***(3)l110.7601.1070.2600.95083.827***Allbonedimensionsareconsideredinmillimeters.AbbreviationsasinTableI.(***,Excludingoutlier TABLEIVComputedbodymassesofArgentinosaurushuin-Antarctosauruswichmannianus.NumberedequationsarethosedenedinTableIISpeciesEquationusedBodymass(kg)A.huinculensis(1)74,717(2)60,166(5)81,548(8)88,115(9)63,158(10)60,432A.wichmannianus(1)28,798(2)25,797(3)35,790(4)34,419(5)33,473(6)47,611(7)30,182 FIGURE6FemurofAntarctosaurusgiganteus,exhibitedintheMuseodeLaPlatabesidesacastofDiplodocuscarnegieiG.V.MAZZETTAetal. A.wichmannianus,whichareintherangeofthevaluesobtainedwiththegeometricscalingmentionedabove.TheaverageofthesevenbodymassescomputedinTableIVisalmost34tonnes.AnumberofmultivariateanalyseswerealsoperformedonthebonedimensionsofthesauropodsfromTableI,buttheseonlyresultedinmarginallyhighercorrelationcoefcientscomparedtothebivariateregressionequationsinTableII.ThefemurofA.wichmannianus(FMNHP13019)is,however,distinctlysmaller(1855mm)thanthegiganticfemurMLP23-316ofA.giganteus(2350mm).AssumingageometricscalingwiththeFMNHspecimen,whichisreasonablesincetheycouldevenbefromthesamespecies,resultsinabodymassofnearly69tonnesforA.giganteus,bettingforthename.Thus,thiscolossuswasevidentlynotthatmuchsmallerthanTheropodsAbodymassof1500kgwasestimatedforC.sastreiusingavolumetricprocedure(Mazzettaetal.,1998).Here,itsbodymasswaspredictedfromtheappendicularbonemeasurementsavailableinBonaparteetal.(1990),usingtheregressionequationsobtainedbyChristiansenandFarina(2004)(TableV).Theaverageofthebodymassvaluespredictedisapproximately2100kgandonlyoneofthemisaboutthevalueobtainedthroughthevolumetricestimation,whilealltheothersareabovethatgure.ThedisarticulatedcranialbonesofG.caroliniinotallowaccuratesizecomparisonwithT.rexAcomparisonbetweentheirrespectiveappendicularbonesshowsthatthefemurofGiganotosaurus(1.43mlong)isabout5cmlongerthanthatof“Sue”(FMNHPR2081),althoughthetibia(1.12mlong)is8cmshorter,asiscommoninmoreplesiomorphiccarnosaursGauthier(1986)(seeChristiansenandBonde,2002).MostbonesincludedintheholotypeofGiganotosaurus(MUCPv-CH-1)indicatethatthisspecieswasatleastsimilarinsizetothelargestknownTyrannosaurusspecimens,orevenbiggerifoneconsidersthefragmentarydentaryspecimenMUCPv-95(CalvoandCoria,1998).Hence,assumingequalsizebetweentheholotypespecimenofGiganotosaurusandtherobustmorphofTyrannosaurus,abodymassofabout8tonnescouldbeconsideredfortheformertakingintoaccountreliablebodymassestimatesforthebiggestspeci-mensofTyrannosaurus(Paul,1997;Henderson,1999).Ontheotherhand,assuminggeometricsimilaritywiththeholotypespecimenofGiganotosaurusabodymassofabout10tonnesisestimatedfortheindividualcorrespondingtothespecimenMUCPv-95(theratioofdentarylengthsbetweenthemis0.926,thereforeitsbodymassis81tonnes).However,tyrannosauridsareveryapomorphic,andthereforeabettercomparisonshouldbemadewiththemoreplesiomorphic(andmuchcloserrelated)carnosaursSinraptor(datapublishedinChristiansen,1998).AsimplelengthcomparisonbetweenGiganotosaurusAllosauruspredictsabodymassof7796kgusingthefemurand5460kgusingthetibia.Thelattermaynotbetooreliablesincebigcarnosaursbecomemorestubby-legged.Whencomparedwiththe1700-kgSinraptordongi,thebodymasspredictionsforGiganotosaurusare7196and4364kg,usingthelengthsoffemurandtibia,respectively.MorereliablebodymassestimatesfortosaurusareshowninTableVI.Thoseestimateswereobtainedusingtheequationsderivedfromthedatabaseoftheropodscitedabove(ChristiansenandFarina,2004).Theaverageofbivariateequationsis5604kg,butitincludesaverylowvaluepredictedfromthedistallateromedialdiameterofthefemur(2369kg).Ifthisoutlierisexcluded,theaverageamountsto6143kg.Multivariateequations,ontheotherhand,yieldedanaverageof6510kg.Fourequationsyieldedverylowbodymassestimates(between3828and4418kg),whiletwoothersproducedveryhighestimates(9268and10,709kg).IfthefourlowervaluesinTableVIareexcluded,theaverageis6846kg,whileifthetwohighervaluesarenottakenintoaccount,theaverageis6278kg.Finally,theaveragewithoutthesixoutliersis6604kg. TABLEVBodymassestimatesforCarnotaurussastrei.Predictionsbasedonbivariateandmultivariateregressionequations(ChristiansenandFarina,2004).(BonemeasurementsarefromBonaparteetal.,1990)Bonedimension(kg)Measurement(mm)BodymassFemorallength10302626Femoralmidshaftanteroposteriordiameter1001795Femoralmidshaftlateromedialdiameter100–Femoraldistallateromedialdiameter197.51488Tibialmidshaftanteroposteriordiameter70–FemorallengthandFemoralmidshaftlateromedialdiameter–2415FemorallengthandFemoraldistallateromedialdiameter–2361FemorallengthandTibialmidshaftanteroposteriordiameter–2339FemoralmidshaftanteroposteriordiameterandFemoraldistallateromedialdiameter–1696Average–2102SOUTHAMERICANDINOSAURS9 DISCUSSIONSauropodsGregory(1905)wasprobablythersttoreportonbodymasspredictioninasauropod.BasedonthereconstructiondesignedbyCharlesKnight,amodeloftheskeletalmountofApatosaurusexcelsuswasmade,andtheestimationofitsbodymassyielded31tonnes,clearlyduetoerroneousbodyproportionsandaveryportlydesign.Errorsinmodelproportionsareparticularlyliabletoleadtoinatedbodymassestimates(Paul,1997;Christiansen,2000).Amongthosesauropodsstudiedhere,Amargasaurusisclearlythesmaller.Asmentionedabove,theestimatedbodymassofthisbizarre-looking,smallsauropodwasabouttwoandahalftonnes.Theothersauropodsinthispaperarerealgiants,andmustbecomparedwiththelargestknowndinosaurseverfound.Brachiosaurushastraditionallybeenconsideredoneofthelargest,ifnotthelargest,sauropodknown,andformanyyearsthiswasprobablytrue.However,thisisclearlynotthecaseanymore.Colbert(1962)wastherstresearchertoreportonthebodymassBrachiosaurus,buthealsousedabadlyproportionedmodel.Additionally,heusedawrongscale.Brachiosaurusdoesnot,asreportedbyColbert(1962),stand609cmatthehips,butratheranestimatedheightof540cm(Paul,1988),andthescalingerroralonewouldleadtoabodymassof63,400kg,notthewidelycitedvalueof78,300kg.MoreaccuratereconstructionspredictabodymassforBrachiosaurusof32(Paul,1988;Paul,1997)to37tonnes(Christiansen,1997).However,notethatinthelatterpaperthebodymassiscloserto40tonnesduetothehigherdensityusedinthecalculations.Alexander(1989)computedabodymassof47tonnesforBrachiosaurus,basedonthecommercialmodelfromtheBritishMuseum(NaturalHistory),whichisalsoproportionallyinaccurate(Paul,1997;Christiansen,2000).Ironically,thenew,lowerbodymassestimatesforBrachiosaurusareverysimilartotherstestimateof40tonnes,based TABLEVIBodymassestimatesforGiganotosauruscaroliniiPredictionsbasedonbivariateandmultivariateregressionequations(ChristiansenandFarina,2004)BonedimensionBodymass(kg)Bivariateanalyses:Femorallength7532Femoralmidshaftperimeter6167Femoralmidshaftanteroposteriordiameter6220Femoraldistallateromedialdiameter2369*Tibialmidshaftperimeter6704Tibialdistallateromedialdiameter4884Fibularproximalanteroposteriordiameter5353Average5604Multivariateanalyses:Femorallengthandleastperimeter7017FemorallengthandFemoralmidshaftlateromedialdiameterFemorallengthandFemoraldistallateromedialdiameterFemorallengthandTibialmidshaftFemorallengthandTibialmidshaftanteroposteriordiameterFemorallengthandTibialmidshaftlateromedialdiameterFemorallengthandTibialdistallateromedialdiameterFemorallengthandFibulardistalanteroposteriordiameterFemorallengthandFibulardistallateromedialdiameterFemoralmidshaftperimeterandTibiallengthFemoralperimeterandTibialmidshaftlateromedialdiameterFemoralmidshaftperimeterandTibialdistallateromedialdiameterFemoralmidshaftanteroposteriordiameterandFemoraldistallateromedialdiameterFemoralmidshaftanteroposteriordiameterandTibialmidshaftperimeterFemoralmidshaftanteroposteriordiameterandTibialmidshaftanteroposteriorFemoralmidshaftanteroposteriordiameterandTibialdistallateromedialdiameterFemoralmidshaftanteroposteriordiameterandFibularmidshaftperimeterFemoralmidshaftanteroposteriordiameterandFibularmidshaftlateromedialFemoralmidshaftanteroposteriordiameterandFibulardistalanteroposteriorFemoraldistallateromedialdiameterandTibialmidshaftperimeterFemoraldistallateromedialdiameterandTibialmidshaftlateromedialTibiallengthandFibularmidshaftTibiallengthandFibulardistalanteroposteriordiameterTibialmidshaftperimeterandFibularmidshaftperimeterTibialmidshaftperimeterandFibularmidshaftlateromedialdiameterTibialmidshaftperimeterandFibulardistalanteroposteriordiameterTibialmidshaftperimeterandFibulardistallateromedialdiameterTibialmidshaftlateromedialdiameterandFibularmidshaftperimeter TABLEVI–BonedimensionBodymass(kg)TibialmidshaftlateromedialdiameterandFibularmidshaftlateromedialTibialmidshaftlateromedialdiameterandFibulardistallateromedialTibialdistallateromedialdiameterandFibularlengthFibularproximalanteroposteriordiameterandFibulardistalanteroposteriorAverage6510*Toolowvalues.Toohighvalues.G.V.MAZZETTAetal. simplyonWernerJanensch’spersonalopinion(Janensch,1938).Impressiveasthisundeniablyis,Brachiosaurushowever,clearlynotthelargestdinosaurknown.ThistitlecurrentlybefallstoArgentinosaurusItprobablydidnot,however,reachthegureof100tonnes,proposedasthemoreconservativeuppermasslimitforalandtetrapodbyHokkanen(1986),unlesssomespecimensweremuchlargerthantheholotype.Unfortunately,thiscannotbecheckeduntilnewndingsareproduced.Otherdinosaursareknown,however,thatmayhaveapproachedinbodymass.“Ultrasauros”(Jensen,1985)wassaidtobeofextraordinarilycolossaldimensions,oftencreditedwithabodymassof100tonnesormore(e.g.Ostrom,1978;Benton,1988;Gillette,1994).Inreality,thescapulocoracoid(250cmlong,not270cmasstatedinJensen,1985)of”cannotbeshowntobedifferentfromthoseofthegenusBrachiosaurus(CurticeandCurtice,1996),anditcouldwellbelongtothetypespeciesB.altithorax.ItisfromaspecimenlargerthantheholotypeFMNH25107,butnotbymorethanaround10orsotonnes(Paul,1988;CurticeandCurtice,1996).Itprobablyhadamassof45–50tonnes.Additionally,equallylargeremainsofB.brancaibeenknown,butclearlynotdiscussed,fornearlyacentury.ThescapulaonHMNSIIisnearlyaslarge(193cm,scapulocoracoid238cm),andanevenlargerscapula(203.5cm)isonexhibitionattheMuseumrNaturkunde,Berlin(Christiansen,Personalobservation).Thisisaslargeasthatof“Thereporteddorsalvertebraof“”isnotevenbrachiosaurianbutfromadiplodocid(CurticeandCurtice,1996).Thetypespecimenof”wasnotthescapulocoracoidbutthatlargediplodociddorsalvertebra,nowreferredtoSupersaurus(BrittandCurtice,1997).Supersaurus(Jensen,1985)isahugediplodocid,andatanestimatedbodymassofaround50tonnesitisthelargestdiplodocidforwhichtherearesubstantialremains(Paul,1988,1997).Seismosaurushalli(Gillette,1987,1991)isnotaslarge,andclaimsofabodylengthof50m(Gillette,1994)arebasedondimensionsotherthanvertebrallengths.Paul(1997)estimatedthatthisanimalwouldhavehadabodymassofaround30tonnes,atanoveralllengthof32–35m.TheonlyothersauropodswhichcouldhavebeensubequalinsizetoArgentinosaurusareknownfromonlyveryfragmentaryremains.Sauroposeidonisagiganticbrachiosaurid(Wedeletal.,2000a)thatappearstohavebeensubstantiallylargerthanB.brancaiHMNSII.However,itwouldprobablynothavehadagreaterbodymassthanandWedeletal.(2000b)suggestedthatitprobablyhadamassof50–60tonnes,subequaltoA.giganteusTheincompletevertebraofthediplodocidAmphicoeliasfragillimus(Cope,1878)apparentlywasofcolossaldimensions,indicatingananimalpotentiallylargerthanevenArgentinosaurus(Appenzeller,1994;Paul,1994,1997).However,thisvertebrahasbeenlostformorethanacentury,makingitstruesizeandphylogeneticafnitiesuncertain.Recently,Smithetal.(2001)describedthepartialskeletonofParalititanstromeri,anextremelylargetitanosauriansauropodfromtheLateCretaceousoftheBahariyaOasis,Egypt.However,andaccordingtotheseauthors,thisnewspeciesisprobablynotaslargeasArgentinosaurusbutrepresentsoneofthebiggestterrestrialvertebratesyetdiscovered.Finally,oneoftheincludedspeciesinthisanalysisA.giganteus)isalsooneofthelargestdinosaurseverdiscovered.Thehugebonesoftheholotypehavelongbeenregardedasremainsofoneofthelargestofallsauropodsknown.Paul(1988)estimateditsbodymassat40–50tonnes,butourresultsindicatethatthisvalueistoolow.Janensch(1938)notedthatitsfemorawerethelargestlongbonesfromanyknownsauropod,andwiththeexceptionoftheonlyknowncompletefemurof,thisstillholdstruetoday.However,itsfemorallengthis235cm,not231cmasgivenbymostpreviousauthors.VanValen(1969)estimatedthatA.giganteushadabodymassofaround80tonnes,basedmainlyoncomparisonswithColbert’s(1962)inatedmassof78tonnesforBrachiosaurus.Asexplainedearlier,ourbodymassestimationforA.giganteusyieldedagureofabout69tonnes,whichisintermediatetothosepointedoutforpreviousauthors.TheropodsAsmentionedabove,avolumetricprocedureyieldedabodymassestimateof1500kgforC.sastrei(Mazzettaetal.,1998).ThebodymassoverestimatesobtainedherebytheusageofallometricequationsbasedonlimbbonedimensionsmaybeduetothephylogeneticcompositionofthedatabaseinChristiansenandFarin(2004),mostlyintegratedbyveryadvancedforms,suchastheverycloselyrelatedtyrannosaursandornithomimids.Asaprimitivetheropod(cladeAbelisauridae),Carnotaurusissubstantiallydifferentinseveralrespectsfromthemoreadvancedones(Bonaparteetal.,1990;Novas,1997a,b).Inanyevent,thisdiscrepancydoesnotaffecttheconclusiononitslocomotorcapabiltyproposedbyMazzettaetal.(1998).Suchaconclusionstatesthatthefemoralstrengthindicator(quantityinverselyrelatedtothebodymass)Carnotauruswashighenoughtoendurestrenousactivities,suggestingthatitmayhavepreyeduponfast-moving,rathersmallprey.Ontheotherhand,G.caroliniimusthavebeenoneofthelargesttheropodseverfound,andeventhelargest.Withabodymassofaboutsixtonnesandahalf(whenonlythepredictionsbasedonSOUTHAMERICANDINOSAURS11 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ette,D.D.1991.Seismosaurushalli,gen.etsp.nov.AnewsauropoddinosaurfromtheMorrisonFormation(UpperJurassic/LowerCretaceous)ofNewMexico.JournalofVertebratePaleontology,417–433.Gillette,D.D.1994.SeismosaurusÑTheEarthShaker.ColumbiaUniversityPress,NewYork.Gregory,W.K.1905.TheweightoftheBrontosaurusScience(NS)Gunga,H.C.,Kirsch,K.A.,Baartz,F.,Rocker,L.,Heinrich,W.-D.,Lisowski,W.,Weidemann,A.andAlbertz,J.1995.NewdataonthedimensionsofBrachiosaurusbrancaiandtheirphysiologicalimplications.Naturwissenschaften190–192.Henderson,D.M.1986.Estimatingthemassesandcentersofmassofextinctanimalsby3-Dmathematicalslicing.,88–106.G.V.MAZZETTAetal. 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