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An Isotopic Analysis of Pleistocene Mammals of the American Southeast

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An Isotopic Analysis of Pleistocene Mammals of the American Southeast What’sForDinner? AnIsotopicAnalysisofPleistocene MammalsoftheAmericanSoutheast PaulaZelanko Advisors:Dr.ThomasHoltzJr. Dr.AlanJayKaufman ChristineFrance GEOL394 Abstract DuringtheRancholabreanNorthAmericanLandMammalAgeofthelate Pleistocene, three megaherbivores are believed to have co-existed in the southeastern region of North America. These include Eremotherium laurillardi (the giant ground sloth), Mammut americanum (the American mastodon), and Mammuthuscolumbi(theColumbianmammoth).Morphologicalandcomparative studiessuggestthatthesegiantherbivorousanimalsallappeartohaveoccupied thesamefeedingniche,whichwouldhaveputextremestressonfoodresources. An alternative interpretation suggests that E. laurillardi was an omnivore that occasionallyconsumedmeat.Totestthesehypotheses,bonesfromanimalsthat occupiedarangeoftrophiclevels(includingsloths,mastodons,andmammoths) in three separate Rancholabrean-aged successions were obtained from the Smithsonian Institution. Collagen was extracted from bone samples for subsequentcarbonandnitrogenisotopicanalysis.BasedonC/Nvaluesitwas determined that bone collagen from two of the study sites were diagenetically altered. Samples from the third (the Upland Bog Formation in Smyth County, Virginia)includingsloth,mastodon,andmammothremains,however,appeared tobewellpreserved.Thenitrogenisotopecompositionsofcollagenfromthese animalssuggestthatthegiantslothsmayhaveoccupiedahighertrophiclevel, and should thus be tentatively classified as omnivores. To confirm this result, furtheranalysesofbonesfromtheUplandBogFormationalongwithadetailed study of the sedimentology and diagenetic environment of all three studied depositsarewarranted. 2 TableofContents Page# Abstract 2 ListofFigures,Charts,andAppendices 4 Introduction 6 Background 7 PreviousMorphologicalStudies 7 StableIsotopes 10 TrophicLevels 11 PreviousIsotopicStudies 12 Samples 12 Methods 13 Results 16 Standards 16 Samples 18 Discussion 20 PrecisionofInstruments 20 ParametersforEvaluatingSampleData 20 AlterationofCollagen 20 Diagenesis 21 TrophicLevels 22 NicheSplitting 24 Conclusion 25 Appendices 27 3 Acknowledgements 31 Bibliography 32 Figures Figure1:Relativesizecomparedtoaveragesizedhuman. Fromlefttoright,Eremotheriumlaurillardi, Mammutamericanum,Mammuthuscolumbi. 6 Figure2:(A)FossilskeletonofEremotheriumlaurillardi, (B)Reconstructionofagiantgroundsloth. 7 Figure3:Dorsal(A)andpalmar(B)viewsofE.laurillardi’s rightmanus(fromCartell1995). 8 Figure4:ReconstructionofMammutamericanum(left)and Mammuthuscolumbi(right)(Kurten,1992). 9 Figure5:Thestepwiseincreaseinδ15N() compositionsof organismsfromdifferenttrophiclevels. 12 Figure6:Localitiesofthestudiedquarriesinthesoutheastern USA.(A)RedstarisSaltvilleQuarry,VA.(B)Bluestar isLadd’sQuarryandgreenstarisWatkinsQuarry,GA. 13 Figure7:Flowchartofprocedurespreformedonbonesamples. 15 Figure8:δ15Nplottedagainstδ13Cfrommultiplemeasurementsofthe ureastandardtoshowprecisionofthemassspectrometer. 17 Figure9:ActualC/Nyieldwith2σuncertaintiesplottedrelativetothe expectedC/Nforglycineof1.7shownbytheredstippledline. 17 Figure10:Helicalstructureandhydrogenbondingincollagen (Kucharz1992andKurten1980). 21 Figure11:C/Nvaluesofbonecollagenfromanimalsofthe SaltvilleQuarry.Sizeofindividualpointmarkersencompasses statisticalerrorwhichis±0.072σ. 22 Figure12:Nitrogenisotopecompositionsofbonecollagenfrom animalsoftheUplandBogFormationatSaltvilleQuarry. Sizeofindividualpointmarkersencompassesstatistical errorwhichis±0.162σ. 23 4 Figure13:Carbonisotopecompositionsofbonecollagenfrom animalsoftheUplandBogFormationatSaltville Quarry.Sizeofindividualpointmarkersencompassesstatistical errorwhichis±0.0242σ. 25 Figure14:Reconstructionofagiantslothsneakinguponitsprey. Beingtooslow,thepreyhasgottenaway. 26 Tables Table1:DataforoneEremotheriumlaurillardisamplefromthe WatkinsQuarry,treatedwiththeinitialtestforsecondary contaminates. 18 Table2:Thesupernatantsamplenumber(spnt)correspondstothebone samplenumbershowninTable3.Allsupernatantsampleswere theproductofthefirstdecalcificationstep.δ15N(‰)valuesare correctedwithrespecttoair;δ13C(‰)valuesarecorrectedwith respecttoVPDB. 19 Table3:Allsamplesweretreatedwiththeresinprocedure.δ15N(‰) valuesarecorrectedwithrespecttoair; δ13C(‰)valuesare correctedwithrespecttoVPDB.SQdenotesSaltvilleQuarry,LQ denotesLaddsQuarry,WQdenotesWatkinsQuarry. 19 Table4:DatafromColtrainetal.(2004)takenfromtheirFigure4 showing15Nenrichmentinbothslothandmastodon bonecollagenfromLosAngelesBasin,California. 23 Table5:DatafromBocherensetal.(1991)Table2. Isotopiccompositionsofbonecollagenfromfossilreindeer Marillac,France. 24 Table6:DatafromDeNiroandEpstein(1985)Table1. Isotopiccompositionsofbonecollagenfromfossildeer fromPalmerandWightman,Florida. 24 Appendices Appendix1:Descriptionofspecimens(a,b,c)andsamplelist(d). 27 Appendix2:ElementalAnalyzersettings 30 5 Introduction Thestudyofpaleoecologyisimportanttothepaleontologicalcommunity becauseitprovidesinformationabouthowancientanimalslivedandinteracted withtheirenvironment.Examiningdietcanbeausefultooltohelpuslearnmore aboutpaleoecologybecause,dietanalysis providesinsightintothefoodchain. Previouspaleodietarystudieshaveexaminedtheconceptoftheniche(Clementz et al., 2003; Feranec and MacFadden, 2000; Zazzo et al., 2000), which is a particularfunctionandpositionofanorganismwithinahabitat.Determinationof theproportionsofherbivorebrowsers,grazers,andintermediatefeeders(mixed feeders)withinacommunityinformsusaboutnichesplitting.Thepartitioningof resourcesallowsforanincreaseinanimaldiversitybecausethecompetitionfor food is decreased (Feranec 2003). The optimum scenario is one species per niche. In the North American Southeast during the Rancholabrean North AmericanLandMammalAge(ca.0.3to0.01Ma)ofthePleistoceneEpoch(1.9 to0.01Ma)therewerethreecolossalanimalsthatappearedtooccupythesame megaherbivore niche: Eremotherium laurillardi (giant ground sloth), Mammut americanum (American mastodon), and Mammuthus columbi (Columbian mammoth).Figure1illustratesgeneralbodysizeoftheseanimals.Considering there are presently no megaherbivores in North America, the question arises, how did these giant herbivores co-exist? One hypothesis suggests that Eremotherium laurillardi was not a strict herbivore, but rather an omnivore, an opportunistic scavenger, an insectivore (Farina, 1996), or even a carnivore (Farina and Blanco, 1996). This would relieve some of the stress on the community food source. Nonetheless, Mammut americanum and Mammuthus columbistillappeartooccupythesameniche.Theyarebothofsimilarsizeand would have utilized the same feeding range. If Eremotherium laurillardi were a trueherbivore,ittoowouldhavetoutilizethesameecospace. Figure 1: Relative size compared to average sized human. From left to right, Eremotherium laurillardi, Mammut americanum, and Mammuthuscolumbi ItisbelievedtheenvironmentoftheSoutheasternUnitedStatesfollowing the last glacial maximum (ca. 18,000 years ago), was similar to today's environment (Pittillo et al., 1998). The vegetation diversity and plant biomass shouldnothaveradicallychangedsincethattime,andshouldbeabletosupport an ecosystem as it did in the late Pleistocene. Currently, Southeastern North 6 Americadoesnotsupportanecosystemwiththreemegaherbivores;indeedwith the loss of the bison there is none. If E. laurillardi, M. americanum, and M. columbialloccupiedthesameniche,thenthiswouldindicateanecosystemthat isunlikeanyoftoday. Performing nitrogen and carbon stable isotopic fractionation studies on thesegiantanimalsaswellasknowncarnivoresandherbivoresfromthesame depositswillproducequantitativedatathatcanbeusedtoexaminetheirdiet.If the data show E. laurillardi to be an herbivore then this species' data will be comparedtotheisotopicdatafromM.americanumandM.columbi.Evaluating thesedatawillshowifthesethreeanimalssplitupthemegaherbivoreniche.If thedatashowE.laurillarditobeanomnivoreorcarnivore,thenthedataofM. americanum and M. columbi will still be compared to see if there was a niche splitting between the two. Therefore my hypothesis is E. laurillardi was an herbivorethatoccupiedthesamemegaherbivorenicheasM.americanumand M.columbi. Background PreviousMorphologicalStudies In depth morphological studies have been preformed on E. laurillardi showingawiderangeofresults(Figure2). (A) (B) Figure2:(A)FossilskeletonofEremotheriumlaurillardi, (B)Reconstructionofgiantgroundsloth. Ground sloths have long been thought to be herbivores (Farina, 1996, see Burmeister,1879).However,Farina(1996)pointedoutseveralcharacteristicsof megatheriids (the family that contains E. laurillardi) that could indicate another type of diet. Megatheriids, as well as megalonychids and nothrotheriids (other familiesofgiantgroundsloth),havegreatcontrolandprecisionovertheirhands andclaws(Figure3)becauseoftheirdevelopedbrains(Farina,1996,seeDozo, 1989) and the biomechanics of their forearms (Farina, 1996, see Aramayo, 1988).Thiscontrolcouldindicatethatslothsusedtheirclawstoslashcarcasses 7 openandtocuttheirmeatintosmallerpiecesinordertomakeiteasiertochew (Farina,1996).Usingtheirclawsthiswaywouldhelpcompensatefornothaving sharpcuttingsurfacesandsectorialdentitionsontheirteeth,whichmammalian carnivores
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