Latest information on Sterkfontein's Australopithecus skeleton and a new look at Australopithecus


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Latest information on Sterkfontein's Australopithecus skeleton and a new look at Australopithecus

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Latest information on Sterkfontein's Australopithecus skeleton and a new look at Australopithecus
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South African Journal of Science
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Clarke, Ronald J.
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Academy of Science for South Africa (ASSAf)
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After a decade of careful excavation, it is now possible to explain how the skeleton came to be in that isolated position in the cavern. Furthermore, it is apparent that the fossil does not belong to either Australopithecus africanus or to A. afarensis, but to an individual belonging to, or closely affiliated to, the second Australopithecus species that is represented in Sterkfontein Member 4 and Makapansgat.
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South African Journal of Science, Vol. 104, no. 11-12 (2008-12).

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Latest information on Sterkfontein’s Australopithecus skeleton and a new look at AustralopithecusR.J. Clarke*AFTERADECADEOFCAREFULEXCAVATION,itisnowpossibletoexplainhowthe skeletoncametobeinthatisolated positioninthecavern.Furthermore,itis apparentthatthefossildoesnotbelongto either Australopithecusafricanus orto A.afa rensis, buttoanindividualbelongingto,or closelyaffiliatedto,thesecond Australopithecus speciesthatisrepresentedinSterkfontein Member 4 and Makapansgat.Introduction Itwas10yearsagointhisjournalthatan announcementwasmadeofthediscovery intheSilberbergGrottooftheSterkfontein Caves,northwestofJohannesburg,ofthe first-everassociatedskullandskeletonof anape-man.1Atthattime,allwehad uncoveredwerethelowerlegswithparts ofthefeet,acompleteskull,andaleft radiusthatwaslatershowntobelongtoa monkey.Althoughitwasnotpossibleto placethefossilintoaspecies,itwasseen tobethatofan Australopithecus differing from Australopithecusafricanus andwas thoughttodatetoolderthanthreemillionyearsago(Myr),possibly3.5Myr.It wassubsequentlydatedto3.3Myrby palaeomagnetism.2Taphonomically,it wasobservedthattheskeletonlayona talusslopeandthatfossilsofotherani malswerevirtuallyabsent,incontrast withtheeasternendofthecaveinfillin theSilberbergGrotto,whichhadadense concentrationofbonesincludingpartial skeletonsofmonkeysandcarnivores.It wasnotedthatthisraisedthequestionof howsuchanintactskeletoncametobein that isolated spot in the cavern. Tenyearsofslow,carefulexcavationin theconcrete-likebrecciahaverevealed theanswertothatquestion.Thegeneral sequenceofeventsthatformedthe Sterkfonteininfillshasbeendescribedby Clarke,3butthereisonebigmystery concerningthisskeleton(classifiedas StW573)thatneedstobeexplained.Ofall thefossils,animalandhominid,recovered fromSterkfonteinsince1936,itisonly StW573thatrepresentsanear-complete skeleton,andifthefeethadnotbeen blastedoffbylimeminers,itwould undoubtedly have been complete. AttheeasternendoftheSilberberg Grotto,boneswereheavilyconcentrated apparentlybywater.Althoughthereare somearticulatedpartsofskeletonsof carnivores,monkeysandbovids,nothing isanywherenearcomplete.Whatthen werethespecificconditionsthatallowed forthepreservationofStW573asacom pleteskeleton?Wehavesofaruncovered theskull,leftarmandhand,32rightarm andhand,rightscapula,rightclavicle, severalribsandvertebrae,sacrumand pelvis,andbothlegswithsomeofthefoot bones.Therestofthefootbones,blasted awaybymining,havenotbeenfound (Figs 1–4). Thelengthoftimetakentoextractthis skeletonfromtheSilberbergGrottohas beengovernedbyseveralfactors.Theindividualbonescomprisingtheskeleton, whilstingeneralanatomicalrelationship tooneanother,haveinsomepartsbeen displacedandbrokenup byancient environmentalfactors,includingtaluscollapse andwater.Becauseofthis,itisnotpossible topredictexactlywhereintheconcretelikebrecciaanyskeletalelementmay occur.Thebonesthemselvesaresoftand canbeeasilydamagedbytoolsifexcava tionistoorapid.Theaimhasbeentolo catethepositionofallelementsofthe skeletonwithinthebrecciawithminimal riskofdamagepriortoremovingblocksto thelaboratoryforfinalcleaning.Another majorconsiderationhasbeentheneedto uncovercluesastowhathappenedto that individual. Thereareseveralmysteriesthatwe wouldliketounravel.Howdidthat individualcometobeinthecave?Whyis theskeletonsouniqueinbeingnearcomplete?Whyarepartsofitbrokenup andatdifferentlevelsfromotherparts? Whyismuchoftheleftpelvisdisinte grated?Whyisthistheonlyhominid fossilsofardiscoveredintheSilberberg Grotto?Whyweretherevirtuallyno otheranimalboneswithitwhenitwas first uncovered? Becauseofthemethodicalandslow excavation,wecannowprovidepossible andprobableanswerstothesequestions. Thecompletenessoftheindividualand lackofanycarnivoredamagetothebones indicatethatitwasnotpreyeduponby carnivoresbutthatitfellintoashaft leadingintothecavern.Thereasonsfor thefallareunknown.Wedoknowthatat theother(eastern)endoftheSilberberg Grottoisaconcentrationofbones,mainly ofcarnivoresandmonkeys,fromanimals thatfellintoanaturaldeathtrap.4The probabilityisthatStW573alsofellintoa Research in ActionSouth African Journal of Science 104 , November/December 2008443 *InstituteforHumanEvolution&SchoolofAnatomical Sciences,UniversityoftheWitwatersrand,PrivateBag3, WITS 2050, South Africa. E-mail:ronald.clarke@wits.ac.za Fig. 1 .The skull and left humerus of StW 573.

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shaft,belowwhichwasatalusslopethat fedintothewesternendoftheSilberberg Grotto.Althoughtherearesomearticu latedpartsofprimate,bovidandcarni voreattheeasternend,thereareno completeornear-completeskeletons. Thisisprobablyduetotheindividual bonesandpartiallyarticulatedelements havingbeentransportedbywaterfrom theiroriginalpointofdeposition.There arecertainlysignsthattheboneswere concentratedandlooselystratifiedby water.3Situation of theAustralopithecusskeleton WhentheStW573skeletonwasfirst beinguncovered,therewasanoticeable near-absenceofotherfossilsinitsvicinity. Onlyamonkeyleftradiusandaleopard half-mandiblewerepresent.Aswehave continuedtodigdeeperinorderto undercuttheskeletonforlifting,wehave uncoveredanincreasingnumberof animalremains,includingtwomonkey craniaandamonkeyulna.Itisnotewor thythatthesebonesareisolatedfinds, andthereisnosignofanyarticulated skeletonofananimal.Whythenshould the Australopithecus besocomplete?The answerseemstobeinitspositiononthe talusslope.Itisontopofthetalusslope, notfarbelowtheroof,andwasapparentlyoneofthelastbodiestofallontothat slopebeforethepointofingresswas blockedandthetaluswassealedoverbya thickflowstone(Fig.5).Suchpureflowstonecandeveloponlywhenthereisno furtherentryofdebris.Thustherewasno opportunityfortheskeletontobebroken upandscatteredbysuchfurtherentryof rocks and sediment. Thebreakagethathasoccurredtothe skeletonhasbeenoccasionedbywater flowingthroughthetalusbeneathit, removingasofterreddishdeposit,and formingacavityintowhichthecentral partoftheskeletonanditssurrounding matrixcollapsed.5Theextensivecavityis stillclearlyvisiblewherethelimeminers havesectioneditbyblastingawaythe brecciadownslopeoftheskeleton.Fur thermore,ourexcavationtoundercut theskeletonhasrevealedsomesmaller cavitieslinedwithcalciumcarbonate withinthetalusdepositandsuggestiveof waterflowthroughthetalus.Itisthis ancientwaterflowthatwasprobably responsibleforthedisintegrationofthe leftsideofthepelvis.Anditisthecollapse ofthecentralpartoftheskeletonand slightmovementsofthesurrounding matrixthatcausedsomeofthebonesto break. ThequestionofwhytheStW573skeleton istheonlyhominidsofarfoundinthe SilberbergGrottoremainsamystery.The cavernhasbeenextensivelyminedand allthequarriedbreccia,inadditionto thebrecciathatweexcavated,hasbeen processed.Althoughitisfullofanimal bones,notasingletoothofahominidhas everbeenrecovered,apartfromthosein theskullofStW573.Thisnear-absenceof hominidfossilscontrastsgreatlywiththe richnessof Australopithecus remainsin Member4.Theanswertothispuzzle couldbeeitherthatearlyinthehistoryof 444South African Journal of Science 104 , November/December 2008Research in Action Fig. 2 .The left forearm and hand of StW 573. Fig. 3 .The left hand of StW 573.Fingers clenched and thumb across palm. Fig. 4 .The right scapula of StW 573 (centre right) in ventral view.Back of skull at top left.

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thecaveinfillingatSterkfontein Australo pithecus wasnotcommoninthevicinityof thecaves,orthatunlikethemonkeysand carnivores,itwasnotinthehabitoffalling downtheshafts.ByMember4times, perhaps700000yearslater,thereare definitesignsthat Australopithecus was beingpreyeduponanditsbonesand teethwerebeingwashedintoalarger cave opening.6,36To which species does StW 573 belong? Whenthe Australopithecus skulland skeletonwasfirstannouncedin1998,it wasnotpossibletodeterminethespecies towhichitbelongs.Itcouldbestatedonly thatitisdifferentfrom A.africanus. Asthe uncoveringofthebonesprogressed,it appearedthattheskullhadsomesimilari tiesto A.afarensis initsmuscularocciput, sagittalcrest,androbustzygomaticarch. Therewere,however,alsosomediffer ences.ItisnowapparentthatStW573 doesnotbelongtoeither A.africanus or A.afarensis, butthatitrepresentsanindi vidualeitherbelongingto,orveryclosely affiliatedto,thesecond Australopithecus speciesthatiswellrepresentedinSterkfonteinMember4andMakapansgat.7,8Thecontinuedremovalofbrecciafrom thecraniumhasrevealedthatthelower partoftheStW573facehasbeenpushed upwardandbackward,whichgaveita falseappearanceofhavingarelatively short,squatface.Ifallowanceismadefor this,thenthecombinationoflongerface, robustzygomaticarch,muscularocciput, smallsagittalcrestatthebackofthe cranium,andlackofsupraorbitalthicken ingdistinguishesthisskullfrom Austra lopithecusafricanus andalignsitclosely withspecimenssuchasStW505and StW252,whichbelongtothesecond Australopithecus speciesasdiscussedbelow.Australopithecus africanusThetypespecimenofthisspeciesisthe childskullfromTaung,9andthereare somecranialspecimensfromSterkfontein andMakapansgatthatclearlyrepresent theadultformofthespecies.These includeTM1511,TM1512,Sts5,Sts17, Sts52,StW53,StW391,andMLD6(FigsA andBinsupplementarymaterialonline). Withinthissamplearespecimensthatcan bedifferentiatedasmalesandfemaleson morphologicalcharactersthatechothose seeninotherlargerhominoidssuchas chimpanzees,thatis,largecaninesinthe malesandsmallinthefemales(Fig.Con line),widerbimastoidareaofthecranium inthemalesandnarrowerinthefemales (Fig.6).ThusTM1511,StW53,and StW391areclearlymales,whereasSts5 andTM1512areclearlyfemales.TM1511 Research in ActionSouth African Journal of Science 104 , November/December 2008445 Fig.5 .Thickflowstone( A–B )thatsealsinskeletonontopoftalus.Thecentralpartofflowstonehasbeenexca vated away. C , Left hand and D forearm; E , left humerus and skull. Fig.6 .ClarkereconstructionofStW53maleAustralopithecusafricanus(topleft)comparedtoSts5femaleA.africanuscast(topright),endocranialcastsofStW53(middlerowleft)andSts5(middlerowright),basalview ofStW53Clarkereconstruction(lowerleft)andSts5cast(lowerright).Notebroadercranialbaseinthemale StW 53.

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andStW53closelyresembleeachother andbothhavelargecaninesocketscom paredtoSts5andTM1512.Furthermore, StW53iswideracrossthemastoidregion thanisSts5(Fig.9).Ofthesespecimens, StW53needstobediscussedindetail, becauseitiscommonlybutincorrectly referredtointextbooksandresearch publications as Homohabilis. In1976,atthesouthwesternendofhis Sterkfonteinexcavation,AlunHughes recoveredhominidteethandcranial fragmentsofoneindividual(StW53) fromthedecalcifiedbrecciawithina solutionpocket.Therightposterior portionofthebraincasewasembeddedin solidbrecciainthewallofthesolution pocket,thusindicatingtheexactlocation andbrecciatypefromwhichtheother fragmentshadbeendecalcifiedand scattered.Thebrecciaatthatwesternend was,atthetime,thoughttobeall Member5withanoverlyingexposureof Member6inasmallareaonthenorthern side.AsMember5hadyieldedabundant earlystonetools,andasnostonetools whatsoeverhadoccurredinMember4,10believedthatStW53mustbeacraniumof early Homo. Subsequently,itwasfrequently referredtoas Homohabilis becauseofits similaritytotheOH24 Homohabilis from OlduvaiGorgeBed1.11,12Laterstratigraphic investigationbyClarke13showedthat StW53didnotinfactcomefrom tool-bearingMember5,butfromahangingremnantofMember4.14Furthermore, ataconferenceinOrce,Spain,in1995,15ClarkeobservedthatStW53andsupposed Homohabilis specimensOH13,OH24, andKNMER1813,hadsmallbrainsand flatnoseslikethoseof Australopithecus, andintheserespectsdifferedgreatly fromthemuchlarger-brainedOH7type specimenof Homohabilis, aswellasfrom KNMER1470 Homohabilis, whichhas aprominentnasalskeleton.Healso referredtotheworkofSpoor16andSpoor etal.,17whofoundthatthebonylabyrinth oftheStW53temporalwasunique amonghominidfossilsindimensionsof semicircularcanals,whichwerebetween thoseofgreatapesandaustralopithecines andthoseofcercopithecoids.Nothingin itsanatomysuggestedthatStW53was anythingbutan Australopithecus andit certainlycamefromthenon-tool-bearing Member4,justliketheother Australo pithecus fossils from Sterkfontein.14Clarke12madeareconstructionofthe StW53cranium‘basedsolelyonanatomi calconsiderationsandsymmetry’.He termedita‘preliminary’reconstruction becausetherewereseveralotherisolated fragmentsofvaultandorbit,someof whichmightpossiblybeincorporatedin anyfuturereconstruction.Furthermore, therewasnocontactbetweenthefacial portionandthefrontalandtemporals. Thus,veryminoradjustmentsmightbe consideredinthefuturetotheangulation andverticalpositionofthefacerelativeto thebraincase.Thisdidnotmeanthat Clarkedidnothavefullconfidenceinthe formandsizeofthebraincaseashehad restoredit.Thereweresomegoodcontacts andsomenearcontactsbetweenfragments oftheposteriorvaultandthis,plusthe smallsizeoftheundistortedfrontal (smallerthanSts5),providedasound basis for the reconstruction. CurnoeandTobias18statedthatthey compared‘thecranium,asinitiallyassem bledby HughesandClarke,withthelater reconstructionbyClarke(1985)12’andthat ‘theanatomicalplacementofanumberof criticalbonesdifferedbetweenthetwo.’ Theythenwentontostate,‘Thus,two differentinterpretationsofthemorphol ogyofStW53haveexisteduntilnow(i.e. studiesoforiginalremains,asassembled byAlunHughes,andalterationstothis restorationmadeoncastpiecesbyClarke duringhisreconstruction).’Thisisuntrue. Therewasnoearlierrestorationofthe cranium,eitherbyHughesandClarkeor byHughesalone.Intheinitialpublication byHughesandTobias,10theseparate portionsofthecraniumarenotassembled.Inanearlierannouncement,19there isaphotographoftheseparatefaceand frontal,leftparieto-occipitalfragment andleftoccipitalcondyleplacedinprofile onaphotographicstandinthedarkroom byHughesandClarketoindicate,asthe captionsays,‘someofthediscovered fragmentsreassembledinanattemptto giveanideaoftheoutlineofthecranium.’ Thesamephotographispublishedby Tobias20withthecaptionstatingthatitis ‘atentativealignmentofsomepartsofthe specimen,effectedbyA.R.Hughesand R.J.Clarke.’Theplasticenesupporting theparieto-occipitalfragmentcanbeseen in this photograph. Thereneverwasathree-dimensional restorationofthecraniumpriortothe Clarkereconstructionof1985,andthere werenodifferencesbetweenthe1976 photographandtheClarke1985recon structionintheanatomicalplacementof thosefewfragments.Nevertheless,Curnoe andTobiasusedthesenon-existentdiffer encestojustifytheir makinga‘ newrecon struction’.Toachievethis,theydissembled theanatomicallysoundnear-contactbe tweentheleftandrightoccipitalportions andseparatedthembyabout8mm.Now, intheir‘reconstruction’thenuchallineis about8mmlongerontherightofthe inionthanitisontheleft(seetheir figures8cand14).Theyhavethusartifi ciallyandunjustifiablywidenedthe braincaseandmadeitasymmetrical. Theyalsointernallyopenedthesutural contactbetweentheleftposteriorparietal fragmentandoccipitalandflexedthe parietalupwardssuchthattheparietal fragment,intheirwords,‘isnowmore elevatedatitsanteriorend’.Thishas madethevaulthigherandtheyhave elongatedthevaultgreatlybyextending thegapabnormallybetweentheposterior braincaseandthefronto-facialportionto produceanoddly elongatedbutrelatively narrowbraincase.Theresultoftheseand othermodificationsisthatthemaxillais greatlytwistedrelativeto themidsagittal plane(theirfigure9).Theycommenton thisasfollows:‘thus,thewholefacial skeletonofStW53istwistedtotherightof themediansagittalplane.Wehavenot correctedforthisinourreconstruction,as Clarke(1985)didinhis,preferringinstead torecognizemorefullytheextentof damagethespecimenhassuffered.’This isuntrue.Clarke12didnotmentionthe correctionofanydistortionandhadno needto,becausetherewasnodistortion of the cranium to correct! Themaxilla,frontalbone,leftparietooccipitalportions,lefttemporal,andleft occipitalcondyle,aswellasseveralother isolatedfragmentsofbraincaseanda rightascendingramusofthemandible, wererecoveredfromthedecalcified brecciaandnoneofthesepieceswas deformedinanyway.Therightposterior portionofthebraincasewasexcavated fromthehardbrecciawallofthesolution pocketwhereitwasexposedintheform ofthemanganese-stainedbrokensection throughtherightparietal,occipitaland temporal.Aphotographofthisispub lishedinTobias,20aswellasadrawing reconstructingthepostulatedsequence ofeventsleadinguptobreakageofthe skull.Themanganesestainingindicated thedecalcifiededgeoftherightbraincase. Someoftheloosefragmentsfromthe decalcifiedbrecciawouldoriginallyhave beenincontactwiththismanganesestainedexposedmargin.Whenthis braincaseportionwasremovedand cleanedofbreccia,itcouldbeseenthat theparietalhadbeenpusheddownwards slightlyinsidethetemporalandoccipital, andtherewassomefracturingandslight displacementofpartsoftheparietaland occipitalnearasterion.Therewas,how ever,noseriousdistortionoftheindivid ualbonefragmentscomprisingthe specimen.Oncetheboneswereseparated andputintheircorrectpositionby Clarke,12thisportionofthebraincase exhibitedgoodlandmarksandsurface contoursthat,togetherwiththeother isolatedfragments,providedanexcellent basisforthereconstructionofanundis 446South African Journal of Science 104 , November/December 2008Research in Action

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tortedcranium.CurnoeandTobias,18however,statedthatthereis‘deforma tionof,anddamageto,therightparietooccipito-temporalfragment’andsaidthat ‘transversecurvatureofthevaultwas moredifficulttoreconstructbecauseof extensivedistortionanddamage,especially ontherightparietalandtemporalbones and on the right part of the occipital.’ TheClarke12reconstructionofthisregion, mirrorimagingtheavailabledataprovided bytheleftparieto-occipitalandtemporal andoccipitalcondylefragments,wasnot deformed.CurnoeandTobias,however, cutupthecastoftherightbraincase portionasreconstructedbyClarke(their figure10)andbentcontactsbetween fragmentsinanunnaturalmanner.They alsoseparatedthegoodcontactbetween twopartsoftherightoccipitalbaseand rotatedtheupperportionclockwiserela tivetothelowerportion,leavingagapof 9mmatthemedialend.Allofthishas producedadeformitythattheyhave mirrorimagedintheirreconstructionof theleftside,producingabizarrelyshaped profilewhenviewedfromtherearthat doesnotresembleanyknownhominid cranium (see their figures 14 and 8c). Reconstruction,inthefossilcontext, meansbuildinguptoitsoriginalform somethingthatisfragmented.Thisis donebyutilizingthepreservedanatomical landmarksandcontours,andthisishow Clarke12madethereconstructedStW53 cranium.CurnoeandTobias18havenot donethis,butinsteadhavewidelyseparatedanear-contact,unrealisticallyflexed sutureandbonecontactsandunnaturally extendedthegapbetweenfrontandback toproduceabraincasethatiswider, higherandlongerthanitshouldbe. Furthermore,itisnowdeformed.Thus theirsisnotavalidreconstructionbecause ithasnotfollowedtheanatomicalguide linesandcontoursandthereforedoesnot reflecttheoriginalformofthecranium.It isaconstructofhowtheythinkitshould be,ratherthanareconstructionofhowit actuallywas.Intheirownwords,Curnoe andTobias18admitthat‘ourreconstruction differsinimportantrespectsfromthe earlierone,especiallyintermsofneuro craniallength,breadth,andheight.How ever,giventhatStW53exhibitsextensive damage,thesedimensionsaremostlikely pronetomucherrorinreconstruction.’ Despitethis,theyhavestillmaintained thatthemaximalcraniallengthoftheir ‘reconstruction’isvirtuallyidenticalto the Homohabilis craniumKNMER1470 (theirfigure18)andtheiroverallconclusion basedontheirartificiallyenlargedand deformedStW53braincase,aswellas theirinterpretationoftheanatomy,isthat it is a representative of Homohabilis. TheClarke12reconstruction,whichwas basedonanatomyandcontoursofthe bones(whichcontraCurnoeandTobias donot‘exhibitextensivedamage’),shows thattheStW53cranialsizeandshape doesnotdiffersignificantlyfrom Austra lopithecusafricanus intheformofSts5 (Fig.6).Thefacialstructureofthetwois verysimilarwithsmall,narrowmuzzle, smallnasalapertureandflatnasalskeleton, andbothhaveanarrowrectangular palate.Thefrontalbonesofbothresemble eachotherinsizeandformwithapromi nentmetopicridge.Thewiderinter mastoidbreadthinStW53isundoubtedly becauseitisamale A.africanus, whereas Sts5isafemale.Thisisindicatedalsoin thedentition.Sts5hassmallercanineand cheekteethsocketsthandoesStW53, whichmoreresemblesSts52andStW391. Initssmallcanineandpremolarsockets, Sts5issimilartoTM1512,whichisalso undoubtedlyafemale.Thelargercanine socketintheapparentmaleshascaused thesockettobulge moreanteriorly ,which cancontributetoalesspronounced appearanceofthepremaxillaryregion.It shouldalsobenotedthatStW53hasthe premaxillarybonevisibleonbothsidesof theuppernasalmargin.Thisisanape-like and Australopithecus characterseenin TaungandMLD6anddoesnotoccurin Homo. HughesandTobias10notedthe coincidenceofStW53fragmentsbeing foundonthedaysrepresentingthe40th anniversaryofBroom’sfirstvisitto Sterkfonteinon9August1936,andhis discoveryofthefirstadultcraniumon17 August1936.Thecoincidencewasactually morestrikingthantheyrealized,because StW53isremarkablysimilartoBroom’s firstadultcranium,TM1511.Thetwo craniaresembleeachotherintheformof theirfaceandteeth,eventhoughthe teethofStW53areheavilyworn,andthe frontalboneofStW53fitsextremelywell withthesizeandcurvatureofthefrontal lobe of the endocast (Sts 60) of TM 1511. Thereisinfactnothingintheanatomy ofStW53toalignitwith Homohabilis (in theformofOH7,KNMER1470and OH65)ratherthanwith Australopithecus. Thetypespecimenof Homohabilis is OlduvaiHominid7(OH7),consistingof thetwoparietalsandmandibleofajuve nile.21Theparietalsaloneindicateamuch larger-brainedhominidthanany Austra lopithecus andtheseparietalsmatchinsize andshapethoseofthenear-complete craniumKNMER1470.22Hence,the1470 craniumcannotbedistinguishedfrom Homohabilis andthereisnojustification foritshavingbeenplacedinaseparate species, H.rudolfensis (e.g.refs23,24).The discoveryofacompletedentitionin maxillaofOH65fromOlduvaiGorge Bed1(ref.25)supportstheplacementof KNMER1470in Homohabilis. Themaxilla ofOH65matchesinshapeandsizethatof 1470andthecheektoothcrowns,though smallbycomparisonwith Australopithecus, havewidely-flaringrootslikethoseof KNMER1470.Thepalatesofbothfossils arebroadandhorseshoe-shaped,thus differingradicallyfromthenarrow,rect angular palates of Australopithecus. Itisratherthesmaller-brained,more Australopithecus -likefossilsOH13,KNM ER1813,OH24andOH62whichshould beremovedfromthetaxon Homohabilis as theyhavenosimilarityto Homohabilis as representedbythetypespecimenOH7, togetherwithKNMER1470andOH65. Thequestionofwhetherthesmallerbrainedformsshouldbeclassedas Australopithecus ratherthan Homo has beenraisedbefore.26,27AsfarasthesmallbrainedStW53isconcerned,thereseems nodoubtthatitshouldbeclassedas A.africanus, apparentlymale,withstrong similaritiestoBroom’soriginal1936 cranium TM 1511, as well as to Sts 5. A secondAustralopithecusspecies in South Africa EversincethediscoverybyBroomof thefirstadult Australopithecus fossilat Sterkfonteincavesin1936,allother Australopithecus fossilsfromthatsitehave generallybeenregardedasbelongingto onespecies.Initially,Broom28namedthe firstcranium,TM1511,as Australopithecus transvaalensis, aspeciesdistinctfromthe childofTaungthathadbeennamed Australopithecusafricanus.9Twoyearslater, followingthediscoveryatSterkfonteinof achildmandibularsymphysiswithavery largecanine,Broom29decidedthatitwas sodistinctfromtheTaungchildthathe shouldmakeitanewgenus, Plesianthropus. Heconsideredthatthelarger-toothedfos silsfromSterkfonteinweremalesandthe smaller-toothedfossilswerefemalesof one species. Dart30namedthefirst Australopithecus fossilfromMakapansgat(theoccipital MLD1)asanewspecies, Australopithecus prometheus, andallsubsequentfossils fromthatsitewereplacedinthesame species.Thus,althougheachofthethree sites,Taung,SterkfonteinandMakapans gat,wereconsideredtohavedifferent speciesofape-man,itdidnotoccurto eitherBroomorDartthattheymayhave morethanonespeciesrepresentedwithin thesitesofSterkfonteinandMakapansgat. Lateritbecamegeneralpracticeto regardallthe Australopithecus fossilsfrom thethreesitesasbelongingtotheone species, A.africanus, andthathasbeenthe prevailingviewuptothepresentday.A dissentingviewhasbeenexpressedby Research in ActionSouth African Journal of Science 104 , November/December 2008447

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Clarke,7,8,13,31,32whopointedoutclear morphologicalratherthansexualdiffer enceswithinthe Australopithecus samples frombothSterkfonteinandMakapansgat. KimbelandWhite33alsosuggestedthere couldbetwoformsof Australopithecus represented.However,theseviewpoints havegenerallybeendisregardedand textbooksandresearchpublications continuetolumpallSouthAfrica Australopithecus fossilsin A.africanus andtodraw conclusionsaboutthatspeciesbasedona verydiversemixtureofcharacters.With thecontinuingdiscoveryofmorefossils, aswellaswithcriticalexaminationofall thosefossils,itiscleartothisauthor thatthereareindeedtwospeciesof Australopithecus representedatbothSterkfonteinandMakapansgatandthatmales andfemalescanbediscernedwithineach species. Thissecond, Paranthropus -likespeciesof Australopithecus isdistinguishedfrom A.africanus bythefollowingcomplexof characters,mostofwhichareexemplified in the StW 252 cranium: 1)Molarsandpremolarsarelargeand bulbous,withcuspssituatedtowards the crown centre. 2)Caninesandincisorsarelargerelative to the cheek teeth. 3)Cheekbonesareprominentandante riorlysituated,suchthatinsideview thenasalregionishiddenbehindthe cheekbone. 4)Fromapositionhalf-wayupthelat eral marginofthenasalaperture,the frontal processofthemaxillaextends laterallyinsteadofcurvingback wards, as it does in A.africanus. 5)Theinterorbitalregioniswide, whereas it is narrow in A.africanus. 6)Nasionissituatedabovethefronto maxillarysuture,closetoglabella, which is not prominent. 7)Thesupraorbitalmarginisthinor minimally developed. 8)Thereisaslighthollowingofthefron tal squame just behind glabella. 9)Thefaceismuchlongerincomparison to A.africanus. 10)Theoccipitalprofileishighandflattened. 11)Thereisasmallsagittalcrestposteriorly in males. Otherspecimensthatexhibitatleast someofthesedistinguishingcharacters andwhichcanbeassignedtothissecond Australopithecus species(Figs7–11)are: Sts71cranium,StW505cranium,StW183 maxilla,StW498maxillaandmandible, StW384mandible,Sts1palate,and MLD2mandible(fromMakapansgat) Thereareseveralotherlesscomplete specimens,includingindividualteeth, that can be assigned to this species. So Paranthropus -likeisthissecondspe ciesthatAguirre34actuallysuggestedthat MLD2shouldbeclassifiedas Paranthropus. Thedentition,however,asexem plifiedincraniumStW252,exhibitslarge caninesandincisors,whichisan Australo pithecus ratherthan Paranthropus charac ter,andthusitcanbesaidonlythatthis secondspeciesisperhapscloselyrelated totheancestryof Paranthropus. Another specieswithsomesimilarcharacteristics includingverylargecheekteethis Australopithecusgarhi ofEthiopia,35butit differsinhavingevenlargercaninesand inlackingthecharacteristic Paranthropus likebulbouscheekteethseenintheSouth African species. Withinthesecond Australopithecus speciesfromSouthAfricaarespecimensthat canbedifferentiatedasmaleandfemale. ThusStW252withitslargerteethand muscularityisayoungmale,StW505 withaposteriorsagittalcrestandworn teethisanoldmale,andSts71withless muscularityandslightlysmallerbutworn teethisanoldfemale(Fig. 11).The cranium ofStW573inMember2appearstohave featuresidentifyingitasprobablyamale ofthissecondspeciesratherthanwith A.africanus, butitsexactaffinitieswillonly bedeterminedwhenthemandiblecanbe 448South African Journal of Science 104 , November/December 2008Research in Action Fig.8 .ComparisonofdentitionofAustralopithecusafricanusmandibleSts52(farleft)andmandibleoflargetoothedspeciesStW384(left),aswellasmaxillaeoflarge-toothedspeciesSts1andStW183(rightandfar right). Fig.7 .CastofrestoredpalateanddentitionofStW 252 (the second species). Fig.9 .MaleAustralopithecusafricanusStW53(left)andmaleofsecondspeciesStW252(right).Notethemuch longer face and wider parietal region in the second species.

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separatedfromthemaxillatoexposethe occlusalsurfacesoftheteethandwhen thedisplacedlowerfaceiscorrectly positioned.Iamextremelygratefulforthehelpprovidedinthe preparationofthismanuscriptbyMeraewinClarke andKathleenKuman.Fundsfortheresearchat Sterkfonteinhavebeenprovidedovermanyyears bythePalaeontologicalScientificTrust,theFord Foundation,theMottFoundation,theEmbassyof FranceinSouthAfrica,theNationalResearch Foundation,theDeBeersChairman’sFund,the NationalGeographicSociety,theWennerGren Foundation,andtheL.S.BLeakeyFoundation.Iam alsogratefultotheUniversityoftheWitwatersrand andtoP.V.Tobias,whohaveprovidedmewiththe opportunitytoworkonthisextremelyimportantsite anditsfossiltreasures.Figures1and2arephoto graphs by Carlo Kaminsky. 1.ClarkeR.J.(1998).Firsteverdiscoveryofawellpreservedskullandassociatedskeletonof Australopithecus.S.Afr.J.Sci. 94 , 460–463. 2.PartridgeT.C.,ShawJ.,HeslopD.andClarkeR.J. (1999).ThenewhominidskeletonfromSterk fontein,SouthAfrica:ageandpreliminaryassess ment. J.Quat.Sci. 14 (4), 293–298. 3.ClarkeR.J.(2006).Adeeperunderstandingofthe stratigraphyofSterkfonteinfossilhominidsite. Trans.R.Soc.S.Afr. 61 , 111–120. 4.PickeringT.R.,ClarkeR.J.andHeatonJ.L.(2004). ThecontextofStW573,anearlyhominidskull andskeletonfromSterkfonteinMember2: taphonomyandpaleoenvironment. J.Hum.Evol. 46 , 277–295. 5.ClarkeR.J.(2002).Newlyrevealedinformation ontheSterkfonteinMember2 Australopithecus skeleton. S.Afr.J.Sci. 98 , 523–526. 6.ClarkeR.J.(2007).TaphonomyofSterkfontein Australopithecus skeletons.In BreathingLifeinto Fossils:TaphonomicStudiesinHonorofC.K.(Bob) Brain, edsT.R.Pickering,K.Schick,andN.Toth, pp.195–201.StoneAgeInstitutePress,Blooming ton, Indiana. 7.ClarkeR.J.(1988).Anew Australopithecus cranium fromSterkfonteinanditsbearingontheancestry of Paranthropus. In EvolutionaryHistoryofthe ‘Robust’Australopithecines, ed.F.Grine,pp.285– 292. Aldinede Gruyter, New York. 8.ClarkeR.J.(1994).Advancesinunderstandingthe craniofacialanatomyofSouthAfricanearlyhomi nids.In IntegrativePathstothePast:EssaysinHonor ofF.ClarkHowell, edsR.S.CorrucciniandR.L. Ciochon, pp. 205–222. Prentice-Hall, New Jersey. 9.DartR.A.(1925). Australopithecusafricanus, the man-ape of South Africa. Nature 115 , 195–199. 10.HughesA.R.andTobiasP.V.(1977).Afossilskull probablyofthegenus Homo fromSterkfontein, Transvaal. Nature 265 , 310–312. 11.LeakeyM.D.,ClarkeR.J.andLeakeyL.S.B.(1971). NewhominidskullfromBedI,OlduvaiGorge, Tanzania. Nature 232 , 308–312. 12.ClarkeR.J.(1985). Australopithecus andearly Homo insouthernAfrica.In Ancestors:TheHardEvidence, ed.E.Delson,pp.171–177.AlanR.Liss,NewYork. 13.ClarkeR.J.(1994b).Onsomenewinterpretations ofSterkfonteinstratigraphy. S.Afr.J.Sci. 90 , 211–214. 14.KumanK.andClarkeR.J.(2000).Stratigraphy, artefactindustriesandhominidassociationsfor Sterkfontein,Member5. J.Hum.Evol. 38 ,827–847. 15.ClarkeR.J.(1999a).Mr,MrsandMiss-conceptions instudiesofhumanancestry.In TheHominidsand theirEnvironmentsduringtheLowerandMiddlePleistoceneofEurasia, ed.J.Gibert,Proc.Interna tionalConferenceofHumanPalaeontology,Orce, Spain, 1995, pp. 327–329. 16.SpoorF.(1993). Thecomparativemorphologyand phylogenyofthehumanbonylabyrinth. Ph.D.thesis, University of Utrecht, the Netherlands. 17.SpoorF.,WoodB.andZonneveldF.(1994).Impli cationsofearlyhominidlabyrinthinemorphol ogyforevolutionofhumanbipedallocomotion. Nature 369 , 646–648. 18.CurnoeD.andTobiasP.V.(2006).Description, newreconstruction,comparativeanatomy,and classificationoftheSterkfonteinStW53cranium, withdiscussionsaboutthetaxonomyofother southernAfricanearly Homo remains. J.Hum. Evol. 50 , 36–77. 19.Anon.(1976).Importantfossilskullfoundat Sterkfontein. S.Afr.J.Sci. 72 , 227. 20.TobiasP.V.(1978).TheearliestTransvaalmembers ofthegenus Homo withanotherlookatsome problemsofhominidtaxonomyandsystematics. Zeit.Morphol.Anthropol. 69 , 225–265. 21.LeakeyL.S.B.,TobiasP.V.andNapierJ.R.(1964).A newspeciesofthegenus Homo fromOlduvai Gorge. Nature 202 , 7–9. 22.Leakey R.E. (1973). Evidence for an advanced Plio-PleistocenehominidfromEastRudolf, Kenya. Nature 242 , 447–450. 23.GrovesC.(1989). ATheoryofHumanandPrimate Evolution. Oxford University Press, Oxford. 24.WoodB.(1992).Originandevolutionofthegenus Homo.Nature 355 , 783–790. 25.BlumenschineR.J.,PetersC.R.,MasaoF.T.,Clarke R.J.,DeinoA.L.,HayR.L.,SwisherC.C.,StanistreetI.G.,AshleyG.M.,McHenryL.J.,SikesN.E., vanderMerweN.J.,TactikosJ.C.,CushingA.E., DeocampoD.M.,NjauJ.K.andEbertJ.I.(2003). LatePliocene Homo andhominidlandusefrom westernOlduvaiGorge,Tanzania. Science 299 , 1217–1221. 26.LeakeyR.E.,LeakeyM.G.andBehrensmeyerA.K. (1978).Thehominidcatalogue.In KoobiFora ResearchProject, Vol.1,edsM.LeakeyandR.E. Leakey. Clarendon Press, Oxford. 27.LeakeyM.D.(1979). OlduvaiGorge,MySearchfor EarlyMan. Collins, London. 28.BroomR.(1936).Anewfossilanthropoidskull from South Africa. Nature 138 , 486–488. 29.BroomR.(1938).Furtherevidenceonthestruc tureoftheSouthAfricanPleistoceneanthropoids. Nature 142 , 897–899. 30.DartR.A.(1948).TheMakapansgatproto-human Australopithecusprometheus.Am.J.Phys.Anthropol. 6 , 259–284. 31.ClarkeR.J.(1990).Observationsonsomerestored hominidspecimensintheTransvaalMuseum, Pretoria.In FromApestoAngels:EssaysinAnthro pologyinhonorofPhillipV.Tobias, ed.G.H.Sperber, pp. 135–151. Wiley-Liss, New York. 32.ClarkeR.J.(1999).Discoveryofcompletearmand handofthe3.3million-year-oldAustralopithecus skeletonfromSterkfontein. S.Afr.J.Sci. 95 ,477–480. 33.KimbelW.H.andWhiteT.D.(1988).Variation, sexualdimorphism,andtaxonomyof Australo pithecus. In EvolutionaryHistoryofthe‘Robust’Aus tralopithecines, ed.F.Grine,pp.461–484.Aldinede Gruyter, New York. 34.AguirreE.(1970).Identificaciode ‘Paranthropus’ enMakapansgat. CronicadelXICongresoNacional deArqueologia, Merida, 1969, pp. 98–124. 35.AsfawB.,White,T.,LovejoyO.,LatimerB., SimpsonS.andSuwaG.(1999). Australopithecus garhi: anewspeciesofearlyhominidfrom Ethiopia. Science 284 , 629–235. 36.PickeringT.R.,ClarkeR.J.andMoggi-CecchiJ. (2004).Theroleofcarnivoresintheaccumulation oftheSterkfonteinMember4hominidfossil assemblage:ataphonomicreassessmentofthe completehominidfossilsample(1936–1999). Am. J.Phys.Anthropol. 125 , 1–15.This article is accompanied by supplementary illustrations online at www.sajs.co.za Research in ActionSouth African Journal of Science 104 , November/December 2008449 Fig.10 .MaleAustralopithecusafricanusStW53(left)andmaleofsecondspeciesStW505(right).Notethe longer, more massive face in the second species. Fig.11 .ReconstructedprofilesofAustralopithecusafricanusfemalebasedonSts5(left),andsecondspecies malebasedonStW252(centre),withfemalecraniumofsecondspeciesSts71(right).Numbersindicatemajor featuresofsecondspeciestocontrastwithA.africanus: 1 ,thinsupraorbitalmarginandincipientsupraglabellar depression; 2 ,anteriorlysituatedcheekbone; 3 ,largecaninesandlargeanteriorlyprojectingincisorsinmale; 4 , robust, large mandible; 5 , vertical, rounded occiput.

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Supplementary material to:Clarke R.J.(2008).Latest information on Sterkfontein’sAustralopithecusskeleton and a new look atAustralopithecus.S.Afr.J.Sci.104 , 443–449. Fig.A .AustralopithecusafricanuschildfromTaung(left),adultfemaleTM1512andadultmaleStW391(upperright),andadultmaleSts52(lowerright)–notalltosame scale.Note the similarity of the facial profiles and also the larger canines in the males Sts 52 and StW 391. Fig. B .Dentition of TM 1511Australopithecus africanuswith the recently discovered left M3and right P3.

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Fig.C .PalatalviewofTM1512femaleAustralopithecusafricanus(left)andStW391maleA.africanus(right).Notethelargercaninesocketandwiderpremolarsinthe male.


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