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MissingOmoL338y-6Occipital-MarginalSinusDrainagePattern:GroundSectioning,ComputerTomographyScanning,andtheOriginalFossilFailtoShowItRALPHL.HOLLOWAY,1*MICHAELS.YUAN,2DOUGLASC.BROADFIELD,3,4DAVIDDEGUSTA,5GARYD.RICHARDS,6,7ADAMSILVERS,8JILLS.SHAPIRO,1,9ANDTIMD.WHITE51DepartmentofAnthropology,ColumbiaUniversity,NewYork,NewYork2DepartmentofAnatomyandCellBiology,SchoolofDentalandOralSurgery,ColumbiaUniversity,NewYork,NewYork3DepartmentofAnthropology,FloridaAtlanticUniversity,BocaRaton,Florida4DepartmentofCellBiologyandAnatomy,MountSinaiSchoolofMedicine,NewYork,NewYork5DepartmentofIntegrativeBiologyandLaboratoryforHumanEvolutionaryStudies,MuseumofVertebrateZoology,UniversityofCalifornia–Berkeley,Berkeley,California6LaboratoryforHumanEvolutionaryStudies,MuseumofVertebrateZoology,UniversityofCalifornia–Berkeley,Berkeley,California7DepartmentofAnatomy,UniversityofthePacific,SchoolofDentistry,SanFrancisco,California8DepartmentofRadiology,MountSinaiHospital,NewYork,NewYork9SchoolofContinuingandProfessionalStudies,NewYorkUniversity,NewYork,NewYorkABSTRACTTheOmoL338y-6occipitalregionhasbeenrecentlystudiedbyWhiteandFalk(1999),whoclaimthatitshowsareadilyidentifiableenlargedleftoccipital-marginalsinus(O/M).Theseobservationsarecontrarytothedirectobservationsofpreviousinvestigators(RakandHowell,1978;Kimbel,1984;Holloway,1981;Holloway,1988).WhiteandFalk(1999)furtherarguethatthepresenceofthisenlargedO/MstronglysuggeststhattheOmoL338y-6hominidwasindeeda“robust”Australopithecus.WeuseddirectsectioningandCTscanningtoanalyzemagnifiedsectionsofahigh-qualityfirst-generationcastofthenewlycleanedoriginalfossil.ThesemethodsfailtoshowanyevidenceofamorphologicallandmarkthatcanbeinterpretedasanenlargedO/M,eitherasaneminenceorasulcus.Incontrast,thesametechniquesusedwithbothSK1585andOH5(“robust”AustralopithecuswithanenlargedO/M)showextremelyvisibleandpalpableenlargedO/M’s.Exami-nationoftheoriginalOmofossilconfirmsthatitlacksanO/M.ThisevidenceclearlyshowsthatanenlargedO/Mcannotbeidentifiedoneithertheoriginalfossilorafirst-generationcast,althoughthisdoesnotruleoutthepossibilitythattheOmoL338y-6hominidwasa“robust”Australopithecus.Webelievethatthedifferencesbetweenobserversregardingthisfeaturearemostprobablyduetodisplacementcausedbyacrackandthedifferentsourcematerialsemployed,i.e.,thedifferencebetweenafirst-generationcastoftheoriginalfossilandathird-orfourth-generationcastoftheendocastmadetwodecadesago.AnatRec266:249–257,2002. ©2002Wiley-Liss,Inc.Keywords:occipital-marginalsinus(O/M);drainagepattern;brainevolution;Australopithecus;brainendocasts;computertomography;groundsectioningIn1981,oneofus(R.L.H.)publishedanendocranialvolumedeterminationandmorphologicalobservationsonaPlio/PleistocenehominidfromtheOmoValley,Ethiopia,theOmoL338y-6specimen(Holloway,1981).Thesmallsizeofthebrainendocast(427ml),thelackofanydetect-ableenlargedoccipital-marginalsinus(O/M),andotherdetailsregardingtheshapeofthecerebellarlobesledR.L.H.tosuggestthatthisspecimenmightnotbea“ro-*Correspondenceto:RalphL.Holloway,DepartmentofAnthro-pology,ColumbiaUniversity,NewYork,NY10027.Fax:(212)854-7347.E-mail:[email protected];Accepted14January2001Publishedonline8March2002THEANATOMICALRECORD266:249–257(2002)©2002WILEY-LISS,INC.Fig. 1. A: Endocranial surface of the first-generation cast of the newly cleaned Omo L338y-6 occipitalbone. The area of debate is outlined as a square and is enlarged in B. There is no morphological evidencepointing to an enlarged left O/M. Note the obvious appearance of a crack line.250 HOLLOWAY ET AL.bust” Australopithecus, as suggested by the discoverers intheir early description (Rak and Howell, 1978).Later, in a 1987 symposium dealing with the issue of“robust” australopithecines (Grine, 1988), R.L.H. indi-cated that he was no longer committed to his previousview, suggesting that the Omo L338y-6 specimen couldhave been either a gracile australopithecine or that of thetaxon Australopithecus aethiopicus. The absence or pres-ence of an enlarged O/M was not an issue at that time.More recently, White and Falk (1999), in addition to thisliterature, have claimed that the Omo L338y-6 shows anenlarged left O/M. They argue that given the presence ofsuch morphology, the small size of the brain endocast, andcertain size and shape parameters of the cerebellum, thisspecimen should be regarded as a clear-cut example ofAustralopithecus robustus (White and Falk, 1999). Theyclaim that the enlarged left O/M is readily visible anddelineate its suggested presence by arrow markers intheir Figure 2 illustration (White and Falk, 1999, p 403).As the enlarged O/M has been consistently used by Falkand her colleagues (Falk and Conroy, 1983; Falk, 1986) toassign taxonomic status, and whereas it appears to bepresent on several different genera (e.g., Kimbel, 1984;Arsuaga et al., 1997; see also O’Loughlin, 1996), it isimportant that this feature be accurately identified. Inline with R.L.H.’s earlier observations (Holloway, 1981,1988), we believe that White and Falk’s (1999) assessmentof the anatomical presence of the enlarged O/M is incor-rect. Our goal in this paper is to test objectively the hy-pothesis that Omo L338y-6 has no identifiable enlargedO/M. We are not herein concerned with the ultimate tax-onomic placement of this specimen, except secondarily.MATERIALS AND METHODSIn order to evaluate the claim of a visible or palpableenlarged left O/M on the Omo L338y-6 occipital bone frag-ment or on the brain endocast, the following materials andprocedures were prepared and followed in our investiga-tions.1. The original fossil specimen was carefully cleaned byG.D.R. under a dissecting microscope (magnification,⫻40). The molding was done by G.D.R. and the casts,among the first 10 from the mold, were made by T.D.W.using COECAL Dental Stone (GC Lab Technologies,Inc., Alsip, IL).2. Serial sections of one cast were produced by G.D.R. bysanding the cast so as to produce sections at approxi-mately 1- to 2-mm intervals perpendicular to the mid-sagittal plane and congruent with the endocranial-ec-tocranial plane. These sections were then scanned anddigitized by D.D. at 600 dpi resolution using a flatbedscanner in gray-scale mode, commencing caudally fromapproximately the opisthionic portion of the foramenmagnum portion and continuing superiorly to approx-imately the lambdoidal portion of the squamous part ofthe occipital. This same procedure was applied to castsof the occipital bones of OH5, an indisputably


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