Functional morphology of the hominoid shoulder, past and present

This thesis presents an :investigation into the functional morphology and form of the skeletal elements of" the shoulder girdle of extant h0111inoids and extinct hO)ll.inids\~hich inhabited the Afr:i.c~n continent during the Late pliocene and Elarly \Ii Ii \Ii, ill Partic'l.l.lcu: emphasis is placed o\~\the \' i\. form of the scapula, clavicle and humerus. \Ii variation in the bony, arthrological and 41.yoloQif\;Lcal I" anatomy' Of this region in extant hominoids is I Pleistocene. examined. In light of biomechaniq~l models II reSUlting from this work, the bony,;anatomy of u hominid shoulder girdle elements examined and i. .1 r;:I~t>. ssil .1,1 . " biomechanical interpretations are made. The fossil shoulder girdle elements exan\ine~ in this study are grouped into four species samples. The first sample (Australopithecus a.:friCaIlUS) comprises Pliocene ,fossils from sterkfontein, South Africa. 'rhe second sampJ.e (A. i.s comprised of fossilo front Hadar, Ethiopia. The third (Homo habilis) and, fourth (ii. boisei) samples comprise fossils from C'lduvai GorgeI Ta:nzania, Koobi For~ll, Ke!nya and omo Valley ~ Ethiopia. When the t!;ossil homi.ndd. remains are scrt.ed into specf.ea, jl~heI:;houlder g;l.rdle elements InelYd:>e used to const.zuct; and contrast specijSiq '1· . ) bitOmechar1,ic::aml odelS of th~ shoulder. Th~~se models e:>fltP10re differernoes in form amon~,r.;tj;ossil hominid. species that may'be reJ,ated to dii.:;eetenc; in behaviour. The models may also be appU.ed to the :~......,..~ interpretation of systemat.ic relationShips amongst early hominids. In o:(.~ierto construct models of early homi:p,ids it is first necessary to establish the,movement, myology and oste0logy of the extant hominoid shoulder. Chapters 4,5 and 6 sUl'l.1Il1ar~n,$eew data and available in,formation concel:"ning shoulder girdle mo.Jementand form. Chapter 7 presents detailed C';escriptiQns Of the fossil hominid ma.terial (u:::::19) available for study. 'rhis descriptive information, in conibination with all of the information derived from Chapters 4 through 6, is then used to inte1.pret, compaxe and contrast the fu.nctional morphology Of the shoulder girdle elements of each species of early hotninid. emphasis is placed .on those features that cart be. directly related to specific :functiOl'l~ Model.s ,,.l the functional morphology of each of t1Je four species are then created. comparisons are made between indJ.vidual Shoulder girdle elements 'cg,fthe different homj.nid as well as between the interpreted total morphology of each species' shoulder girdle. The study concludes that the functional m~>l':phologyof the shoulder girdle Qf A. afriaanus is unique ~unorJ.gstknown hominoic1~mode'l.s in that it poasesaes shoul<;ier girdle mo;t,'ph.oo.)gy adapted to bobh suspen ory behaviour and bipE~d;;d~i.srn. TIte suspensory adaptations are :Lndi9ated by the overall ape morphology of the humeri, claviculae and heCid.of the scapulae, whilst bipedalism is mainly (J G indicated. by a broad, human-like inf.Ell:'ior'an9,'].eof " = the scapula. Several' RpparentlY prim.itive featu:r:es" are present in,..the A. africanus Ejcapl,1la,incl~dirtg a 0i,? ..... . _ .. '. \ shortened scapular 'n~ck, that ind:l.Cate'-\poss~ple ancestry f.roma quadru:pedal form. ~p.e functi<:> morphology of the A. afarens.ts shoulder is founa .to be more diffi.cult to interpret d'.le to poor f(i:; ,pre.~ervationt but the hypothesised znodel'~does not diffe):: substantially from th~t constructed for A. _c,~) . ..' .', 1) (; a£ricanus. The few robust aURtra.lopithecine,.,(A. sho~~der girdle elements appear to possess ~,.. similar morpJ;lologi.esto A. a.:falyrnsis and )1- africanus. There ara .no'l:.SUfi:'lc:tently well preServedoH. habili.s shoulder girdle elements preserved to 'makemeffilningfulinterpreta.tions about the functional morphology of this, specie~:' .' n the lack of comparable elements amongst the two (I 1arger samples (...21.. a:faJ;'ensi.s and ,fl. arr:J;canus) I .it '..':::/ is not knownwhether the features found to be apparently unique to either species are useful as n taxonomic indicators.
A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg 1994.