New discoveries of A. africanus fossils from Member 4 Sterkfontein reveal a body form quite unlike earlier
Australopithecus species. The new adult material consists of over 48 fore- and hindlimb specimens and
includes an associated partial skeleton, Stw 431. The forelimbs are relatively large: the average size of their
joints corresponds to a modern human with body mass of 53 kg. The hindlimbs are much smaller with an
average size matching a modern human of only 33 kg. Analyses of the Stw 431 partial skeleton confirm
these results. In contrast, A. afarensis and anamensis more closely approximate a human pattern of
forelimb to hindlimb joint size. This is an unanticipated complication in our understanding of early human
evolution. In general, craniodental morphology tracks time in species of Australopithecus: A. anamensis
(3.5-4.1 Ma) is the most primitive with a strongly sloping symphysis, large canine roots, etc., A. afarensis
(3.0-3.6 Ma) is less primitive, and A. africanus (2.6-3.0 Ma) shares many derived characteristics with early
Homo (e.g., expanded brain, reduced canine, bicuspid lower third premolar, reduced prognathism, greater
flexion of the cranial base, deeper TMJ). The new postcranial material, however, reveals an apparently
primitive morphology of relatively large forelimb and small hindlimb joints resembling more the pongid
than the human pattern. More pongid-like proportions are also present in the two known associated partial
skeletons of H. habilis (OH 62 and KNM-ER 3735). This may imply either (1) that A. africanus and H. habilis evolved craniodental characters in parallel with the lineage leading to later Homo, or (2) that fore- to
hindlimb proportions of A. afarensis (and perhaps A. anamensis) evolved independent of the lineage leading
to Homo and does not imply a close phylogenetic link with Homo. Both of these explanations or any other
phylogeny imply Homoplasy.
Abstract © 1998 Academic Press
Read Berger and McHenry’s complete paper at the Journal of Human Evolution Web site.
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