The capitate of Australopithecus afarensis and A. africanus

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Abstract

The capitates of Australopithecus afarensis (AL 288-lw and AL 333–40) and A. africanus (TM 1526) have the identical combination of modern pongid, modern hominid, and unique characteristics. These traits include the combination of a length that is proximodistally shortened (Homo sapiens-like), a facet for the second metacarpal that is distolaterally facing (unique), the reduced styloid process on the third metacarpal (pongidlike), a dorsally placed trapezoid facet (pongidlike), mediolaterally constricted metacarpal III facet (pongidlike), a prominent palmar beak (pongidlike), a single elongated facet for the second metacarpal (H. sapiens-like), a waisted neck (pongidlike), and a reduced amount of “cupping” in the third metacarpal facet (H. sapiens-like).

In overall shape the bones are more like H. sapiens than other extant hominids, although they are uniquely different. The two A. afarensis capitates provide no evidence that there are two postcranial morphotypes at Hadar. Available evidence shows that A. afarensis and A. africanus are strikingly similar postcranially. The morphological differences between the capitate of Australopithecus and H. sapiens may relate to the retention of climbing ability and an absence of certain grip capabilities in these early hominids.

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