The first bipeds: a comparison of theA. afarensis and A. africanus postcranium and implications for the evolution of bipedalism

Although the postcranium of Australopithecus africanus is uniquely different from all extant hominoids, it is nearly identical to A. afarensis. This similarity is surprising because the two species are distinctly different in their dental and cranial anatomy. It implies that the unique postcranial configuration seen in these early hominids was a relatively stable adaptation that was not gradually changing through time towards a form more like that seen in Homo. The simplest explanation of this stability is that natural selection was maintaining a structural adaptation for locomotor behaviors unlike those seen in any extant hominoids.

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