The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

A reconstruction of the Sts 65 Australopithecus africanus pelvis with implications for birth in early hominins


Department of Anthropology, Boston University

Thursday Afternoon, Ballroom C Add to calendar

Characterizing australopithecine pelvic morphology has been extremely difficult in part because of limited fossilized pelvic material. Sts 65, an undistorted, yet under-studied, adult right female ilium and pubis from Member 4 of Sterkfontein, South Africa, provides an opportunity to reexamine variation in the australopithecine pelvis. Here we digitally reconstruct the superior aspect of the Sts 65 pelvis with Autodesk Maya by mirroring the right ilium and articulating the two ilia using a scaled and mirrored digital model of the Sts 14 sacrum. Points along the arcuate line were used to properly orient the ilia to the sacrum. Both Sts 14 and Sts 65 exhibit similar overall morphologies: laterally flared ilia, small size, and an inferiorly directed pubis. However, the inlet shape of Sts 65 differs markedly in appearance, being more anterior-posteriorly elongated (Brim index: 79.5). As inlet brim indices can vary widely in modern human females, it is unlikely that Sts 65 and Sts 14 belong to different species or different sexes. The extremely large size of other australopithecine pelves (such as StW 431) allow us to infer that Sts 65 is another female. By comparing the inlet dimensions to the cranial dimensions of a neonatal australopithecine (based on an ape model), we suggest that infant australopiths would have entered the birth canal transversely and that the cephalopelvic ratio was human-like, not ape-like. These data imply a challenging, human-like birth process, though it is unclear whether a human-like rotational birth occurred in Sts 65.

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