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

Australopithecus afarensis probably lacks a midfoot break


Anthropology, SUNY Buffalo State

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The Au. afarensis MT 4 fossil A. L. 333-160 was analyzed using three-dimensional morphometrics to test the hypothesis that the proximal articular surface is flat as in humans rather than highly convex as in apes. A humanlike articular surface would suggest that Au. afarensis lacked apelike tarso-metatarsal flexibility associated with a midfoot break. A principal components analysis compared the proximal articular surface shape of A.L. 333-160 to Pan, Gorilla, Hylobates, and habitually shod and unshod humans. The hypothesis cannot be falsified. A. L. 333-160 has a flat articular surface that is indistinguishable from unshod humans and is similar to OH 8 (H. habilis) and StW 628 (possibly Au. africanus). The surface shapes represented by these fossils are all consistent with a rigid lateral midfoot. Articular surface size is significantly different between all groups except the unshod human group and Pan. Regression analysis revealed no significant relationship between size and shape for PC 1, which is the most important axis for distinguishing the shape differences between humans and apes. There is a significant relationship between size and shape on the PC 2 axis. This axis shows that Hylobates has extreme proximal surface curvature that extends to the dorsal side of the metatarsal. In this sample shod and unshod humans are significantly different in size, and significantly different in shape on the PC 2 axis. Though there is much overlap, some unshod humans have a marginally flatter surface. It is unclear whether this is due to size or being habitually unshod.

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