The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Trabecular architecture of fossil hominin first metacarpals


1Dept. of Human Evolution, Max Planck Institute for Evolutionary Anthropology, 2Dept. of Anthropology, University of Northern British Columbia

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Two hominin first metacarpals – SK 84 and SKX 5020 - from Swartkrans have been the centre of much debate regarding both their taxonomic affiliation and their potential inference for stone tool-making in early hominins. Variation in size and external morphology has led some to attribute these fossils to different species; SK 84 as early Homo and SKX 5020 as Au. robustus, but attributing tool-making ability to both. In contrast, others feel such variation can be accommodated within a single taxon and, if both are considered early Homo, tool-making ability is constrained to the genus Homo.

Here we address this debate from a new perspective using micro-CT and an analysis of trabecular bone structure. We investigate variation in trabecular architecture in these fossils in comparison with Au. africanus StW 418 and an extant sample of Pan (n=15) and Homo (n=10). Compared with SK 84, SKX 5020 is more similar to humans in having higher trabecular separation, lower trabecular number and a lower degree of anisotropy in the first metacarpal head, though all fossil specimens are generally more similar to Pan than the derived condition of recent humans. These results suggest that if SK 5020 and SK 84 do not belong to the same species, than it may be more reasonable that SKX 5020 be attributed to early Homo, rather than SK 84. General similarity of all fossils to Pan indicates that there is not a clear tool-making signal in the trabecular structure of either specimen.

This research is supported by the Max Planck Society and the Natural Science and Engineering Research Council of Canada.

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