Thursday, September 22, 2011

The hand of Australopithecus sediba

Kivell et al, 2011 Fig 1 (Left view = palmar, Right view = dorsal)
Kivell and colleagues report on the nearly complete hand of Malapa Hominin 2 (MH2), which has been attributed to Australopithecus sediba, a possible ancestor to genus Homo from the site of Malapa in South Africa. By nearly complete, I mean it is only missing a couple of wrist bones and the distal phalanges of the four non-thumb fingers. And everything that is preserved is in amazingly good condition. 

The biggest question about the A. sediba hand fossils is: did this species make tools?  The authors' answer is yes: A. sediba had hand morphology which would allow it to make tools. How they arrive at this conclusion is interesting. One of the major hand fossils that they compare with this hand is the OH7 Homo habilis hand from Olduvai Gorge. H. habilis (handy man) has been considered a tool-maker  since these fossils were discovered over fifty years ago in direct association with Oldowan stone tools. Kivell et al. compare the morphology of the MH2 hand with OH7 and find that MH2 has some derived features such as "reorientation of the scaphoid and capitate intercarpal articulations" (Kivell et al. 2011, pg 1416) which are lacking in OH7. Thus, they argue, these features indicate that the MH2 hand is more derived than the OH7 hand, and might be a "better potential morphotype for the basal Homo hand morphology" than OH7 (Kivell et al. 2011, pg 1416). They make this argument even though A. sediba is neither assigned to Homo nor found in association with tools. One possibility that they raise is that OH7 is not H. habilis at all, but rather belongs to P. boisei.  Could be, but what is for certain is that the MH2 hand skeleton is going to be a very interesting part of the debate surrounding manual functional morphology, locomotion, and tool use in the future. 

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