The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)


Three-dimensional shape analysis of the distal femur of Australopithecus sediba

ADAM D. SYLVESTER1, JEREMY M. DESILVA2, STEVEN E. CHURCHILL3 and LEE R. BERGER4.

1School of Life Sciences, University of Glasgow, 2Department of Anthropology, Boston University, 3Department of Evolutionary Anthropology, Duke University, 4Evolutionary Studies Institute, University of the Witwatersrand

March 26, 2015 2:00, Grand Ballroom C Add to calendar

The knee has been central to debates concerning the walking kinematics of early hominins because of its weight bearing role during locomotion. Here we carry out a three-dimensional geometric morphometric analysis of the distal femur U.W. 88-63 (Australopithecus sediba) comparing it to extant and extinct hominids.

Virtual surface models were created of 93 distal femora representing three extant hominid species and six hominin fossils, including the specimen U.W. 88-63. To quantify shape variation, sliding semi-landmarks were distributed across each distal femoral articular surface. A combination of statistical and geometric approaches was used to reconstruct the missing medial condyle of U.W. 88-63 based on the extant and extinct reference samples. Two separate procedures, Generalized Procrustes Analysis and a functionally constrained Procrustes, were used to align all specimens. Parallel analyses were conducted using the coordinates representing only the condyles and the patellar surface. Shape variation was summarized using between group principal components analysis and shape differences were quantified using partial Procrustes distances and root mean square values.

U.W. 88-63 lies outside the shape space bound by the reference sample, but is closest in shape to the average modern human distal femur relative to other species averages. Separate analyses of the condyles and patellar surface reveal that the condyles of U.W. 88-63 are closest in shape to other australopiths, while the patellar surface is closest in shape to modern humans. U.W. 88-63 appears to combine early hominin condyles with a more modern patellar surface.