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

Reconstructing australopithecine midstance using femoral condyle curvature


Deptartment of Human Evolution, Max Planck Institute for Evolutionary Anthropology

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Although it is universally agreed that australopiths were bipeds, the exact nature of their bipedalism continues to be debated. Some researchers argue that australopiths engaged in a modern form of bipedalism, while others suggest that these early hominins would have walked with deeply flexed knees and hips. This project examines the curvature of the medial femoral condyle among mammals, finding that regions of low curvature correlate with knee midstance angles during walking.

Sixty femora representing 16 mammalian species were surface scanned creating virtual surfaces models. Medial and lateral condyles were trimmed from the rest of the distal femur, and condyle profiles relative to the axis of knee flexion/extension were extracted as coordinate landmarks. These landmarks were treated as sliding landmarks in a geometric morphometric analysis. Species-average medial condyle profiles were created and a region of low curvature was identified. The position of the region of low curvature was quantified using a novel metric termed the angle to low curvature. Kinematic knee angles were collected from the literature and were regressed against the angle to low curvature metric at one percent increments of the gait cycle.

The highest correlation (r = 0.77) between the angle to low curvature metric and knee angle occurs at 29% of the total gait cycle, which is midstance for most mammals. The resulting regression equation predicts a midstance knee angle of 166 degrees for humans and 125 degrees for chimpanzees. It also predicts knee midstance angles of 171 and 164 degrees for two australopithecine distal femora.

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