1Department of Vertebrate Paleontology, American Museum of Natural History, 2Department of Anthropology, Lehman College, CUNY, 3Department of Anthropology, Graduate Center, CUNY, 4NYCEP
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The foot is one of the most informative areas of the body when reconstructing the locomotion of extant hominoids and fossil hominins as inferred from skeletal remains. The functional relationships between the articular facets of the tarsals, particularly those of the “rearfoot” (the talus, navicular, calcaneus and cuboid) are central to understanding how weight is distributed through the foot to the substrate during locomotion. These relationships have many morphological components, including the angulation between facets, their individual surface morphology, and their relative size.
While studies of facet surface areas have traditionally used the product of simple linear measurements, such techniques do not reflect the often complex surface topologies. Using high resolution 3D laser surface scans of the talus, cuboid and navicular of gorillas (13), chimpanzees (18), modern humans (18) and fossil hominins (5), we were able to extract precise surface areas of the articular facets. For each element, individual surface areas were size-corrected using the total volume of that element. Surface areas were also compared to each other using ratios, which were then pooled and subjected to principal components analysis.
Results indicate that the size relationships between the articular facets of Plio-Pleistocene fossil hominins were mosaic, depending on the taxon. Of noticeable interest are the fossil hominin tali from Koobi Fora (1.7Ma), whose facet size ratios and size-adjusted values fall outside the range of modern human variation, indicating a unique weight distribution pattern through the upper and lower ankle joints.