1Department of Pathology and Anatomical Sciences, University of Missouri School of Medicine, 2Department of Anthropology, University of Arkansas
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Hip joint diameter is highly correlated with body size in primates, yet our ability to infer joint size in fossil hominins is frequently impeded by the fragmentary nature of most fossil pelves. New 3D technologies can be used to fit spheres to the lunate surface, potentially allowing hip joint diameter estimates. However, the reliability of these techniques must first be established.
Best-fit spheres were fit to the lunate surface of 3D polygonal models of extant primate (n=117) and human (n=22) pelves in PolyWorks software. Spheres were also fit to standardized and random lunate regions. Two observers conducted multiple data-collecting trials each, with inter- and intraobserver error <2%. These techniques were then applied to undistorted Plio-Pleistocene hominin pelves (n=13).
The results of this study indicate that digital sphere-fitting techniques are precise (mean error ≤ 1%) and that the lunate does not need to be completely preserved to accurately infer hip dimensions. Joint diameter can be predicted by spheres fit to the cranial and caudal halves of the lunate, allowing for new hip joint diameter estimates to be derived for several hominins. However, we found that fitting a sphere to small portion of lunate (1 cm2) has a mean prediction error of 8% in extant primates, suggesting these techniques must be used cautiously in largely incomplete fossil acetabulae (e.g., KNM-ER 1808, TM 1605, MLD 25). These techniques provide hip joint size estimates comparable to those derived from hominin femoral head diameters and will increase our sample of fossil body size estimates.
This study was funded by NSF, Wenner Gren Foundation, LSB Leakey Foundation.