1Evolutionary Studies Institute, University of the Witwatersrand, 2School of Geosciences, University of the Witwatersrand, 3Department of Anthropology, Indiana University, 4Department of Biological Sciences, Marshall University, 5Human Origins Program, Department of Anthropology, National Museum of Natural History, Smithsonian Institution, 6Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California
April 14, 2016 , Atrium Ballroom C
The hominoid tibiotalar joint transmits weight-bearing loads between the foot and more proximal parts of the lower limb. Its loading history reflects hominoid foot interaction with substrates during stance phase, and summarily during locomotor modes in which hind limbs bear weight. Radiodensity within subchondral bone reflects habitual joint reaction forces in a number of primate joints, meaning it is useful for inferring joint loading regimes. Areas of higher compressive forces are relatively denser than areas of lower compressive forces. More expansive areas of relatively high radiodensity indicate more expansive joint areas subjected to these high compressive forces. Here we test whether variable degrees of habitual dorsiflexion in the tibiotalar joint of hominoids are reflected in radiodensity patterns of subchondral bone in their tibial plafond. Specifically, we predict more frequent (habitual) dorsiflexion of the tibiotalar joint is associated with more expansive areas of relative high radiodensity in the anterior half of the joint than the posterior. To evaluate this hypothesis, we quantified radiodensity in distal tibiae of a large sample of primates, emphasizing hominoids, using computed tomography osteoabsorptiometry (CT-OAM). African apes tend to exhibit greater high radiodensity areas in the anterior compared to the posterior half of the joint. Interestingly, many hominoids, including some humans, tend to exhibit local high radiodensity areas where the neck of the talus contacts the anteromedial margin of the distal articular surface. Internal properties of hominoid distal tibiae provide evidence that may be useful for interpreting functional morphology of external features of the hominoid distal tibia.