1Institute for Human Evolution, University of the Witwatersrand, 2Department of Anthropology, Indiana University, 3Department of Anatomical Sciences, Stony Brook University, 4Cultures and Histories Section, Queensland Museum
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Recent comparative studies of subchondral bone in primate distal radii and distal tibiae suggest unique loading patterns in humans relative to other primates. Following theoretical expectations, human distal radii (radiocarpal joints) appear to experience the least amount of weight-bearing (compressive) loads compared to the same joints of quadrupedal and suspensory primates. Contrary to theoretical expectations, however, human distal tibiae (talocrural joints) do not appear to experience more weight-bearing (compressive) loads compared to these joints in quadrupedal and suspensory primates. This is surprising given the different distribution of weight support by hind limbs during bipedal versus quadrupedal gaits. The aim of this study is to characterize analogous measures of weight-bearing (compressive) loads in subchondral bone of distal radii and tibiae of habitual bipedal and quadrupedal Australian marsupials. Specifically, we address whether radiodensity patterns of bipedal marsupials differ from those of quadrupedal marsupials, and if so, whether they differ in the same manner or a different manner than those of primates exhibiting the same gait characterizations.
We acquired image data from the distal radii and tibiae of marsupial bipeds (kangaroos), terrestrial quadrupeds (e.g., Tasmanian devils, wombats), and arboreal quadrupeds (koalas, possums), using computed tomography and following published protocols. From image stacks, we created maximum intensity projection maps (MIPs) that were color-coded and binned into eight groups. We compare distributions of relative maximum radiodensities within and across marsupial joint surfaces. Uniqueness of the human signal is discussed in the context of the comparisons of analogous primate and marsupial models for weight-bearing (compressive) loads.
This work is based upon research supported through the African Origins Platform of the Department of Science and Technology (South Africa), the National Research Foundation (South Africa), and the University of the Witwatersrand.