Subchondral Bone Apparent Density and Locomotor Behavior in Extant Primates and Subfossil Lemurs <Emphasis Type="Italic">Hadropithecus</Emphasis> and <Emphasis Type="Italic">Pachylemur</Emphasis> |
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Authors: | John D Polk Scott A Williams Jeffrey V Peterson Charles C Roseman Laurie R Godfrey |
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Institution: | (1) Department of Anthropology, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA;(2) Department of Anthropology, San Diego State University, San Diego, CA 92182, USA;(3) Department of Anthropology, University of Massachusetts, Amherst, MA 01003, USA |
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Abstract: | We analyze patterns of subchondral bone apparent density in the distal femur of extant primates to reconstruct differences
in knee posture, discriminate among extant species with different locomotor preferences, and investigate the knee postures
used by subfossil lemur species Hadropithecus stenognathus and Pachylemur insignis. We obtained computed tomographic scans for 164 femora belonging to 39 primate species. We grouped species by locomotor preference
into knuckle-walking, arboreal quadruped, terrestrial quadruped, quadrupedal leaper, suspensory and vertical clinging, and
leaping categories. We reconstructed knee posture using an experimentally validated procedure of determining the anterior
extent of the region of maximal subchondral bone apparent density on a median slice through the medial femoral condyle. We
compared subchondral apparent density magnitudes between subfossil and extant specimens to ensure that fossils did not display
substantial mineralization or degradation. Subfossil and extant specimens were found to have similar magnitudes of subchondral
apparent density, thereby permitting comparisons of the density patterns. We observed significant differences in the position
of maximum subchondral apparent density between leaping and nonleaping extant primates, with leaping primates appearing to
use much more flexed knee postures than nonleaping species. The anterior placement of the regions of maximum subchondral bone
apparent density in the subfossil specimens of Hadropithecus and Pachylemur suggests that both species differed from leaping primates and included in their broad range of knee postures rather extended
postures. For Hadropithecus, this result is consistent with other evidence for terrestrial locomotion. Pachylemur, reconstructed on the basis of other evidence as a committed arboreal quadruped, likely employed extended knee postures in
other activities such as hindlimb suspension, in addition to occasional terrestrial locomotion. |
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