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Keywords:

  • cortical bone;
  • femur;
  • locomotion;
  • fossil primates;
  • Miocene apes

Abstract

The relationship between femoral neck superior and inferior cortical thickness in primates is related to locomotor behavior. This relationship has been employed to infer bipedalism in fossil hominins, although bipeds share the same pattern of generalized quadrupeds, where the superior cortex is thinner than the inferior one. In contrast, knuckle-walkers and specialized suspensory taxa display a more homogeneous distribution of cortical bone. These different patterns, probably related to the range of movement at the hip joint and concomitant differences in the load stresses at the femoral neck, are very promising for making locomotor inferences in extinct primates. To evaluate the utility of this feature in the fossil record, we relied on computed tomography applied to the femur of the Late Miocene hominoid Hispanopithecus laietanus as a test-case study. Both an orthograde body plan and orang-like suspensory adaptations had been previously documented for this taxon on different anatomical grounds, leading to the hypothesis that this fossil ape should display a modern ape-like distribution of femoral neck cortical thickness. This is confirmed by the results of this study, leading to the conclusion that Hispanopithecus represents the oldest evidence of a homogeneous cortical bone distribution in the hominoid fossil record. Our results therefore strengthen the utility of femoral neck cortical thickness for making paleobiological inferences on the locomotor repertoire of fossil primates. This feature would be particularly useful for assessing the degree of orthograde arboreal locomotor behaviors vs. terrestrial bipedalism in putative early hominins. Am J PhyAnthropol 2012. © Wiley Periodicals, Inc.