Phylogenetic Influence on Bone Material Stiffness in the Mandibles of Cercopithecid Primates.

OBJECTIVES: Variation in the material properties of bone has been linked to functional activity in mammals, including primates. This coheres to the paradigm that skeletal morphology, in general, provides insight into species-specific physical activity patterns. The role of phylogenetic history in conditioning bone material properties, however, is largely unexplored, despite consensus that patterns of morphological variation should be sensitive to degrees of relatedness among sampled taxa.

MATERIALS AND METHODS: We collected microindentation hardness data (a measure of bone material stiffness) from the mandibles of five sympatric primate species from Taï Forest, Côte d'Ivoire to test the hypothesis that degree of relatedness, rather than species differences in diet and feeding behavior, is more strongly associated with bone material variation. This hypothesis is tested using a generalized linear mixed model with Bayesian inference.

RESULTS: Phylogenetic distance has a significant association with bone stiffness, with colobines exhibiting more compliant bone than cercopithecines. The alternative hypothesis, that differences in dietary mechanical demands are reflected in bone stiffness variation, is not supported.

DISCUSSION: While these findings suggest a role for phylogeny in constraining skeletal adaptation, a functional explanation is not necessarily precluded. Ingestive behavioral differences between subfamily members may provide a biomechanical framework for explaining what is, at present, a nebulous invocation of phylogenetic "baggage."