1Anthropology, University of Florida, 2Anthropology, The Ohio State University
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In this study we test the hypothesis that spatial autocorrelation of mandibular bone stiffness is associated with elastic modulus distribution patterns that maximize structural stiffness. Using previously collected microindentation data, we found a general pattern of positive spatial autocorrelation of bone stiffness in the mandibles of four monkey species (Procolobus badius, Colobus polykomos, Cercocebus atys, and Cercopithecus diana) from Taï Forest, Cȏte d’Ivoire. This finding indicates that the distribution of mandibular bone stiffness is non-random, which potentially impacts biomechanical interpretations.
These same microindentation data were used to develop heterogeneous models of bending stiffness of mandibular coronal sections from the four species. These weighted moments of inertia (WMOI) differ from unweighted (homogeneous) moments of inertia (UMOI) by accounting for intra- and inter-individual variation in bone material stiffness (Bhadavadekar et al. AJPA 131:243–251). We calculated WMOI based on 1) average modulus within a section and 2) assignment of local modulus values in discretized sections. Lower observed WMOI in discretized sections would undermine the hypothesis under test.
Inclusion of average elastic modulus data in structural property calculations magnifies the apparent stiffness of Cercocebus mandibles relative to those of other monkeys, while colobine mandibles exhibit reduced stiffness. This underscores the interpretive costs of ignoring elastic modulus variation, which is inherent in the comparative application of UMOI. Examination of discretized weighted moments suggests that mandibular bone stiffness is not distributed in a manner that maximizes structural rigidity. Systematic differences in bone stiffness have implications for inferring strain magnitudes in comparative contexts.
Supported by NSF BCS-0922429 and 0921770.