CARLSON, K.J.; Stony Brook University: Links between limb bone cross-sectional geometry and locomotor behaviors of African apes

African apes, whose locomotor repertoire is well-known from field observations, provide a unique opportunity for quantitatively assessing the relationship between limb morphology and locomotion. The narrow phylogenetic relationship of African apes, coupled with their diverse locomotor behaviors, magnifies the promise of such an approach. Arboreal supports are more three-dimensional than terrestrial ones, and therefore seem likely to require less predictable, and more variable, limb placements during locomotion. This would encourage more variable orientations in limb bending load regimes for apes exhibiting more arboreal than terrestrial locomotion. To test this, I examined whether the percentage of total locomotion occurring arboreally correlated negatively with the ratio of maximum to minimum principal moments of area (i.e., maximum to minimum bending rigidity). I also tested whether arboreal behaviors (e.g., scrambling) involving more erratic limb placements showed higher negative correlations with these ratios than other arboreal behaviors (e.g., quadrupedal walking). Cross-sectional data from femora and humeri of 222 specimens, representing all three ape species (Pan paniscus, P. troglodytes, and G. gorilla), and all commonly recognized subspecies, were acquired using computed tomography. Generally, when arboreal locomotion comprised a greater percentage of total locomotion, a group displayed more similar maximum and minimum principal moments of area. However, no consistent patterns emerged when correlating specific behaviors and the ratio of maximum to minimum principal moments of area. Thus, while arboreal locomotion seems broadly associated with more equal maximum and minimum diaphyseal rigidities (i.e., a rounder diaphysis), extending this association to specific behaviors is problematic.