¹Evolutionary Anthropology Lab, University of Minnesota, ²Human Origins Program, Department of Anthropology, National Museum of Natural History, Smithsonian Institution, ³Department of Anatomy, Midwestern University

Thursday Morning, 301D

Western gorillas (Gorilla gorilla) are known to climb significantly more often than eastern gorillas (Gorilla berengei), a behavioral distinction directly attributable to major differences in their respective ecological habitats. Current evidence suggests that the lineages leading to eastern and western gorillas began diverging from one another between approximately 1 and 3 million years ago. Thus, gorillas offer a special opportunity to examine to what degree morphology of recently diverged taxa may be ‘fine-tuned’ to differing ecological requirements. Prior research revealed shape variation of the medial cuneiform in gorillas corresponding to an ecological divergence between eastern and western taxa. The analysis of gorilla tarsal variation is furthered here through an assessment of talar morphology (N = 40) using 3D geometric morphometrics. Talus shape was captured with a series of landmarks and semi-landmarks superimposed by a generalized Procrustes analysis. Principal components analyses of talus shape clearly separate eastern from western taxa, and a multivariate analysis of variance shows that these shape differences are statistically significant. Relative to western gorillas, eastern gorillas are characterized by a distally wide but proximodistally shorter trochlea, a proximodistally shorter lateral malleolar facet, an expanded medial malleolar facet, a mediolaterally wider proximal calcaneal facet, and a more medially-oriented talar head. Several of these shape differences can be linked biomechanically to the facilitation of climbing in western gorillas and to stability and load bearing on terrestrial substrates in the eastern taxa, providing an important comparative model for studying morphological variation in groups known only from fossils (e.g., early hominins).

This research was supported by a Wenner-Gren Foundation post-PhD grant to M.W.T (Grant No. 7822).