Ecological divergence and calcaneal‐cuboid morphology in gorillas

Abstract

AbstractObjectivesGorillas are diverse behaviorally and ecologically with higher frequencies of arboreality and frugivory observed in populations living at lower altitudes compared to those living at higher altitudes. Previous studies have shown that the more arboreal western lowland gorilla has hallucial tarsometatarsal and talocrural joint morphologies associated with enhanced hallucial abduction and foot inversion capabilities whereas the more terrestrial eastern gorilla does not. Here we examine how known ecological and behavioral differences among gorillas relate to variation in calcaneal and cuboid morphology. Specifically, we test whether gorillas that climb more frequently (i.e., western lowland and lowland grauer gorillas) have cuboid‐metatarsal and calcaneocuboid morphologies that facilitate increased foot mobility compared to those that climb less often (i.e., mountain and highland grauer gorillas).MethodsWe quantify the relative areas of articular and nonarticular surfaces, angles between articular surfaces, articular surface curvatures, the relative length and depth of the calcaneocuboid joint, and the relative size of the calcaneal tuber using three‐dimensional models of gorilla calcanei and cuboids (n = 90 and 81, respectively).ResultsOur results, based on univariate and multivariate analyses, show that western and eastern gorillas follow our predicted arboreal‐terrestrial morphocline in terms of their calcaneal and cuboid morphology; however, highland and lowland grauer gorilla populations do not.ConclusionsThis study has implications for understanding gorilla foot function and the evolutionary processes responsible for producing the morphological patterns among living gorilla populations. Future studies of gorilla morphological diversity may provide a useful comparative model for studies of locomotor evolution in extinct clades.