Abstract
Primate locomotor evolution, particularly the evolution of bipedalism, is often examined through morphological studies. Many of these studies have examined the uniqueness of the primate forelimb, and others have examined the primate hip and thigh. Few data exist, however, regarding the myology and function of the leg muscles, even though the ankle plantar flexors are highly important during human bipedalism. In this paper, we draw together data on the fiber type and muscle mass variation in the ankle plantar flexors of primates and make comparisons to other mammals. The data suggest that great apes, atelines, and lorisines exhibit similarity in the mass distribution of the triceps surae. We conclude that variation in triceps surae may be related to the shared locomotor mode exhibited by these groups and that triceps surae morphology, which approaches that of humans, may be related to frequent use of semiplantigrade locomotion and vertical climbing.