Major Transformations in the Evolution of Primate Locomotion

Compared to other mammalian orders, Primates use an extraordinary diversity of locomotor behaviors, which are made possible by a complementary diversity of musculoskeletal adaptations. Primate locomotor repertoires include various kinds of suspension, bipedalism, leaping, and quadrupedalism using multiple pronograde and orthograde postures and employing numerous gaits such as walking, trotting, galloping, and brachiation. In addition to using different locomotor modes, primates regularly climb, leap, run, swing, and more in extremely diverse ways. As one might expect, the expansion of the field of primatology in the 1960s stimulated efforts to make sense of this diversity by classifying the locomotor behavior of living primates and identifying major evolutionary trends in primate locomotion. The most notable and enduring of these efforts were by the British physician and comparative anatomist John Napier (e.g., Napier 1963, 1967b; Napier and Napier 1967; Napier and Walker 1967). Napier’s seminal 1967 paper, “Evolutionary Aspects of Primate Locomotion,” drew on the work of earlier comparative anatomists such as LeGros Clark, Wood Jones, Straus, and Washburn. By synthesizing the anatomy and behavior of extant primates with the primate fossil record, Napier argued that