Primates, Quadrupedalism

The study of locomotor adaptations is fundamental to the study of primate evolution and ecology. The primates are particularly interesting because they manifest a remarkable diversity of locomotor styles. While workers have often focused on masticatory morphology, data on patterns of locomotion also provide information on the niches occupied by recent and fossil species. While some other mammalian orders contain arboreal, semiterrestrial, and terrestrial representatives, few show the diversity of locomotor modes that are exhibited in the primates. Arboreal primates include various types of quadrupeds, brachiators, “quadrumanus” climbers, and vertical clingers and leapers. Terrestrial primates include quadrupedal forms and the unique striding bipedal hominins.

While considerable attention has been devoted to the unique and spectacular forms of primate locomotion, such as brachiation and vertical clinging and leaping, the most common locomotor mode received comparatively little attention until recently. Most primate species are quadrupedal, and the quadrupedal species often bridge the gap between locomotion on the ground and in the arboreal milieu. The assumption that all primate quadrupeds are basically the same in their anatomy and behavior is inaccurate because of both phylogenetic and ecological considerations. In a phylogenetic sense, quadrupeds are represented in a variety of infraorders, including Lemuriformes, Chiromyiformes,Loriformes, and Simiiformes. Within the Simiiformes, the Platyrrhini include clawed forms and other species with prehensile tails. In contrast, there are no known catarrhines with either claws or prehensile tails. Within the various primate families, a diversity of ecological niches are occupied.

John and Prue Napier characterize quadrupedal primates as using fore- and hind-limbs together during walking and running. They have differentiated generalized quadrupeds and “semibrachiators”: In the former, arms and legs contribute about equally to locomotion; in the latter, the forelimbs are supportive, and the hind limbs are propulsive. Michael D. Rose points out that the term quadrupedalism can be used in two ways. It can be used to describe locomotor activity in which the animal stands and moves on all four limbs, locomotion is on horizontal or almost horizontal supports, and locomotion occurs above the support surface (in distinction to suspension). Rose also states that the term is used in a broader sense—to refer to a locomotor repertoire that has a major element of quadrupedal behavior in it.