ABSTRACT
Approximately 200 species of living primates are distributed throughout the world (Figure 14.1). Three sets of characteristics define a primate (Benton, 1990a). First, primates exhibit adaptations for arboreal life. The tree-dwelling mode of life was a key ecological component in the evolutionary emergence of primates. Among these adaptations are the grasping hands and feet, with opposable thumb and big toe. Walking and moving on trees requires a firm grasp of the branches. Grasping is aided by the replacement of claws by flat nails and the presence of sensitive tactile pads in each digit. The arms of primates are attached to shoulder bones that possess a great deal of mobility, compared to other mammals. Because of a mobile shoulder joint, arms can be rotated in an almost full circle. In gibbons (Hylobates spp.), these features are highly developed and critical for brachiation, a mode of locomotion consisting of using the arms to move
from branch to branch. In the New World monkeys of South America (e.g., capuchins, marmosets), which are almost exclusively arboreal, the tail is used as an additional prehensile extremity.
