At that time, Africa and South America were much closer together than they are now, there were numerous islands between the two continents, and the relatively small oceanic gaps that remained could have been traversed when animals became isolated on large masses of drifting vegetation. The pelage in primates varies in texture from velvety soft to harsh and coarse. The hair has various arrangements, sometimes forming crests on the head, fringing the face with whiskers, forming a mantle on the shoulders, or falling from the sides or over the rump. In primates, except people, the first digits of the hind feet are opposable, and usually the thumbs are also opposable. This power of opposition makes the hands and feet good grasping organs and thus aids in climbing.
Most primates have five digits on each limb.
When they are walking or running, the sole of the foot and heel touch the ground, giving plantigrade locomotion, but there are exceptions to this general rule. The fingers and toes of many forms have flat nails, but some species have modified clawlike nails on certain digits. A tail is absent in the Hominidae, Pongidae, and Hylobatidae and in a few species of other families. When a tail is present, it varies from a mere knob to an appendage considerably longer than the head and body. A few of the New World monkeys have prehensile tails.