The ordinal name primates, means the first or primary animals. This naming convention reflects the egocentric orientation of humans, but is of no help in defining the group of mammals included in it. Primates are mainly arboral mammals, but terrestrial forms occur in several groups. Most primates are omnivorous.
Several groups are almost entirely herbivorous.
The galagos and tasrsiers are largely insectivorous. Most primates are pentadactyl, although some fingers are shorter in some Lorises. The thumb is reduced in several brachiating forms and completely absent in spider monkeys. These prehensile and apposable digits yield a hand or foot with great dexterity, allowing the animal to better grasp and manipulate objects. In general the sense of smell in primates becomes less acute as the hand becomes better adapted for manipulation.