There are 32 different species of primates in Peru. These are divided into three large taxonomical families which group together the primates found in the New World: Callithricidae, which includes tamarins and marmosets; Callimiconidae, which comprises one unique species (Goeldi's monkey); and the Cebidae, the largest of the three groups which includes common squirrel monkeys, capuchin monkeys, dusky titi monkeys, night-monkeys, howler monkeys, woolly monkeys and spider monkeys, among others.
Monkeys of the Old World (order Platyrrhini) can be distinguished from those of the New World (order Catarrhini) by a series of morphological differences which are the product of the adaptation of the latter to the tropical environment in which they live. The most noticeable of these is the shape of their noses. The former (including those of man), feature elongated noses with large nostrils on each side that point downwards while the latter, have wide, flat and often sloping noses.
American monkeys are powerfully built. Their faces, flattened and devoid of hair, have large eyes, small ears and short necks. Their hind legs are generally very long and have prehensile claws at the ends. In most cases, American monkeys also have long prehensile tails which act like a fifth limb. They are, for the most part, tree-dwelling, and come down from their tree habitats only to drink water or to cross open spaces.
Another characteristic of American monkeys is their ability to change color dramatically according to their geographical location. As a result, a species can change the color of its fur within a wide range of shades, from black and ochre to yellow, depending on the latitude of its habitat.
Monkeys scatter the seeds from the fruits they eat over large areas, contributing to the regeneration of the dominant lianas vines and trees of the Amazon forest, home to practically all of Peru's monkeys. The only exceptions are the white-fronted capuchin monkey, which is also found in certain areas of the Andes' western slopes in the northern departments of Piura and Tumbes, and the howler monkey of Tumbes, which is found only in the northernmost tropical forests of the Pacific.