Peru boasts 32 species of primates, which are scattered among the three families that comprise New World monkeys. These are: Callithricidae, which includes marmosets and tamarins; Cebidae, the largest group, that includes capuchin monkeys, woolly monkeys, spider monkeys, and others; and Callimiconidae, which only has one species, the Goeldi’s Monkey.
New World monkeys differ from Old World monkeys mainly in the shape of their noses, which have adapted to the tropical environments that they are found in. Old World primates, including humans, have long noses with downward pointing nostrils on either side. New World primates have wide, flatter and sloping noses.
Monkeys of America have sturdy builds with flat, hairless faces, big eyes, diminutive ears and short necks. They normally have long back legs with prehensile (used for grasping) claws at the end. They almost always possess a prehensile tail that is used to grab onto branches, swing from branch to branch, and for balance.  Most American monkeys live in trees, and may descend only to quench their thirst or to cross over areas lacking in trees.
American monkeys also change color, depending on the latitude of their habitat, so it is possible to see a wide variety of fur colors among one species. One may find specimens that are black, yellow, rusty and any shade in between, depending on the location, that all belong to one species.
Because monkeys are largely fruit-eaters, they contribute to the re-growth of the liana vines and trees in their woodland homes. Nearly all of the monkeys of Peru live in the Amazon rainforest. Exceptionally, the white-fronted capuchin monkey is also encountered on the western slopes of the Andes in the departments of Tumbes and Piura. The Tumbes howler monkey is found in the far northern tropical forests of the Pacific coastal regions.
Some of the most interesting species of monkeys in the Amazon are:
The Goeldi’s Monkey lives in Peru, Brazil, Colombia and Bolivia. They are small with long hair that sticks out around their head. They somewhat resemble the Tamarin monkeys; and like them, they possess claws instead of nails. Their teeth and the shape of their head, however, are more reminiscent of the Capuchin and other monkeys of the Cebidae family. They also possess 36, rather than 32 teeth. These traits have placed them into their own distinct taxonomic family, the Callimiconidae.
The Yellow-handed Titi Monkey is one of three species of monkeys in the genus Callicebus, in the Cebidae family, which includes the capuchin monkeys. The other two species of tit monkeys are the Dusky Titi monkey and the Masked Titi monkey. The Yellow-handed titi is found in the western Amazon basin east of the Andes Mountains, in Peru, Colombia, Venezuela and Brazil. As their name indicates, they have yellow hands. One of the interesting features of the titi monkeys is the fact that the father performs most of the care of the young, giving the baby to the mother only to nurse. The Yellow-handed titis perform an intensive grooming ritual just before dusk. They then gather together to sleep, entwining their tails.

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