New World monkeys are small to medium in size. They are distinguished from their cousins the Old World monkeys by their flat nose—in fact, the name Platyrrhini means "flat nose". New World monkeys also differ from Old World monkeys in that all species are tree-dwelling (arboreal) primates. Only capuchins forage on the forest floor, but they are not truly adapted for life on the ground and spend much of their time up in the trees.
Many Old World monkey species have descended to the ground where they inhabit grasslands and other terrestrial habitats. The South American jungle habitat of New World monkeys though offers many arboreal niches and they have taken full advantage of that fact. New World monkeys exhibit a wide variation in lifestyles and diet.
New World monkeys have a variety of ways they get around. Most groups are quadrupedal climbers, but some groups such as the squirrel monkeys and capuchins, are squirrel-scamperers. Spider monkeys and woolly monkeys brachiate (swing from branch to branch using their arms) with the assistance of a prehensile tail.
The Callitrichidae include marmosets, tamarins and lion tamarins. Members of this group are the smallest of the simian primates. They feed on fruit, gum, insects and sap.
The Cebidae include the capuchin monkeys and squirrel monkeys. Members of this group are small monkeys that feed on fruit and insects.
The Aotidae are the night monkeys (also referred to as the owl monkeys). Members of this group live in high elevation habitats and therefore have thicker fur than other monkeys. They are nocturnal and have large eyes which enable them to see better in low light.
The Pitheciidae include titis, saki monkeys and uakaris. Most members of this group inhabit the Amazon river basin in Brazil, although a few species are found in Columbia and Bolivia. Members of this group are small to medium sized monkeys and have long fur with contrasting coloration.
The Atelidae include howler monkeys, spider monkeys, woolly monkeys, and woolly spider monkeys. Members of this group inhabit forests throughout Central and South America. They are medium in size and have long prehensile tails. They move from branch to branch by swinging from their arms and tail (this locomotion method is called brachiation).