New World Monkeys

The New World monkeys of Central and South America belong to the family Cebidae and to the family Callitrichidae (the marmosets and tamarins). The Cebidae, or capuchin-like monkeys, are distinguished from the marmosets and tamarins by their possession of nails instead of claws on most fingers and toes, and three molars instead of two on either side of each jaw. Finally, cebids tend to give birth to one offspring at a time, while the marmosets and tamarins tend to have twins.

Cebid monkeys include capuchins (Cebus), night monkeys or douroucoulis (Aotus), titis (Callicebus), squirrel monkeys (Saimiri), sakis (Pithecia), bearded sakis (Chiropotes), uakaris (Cacajao), howler monkeys (Alouatta), spider monkeys (Ateles), the woolly spider monkey (Brachyteles arachnoides), and woolly monkeys (Lagothrix).

Cebid monkeys are all arboreal tree dwellers that feed on leaves, fruit, birds' eggs, tree frogs, and bark-dwelling insects and their larvae. The night monkey or douroucouli (Aotus trivirgatus), is the only nocturnal New World monkey; the rest are diurnal, or active during the day.

The cebid monkeys vary in size from the squirrel monkey (S. sciureus) with a body length of 10 in (25 cm) plus a 15 in (38 cm) tail, and a weight of about 1.5 lbs (0.68 kg), to the woolly spider monkey, or muriqui, which has a body length of 18 in (46 cm), plus a 30 in (75 cm) tail, and weighs about 35 lb (17.5 kg). The males and females of most species of cebid monkeys are approximately the same size, but the two sexes often have different colorings, a phenomenon known as sexual dimorphism.

The larger species of cebid monkeys have a prehensile tail with a naked patch at the base that has fingerprint-like ridges for sensitive gripping. The smaller, more agile monkeys do not have a prehensile tail, but can nevertheless readily leap from branch to branch.

The group territories of different species of New World monkeys often overlap, and as many as five different species have been found living in one tree, usually at different levels. Some monkey groups have been known to establish long-lasting "friendships" with the social groups of a different monkey species.

The average gestation period of New World monkeys is about 145 days, which is about three weeks shorter than the gestation period of Old World monkeys, although some New World monkeys gestate as long as 225 days. The breasts of cebid monkeys are located near the armpits so that they can be reached by the young riding on the mother's back. Unlike humans, apes, and most Old World monkeys, female New World monkeys do not menstruate. In general, the smaller species are monogamous, living in family groups with only one male and one female, while the larger species tend to be polygamous with one male and a harem of several females.