Like Madagascar, South America was isolated by ocean for most of its long history. The primates that eventually colonized its shores made an improbable crossing of vast distances over open water.
A handful of lucky travelers found solid ground and a landscape in which their descendants could flourish. In their new tropical wilderness, in the rainforests before the Amazon, they developed into a completely separate lineage: the species-rich platyrrhines, or New World monkeys.
Apart from their distinctive nostrils, broadly set and directed to either side, the platyrrhines are set apart from their distant catarrhine kin by their lack of cheek pouches and sitting pads – and by the presence, in many species, of a fully prehensile tail. These prehensile tails, as strong and agile as any other limb, allow for easy maneuvering through the dense canopy environment. The lower portion of the tail has a firm, fleshy pad on its inside curl that allows for an improved grip on branches, essentially a fifth palm. Like a human palm, the pad is covered with a unique pattern of fine ridges, collectively called a dermatoglyph, as detailed and unique as any fingerprint.
Based on their body size, the primates of the New World may be divided into two major groups: the smaller Callitrichidae, including the dozens of species of marmosets and tamarins, and the larger Cebidae and their allies, including several families of varied forms: the squirrel monkeys and night monkeys, the titi monkeys and the capuchins, the seed-eating sakis and uakaris, the howler monkeys, and the largest of the New World species, the spider monkeys, woolly monkeys and the muriquis.
ACTIVITY: Find these species on our Interactive Primate Tree.
Where They Live
New World monkeys are usually much smaller than the African and Asian anthropoids and more restricted to the forest habitat. Unlike the many terrestrial species of African primates – the baboons, the mandrills, the patas monkeys – few of the New World monkeys are specifically adapted for living on the ground. In general, New World monkeys keep to the trees whenever possible. Only the capuchins are truly adept at foraging on the forest floor, but even they are not so much permanent residents as adaptable visitors.
Marmosets & Tamarins
The marmosets and tamarins together form the family Callitrichidae (or the subfamily Callitrichinae, depending on the taxonomy used), occupying much of the Amazon Basin and, in a few cases, extending into southern Central America
. Their habitats are quite diverse: primary rainforest, secondary growth, semideciduous dry forest, gallery forest and (in rare cases) dune forest and bamboo thickets. They are by far the smallest of the New World primates. Most marmosets are no larger than the average squirrel, and two of the most compact, the dwarf and pygmy marmosets, are barely chipmunk-sized. Many aspects of their anatomy set them apart from the larger platyrrhines:
- They have claws instead of flattened nails, with the exception of a single nail on each big toe;
- Their thumbs are not opposable; and
- They have a unique sequence of teeth.
ARTICLE: Marmoset Q&A with Russell A. Mittermeier and Anthony Rylands
Nearly all species of marmosets and tamarins commonly give birth to twins and live in groups of up to twenty individuals. Once thought to be strictly monogamous, recent field research has shown that their social structure may include multi-male/multi-female groups. The groups are intensely territorial and defend their range with a variety of calls, visual displays, scent-marking and facial expressions. Most importantly for their social dynamics, infants are often looked after by family members other than the mother; often it is the father who carries the young – a valuable assist to mothers who are almost always raising twins.
The Larger Platyrrines
The other platyrrhines are a large and diverse group of species; they include the world’s only true nocturnal monkey, the night monkey or douricouli, and the only monkeys with prehensile tails – the capuchins, howlers, spider monkeys, woolly monkeys and muriquis.
Virtually all the platyrrhines are exclusively tree-dwelling, living in a broad spectrum of tropical and subtropical forests. They will only occasionally and reluctantly descend to the ground to travel between forest patches – and for just this reason, the fragmentation of rainforest is especially dangerous for them.
ACT: Protect an Acre of Forest Now
The social structure of New World monkeys is often complex and varies widely, ranging from strict monogamy in the titi monkeys to enormous groups of dozens or hundreds in the squirrel monkeys.
Anatomy follows diet, and there are parallels and convergences to be found: the leaf-eating howler monkeys, similar to the African and Asian colobines, have flat grinding teeth and a large gut for digesting vegetation; one local name for howlers in Brazil, barrigudo, means “big belly.”
Threats to New World Monkeys
Over a third of all Neotropical primates are in serious danger of becoming extinct as more forest is lost every year to agriculture, ranching, commercial logging and hydroelectric projects. Subsistence hunting and the pet trade, while not yet as intense as in Asia or Africa, continue to exert dangerous pressures on primate populations that are already declining.
LEARN MORE: Learn more about threats to primates.
The marmosets and tamarins – too small to be much value as food – are usually spared from hunting pressure. But certain species inhabit some of the most degraded tropical forests on Earth. The lion tamarins of Brazil, for instance, are among the most endangered of New World monkeys. These radiantly golden-hued species survive only in the last fragments of the Atlantic Forest, a shattered biome that has been ground down to less than five percent of its original extent.
Strenuous efforts by Brazilian conservationists, carried out over decades, have so far kept the lion tamarins just this side of extinction – but many more New World monkeys require urgent attention as well.