New World monkey

New World monkeys are the five families of primates that are found in Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Platyrrhini parvorder and the Ceboidea superfamily, which are essentially synonymous since Ceboidea is the only living platyrrhine superfamily. They differ from other groupings of monkeys and primates, such as the Old World monkeys and the apes.

Characteristics
New World monkeys are small to mid-sized primates, ranging from the Pygmy Marmoset (the world's smallest monkey), at 14 to 16 cm (5.5 to 6.3 in) and a weight of 120 to 190 grams (4.2 to 6.7 oz) to the Southern Muriqui, at 55 to 70 cm (22 to 28 in) and a weight of 12 to 15 kg (26 to 33 lbs). New World monkeys differ slightly from Old World monkeys in several aspects. The most prominent phenotype distinction is the nose, which is the feature used most commonly to distinguish between the two groups. The scientific name for the New World monkeys, Platyrrhini, means "flat nosed". The noses of New World monkeys are flatter than the narrow noses of the Old World monkeys, and have side-facing nostrils. New World monkeys are the only monkeys with prehensile tails—in comparison with the shorter, non-grasping tails of the anthropoids of the Old World.

New World monkeys (except for the howler monkeys of genus Alouatta) also typically lack the trichromatic vision of Old World monkeys. Colour vision in New World primates relies on a single gene on the X-chromosome to produce pigments that absorb medium and long wavelength light, which contrasts with short wavelength light. As a result, males rely on a single medium/long pigment gene and are dichromatic, as are homozygous females. Heterozygous females may possess two alleles with different sensitivities within this range, and so can display trichromatic vision.

Platyrrhines also differ from Old World monkeys in that they have twelve premolars instead of eight; having a dental formula of (consisting of 2 incisors, 1 canine, 3 premolars, and 3 molars. This is in contrast with Old World Anthropoids, including humans, gorillas, chimps, bonobos, siamangs, gibbons and orangutans, which share a dental formula of ) New World monkeys in the family Atelidae are the only primates with tails that are prehensile. Many New World monkeys are small and almost all are arboreal, so knowledge of them is less comprehensive than that of the more easily observed Old World monkeys. Unlike most Old World monkeys, many New World monkeys form monogamous pair bonds, and show substantial paternal care of young. They eat fruits, nuts, insects, flowers, bird eggs, spiders, and small mammals. Unlike humans and most Old World monkeys, their thumbs are not opposable (except for some Cebids).

Origin
About 40 million years ago the Simiiformes infraorder split into parvorders Platyrrhini (New World monkeys—in South America) and Catarrhini (apes and Old World monkeys—in Africa). The Platyrrhini are currently conjectured to have migrated across the Atlantic Ocean to South America on a raft of vegetation.

At that time, the Isthmus of Panama had not yet formed, ocean currents and climate were quite different, and the Atlantic Ocean was less than the present 2800 km width by about a third; possibly 1,000 km less, based on the current estimate of the Atlantic mid-ocean ridge formation processes spreading rate of 25 mm/year.

Classification
The following is the listing of the various platyrrhine families, and their placement in the Order Primates:
 * ORDER PRIMATES
 * Suborder Strepsirrhini: lemurs, lorises, etc.
 * Suborder Haplorrhini: tarsiers, monkeys and apes
 * Infraorder Tarsiiformes
 * Family Tarsiidae: tarsiers
 * Infraorder Simiiformes
 * Parvorder Platyrrhini: New World monkeys
 * Family Callitrichidae: marmosets and tamarins
 * Family Cebidae: capuchins and squirrel monkeys
 * Family Aotidae: night or owl monkeys (douroucoulis)
 * Family Pitheciidae: titis, sakis and uakaris
 * Family Atelidae: howler, spider, woolly spider and woolly monkeys
 * Parvorder Catarrhini: Old World monkeys, apes and humans