|New World monkeys|
A New World monkey is any member of the primate clade Platyrrhini, comprised of four Central and South America families: Cebidae (marmosets, capuchins, squirrel monkeys, tamarins), Aotidae (night or owl monkeys), Pitheciidae (titis, sakis, uakaris), and Atelidae (howler, spider, and woolly monkeys). Members of the Platyrrhini ("flat-nosed") parvorder are typically characterized by relatively broad noses with side-facing, widely separated nostrils, as opposed to the close-set, downward or forward facing nostrils of the Old World monkeys placed in the parvorder Catarrhini. In addition, New World monkeys, many of which have long tails, have a number of species with prehensile tails (adapted for grasping or holding), whereas the tails of Old World monkeys, if present, are never prehensile.
New World monkeys, with their high intelligence, manual dexterity, and unique behaviors, are not only popular attractions for human beings in the wild or in zoos, but some even have been trained as helpers for quadriplegics (See capuchin monkey.) Some are used in laboratory or medical research, while others are raised as pets. Ecologically, New World monkeys provide an important role in tropical food chains, from southern Mexico in North America to South America. These omnivores consume vegetative material (fruits, nuts, leaves, etc.) and some invertebrates (insects, crabs, clams) and small vertebrates, and in turn are preyed upon by large felids, birds of prey, and snakes.
New World monkeys are one of three major informal groups of the biological order Primates, the other two groups being (1) prosimians and (2) monkeys and apes of the Old World. Together, the New World monkeys and the Old World monkeys and apes are considered to be "higher primates," or simians (infraorder Similformes), while the prosimians (such as lemurs) are considered to be the "lower primates." The term monkey thus refers to any simian that is not an ape or any primate that is neither an ape or a prosimian. In reality, monkeys are not a single coherent group and therefore do not have any particular traits that they all share. The New World monkeys are found in Mexico, Central America, and South America, and the Old World monkeys are located in Africa, central to southern Asia, Japan, and India.
Technically, the distinction of platyrrhines (New World monkeys) from catarrhines (Old World monkeys and apes) depends on the structure of the nose, which is the feature most commonly used 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 New World monkeys have side facing nostrils versus the close-set, downward or forward facing nostrils of Old World monkeys.
New World monkeys differ slightly from Old World monkeys in several other aspects. New World monkeys (except for the howler monkeys of genus Alouatta (Jacobs et al. 1996)) lack the trichromatic vision of Old World monkeys (Carroll 2006). Other distinctions include the presence of a tubular ectotympanic (ear bone) in Old World monkeys and the presence of twelve premolars in catarrhines, versus eight in platyrrhines. Some New World monkeys, such as those in the family Atelidae, have tails that are prehensile. Catarrhines lack prehensile tails.
New World monkeys are small to mid-sized primates, ranging from the pygmy marmoset (the world's smallest monkey), at 14 to 16 centimeters (5.5 to 6.3 inches) and a weight of 120 to 190 grams (4.2 to 6.7 ouches) to the southern muriqui, at 55 to 70 centimeters (22 to 28 inches) and a weight of 12 to 15 kilograms (26 to 33 pounds).
Spider monkeys, which are those New World monkeys comprising the genus Ateles of the family Atelidae, have an average body length of 50 centimeters (20 inches) and a weight of 6.4 kilograms (14 pounds), with very long prehensile tails that may measure up to 90 centimeters (3 feet). Capuchin monkeys, comprising the genus Cebus of the family Cebidae, reach a length of 30 to 56 centimeters (12-22 inches), with tails that are just as long as the body, and weigh up to 1.3 kilograms (2 pounds, 13 ounces). Squirrel monkeys, comprising the genus Saimiri of the family Cebidae, grow to 25 to 35 centimeters (9.8 to 13.8 inches) long, plus a 35 to 42 centimeter (13.8 to 15.5 inches) tail, and weigh 750 to 1100 grams (1.7 to 2.4 pounds). Remarkably, the brain mass to body mass ratio for squirrel monkeys is 1:17, which gives them the largest brain, proportionately, of all the primates. Humans have a 1:35 ratio.
Almost all New World monkeys are arboreal, some rarely coming to the ground, so knowledge of them is less comprehensive than that of the more easily observed Old World monkeys. Most New World monkeys, such as the capuchins and squirrel monkeys, are diurnal and spend much of their day searching for food, while sleeping in trees at night.
Unlike most Old World monkeys, many New World monkeys form monogamous pair bonds, and show substantial paternal care of young. Some live together in very large groups, such as the squirrel monkeys that have multi-male/multi-female groups of up to 500 members, those these groups may occasionally break into smaller troops.
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) (Shumaker and Beck 2003).
With the lack of any fossil monkeys found in North America, and the continents of Africa and South America separated for a hundred million years, the Platyrrhini are currently conjectured to have migrated across the Atlantic Ocean to South America (Beard 2004). One speculation is that this could have occurred on a raft of vegetation, similar to the vast pieces of floating mangrove forest that storms occasionally break off from the tropical African coast (Beard 2004). At the time of the split 40 million years ago, the Atlantic Ocean at its narrowest between the continents was about 1500 kilometers (940 miles), almost half the distance seen today with the narrowest separation about 2920 kilometers (1,825 miles) (Beard 2004).
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