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Monkey is any of a large and varied group of mammals of
the primate order. The term monkey includes all
primates that do not belong to the categories human, ape,
or prosimian; however, monkeys do have certain common
features. All are excellent climbers, and most are
primarily arboreal. Nearly all live in tropical or
subtropical climates. Unlike most of the prosimians, or
lower primates, they are almost all day-active animals.
Their faces are usually flat and rather human in
appearance, their eyes point forward, and they have
stereoscopic color vision. Their hands and feet are highly
developed for grasping; the big toes and, where present,
the thumbs are opposable. Nearly all have flat nails.
Monkeys habitually sit in an erect posture. Unlike the
apes, most cannot swing arm-over-arm (the spider monkey is
an exception) but move about in trees by running along the
branches on all fours; their skeletal structure is similar
to that of other four-footed animals. Monkeys live in
troops of up to several hundred individuals and travel
about in search of food, having no permanent shelter. As
in apes and humans, the female has a monthly reproductive
cycle, and mating may occur at any time, but in some
species mating is seasonal. Usually only one infant is
born at a time; it is cared for by the mother for a long
period. There are two large groups, or superfamilies, of
monkeys: Old World monkeys (Cercopithecoidea) and New
World monkeys (Ceboidea).
Old World Monkeys
T he Old World
monkeys are found in S Asia, with a few species as far N
as Japan and N China, and in all of Africa except the
deserts. Most are arboreal, but a few, such as baboons and
some species, are ground dwellers. Some Old World monkeys
lack tails; when a tail is present it may be long or short
but is never prehensile (grasping). The nostrils are close
together and tend to point downward. Many species have
cheek pouches for holding food, and many have thick pads
(called ischial callosities), on the buttocks. Their
gestation period is five to nine months. Adult Old World
monkeys have 32 teeth. The Old World monkeys, sometimes
called true monkeys, are more closely related to the apes
and humans than they are to the New World monkeys; the two
monkey groups probably evolved separately from ancestral
primates.
T he Old World
monkeys include the many species of macaque, widely
distributed throughout Africa and Asia. The rhesus monkey,
commonly used in laboratory experiments, is an Asian
macaque. Related to the macaques are the baboons of Africa
and SW Asia, as well as the mandrill and mangabey of
Africa. The guerezas, or colobus monkeys (genus Colobus),
are very large, long-tailed, leaf-eating African monkeys.
Their Asian relatives, the langurs and leaf monkeys,
include the sacred monkeys of India. The snub-nosed monkey
of China and the proboscis monkey of Borneo are langurlike
monkeys with peculiar snouts. The guenons (Cercopithecus)
are a large group of long-legged, long-tailed, omnivorous
monkeys found throughout sub-Saharan Africa. One very
widespread guenon species is the green monkey, or vervet,
with olive-brown fur.
N ew
World Monkeys
The New World monkeys are found from S Mexico to
central South America, except in the high mountains, and
are classified into two families (Callatrichids and Cebids).
The Callatrichids are very small, while the Cebids are
similar in size to the Old World monkeys. They are all
thoroughly arboreal and most have long, prehensile tails
with which they can manipulate objects and hang from
branches. In most the thumb is lacking. They have widely
separated nostrils that tend to point outward; they lack
cheek pouches and ischial callosities. Their gestation
period is four to five months. Adults of most New World
species have 36 teeth.
The New World monkeys include the marmosets and
tamarins, small monkeys with claws that are classified in
a family of their own, the Callithricidae. The rest of the
New World monkeys are classified in the family Cebidae.
They include the capuchin (genus Cebus), commonly
seen in captivity, which has a partially prehensile tail.
Prehensile tails are found in the spider monkey and woolly
monkey as well as in the howler monkey, the largest member
of the family, which has a voice that carries several
miles. Smaller forms with nonprehensile tails are the
squirrel monkey and titi, the nocturnal douroucouli, or
owl monkey, the saki, and the ouakari.
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