Monkey

The term "monkey" is used to denote any higher primate (suborder Anthropoidea) that is not an ape. Thus, it includes both members of the New World monkeys (infraorder Platyrrhini) as well as the Old World monkeys (infraorder Catarrhini, superfamily Cercopithecoidea). Monkeys have little in common with each other except for the fact that most are quadrupedal, but this does not eliminate all other primates. It is unclear where the name "monkey" originated, although a common interpretation is that it relates to the medieval term "moneke", meaning manikin.

Old World (Catarrhine) Monkeys
The OldWorld monkeys are the largest and most diverse family of primates, covering about ninetyfive species and ranging over most of Africa, Asia, and Indonesia. The name Catarrhine means "downward-nosed", referring to the fact that the nostrils are close together and point forward and down. Catarrhine monkeys include macaques, mangabeys, baboons, mandrills, velvet monkeys, guenons, colobuses, proboscis monkeys, and langurs. There are two subfamilies: the leaf-eating, arboreal Colobinae (examples include the colobus and the langur), and the omnivorous, often ground-dwelling Cercopithecinae (including the baboons, mandrills, macaques, and guenons). The Colobinae have a rather complex stomach and digestive system, whereas the Cercopithecinae have a simple stomach combined with cheek pouches in which food can be stored. The macaques are the greatest in number among the OldWorld species, as well as the most widespread. The most northerly is the Japanese macaque, which can live in cold, snowy climates. Other macaques live in dry, almost desertlike conditions in the tropics. Old World species are generally larger than New World species, and there is considerable sexual dimorphism. Most have bare buttock pads, which may be brightly colored. Their tails are seldom fully prehensile, and may be significantly reduced in size. Almost all are active during the day, with excellent vision, hearing, and sense of smell. They communicate almost entirely by sight and sound, displaying a wide range of calls. Many display a range of facial expressions, used for communication with their own species as well as with other species nearby. Most are fully arboreal, but baboons are ground feeders, and macaques live both on the ground and in the trees. When more than one species of monkey dwells in the same locality, the various species generally occupy different vegetation levels in order to avoid competition. This behavior is known as arboreal stratification. Most authors recognize four layers of vegetation in the tropics: the ground layer, lower canopy, middle canopy, and upper canopy. For instance, in the African guenons (Cercopithecus spp.), DeBrazza's monkey lives at the ground level, the red-tailed monkey sleeps in the middle canopy but spends the day on the ground, the blue guenon lives in the upper canopy but forages in the middle, and the Diana monkey lives solely in the upper canopy.

New World (Platyrrhine) Monkeys
The New World monkeys are a highly successful and diversified group colonizing Central and South America. The term usually refers to the infraorder Platyrrhini, meaning "flat-nosed." As compared with the Catarrhine monkeys, the nostrils of the Platyrrhines are broadly separated and usually point to the sides. Members of the Platyrrhines include capuchins, howler monkeys, sakis, woolly monkeys, squirrel monkeys, and uakaris, a total of about forty-five species. NewWorld monkeys have long, thin fingers on each hand, with flattened or curved nails. Although their thumbs are not opposable, as they are in the human, the big toe can be opposed against the other toes for gripping branches tightly.NewWorld monkeys are excellent runners and jumpers, swinging and leaping through their densely wooded habitats. Their tails are fully prehensile; they can grasp objects at the tip and curl around a branch and support the full body weight of the animal. In almost all cases, the tail is at least as long as the head and body, and it acts as a balancing organ, often being held in a curled pattern. None of the New World monkeys are ground dwellers, unlike the baboons and other OldWorld monkeys. None of them have cheek pouches, and sexual dimorphism is rarely seen. New World monkeys are gregarious and live in family-based groups with much vocal and visual communication. They have highly developed olfactory organs that may also be used for communication. Males of many species contain a glandular patch on the sternum (breastbone) which they rub against tree branches to act as scent markers. Marking by means of urine and feces is also common. For instance, night monkeys coat their hands and feet with urine so that they leave a telltale scent wherever they go. Families are well developed in most species of monkeys, although females do most of the caring for their offspring. Mothers usually carry their young on their backs until they are ready to move through the canopy on their own. Group size seems to depend primarily on the productivity and abundance of the foods typically eaten by the species. Species that live in small groups tend to feed on small, scattered, or scarce resources such as insects, small vine fruit, or newly emerged leaves of bamboo. Species that form large groups use abundant or clumped resources, such as fruits on large fig trees. Small family groups are typically one to three animals, while large groups may involve seven to twenty members.