Primates

Primates are an order of mammals that includes humans, apes, monkeys, and prosimians (see Figure 1). Prosimians are sometimes referred to as lower primates, where the rest of the order is referred to as higher primates. In general, primates have a large range of variability in body size. The smallest primate is the pygmy mouse lemur from Madagascar. It is only 20 cm (8 in) from its nose to its tail and weighs only 30 gm (1 oz). This species is dwarfed by the largest primate—the lowland gorilla of Africa, which weighs in at about 180 kg (400 lb). The physical characteristics of primates reflect several evolutionary trends. Perhaps the most important of these is the adaptation of the hands and feet for grasping. The characteristics associated with this trend include highly mobile digits with opposable thumbs and flat fingernails instead of claws on the hands and feet. In addition, primates have very sensitive pads on the undersides of their fingers and toes that facilitate gripping.

Another important trend is the progressive increase in the relative and absolute size of the brain. The visual cortex and cerebral cortex have increased in size and complexity, while the olfactory centers of the brain have decreased in size. This is associated with increased dependence on sight and a decreased importance of smell. A trend toward a gradual foreshortening of the muzzle reflects the decline in the importance of smell and increased importance of vision. Forward projecting eyes provide primates with depth perception, so important to living and moving around in trees. Primates also have eye sockets encircled or enclosed in bone, to protect these very important organs. Finally, all primates show a tendency for erectness, or upright posture during feeding, locomotion, or rest. The more centrally placed foramen magnum in the base of the skull (where the spinal cord attaches to the head) reflects this tendency.

Most primates are omnivorous, with diets that include plants, insects, and occasionally small mammals. Most primates are diurnal

Figure 1

Primate Taxonomy

Order Primates

Subfamily Pitheciinae

Semiorder Euprimates

Tribe Pitheciini

Suborder Strepsirhini

Tribe Homunculini

Infraorder Lemuriformes

Family Cebidae

Superfamily Lemuroidea

Subfamily Cebinae

Family Lemuridae

Subfamily Callitrichinae

Subfamily Lemurinae

Tribe Callimiconini

Subfamily Hapalemurinae

Tribe Callitrichini

Superfamily Indroidea

Infraorder Catarrhini

Family Indridae

Parvorder Eucatarrhini

Family Lepilemuridae

Superfamily Cercopithecoidea

Subfamily Lepilemurinae

Family Cercopithecidae

Family Daubentoniidae

Subfamily Cercopithecinae

Superfamily Lorisoidea

Tribe Ceropithecini

Family Lorisidae

Subtribe Cercopithecinia

Family Galagidae

Subtribe Allenopithecina

Family Cheirogaleidae

Tribe Papionini

Family Pseudopottidae

Subtribe Papionina

Suborder Haplorhini

Subtribe Macacina

Hyporder Tarsiiformes

Subfamily Colobinae

Superfamily Tarsioidea

Subtribe Colobina

Family Tarsiidae

Subtribe Presbytina

Hyporder Anthropoidea

Superfamily Hominoidea

Infraorder Platyrrhini

Family Hylobatidae

Superfamily Ateloidea

Family Hominidae

Family Atelidae

Subfamily Homininae

Subfamily Atelinae

Tribe Hominini

Tribe Atelini

Tribe Gorillini

Tribe Alouattini

Tribe Panini

(active during the day), although many (especially the smaller species) are active during the night (nocturnal). Primates are typically sociable and often live in complex social groups. Exceptions include smaller primates, especially nocturnal ones, which tend to be solitary. Baboons live in the largest groups, sometimes consisting of more than one hundred members. Relative to other mammals, primates have a tendency for prolonged periods of infant dependency and a long period of socialization. This is related to their complex social behavior, which must be learned over the animal's lifetime.

Primate ancestors were tree dwellers, and, with the sole exception of humans, all primates spend some time in trees. Consequently, all primates retain characteristics that are adapted to tree living, even though some have since adapted to living primarily on the ground. Almost all primates are quadrupedal (that is, they walk on four legs) to some extent, but the different species exhibit a wide range of locomotion. Some are uniquely adapted to brachi-ating (swinging) under tree limbs (for example, gibbons), and others (for example, sifakas) have unique adaptations for clinging and leaping from tree trunk to tree trunk.

Primates inhabit a wide range of habitats, from dry desert savannas to lush tropical forests. Geographically, primates are primarily restricted to tropical areas of the world, including Central and South America, Africa, India, and southeast Asia. Two exceptions are the Barbary macaque, which can be found in northern Africa and on the Rock of Gibraltar, and the Japanese macaque, which can be found on both of the main islands of Japan.

—Ken Mowbray and Shara Bailey

See also: Great Apes; Homo Sapiens; Human Evolution; Monkeys

Bibliography

Conroy, Glen. 1990. Primate Evolution. New York: W. W. Norton; Falk, Dean. 2000. Primate Diversity. New York: W. W. Norton; Tattersall, Ian. 1982. The Primates of Madagascar. New York: Columbia University Press.

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