Extant Primates

Evolution of the Order Primates can be traced back to the early Tertiary period and the order is considered to have developed as an offshoot of a group of small, nocturnal, insectivorous mammals known as tree shrews. Several sub-orders are recognized:

A lemur (Propithecus verrauxi), endemic to the island of Madagascar off the east coast of Africa. Lemurs feature a somewhat elongated snout with minimal overlap of the visual field of its two eyes. Given the general trends in primate evolution, these are considered "primitive" characters.

A loris (Loris tardigradis) from India. The snout is somewhat elongated (less so than in lorises) and the eyes are rotated toward the front of the face, providing stereoscopic vision.

The rain-forests of southeast Asia provide the habitat for many tarsiers, including this one (Tarsius bancanus) from Borneo. Notice the flattened face, with the eyes rotated forward, and the grasping digits on the fore and hind limbs.

While somewhat showier than most, this golden lion tamarin (Leontopithecus rosalia) from Brazil is otherwise typical of the group. The most obvious features include a prehensile (grasping) tail and nostrils that open laterally. The prehensile tail may reflect a unique adaptation to South American tropical forests, which are flooded for as much as several months each year, requiring that the monkeys spend all of their time in the trees.

This species (Macaca fuscata) is atypical in that it lives in the temperate climate of north-central Japan (note the snow in the background).

Old World monkeys lack a prehensile tail and the nostrils open downward, as in the Anthropoid Apes (including humans). In contrast to the pronounced seasonal flooding of New World tropical forests, the tropical forests of Africa, in particular, are upland forests were flooding is not a major selective factor. As a consequence, although highly adapted to an arboreal mode of life, African monkeys spend a significant amount of time on the ground and some, like baboons, are entirely ground dwelling.

Gibbons (Hylobates) are highly specialized for an arboreal mode of life. Their hind limbs are short, relative to body size, and weakly developed. In contrast, the forelimbs are long and quite strong. Gibbons swing from branch to branch (brachiation) using the arms and both the wrist and shoulder joints have a wide range of movement. Gibbons are the smallest and lightest of the apes, consistent with a life largely confined to the trees. They are found in southeast Asian tropical forests and are the only apes that are monogamous. They are threatened by loss of habitat and are also hunted for food.

Orangutans (Pongo) are shy animals living in small groups in the forests of Borneo and Sumatra. They spend much of their time in the trees (note the elongated arms and relatively short legs, but do occasionally forage on the forest floor. Known locally as the "old man of the forest", orangutans are severely threatened by hunting, trapping for export, and habitat destruction despite protection efforts by government.

Gorillas (Gorilla) are the largest of the living primates (adult males can reach 2 m in height with a weight of 200 kg) and are confined to the tropical forests of equatorial Africa. Despite their reputation for ferocity, gorillas are basically quite shy, although the males will put on an impressive display to permit the retreat of females and young if the family groups are disturbed. The groups consist of an older, dominant male and a variable number of females with young of both sexes. Young males are typically driven from the group when they become large enough to challenge the alpha male. Smaller animals (primarily females and young) may build temporary nests in low trees at night, but adult males are typically too large for such behavior. Gorillas are herbivores that spend most of the day on the ground foraging for food, although significant amounts of time are devoted to complex social interactions between the larger animals and play among the young. Despite official protection efforts, gorillas are threatened by poaching (hunting for food and trophies and illegal trapping for export) and habitat encroachment.

Chimpanzees (Pan) are the modern apes most closely related to humans, based on studies of their anatomy, physiology, and DNA. It has been estimated that as much as 99% of the human and chimp DNA sequence is essentially identical. Chimps live in very open forests and on forest borders, foraging in both the forests and more open plant communities. They are omnivores and feed on both plants and animals. They hunt small animals and will scavenge the kills of larger carnivores if permitted to do so. While they are adept at climbing trees, they spend much of their time on the ground with the characteristic "knuckle-walking" locomotion illustrated by this female. By the standards of other apes, chimps live in rather large bands with social hierarchies vigorously maintained by males.

Chimpanzees can use simple tools (small sticks to extract termites from their nests, for example) and their social behavior is complex. Although behavior within the group is highly regulated and usually non-violent, groups will wage the equivalent of war against other groups, killing males that they catch away from the main group until they are able to appropriate the females. Such campaigns typically involve the killing of all the young in the rival group. Chimps will eat the dead animals in such instances. While more numerous than gorillas, chimpanzees face many of the same problems. Although trade in the wild animals is strictly regulated, a great deal of poaching occurs to meet the demands of foreign zoos and medical laboratories.