Primates are an order of mammals. Most primates are characterized by well-developed binocular vision, a flattened, forward-oriented face, prehensile digits, opposable thumbs (sometimes the first and second digits on the feet are also opposable), five functional digits on the feet, nails on the tips of the digits (instead of claws), a clavicle (or collarbone), a shoulder joint allowing free movement of the arm in all directions, a tail (except for apes), usually only two mammae (or teats), relatively large development of the cerebral hemispheres of the brain, usually only one offspring born at a time, and having a strong social organization. Most species of primates are highly arboreal (that is, they live in the forest canopy), but some live mostly on the ground. Primates first evolved early in the Cenozoic Era, about 60 million years ago. The ancestral stock of the primates is thought have been small, carnivorous animals similar to modern tree shrews (family Tupaiidae).
There are about 12 families and 60 genera of living primates (the numbers vary depending on the particular zoological study being consulted). Most species of primates inhabit tropical and sub-tropical regions, and most occur in forested habitats. Primates are divided into two sub-orders, the Prosimii (or prosimians) and the Anthropoidea (monkeys and apes). The families and examples of component species are given below.
Prosimii. This sub-order of primates has a relatively ancient evolutionary lineage, and includes several families of lemurs, lorises, and tarsiers, all of which have fox-like snouts, long tails, and inhabit forests.
Cheirogaleidae. This is a family of five species of dwarf or mouse lemurs, which only occur on the island of Madagascar, off Africa in the Indian Ocean. An example is the hairy-eared dwarf lemur (Allocebus trichotis).
Lemuridae. This is the largest family of lemurs, consisting of about 10 species, which only occur on Madagascar and the nearby Comoro Islands. Examples are the black lemur (Eulemur macaco) and the ring-tailed lemur (Lemur catta).
Megaladapidae. This is a family of two species of sportive lemurs, which also only occur on Madagascar. An example is the gray-backed sportive lemur (Lepilemur dorsalis).
Indridae. This is another family of prosimians of Madagascar, including four species known as wooly lemurs. An example is the indri (Indri indri).
Daubentoniidae. This family has only one species, the aye-aye (Daubentonia madagascariensis) which live in the forests of Madagascar.
Lorisidae. This prosimian family of 12 species occurs in forests of South Asia, Southeast Asia, and Africa. Examples are the slender loris (Loris tartigradus) of India and the potto (Perodicticus potto) of tropical Africa.
Tarsiidae. This family includes three species of small prosimians that inhabit forests of islands of Southeast Asia. One example is the Philippine tarsier (Tarsius syrichta).
Anthropoidea. This sub-order includes the Old World monkeys, the New World monkeys, the marmosets, and the apes. The various monkeys are relatively small, arboreal, and have tails, while the apes are larger, relatively intelligent, and lack a tail. Most species of anthropoid primates are arboreal and inhabit forests, but some do not.
Callitrichidae. This family includes about 33 species of small marmoset monkeys of tropical forests of South America and Panama. Examples include the golden-headed lion tamarin (Leontopithecus chrysomelas) and the pygmy marmoset (Cebuella pygmaea), both occurring in Brazil.
Cebidae. This family includes about 37 species of New World monkeys, distinguished by their prehensile (or grasping) tail, and nostrils separated by a relatively wide partition. Examples are the dusky titi monkey (Cellicebus cupreus) of northern South America and the Central American squirrel monkey (Saimiri oerstedii) of Costa Rica and Panama.
Cercopithecidae. This family includes about 60 species of Old World monkeys of Africa and Asia, characterized by non-prehensile tails, closely placed nostrils, and (usually) bare skin on the buttocks. Examples include the black colobus (Colobus satanas) of central Africa, the rhesus macaque (Macaca mulatta) of South Asia, the mandrill (Mandrillus sphinx) of West Africa, and the proboscis monkey (Nasalis larvatus) of Borneo.
Hylobatidae. This is a family of six species of gibbon apes, which are tail-less, highly arboreal and agile, and have loud, complex vocalizations (known as "songs"). Examples are the black gibbon (Hylobates concolor) of Southeast Asia and the siamang (Symphalangus syndactylus) of Malaysia and Sumatra.
Hominidae. This family includes five species of great apes, which are relatively large and robust, lack a tail, and are the most intelligent and socially complex species of primates. This group includes the gorilla (Gorilla gorilla) of Central Africa, the pygmy chimpanzee (Pan paniscus) of Congo, the chimpanzee (Pan troglodytes) of Central Africa, the orangutan (Pongo pygmaeus) of Borneo and Sumatra, and humans (Homo sapiens) who have worldwide distribution. All hominidae, with the exception of humans, only inhabit tropical forests.
Humans evolved about one million years ago. They are now by far the most widespread and abundant species of primate, living on all of the continents, including Antarctica. Humans are also the most intelligent species of primate, and probably of any species. Humans have undergone extremely complex cultural evolution, characterized by adaptive, progressive discoveries of social systems and technologies that are allowing this species to use the products of ecosystems in an increasingly efficient and extensive manner. Habitat changes associated with human activities, coupled with the harvesting of many species and ecosystems as resources, are now threatening the survival of numerous other species and natural ecosystems. This includes almost all other species of primates, whose populations have declined to the degree that the World Conservation Union (IUCN) considers them threatened by extinction.