A primate (i// PRY-mayt) is a mammal of the order Primates (Latin: "prime, first rank"). In taxonomy, primates include two distinct lineages, strepsirrhines and haplorhines. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment. Most primate species remain at least partly arboreal.
With the exception of humans, who inhabit every continent, most primates live in tropical or subtropical regions of the Americas, Africa and Asia. They range in size from Madame Berthe's mouse lemur, which weighs only 30 g (1 oz), to the eastern gorilla, weighing over 200 kg (440 lb); that is, without taking into account the weight of particular human individuals, reaching up to 635 kg (1,400 lb). Based on fossil evidence, the earliest known true primates, represented by the genus Teilhardina, date to 55.8 million years old. An early close primate relative known from abundant remains is the Late Paleocene Plesiadapis, c. 55–58 million years old. Molecular clock studies suggest that the primate branch may be even older, originating near the Cretaceous–Paleogene boundary or around 63–74 mya.
The order Primates was traditionally divided into two main groupings: prosimians and anthropoids (simians). Prosimians have characteristics more like those of the earliest primates, and include the lemurs of Madagascar, lorisoids, and tarsiers. Simians include monkeys, apes and hominins. More recently, taxonomists have preferred to split primates into the suborder Strepsirrhini, or wet-nosed primates, consisting of non-tarsier prosimians, and the suborder Haplorhini, or dry-nosed primates, consisting of tarsiers and the simians.
Simians are divided into two groups: catarrhine (narrow-nosed) monkeys and apes of Africa and Southeast Asia and platyrrhine ("flat-nosed") or New World monkeys of South and Middle America. Catarrhines consist of Old World monkeys (such as baboons and macaques), gibbons and great apes; New World monkeys include the capuchin, howler and squirrel monkeys. Humans are the only extant catarrhines to have spread successfully outside of Africa, South Asia, and East Asia, although fossil evidence shows many other species were formerly present in Europe. New primate species are still being discovered. More than 25 species were taxonomically described in the decade of the 2000s and eleven have been described since 2010.
Considered generalist mammals, primates exhibit a wide range of characteristics. Some primates (including some great apes and baboons) are primarily terrestrial rather than arboreal, but all species possess adaptations for climbing trees. Locomotion techniques used include leaping from tree to tree, walking on two or four limbs, knuckle-walking, and swinging between branches of trees (brachiation).
Primates are characterized by large brains relative to other mammals, as well as an increased reliance on stereoscopic vision at the expense of smell, the dominant sensory system in most mammals. These features are more developed in monkeys and apes and noticeably less so in lorises and lemurs. Three-color vision has developed in some primates. Most also have opposable thumbs and some have prehensile tails. Many species are sexually dimorphic; differences include body mass, canine tooth size, and coloration. Primates have slower rates of development than other similarly sized mammals and reach maturity later, but have longer lifespans. Depending on the species, adults may live in solitude, in mated pairs, or in groups of up to hundreds of members.