any of more than 300 species of monkeys, apes, and other mammal s of the order Primates.
Primates are distinguished from other mammals by one or more of the following traits: unspecialized structure, specialized behaviour, short muzzle, comparatively poor sense of smell, prehensile five-digit hands and feet possessing flat nails instead of claws, acute vision with depth perception due to forward-facing eyes, large brain, and prolonged pre-and postnatal development. Most species bear a single young and live in troops headed by a male. The prosimians include eight families: lemur s (families Lemuridae, Indriidae, Cheirogaleidae, and Megaladapidae), the aye-aye (Daubentoniidae), galago s (Galagonidae), loris es (Loridae), and tarsier s (Tarsiidae). The anthropoids (a group called the Catarrhini) include nine families: Old World monkeys (Cercopithecidae), the lesser {{link=ape">ape s (Hylobatidae), the great apes (Pongidae), and humans (Hominidae). The great apes are sometimes classified with humans in Hominidae. Although the first primates may have originated as early as 90 million years ago, the oldest known fossil remains are about 55 million years old.