Primates

Primates (infraclass Eutheria, cohort Unguiculata) An order of mammals that have adapted to arboreal life and in some forms secondarily to life on the ground. Perhaps arising from this adaptation, eyes and ears are well developed, with binocular vision in many forms and the sense of smell is less developed, the snout commonly being reduced. The brain case is large, the olfactory region often being reduced. The neck is very mobile, shoulders and hips permit large limb movement, and the limbs are wholly free from the body wall. The clavicle is strong, the scapula can be rotated, the radius and ulna are separate and jointed, and the tibia and fibula are separate (except in Tarsiiformes). Digits are often long, with sensitive pads at their tips and most forms have flat nails rather than claws. The pollex is always opposable, the hallux often so. The teeth are unspecialized; the diet usually omnivorous. In monkeys, apes, and humans the uterus is single and the foetal and maternal bloodstreams are separated only by the walls of the foetal vessels. Usually there is a single pectoral pair of mammae. The number of young produced is small and parental care continues long after birth. The Primates are divided into two suborders, Prosimii and Anthropoidea, or Strepsirrhini and Haplorrhini, but the (extinct) Plesiadapiformes are nowadays commonly regarded as a third. The mammals diverged from shrew-like ancestors in the Cretaceous. Both strepsirrhines and haplorrhines appeared in the Eocene. The time at which the hominid line diverged from that of the African apes (gorilla and chimpanzee) is controversial: times of as much as 20 million and as little as 4.5 million years ago are suggested, but the latter time is now increasingly believed to be the more accurate.