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Simiiformes

Simiiformes (Anthropoidea; cohort Unguiculata, order Primates) A suborder (or infra-order) that comprises the monkeys (Ceboidea and Cercopithecoidea), apes, and humans (Hominoidea). Old World monkeys and apes have a common ancestor and diverged in the Oligocene or early Miocene; New World monkeys had separated earlier (early Oligocene or late Eocene). The so-called Dryopithecines of the succeeding Miocene were undoubted hominoids. The traditional palaeontological view is that these Miocene apes gave rise in turn to three new lines, one leading to the gibbons, another to the great apes, the third to humans. However, on the basis of anatomical characteristics and genetic criteria, it has long been maintained that ancestors of both the gibbons and the orang-utan diverged from the ancestral line of the humans, gorillas, and chimpanzees at an early date and that only subsequently did that line split; recent palaeontological evidence now tends to support this second view. In some classifications the New World monkeys are placed in a suborder or infra-order (Platyrrhini) separate from that used for the Old World monkeys, apes, and humans (Catarrhini). The head is rounded, the neck mobile, the brain large with the cerebral hemispheres well developed, the olfactory region reduced, and the occipital and frontal regions enlarged. The face is hairless except for well-defined regions, the upper lip is entire, with no moist muzzle, and capable of extrusion. The face is mobile and used in expressing emotion. The orbits are forward-facing, the external ears small, their edges often rolled over, the lower incisors vertical. There is one pair of pectoral mammae. In all families except Callitrichidae all the digits bear flattened nails. The thumbs and big toes are opposable in some families. The tactile sense is highly developed. In many species social life is highly organized and based on sight rather than smell. Some species are arboreal, others ground-dwelling. Of some 230 species known, 180–90 survive to the present day.

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