Baboons are closer kin to you than to South American monkeys
Old World monkeys split from the ancestors of apes, including us, between 25 and 30 million years ago. Their shared lineage parted from New World monkeys far earlier, some 45 to 55 million years back. Strictly by family tree, apes are simply a branch of monkeys.
The family Cercopithecidae is the largest among primates, with 24 genera and 139 recognised species, from baboons and macaques to colobus monkeys, mandrills, geladas and the proboscis monkey. All living members share a common ancestor about 14 million years old. They live today across Africa and Asia, in rainforest, savanna, scrub and mountains, and once ranged widely through Europe.
Size varies enormously. The Angolan talapoin, smallest of the group, measures 34 to 37 centimetres in head and body and weighs 0.7 to 1.3 kilograms. The male mandrill, largest of all, reaches around 70 centimetres and up to 50 kilograms, with females much smaller. Faces range from long-snouted to flat-nosed, often brightly coloured. Some, like colobus monkeys, live in trees, while baboons live on the ground.
A few anatomical clues separate the groups. The family name means tailed ape, and most species do have tails, but unlike those of New World monkeys they cannot grip. Old World monkeys and apes share downward-facing nostrils, where New World monkeys' nostrils face sideways, and both carry eight premolars rather than twelve. Monkey and ape teeth are equal in number but differ in shape. Two subfamilies exist: the mostly African Cercopithecinae, which include the Asian and North African macaques, and the Colobinae, covering most Asian genera plus Africa's colobus monkeys.
Because apes emerged within the same branch, any consistent definition of monkey ends up including apes. Under one broad reading, even New World monkeys arose from Old World ancestors that somehow reached the Americas around 40 million years ago. In the wild, most species eat mainly plants, especially fruit, but they are opportunists, taking flowers, leaves, bulbs, insects, snails, small mammals and, near people, rubbish and handouts.
Source: Old World monkey
