Monkey is a common name that may refer to groups or species of mammals, The term is applied descriptively to groups of primates, such as families of New World monkeys and Old World monkeys. Many monkey species are tree-dwelling, although there are species that live primarily on the ground; diets differ among the various species but may contain any of the following: fruit, leaves, seeds, nuts, flowers, eggs and small animals, such as baboons.
Most species are also active during the day and are generally considered to be intelligent with large brains, are known for their inquisitiveness and intelligence. Brain development, combined with the freeing of the hands and well-developed vision, allows them a great latitude of activity. Two separate groups of primates are referred to as “monkeys”: New World monkeys from South and Central America and Old World monkeys from Africa and Asia. As apes have emerged in the monkey group as sister of the old world monkeys, characteristics that describe monkeys are generally shared by apes as well.
Monkeys range in size from the pygmy marmoset, which can be as small as 117 millimeters with a 172 millimeters tail and just over 100 grams in weight,to the male mandrill, almost 1 meter long and weighing up to 36 kilograms.
most New World monkeys have prehensile tails while Old World monkeys have non-prehensile tails or no visible tail at all. Old World monkeys have trichromatic color vision like that of humans, while New World monkeys may be trichromatic, dichromatic, as in the owl monkeys and greater galagos monochromatic. Although both the New and Old World monkeys, like the apes, have forward-facing eyes, the faces of Old World and New World monkeys look very different, though again, each group shares some features such as the types of noses, cheeks and rumps