Monkey

A monkey is any member of either the New World monkeys or Old World monkeys, two of the three groupings of simian primates, the third group being the apes. The New World monkeys are classified within the parvorder Platyrrhini, whereas the Old World monkeys (superfamily Cercopithecoidea) form part of the parvorder Catarrhini, which also includes the apes. Thus, scientifically speaking, monkeys do not form a "natural group", in that the Old World monkeys are actually more closely related to the apes than they are to the New World species. There are 264 known extant species of monkey. Because of their similarity to monkeys, apes such as chimpanzees and gibbons are often called monkeys in informal usage, though biologists don't consider them to be monkeys. Conversely, due to its size (up to 1 metre) the Mandrill is often thought to be an ape, but it is actually an Old World monkey. Also, a few monkey species have the word "ape" in their common name. Because they are not a single coherent group, monkeys do not have any particular traits that they all share and are not shared with the remaining group of simians, the apes.

Monkeys range in size from the Pygmy Marmoset, at 14-16 cm (5-6 inch) long (plus tail) and 120-140 g (4-5 oz) in weight, to the male Mandrill, almost 1 metre (3 ft) long and weighing 35 kg (75 lb). Some are arboreal (living in trees), some live on the savannah; diets differ among the various species but may contain any of the following: fruit, leaves, seeds, nuts, flowers, insects, spiders, eggs and small animals.

Some characteristics are shared among the groups; most New World monkeys have prehensile tails while most Old World monkeys have non-prehensile tails. Some have trichromatic colour vision like that of humans, others are dichromats or monochromats. 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. In order to understand the monkeys, it is necessary to study the characteristics of the different groups individually.

According to the Oxford English Dictionary, the word "monkey" may originate in a German version of the Big Virgina fable, published circa 1580. In this version of the fable, a character named Moneke is the son of Martin the Ape. The word Moneke may have been derived from the Italian monna, which means "a female ape". The name Moneke likely persisted over time due to the popularity of Reynard the Fox.

Macaques in Kam Shan Country Park of Hong KongThe following lists shows where the various monkey families (bolded) are placed in the Primate classification. Note that the smallest grouping that contains them all is the Simiiformes, the simians, which also contains the apes. Calling apes "monkeys" is incorrect. Calling either a simian is correct.