Monkeys are primates that are indigenous to Africa Central America, and South America. Monkeys are classified into two subsections, New World Monkeys and Old World Monkeys. There are 264 known living species of monkeys throughout the world, and are generally considered to be among the most intelligent of mammals. Monkeys are very different from apes, most notably because monkeys have tails and apes do not.
A Brief History of Monkeys
About 40 million years ago, the Simiiformes infraorder split into Parvorders Platyrrhini (New World Monkeys in South America) and Catarrhini (Apes and Old World Monkeys in Africa). The individuals whose descendants would become Platyrrhini are currently conjectured to have migrated to South America either on a raft of vegetation or via a land bridge. There are two possible rafting routes, either across the Atlantic Ocean from Africa or across the Caribbean from North America. However, there is no fossil record to support the hypothesis of a migration from North America. The land bridge hypothesis relies on the existence of Atlantic Ocean ridges and a fall in the sea level in the Oligocene. This would have either produced a single land bridge or a series of mid-Atlantic islands to act as stepping stones for the migration.
At that time, the Isthmus of Panama had not yet formed. Also, ocean currents and climate were quite different, and the Atlantic Ocean was approximately only 1/3 of the width that it is today based on the current estimate of the Atlantic mid-ocean ridge formation processes spreading rate of 25mm per year.
New World Monkeys
New World monkeys are the five families of primates that are found in Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. They differ from other groupings of monkeys and primates, such as the Old World Monkeys and the apes.
New World Monkeys are small to mid-sized primates. New World Monkeys differ slightly from Old World Monkeys in several aspects. The most prominent distinction is the nose, which is the feature used most commonly to distinguish between the two groups. The scientific name for the New World Monkeys is Platyrrhini; which means “flat nosed”. The noses of New World Monkeys are flatter than the narrow noses of the Old World Monkeys, and have side-facing nostrils. New World Monkeys are the only monkeys with prehensile tails, which differs in comparison with the shorter, non-grasping tails of the Old World Monkeys.
Old World Monkeys
Old World Monkeys are a group of primates that are native to Africa and Asia today, and are also known from Europe in the fossil record. They inhabit a range of environments from the tropical rainforests to Savanna, as well as shrubland and mountainous terrain. Old World Monkeys include many of the most familiar species of nonhuman primates, such as Baboons and Macaques.
Old World Monkeys are medium to large sized primates. By superficial appearance, Old World Monkeys are unlike apes in that most have tails (the family name means “tailed ape”), and unlike the New World Monkeys (Platyrrhines) in that their tails are never prehensile. Technically, the distinction of Old World Monkeys from New World Monkeys depends on the structure of the nose, and the distinction of Old World Monkeys from apes depends on dentition (the number of teeth is the same in both, but they are shaped differently). In New World Monkeys, the nostrils face sideways, whilst in Old World Monkeys, they face downwards. Other distinctions include both a tubular ear bone, and eight (rather than twelve) premolars in Old World Monkeys.