Monkeys are a diverse group of primates, distinguished from apes and prosimians by physical traits like having tails and typically smaller body sizes. The term “monkey” is a broad classification that covers a wide variety of species across multiple continents. Pinpointing a single, fixed count for the number of different kinds of monkeys is complicated due to ongoing discoveries and the fluid nature of biological classification. However, the current scientific understanding offers a clear picture of the variety within this primate lineage.
The Definitive Answer: Counting the Species
The question of how many kinds of monkeys exist usually refers to the number of recognized species, a number that has steadily increased with modern genetic analysis and field research. Currently, the collective count of all extant monkey species sits approximately between 260 and 340. This range reflects the continuous process of reclassification, where scientists sometimes “split” a single, widely distributed species into several distinct ones after finding significant genetic differences. Detailed counts often place the total number of monkey species at around 330 or more, divided between the two major global groups. Monkeys constitute the largest portion of the primate order in terms of species diversity.
The Major Divide: Old World vs. New World
The classification of all monkeys is determined by a major evolutionary separation that occurred roughly 30 to 40 million years ago. This ancient divergence established two distinct groups, known as the Catarrhines and the Platyrrhines, based on their geographical isolation and subsequent evolutionary paths. The Catarrhines are commonly referred to as the Old World monkeys, and they are native to Africa and Asia. In contrast, the Platyrrhines are the New World monkeys, exclusively inhabiting the tropical regions of Central and South America. This geographical split represents the primary framework for understanding the anatomical differences between the two groups. The names themselves, derived from Greek, describe the most noticeable physical distinction.
Characteristics of New World Monkeys
New World monkeys (Platyrrhines) are characterized by traits adapted to their purely arboreal lives in the American rainforests. Their scientific name, meaning “flat-nosed,” refers to their nostrils that are widely spaced and open to the side. Many species, such as spider and howler monkeys, possess a unique physical adaptation: a prehensile tail. This specialized tail is muscular, highly flexible, and can be used like a fifth limb for grasping branches and supporting their body weight while navigating the canopy. A further distinguishing feature is their dental structure, which typically includes three premolar teeth in each quadrant of the jaw, resulting in a dental formula of 2.1.3.3. New World monkeys include diverse families like the marmosets, tamarins, capuchins, and squirrel monkeys.
Characteristics of Old World Monkeys
Old World monkeys (Catarrhines) possess physical features distinct from New World groups. Their name, meaning “downward-nosed,” describes their narrow nostrils that face downward. None of the Old World species have a prehensile tail; while a tail may be long, it is never capable of grasping or supporting weight. A shared characteristic across nearly all Old World monkeys is the presence of ischial callosities. These are tough, hairless patches of skin on their buttocks that allow them to sit comfortably on rough branches or the ground for extended periods. Their dental formula is 2.1.2.3, featuring only two premolar teeth per quadrant, which is a key difference from the New World species. Examples include the terrestrial baboons and mandrills, as well as the more arboreal macaques and colobus monkeys.