The order Primates encompasses a remarkable array of life forms, characterized by traits like grasping hands, large brains, and complex social structures. Within this diverse biological group, the term “monkey” refers to a large and varied collection of species, which are broadly separated based on their geographical origin and distinct physical characteristics. Exploring the different types of monkeys means examining the two major evolutionary branches that have adapted to vastly different continents and environments.
Setting the Boundaries: What Qualifies as a Monkey?
The term “monkey” describes members of the infraorder Simiiformes that are not apes. Monkeys, along with apes and humans, belong to the suborder Haplorhini, often called the “dry-nosed” primates. A key difference separating monkeys from their closest relatives, the apes (Hominoids), is the presence of a tail in almost all monkey species, which apes completely lack.
Monkeys are also generally smaller than apes, exhibit a more quadrupedal form of locomotion, and have a narrower chest and shoulder structure better suited for moving on all four limbs. They are distinguished from the more primitive primates, the Prosimians (Strepsirrhines), by their greater reliance on sight over smell and their larger brain-to-body size ratio. This collective group of tailed, non-ape simians is officially divided into two main parvorders based on where they evolved: the New World and Old World monkeys.
New World Monkeys: Characteristics and Groups
The New World Monkeys, or Platyrrhini, are found exclusively in the tropical regions of Central and South America. Their parvorder name, Platyrrhini, translates to “flat-nosed,” referring to their wide-set nostrils separated by a broad septum that point sideways. This group also possesses a unique dental structure compared to their Old World relatives, typically featuring three premolar teeth in each quadrant of the jaw.
Many New World species are famed for their prehensile tails, a specialized appendage that can grasp objects and serve as a “fifth limb” for climbing and balance. The Marmosets and Tamarins (Callitrichidae) are among the smallest primates and have claws on all digits except the big toe, an adaptation for gouging tree bark to access gum. They also stand out for their reproductive strategy, frequently giving birth to twins, a rarity among other primates.
The Capuchins and Squirrel Monkeys (Cebidae) are known for their relatively large brains and high intelligence, with Capuchins specifically demonstrating complex tool use in the wild. The Howler, Spider, and Woolly Monkeys (Atelidae) are generally larger and frequently use their strong prehensile tail for suspension. Howler monkeys are further distinguished by an enlarged hyoid bone in the throat, which allows them to produce incredibly loud, resonant vocalizations that travel long distances through the dense forest canopy.
Old World Monkeys: Characteristics and Groups
The Old World Monkeys belong to the family Cercopithecidae and are native to Africa and Asia. They are part of the parvorder Catarrhini, meaning “downward-nosed,” characterized by narrow nostrils that face downward, much like apes and humans. Unlike their New World counterparts, Old World monkeys possess only two premolar teeth per jaw quadrant, totaling 32 teeth.
A consistent feature of this group is the absence of a prehensile tail; while most species have a tail, it is non-grasping and used primarily for balance. Many Old World monkeys have specialized patches of hardened skin on their buttocks called ischial callosities, which provide a cushion for sitting comfortably for extended periods. The family is divided into two major subfamilies, each with distinct dietary and anatomical specializations.
Cercopithecinae
The Cercopithecinae subfamily includes species like Macaques, Baboons, and Guenons, and is characterized by the presence of cheek pouches used to store food while foraging. Baboons are a notable example, often being highly terrestrial and exhibiting pronounced sexual dimorphism, with males significantly larger than females.
Colobinae
The second subfamily, the Colobinae (Colobus monkeys and Langurs), lacks cheek pouches but possesses complex, multi-chambered stomachs. This specialized digestive system allows them to break down the cellulose in large quantities of leaves, which form the bulk of their diet.