Old World vs. New World Monkeys: 7 Key Differences

The terms “Old World” and “New World” emerged after Christopher Columbus sailed the ocean blue in 1492 and came upon another world, with the former expression used to describe the continents of Africa, Asia, and Europe while the new discoveries of North and South America earned the latter moniker. In a biological context, the terms describe species only found in these geographic locations, but the differences extend far beyond geography, especially when it comes to primates.

Scientific Classification

The primate kingdom—composed of monkeys and apes—is incredibly diverse. Over the years, there have been plenty of revisions to their taxonomy (and there could be more changes as scientists learn more about them). And while Old World and New World monkeys share many characteristics, which their taxonomy reflects, they diverge taxonomically and there is good reason for this.

Old World monkeys (and apes) and New World monkeys belong to the same domain, kingdom, phylum, class, order, suborder, and infraorder. However, their differences beyond infraorder are significant enough to warrant a split. Old World monkeys fall under the parvorder Catarrhini, whereas New World monkeys belong to its sister parvorder, Platyrrhini.

Old World Monkeys

Old World monkeys belong to the family Cercopithecidae, which includes two subfamilies, Cercopithecinae (cercopithecines) and Colobinae (colobines). Between the two subfamilies are 24 genera and more than 130 recognized species. Old World monkeys include baboons, macaques, colobuses, langurs, and guenons, among others. These monkeys are also technically known as cercopithecoids. According to Frost, Rosenberger, and Hartwig, “Relative to other primate groups they are geographically widespread, taxonomically diverse, and ecologically flexible” (1).

New World Monkeys

New World monkeys comprise five families: Callitrichidae (marmosets and tamarins), Cebidae (capuchins and squirrel monkeys), Aotidae (night or owl monkeys), Pitheciidae (titis, sakis, and uakaris), and Atelidae (howler, spider, woolly spider, and woolly monkeys). Within these families are 19-21 genera and more than 150 species.

Old World Monkeys vs. New World Monkeys: 7 Key Differences

1. Geographic Location

An Old World monkey won’t be found in the New World, not unless it was transplanted from Africa, Asia, or Europe to the Americas, and vice versa. Today, nearly all extant Old World monkeys live in Africa and Asia; however, there is one notable exception living in Europe. The Barbary macaques of Gibraltar are the only wild monkey population in Europe, and it is believed that their distribution once extended throughout Europe.

As for their habitats, Old World monkeys can and do live in a wide variety of habitats, including tropical, temperate and swamp forests, woodlands, savannahs, deserts, and high altitudes in both Africa and Asia. While New World monkeys are found in the Americas, their range is limited to tropical and subtropical forests in southern Mexico and Central and South America.

2. Nose Shape

As previously mentioned, Old World and New World monkeys belong to the parvorders Catarrhini and Platyrrhini, respectively. This classification describes nose shape. The giveaway is rhin, from Ancient Greek meaning “nose” and from which English also gets the terms “rhinoplasty” (nose job) and “rhinoceros” (horn on the nose). Katà means “down” and platy “flat.” Therefore, catarrhine or Old World monkeys have downward- or forward-facing nostrils, whereas the nostrils on New World monkeys or platyrrhines face to the side and are flatter.

Additionally, New World monkeys’ noses tend to be shorter and do not have the moist rhinarium, the hairless area around the nostrils that helps with scent. They have a wide septum. These monkeys also rely heavily on their eyesight compared with their sense of smell to navigate their world. Old World monkeys, on the other hand, feature a narrow septum; that is, their nostrils are closer together.

3. Habitat

A world—neither old nor new—may be happening just above your head while on a walk in a tropical or subtropical forest in the Americas, as nearly all New World monkeys dwell in trees. These arboreal creatures reproduce, forage and eat, sleep, and socialize in the heavy foliage found in the New World. Their tree-dwelling also makes them harder to observe, so less is generally known about many New World monkey species.

In contrast, Old World monkeys are much easier to observe as many of them spend a lot more time on the ground. There are a few species of Old World monkeys that live in rainforests and climb trees, such as Angolan colobus monkeys, but many more live in savannahs and mountainous regions—places with few trees—thereby making these monkeys mostly terrestrial, although not exclusively so.

4. Tail Anatomy

Just about every species of primate (except those from the Hominidae family, i.e., apes, gorillas, chimpanzees, orangutans, gibbons, and bonobos) have tails. Function, however, distinguishes Old World and New World monkeys. The tails of New World monkeys function like a fifth hand. Their tails are prehensile, meaning they are used for “seizing or grasping especially by wrapping around.” Prehensile tails are a common feature found in arboreal (tree-living) animals.

In contrast, Old World monkey tails are not prehensile, are shorter, and cannot be used to grab anything. These monkeys spend much more time on the ground, so their lifestyle does not require such a design or adaptation.

5. Padded Buttocks

There must be a joke to be made in the fact that Old World monkeys have shorter tails and padded butts. All Old World monkeys have sitting pads or ischial callosities, thickened layers of tissue overlaying expansions of their hip bones. In other words, they worked their butt and/or tails (or part of them) off. The calloused skin protects their hip bones, providing their butts with a cushion for comfort.

In contrast, New World monkeys do not have ischial callosities, which makes for a quick and easy way to distinguish New World from Old World monkeys.

6. Thumbs

Like humans and other primates, Old World and New World monkeys have 10 fingers and 10 toes on their hands and feet, respectively. However, most Old World monkeys have opposable thumbs, which they can move freely and independently, and nails. Some species like colobus monkeys have reduced or absent thumbs. Old World monkeys generally have greater precision, strength, and dexterity in their hands and feet compared to their cousins in the New World (but not compared to humans).

Most New World monkeys do not have fully opposable thumbs, though some species (capuchins) have partially opposable thumbs. Their hands tend to be hook-shaped, and like their cousins across the ocean, they have nails. One notable exception are those New World monkeys from the Callitrichidae family, which includes marmosets and tamarins; they have claw-like nails on all their digits, except the big toe, which has a nail. The University of Edinburgh says this, “Their big toes are large and strongly opposable but their thumbs are imperfectly opposable and their fingers cannot grip well.” The hands of New World monkeys, compared to those of Old World monkeys, also have greater sensitivity to touch and textures.

7. Teeth

The dental arrangement among primates does not vary significantly. However, it varies slightly. Like humans and apes, Old World monkeys feature 32 teeth: eight incisors for biting off food, four canines for piercing and tearing, and eight premolars and 12 molars for grinding fibrous food. This arrangement, written 2/1/2/3 representing incisors, canines, premolars, and molars for one quadrant of the mouth, changes in New World monkeys.

New World monkeys’ dental arrangement is 2/1/3/3, meaning they have 36 teeth. However, there are exceptions. Pygmy marmosets have 32 teeth: 12 premolars and eight molars.

Summary of Differences