What is the difference between New World monkeys and Old World monkeys? New World monkeys (Platyrrhini) live in Central and South America and have wide, flat noses with sideways-facing nostrils. Old World monkeys (superfamily Cercopithecoidea, which sits inside the Catarrhini) live in Africa and Asia and have narrow noses with nostrils that point downwards. Only some New World monkeys have a prehensile tail, and among monkeys only Old World monkeys have hard sitting pads called ischial callosities.
New World monkeys vs Old World monkeys at a glance
Scientists sort monkeys into two big groups, named after where they live. The New World means the Americas. The Old World means Africa and Asia (and, thanks to one famous colony of Barbary macaques, a corner of Europe at Gibraltar). The two groups split from a shared ancestor roughly 40 million years ago, and they have been evolving separately ever since.
The formal names are worth knowing for exams. New World monkeys belong to the parvorder Platyrrhini, which means “flat-nosed”. Old World monkeys belong to the superfamily Cercopithecoidea, which sits inside the parvorder Catarrhini, meaning “downward-nosed”. The catarrhines also include the apes, which we come back to later.
The two picture cards above show five familiar members of each group. Below, the table sets out every major difference side by side, and the rest of the article explains each one.
The big comparison table: Platyrrhini vs Catarrhini
| Feature | New World monkeys (Platyrrhini) | Old World monkeys (Catarrhini) |
|---|---|---|
| Where they live | Central and South America (southern Mexico to northern Argentina) | Africa and Asia, plus Gibraltar in Europe |
| Nose | Flat, wide septum, nostrils face sideways | Narrow septum, nostrils close together and face downwards |
| Dental formula (one side of each jaw) | 2.1.3.3 (36 teeth); marmosets and tamarins 2.1.3.2 (32 teeth) | 2.1.2.3 (32 teeth) |
| Premolars | 12 in total | 8 in total |
| Tail | Present in all; prehensile in the howler, spider, woolly and woolly spider monkeys, and semi-prehensile in capuchins | Present, short or long, or tiny; never prehensile |
| Ischial callosities (hard sitting pads) | Absent | Present |
| Cheek pouches | Absent | Present in the subfamily Cercopithecinae (baboons, macaques, guenons); absent in leaf-eating colobines |
| Colour vision | Mostly variable: males dichromatic, some females trichromatic; howler monkeys are generally trichromatic | Routinely trichromatic (all individuals) |
| Size | Pygmy marmoset about 100–140 g up to southern muriqui about 12–15 kg | Talapoin about 0.7–1.3 kg up to male mandrill about 30 kg or more |
| Nocturnal species | Yes: night monkeys (Aotus) | No |
| Number of families | Five: Callitrichidae, Cebidae, Aotidae, Pitheciidae, Atelidae | One family, Cercopithecidae, with two subfamilies |
| Related to humans? | More distantly | More closely (apes and humans are also catarrhines) |
Eight quick clues to tell them apart
Wildlife photos rarely show teeth or colour vision, so here are the clues you can actually use when you meet a monkey, in order of how easy they are to spot.
- Where is it? A monkey in a rainforest in Peru is a New World monkey. A monkey in Kenya, India or Japan is an Old World monkey. Location settles almost every case in the wild.
- Is the tail gripping? A tail that curls round a branch like a hand belongs to a New World monkey. No Old World monkey has one.
- What does the nose look like? A broad, flat nose with outward-facing nostrils is New World.
- Is there a bare, brightly coloured patch on the rump? That is an ischial callosity, so the monkey is an Old World monkey. Baboons and mandrills show theirs clearly.
- Is it tiny and clawed? Marmosets and tamarins are small New World monkeys with claw-like nails.
- Is it active at night with huge eyes? Only the night monkey of Central and South America does this.
- Is it a heavy, ground-walking monkey? Baboons, mandrills and drills are Old World monkeys. No New World monkey spends its life on the ground like them.
- Does it have no tail at all? Then it is probably not a monkey. Apes such as gorillas and chimpanzees are tailless.
Flip cards: New World or Old World?
Try the cards below. Read the clue on the front, decide which group it points to, then tap to check.
New World monkeys: the five families
New World monkeys are found from southern Mexico to northern Argentina, in rainforest, dry forest, savanna edges and mountain forest. They are all tree-dwellers, and there are well over 100 species. They are sorted into five families: Callitrichidae, Cebidae, Aotidae, Pitheciidae and Atelidae. For a close look at the species of the Amazon basin in particular, see our guide to monkeys in the Amazon rainforest.
| Family | Examples | What makes it special |
|---|---|---|
| Callitrichidae | Marmosets, tamarins | Smallest monkeys; claw-like nails; usually give birth to twins |
| Cebidae | Capuchins, squirrel monkeys | Omnivores; capuchins use tools; capuchin tail semi-prehensile |
| Aotidae | Night (owl) monkeys | Large eyes; the only mainly nocturnal monkeys |
| Pitheciidae | Titis, sakis, uakaris | Strong teeth for cracking hard seeds; tails not prehensile |
| Atelidae | Howler, spider, woolly and woolly spider (muriqui) monkeys | Fully prehensile tails; the largest New World monkeys |
Callitrichidae: marmosets and tamarins
This is the family of the tiny monkeys. The pygmy marmoset is about 12–15 cm long (head and body) and weighs roughly 100–140 g, which makes it the smallest monkey in the world. Instead of flat nails, most callitrichids have sharp claws, which let them cling to tree trunks like squirrels and feed on sap and gum. Callitrichids are also the only primate group that regularly gives birth to twins, which make up more than 80% of births in the species studied.
Callitrichids also differ in their teeth: they have two molars per side instead of three, giving a dental formula of 2.1.3.2 and a total of 32 teeth.
The emperor tamarin is named for its long white moustache. The cotton-top tamarin of Colombia is listed as Critically Endangered by the IUCN, mainly because its forest has been cleared.
Cebidae: capuchins and squirrel monkeys
Cebidae today means the capuchins (genera Cebus and Sapajus) and the squirrel monkeys (Saimiri), about 29 species in all. They are omnivores that eat mostly fruit and insects. Bearded capuchins in Brazil crack nuts with stone hammers and anvils, which is among the best-known examples of tool use in a wild monkey. The capuchin tail is semi-prehensile: it can help to hold on, but it cannot support the monkey’s weight like a spider monkey’s.
Aotidae: night monkeys
The night monkey, or owl monkey, is the one monkey that is mainly active in the dark. Its large eyes gather as much light as possible. Researchers have found that some populations are cathemeral, meaning active by both day and night, so “nocturnal” is the best general description rather than an absolute rule.
Pitheciidae: titis, sakis and uakaris
Pitheciidae are known for hard-seed feeding. Sakis and uakaris have strong teeth that crack open the tough shells of unripe fruit and seeds, which many other animals cannot eat. The bald uakari has a startling bright red face and a short tail. Titi monkeys are smaller, with soft, thick fur, and are often seen sitting close together.
Atelidae: howler, spider, woolly and woolly spider monkeys
Atelidae is a small family of just four genera and 26 species, but it includes the largest New World monkeys and the champions of the prehensile tail. The tail is long and strong, and the underside of its tip is almost hairless, with a ridged, sensitive pad like a fingertip. Atelids use it as a fifth limb to hang, grasp fruit and cross gaps in the canopy.
Howler monkeys eat mainly leaves, and are famous for being among the loudest land animals: their roars can carry up to about 4.8 km through the forest. A howler weighs roughly 7–10 kg. The southern muriqui, or woolly spider monkey, is the largest New World monkey at about 12–15 kg.
The prehensile tail: only some New World monkeys
A common mistake is to say that “New World monkeys have prehensile tails”. In fact, only some do. Marmosets, tamarins, titis, sakis, uakaris and night monkeys all have ordinary tails that are used for balance, not for gripping. The fully prehensile tails belong to the Atelidae, and capuchins have a semi-prehensile one. That is why the exam-friendly wording is “prehensile tail in some New World families, in no Old World monkey”.
Colour vision: trichromacy and the howler monkey
Humans have trichromatic colour vision: three kinds of cone cell, tuned to blue, green and red-ish light. Having three lets us separate reds from greens. Animals with just two kinds of cone are dichromats, and see the world a bit like a red-green colour-blind person.
Most New World monkeys have a variable system. The gene for the green–red pigment sits at a single spot on the X chromosome, and different versions of it exist in the same species. Males have only one X chromosome, so in most species every male is a dichromat (night monkeys have a single pigment and are monochromats, and male howlers are trichromats). Females have two X chromosomes. A female who inherits two different versions is a trichromat, while one who inherits two identical versions is a dichromat. So within a troop, some females see in three colours and everyone else sees in two.
Howler monkeys are the exception. They are generally regarded as routine trichromats, because their pigment genes are arranged like those of Old World monkeys, so males and females alike see three colours. Scientists have suggested that this helps them spot young, reddish leaves, which are more nutritious. A 2013 study of wild howlers found some hybrid pigment genes, so the picture is not completely settled.
Reveal question: colour vision
Why can a female marmoset see three colours when her brother cannot? (3 marks)
The green–red pigment gene lies on the X chromosome and has several versions. A male has one X chromosome, so he has only one version and two types of cone. A female has two X chromosomes. If they carry different versions, she has three types of cone and is trichromatic.
Size and habitat of New World monkeys
New World monkeys range from 120 g to about 15 kg, so none is as heavy as the biggest baboons and mandrills. They live almost entirely in trees, from the Amazon canopy to cloud forest in the Andes foothills. Counts of genera and species vary with the taxonomy used (a listing of the genera gives about 22), so treat any single species count as approximate. For a wider look at how mammals are grouped, see our overview of families of mammals.
Old World monkeys: the family Cercopithecidae
All Old World monkeys belong to a single family, Cercopithecidae. It is the largest primate family, with roughly 130–140 species in 22–24 genera (the exact numbers depend on the taxonomy). They live across sub-Saharan Africa and in central, southern and eastern Asia, including most of Japan, plus the northwest corner of Africa and Gibraltar. Fossils show that Old World monkeys once also lived across much of Europe.
The family has two subfamilies, and the difference between them is mostly about food:
| Subfamily | Diet | Cheek pouches? | Stomach | Examples |
|---|---|---|---|---|
| Cercopithecinae | Omnivorous (fruit, seeds, insects, more) | Yes | Simple | Baboons, macaques, mandrills, drills, guenons, vervets, talapoins, geladas |
| Colobinae | Mostly leaves | No | Complex, for digesting leaves | Colobus monkeys, langurs, douc langurs, proboscis monkey |
Cercopithecinae: baboons, macaques and relatives
The baboons (genus Papio) are big, mainly ground-living monkeys of African savanna. They walk on all four limbs. The macaques are the most widespread group of non-human primates: they live from Gibraltar (the Barbary macaque) to Japan (the Japanese macaque). Mandrills and drills are forest monkeys of west-central Africa, and the largest of all monkeys. A male mandrill is about 70 cm long and commonly weighs around 30 kg, and the heaviest reports are near 50 kg. The drill is listed as Endangered by the IUCN.
At the small end of the family are the guenons, vervets and talapoins. The Angolan talapoin is the smallest Old World monkey: it is 34–37 cm long and weighs 0.7–1.3 kg, so even the smallest Old World monkey is far heavier than a pygmy marmoset.
Colobinae: leaf-eating monkeys
Colobines are specialist leaf eaters. Their stomach has several chambers where bacteria help to break down tough leaves, a bit like the stomach of a cow, and they lack cheek pouches. The colobus monkeys are African. The langurs, douc langurs and proboscis monkey are Asian. Some taxonomists put the odd-nosed monkeys such as the proboscis monkey and the doucs in their own group within Colobinae.
The mantled guereza is listed as Least Concern, while the red-shanked douc of Vietnam, Laos and Cambodia is listed as Critically Endangered.
Ischial callosities: the sitting pads
An ischial callosity is a patch of thick, hairless, toughened skin over the sitting bones at the rear of the pelvis (the ischia). Old World monkeys have them and New World monkeys do not. The pads work like built-in seat cushions, and they let a monkey sit upright for a long time on a slender branch or a rock, out of reach of predators. In baboons, geladas and mandrills the skin around the pads can be bright pink or red, which is why the rump of the drill above is so noticeable.
Cheek pouches: a built-in snack bag
Cheek pouches are stretchy pockets inside the cheeks. A cercopithecine such as a baboon or macaque can stuff food into them quickly while feeding in the open, then chew it later somewhere safe. Colobines, which eat leaves rather than grabbing food in a hurry, do not have them. New World monkeys do not have them either. It is a neat example of an adaptation linked to diet and to risk of competition from other animals (see our article on adaptations in plants and animals).
Teeth: 2.1.3.3 vs 2.1.2.3
A dental formula lists the incisors, canines, premolars and molars in one quarter of the mouth (one side of the upper or lower jaw). Multiply by four to get the total.
New World: 2.1.3.3 → 2 + 1 + 3 + 3 = 9 per quarter → 36 teeth
Old World: 2.1.2.3 → 2 + 1 + 2 + 3 = 8 per quarter → 32 teeth
The only difference is the premolars: New World monkeys have three in each quarter (12 in total) and catarrhines have two (8 in total). Our own teeth follow the Old World pattern, 2.1.2.3, so a human adult has 32 teeth. Marmosets and tamarins, which have only two molars in each quarter, are the exception in the New World with a total of 32.
How many teeth does a spider monkey have, and how many does a baboon have? (2 marks)
A spider monkey is a New World monkey with the formula 2.1.3.3, so it has 4 × (2 + 1 + 3 + 3) = 36 teeth. A baboon is an Old World monkey with 2.1.2.3, so it has 4 × (2 + 1 + 2 + 3) = 32 teeth.
Apes are catarrhines, but they are not monkeys
This is the part that confuses many students. The Catarrhini include the Old World monkeys and the apes: gibbons, orangutans, gorillas, chimpanzees, bonobos and humans. So apes are catarrhines, with the same narrow nose and 2.1.2.3 teeth, but they are not monkeys. The easiest test is the tail: apes have no tail at all, while almost every monkey has one (the Barbary macaque is a tailless exception).
Apes and Old World monkeys split from a shared ancestor roughly 25 million years ago. That makes Old World monkeys our closer relatives than New World monkeys, although we are still very distant cousins. If you are curious how an ape compares with a human, read humans vs apes: who would win in a fight?
Evolution: how did monkeys reach South America?
New World monkeys are a puzzle. The oldest known fossil monkeys of the Americas look like African relatives, yet the Atlantic Ocean lay between the two continents even then. The leading explanation is that their ancestors rafted across the Atlantic from Africa on floating mats of vegetation, torn from river banks during storms, at some point around 35–40 million years ago.
- Molecular clocks (DNA comparisons) put the split between New World and Old World lineages at about 40 million years ago, with estimates ranging from roughly 35 to 44 million years ago.
- Fossils from Santa Rosa in the Peruvian Amazon include Perupithecus, estimated at about 36 million years old, the oldest known stem New World monkey (later zircon dating of the Santa Rosa site suggests it may be younger, nearer 30 million years). Its age is based on rodent fossils found with it, rather than a radiometric date.
- A later find, Ucayalipithecus, is not a New World monkey at all but a parapithecid, a group otherwise known from Afro-Arabia, so it records a second, separate crossing. Computer models suggest its ancestors crossed between about 35 and 32 million years ago, around the time that sea level fell sharply near the Eocene–Oligocene boundary.
- Distance: Africa and South America were closer than they are now. A source landmass was probably about 1,500–2,000 km away from South America.
The exact route is still debated, so scientists describe rafting as the best-supported idea rather than a proven fact. After arriving, the survivors spread through South and Central America and evolved into the five families we see today. For a look at what happens when a monkey’s colouring goes wrong, see our guide to albino monkeys.
In the Old World, apes and monkeys went on to diverge from each other around 25 million years ago, and Old World monkeys spread across Africa and Asia. For how monkeys fit within the wider tree of life, see the five groups of vertebrates.
Sorting challenge: tick the Old World monkey traits
Below are twelve statements about monkeys. Tick only the ones that are true of Old World monkeys (Catarrhini), then open the answer to check. Your ticks are remembered in your browser.
- Nostrils point downwards and sit close together
- Dental formula 2.1.3.3
- Prehensile tail used as a fifth limb
- Ischial callosities (hard sitting pads)
- Found in Africa and Asia
- Flat nose with sideways-facing nostrils
- Some have cheek pouches
- All individuals are trichromatic
- Includes the night monkey
- Dental formula 2.1.2.3
- Includes marmosets and tamarins
- Includes baboons, macaques and colobus monkeys
Show the answer
Old World traits: downward-pointing nostrils close together; ischial callosities; found in Africa and Asia; some have cheek pouches; all individuals trichromatic; dental formula 2.1.2.3; includes baboons, macaques and colobus monkeys. New World traits (do not tick): dental formula 2.1.3.3, prehensile tail, flat nose with sideways nostrils, night monkey, marmosets and tamarins.
Reveal questions: check your understanding
Explain why a monkey with a prehensile tail must be a New World monkey. (2 marks)
No Old World monkey has a prehensile tail. Fully prehensile tails evolved only in the New World family Atelidae (howler, spider, woolly and woolly spider monkeys), and capuchins have a semi-prehensile tail.
Why are apes catarrhines but not monkeys? (2 marks)
Apes share the narrow downward-facing nose and 2.1.2.3 teeth of the Catarrhini, and they descend from the same ancestors as Old World monkeys. But apes have no tail, whereas almost all monkeys have one, so they are placed in a separate group, Hominoidea.
Describe how New World monkeys may have reached South America. (3 marks)
Their African ancestors probably rafted across the Atlantic on floating vegetation, roughly 35–40 million years ago. The oldest fossils, such as Perupithecus from Peru, were estimated at about 36 million years old (some later dating suggests younger). The exact route is still debated.
Give one adaptation of a colobus monkey that suits a diet of leaves. (1 mark)
A complex, multi-chambered stomach in which bacteria help break down tough leaves. Colobines also lack cheek pouches.
Frequently asked questions about New World and Old World monkeys
What is the main difference between New World and Old World monkeys?
The simplest difference is geography: New World monkeys live in the Americas and Old World monkeys live in Africa and Asia. They also differ in their noses (flat with sideways nostrils, or narrow with downward ones), teeth (2.1.3.3 or 2.1.2.3), and tails.
Do all New World monkeys have prehensile tails?
No. Fully prehensile tails are found only in the Atelidae, which are the howler, spider, woolly and woolly spider monkeys. Capuchins have a semi-prehensile tail. Marmosets, tamarins, night monkeys, titis, sakis and uakaris have tails used for balance only.
What are ischial callosities?
Ischial callosities are hard, hairless pads of skin over the sitting bones. They let Old World monkeys sit upright on branches or rocks for long periods. New World monkeys do not have them, and neither do humans.
Why do Old World monkeys have cheek pouches?
Cheek pouches in the Cercopithecinae, such as baboons and macaques, let a monkey quickly store food and eat it later in a safer place. Leaf-eating colobines do not have them. New World monkeys also lack them.
Are apes monkeys?
Apes are not monkeys. Gorillas, chimpanzees, orangutans, gibbons and humans are apes in the Catarrhini and have no tail. Almost all monkeys have a tail; a few, such as the Barbary macaque, are tailless. Apes and Old World monkeys are closer relatives than New World monkeys.
What is the dental formula of New World and Old World monkeys?
Most New World monkeys have 2.1.3.3, which means 36 teeth. Marmosets and tamarins have 2.1.3.2, which means 32 teeth. Old World monkeys, apes and humans have 2.1.2.3, which means 32 teeth.
Can New World monkeys see colour?
Yes, but in a variable way. In most species males are dichromats and see fewer colours (night monkeys see in only one colour). Some females are trichromats and see three colours. Howler monkeys are generally regarded as trichromatic, like Old World monkeys.
How did monkeys get to South America?
The best-supported idea is that their African ancestors rafted across the Atlantic on floating vegetation around 35–40 million years ago. The oldest fossil monkeys in South America, from Peru, were estimated at about 36 million years old, though the dating is debated. The route is still debated.
Which is bigger, a New World monkey or an Old World monkey?
The biggest Old World monkeys are bigger. A male mandrill commonly weighs about 30 kg, while the largest New World monkey, the southern muriqui, weighs about 12–15 kg. The smallest monkey, the pygmy marmoset, is a New World monkey weighing around 100–140 g.
Are there New World monkeys in Africa or Old World monkeys in the Americas?
Not naturally. Introduced populations exist, for example vervet monkeys in the Caribbean, rhesus macaques in Puerto Rico and Florida, and squirrel monkeys in Florida, but none is native. New World monkeys live only in Central and South America. Old World monkeys live in Africa and Asia, plus a small population of Barbary macaques at Gibraltar in Europe. Old World monkeys are not native to the Americas.
