An adaptive or evolutionary grade among the primates, represented by members of two of the three modern anthropoid superfamilies. The New World, platyrrhine monkeys (Ateloidea) and Old World, catarrhine forms (Cercopithecoidea) probably reached a monkey level of adaptation independently some time after their separation from a common ancestor, perhaps 40 million years ago. The term monkey is not indicative of taxonomic or phylogenetic relationship: the closest relatives of the cercopithecoids are not the ateloid monkeys but the Old World apes and humans.
The Ateloidea comprise two families, while the living Cercopithecoidea are today considered to comprise only one family, with two subfamilies. A modern classification of the Anthropoidea follows:
Hyporder Anthropoidea
Infraorder Platyrrhini
Superfamily Ateloidea (New World or platyrrhine monkeys)
Family Atelidae
Subfamily Atelinae (howler and spider monkeys)
Subfamily Pitheciinae (saki, owl, and titi monkeys)
Family Cebidae
Subfamily Cebinae (capuchin and squirrel monkeys)
Subfamily Callitrichinae (marmosets and tamarins)
Subfamily Branisellinae (extinct early ateloids)
Infraorder Catarrhini (Old World anthropoids)
Parvorder Eucatarrhini (modern catarrhines)
Superfamily Hominoidea (gibbons, great apes, and humans)
Superfamily Cercopithecoidea
Family Cercopithecidae (Old World or catarrhine monkeys)
Subfamily Cercopithecinae (cheek-pouched monkeys: macaques, baboons, guenons, and mangabeys)
Subfamily Colobinae (leaf eaters: langurs and colobus)
Subfamily Victoriapithecinae (extinct early cercopithecids)
Parvorder Eocatarrhini (archaic catarrhines)
Family Pliopithecidae (later archaic catarrhines)
Family Propliopithecidae (early archaic catarrhines)
Infraorder Paracatarrhini (extinct early anthropoids)
Family Parapithecidae (extinct Egyptian monkeys)
Family Oligopithecidae (extinct archaic anthropoids)
Monkeys are hard to characterize as a group because of their great diversity, and because much of the discussion reflects a comparison with the apes. Both monkeys and apes contrast with the prosimian grade in that they are typically large,
diurnal animals that live in social groups. Monkeys differ from apes in their possession of a tail, a smaller brain, quadrupedal pronograde
posture, and a usually longer face. They are generally smaller than apes, but large monkeys
outweigh gibbons. Like almost all primates, monkeys are
pentadactyl, with nails rather than claws on the digits in most cases. They have
pectoral mammary
glands and well-developed vision. Monkeys are primarily
vegetarian and inhabit forested tropical or
subtropical regions of Africa, Asia, and South America. The differences between the New and Old World monkeys are summarized in the table.
Major contrasts between New and Old World monkeys and special features of each Ateloidea (New World species) | Cercopithecoidea (Old World species) |
Nose platyrrhine (nasal septum wide, nostrils open to sides) | Nose catarrhine (septum narrow, nostrills open downward) |
Tail long, prehensile in atelines and Cebus only | Tail short to long, nonprehensile |
3 premolar teeth in each quadrant | 2 premolars in each quadrant |
24 deciduous, 36 permanent teeth (4 fewer in Callitrichinae), I 2/2C 1/1 P 3/3 M 3/3/(M 2/2 in Callitrichinae) | 20 deciduous, 32 permanent teeth, I 2/2 C 1/1 P 2/2 M 3/3 |
| Ischial callosities present |
Jaws and teeth lightly built in Cebidae; more robust in Atelidae, with deep lower jaw | Cheek pouches in Cercopithecinae |
Sacculated stomach in Colobinae | |
Fingers and toes with curved nails (clawlike in Callitrichinae) | All nails tend to be flattened |
Big toe opposable, thumb not fully so and sometimes reduced in Cebidae | Thumb and big toe opposable, thumb reduced in colobinae |
Old World species are found throughout all the warmer regions of the Eastern Hemisphere, except Australia and Madagascar. Many of the familiar monkeys are included in this family, such as the rhesus macaque, Barbary “ape”, mangabey, baboon, and mandrill.
The New World monkeys or ateloids occupy forested areas from southern Mexico to Argentina. They are divided into two main groups, or families (their major characteristics are given in the table). All are arboreal, including a few with prehensile tails; there is no living form, nor any evidence of a fossil form, that has come to the ground habitually. Familiar monkeys included in this group are marmosets, capuchins, titis, sakis and nakaris, howler monkeys, and spider and wool monkeys. See also Apes; Primates.