Science, Tech, Math › Animals & Nature Old World Monkeys Share Flipboard Email Print Photo © Anup Shah / Getty Images. Animals & Nature Mammals Amphibians Birds Habitat Profiles Reptiles Wildlife Conservation Insects Marine Life Forestry Dinosaurs Evolution View More By Laura Klappenbach Ecology Expert M.S., Applied Ecology, Indiana University Bloomington B.S., Biology and Chemistry, University of Illinois at Urbana-Champaign Laura Klappenbach, M.S., is a science writer specializing in ecology, biology, and wildlife. our editorial process Laura Klappenbach Updated January 17, 2020 Old World monkeys (Cercopithecidae) are a group of simians native to Old World regions including Africa, India, and Southeast Asia. There are 133 species of Old World monkeys. Members of this group include macaques, guenons, talapoins, lutungs, surilis, doucs, snub-nosed monkeys, probosci's monkey, and langurs. Old World monkeys are medium to large in size. Some species are arboreal while others are terrestrial. The largest of all Old World monkeys is the mandrill which can weigh as much as 110 pounds. The smallest Old World monkey is the talapoin which weighs about 3 pounds. Old World monkeys are generally stocky in build and have forelimbs that are in most species shorter than hind limbs. Their skull is heavily ridged and they have a long rostrum. Almost all species are active during the day (diurnal) and are varied in their social behaviors. Many Old World monkey species form small to medium-sized groups with complex social structures. The fur of Old World monkeys is often gray or brown in color although a few species have bright markings or more colorful fur. The texture of the fur is not silky nor is it woolly. The palms of the hands and soles of the feet in Old World monkeys are naked. One distinguishing characteristic of Old World monkeys is that most species have tails. This distinguishes them from the apes, who do not have tails. Unlike New World monkeys, the tails of Old World monkeys are not prehensile. There are a number of other characteristics that distinguish Old World monkeys from New World monkeys. Old World monkeys are comparatively larger than the New World monkeys. They have nostrils that are positioned close together and have a downward-facing nose. Old World monkeys have two premolars that have sharp cusps. They also have opposable thumbs (similar to the apes) and they have nails on all fingers and toes. New World monkeys have a flat nose (platyrrhine) and nostrils that are positioned far apart and open either side of the nose. They also have three premolars. New World monkeys have thumbs that are in line with their fingers and grip with a scissor-like motion. They do not have fingernails except for some species that have a nail on their largest toe. Reproduction Old World monkeys have a gestation period of between five and seven months. Young is well developed when they are born and females usually give birth to a single offspring. Old World monkeys reach sexual maturity at about five years of age. The sexes often look quite different (sexual dimorphism). Diet Most species of Old World monkeys are omnivores although plants form the larger portion of their diet. Some groups are almost entirely vegetarian, living on leaves, fruit, and flowers. Old World monkeys also eat insects, terrestrial snails, and small vertebrates. Classification Old World monkeys are a group of primates. There are two subgroups of Old World monkeys, the Cercopithecinae and the Colobinae. The Cercopithecinae include primarily African species, such as mandrills, baboons, white-eyelid mangabeys, crested mangabeys, macaques, guenons, and talapoins. The Colobinae include mostly Asian species (although the group does include a few African species as well) such as black and white colobuses, red colobuses, langurs, lutungs, surilis doucs, and snub-nosed monkeys. Members of the Cercopithecinae have cheek pouches (also known as buccal sacs) that are used to store food. Since their diet is quite varied, Cercopithecinae has non-specialized molars and large incisors. They have simple stomachs. Many species of Cercopithecinae are terrestrial, although a few are arboreal. The facial muscles in Cercopithecinae are well developed and facial expressions are used to communicate social behavior. Members of the Colobinae are folivorous and lack cheek pouches. They have complex stomachs.