Old World Monkeys range from Africa to Asia. They differ from the apes by having tails. They differ from the New World monkeys by having narrow, ridged noses with downward-facing nasal openings. All 156 species belong to one Family Cercopithicidae.
About half of the Old World Monkeys are called “cheek-pouched”, because they have expandable cheeks. These monkeys include guenons, macaques, vervet monkeys, mangabeys, baboons and mandrills. Most of this group lives in Africa, but macaques primarily live in Asia. Guenons and macaques represent the two most numerous types, having about 20 species each.
The other half of the Old World Monkeys are called “leaf-eating”. This group includes colobus monkeys, langurs, leaf monkeys and a few species collectively called “odd-nosed” monkeys (like the proboscis monkeys). Most of this group lives in Asia, but the 20 colobus monkeys are found primarily in Africa.