Monkeys look somewhat like apes such as chimpanzees, orangutans, and gorillas. But monkeys differ from apes in several ways. For instance, every monkey has a tail, even if it is just a tiny nub. Apes do not have tails. Monkeys also generally have narrower chests than apes do.
There are about 200 species, or types, of monkey. Scientists divide them into two groups, Old World monkeys and New World monkeys. Old World monkeys include baboons, drills, mandrills, macaques, guenons, langurs, and colobus monkeys. Among the New World monkeys are marmosets, tamarins, howler monkeys, spider monkeys, squirrel monkeys, woolly monkeys, and capuchins. Monkeys vary greatly in size. The pygmy marmoset is only about 6 inches (14 centimeters) long, not including the tail. The largest baboons may grow to 45 inches (115 centimeters) in length.
On the whole, Old World monkeys are larger than New World monkeys. Old World monkeys also have narrower noses than New World monkeys do. New World monkeys usually have long tails. Some kinds even use their tails to hold onto branches. By contrast, some Old World monkeys have only short stubs for tails.
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