Squirrel monkey, primate of the New World monkey family, Cebidae. They live in the rain forests in Central and South America. Small in size, no longer than 1 ft (30 cm), they weigh no more than 2 lb (0.9 kg). They use their dark-tipped tail for balance as they travel in large groups, single file behind a leader, on paths through the forest trees. Squirrel monkeys have white fur on their undersides and faces, dark facial features, and large eyes. Their fur color ranges from black to gray or reddish brown and olive green to yellow. They are used as laboratory animals and make good pets when kept with other squirrel monkeys.