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a family of American monkeys. Unlike other monkeys, the Callithricidae have clawlike nails on all their digits except the big toe of the hind legs. Their fur is thick and silky, and there are tufts on the ears. The tail is usually very hairy. The body measures 13–37 cm long and the tail, 15–42 cm. The Callithricidae weigh anywhere from 70 to 1,000 g. Their coloring varies, but the colors black and white predominate. Unlike other monkeys, the Callithricidae have two large molars (instead of three) on each side of the upper and lower jaw. They are the most primitive of the modern-day monkeys. There are four genera comprising 33 species. They are distributed in northern South America and in Central America. The Callithricidae inhabit tropical forests and are very agile and quick. When moving among the branches they often use their tails as a counterbalance. Females give birth to one to three young (other monkeys, one or two). The best-known are the marmosets, the tamarins, and the lion-headed marmosets.