The marmosets are a group of New World monkeys. There are 22 marmoset species in four genera. All are in the biological family Callitrichidae. The term marmoset is also used in reference to the Goeldi's marmoset, Callimico goeldii, which is closely related.
Most marmosets are about 20 centimetres (8 in) long. Compared to other monkeys, they have some primitive features. They have claws rather than nails, they lack wisdom teeth, and their brain layout seems to be relatively primitive. Their body temperature is unusually variable, changing by up to 4 °C (7 °F) in a day. Marmosets are native to South America and have been found in Bolivia, Brazil, Colombia, Ecuador, Paraguay and Peru. They have also been spotted in Central America.
Marmosets are highly active, living in the upper canopy of forest trees, and feeding on insects, fruit and leaves. They have long lower incisors, which allow them to chew holes in tree trunks and branches to harvest the gum inside; some species are specialised feeders on gum.
Marmosets live in family groups of three to 15. There are one or two breeding females, an unrelated male, offspring and other family members and unrelated individuals. Their mating systems are highly variable and include monogamy, polygyny and occasionally polyandry.
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