Marmosets are some of the smallest monkeys in the world! The pygmy marmoset (Callithrix pygmaea) hold the title as smallest true monkey in the world. (The smallest primate is the pygmy mouse lemur.)
Adults are about 5 inches long with an 8 inch tail and weigh only 4-7 ounces! They live in groups of two to nine individuals, usually a breeding pair and offspring. The monogamy found in pygmy marmosets is pretty unique among primates. They are found in central South America and are active in the trees during the day.
Dominant females will produce fraternal twins after about 4.5 months of gestation. After birth, the young are usually carried by the male or other juveniles in the group and return to the mother for nursing. Pygmy marmosets reach maturity after about 1.5 years and can live up to 12 years in the wild and 20 years in zoos.
Pygmy marmosets face danger from habitat loss as well as the pet trade, even though monkeys do not make good pets, even these tiny guys.