The smallest species of monkey is the pygmy marmoset (Cebuella pygmaea). Also known as the dwarf monkey, the pygmy marmoset is native to the rainforests of the Amazon basin in South America, including Brazil, Peru, Colombia, and Ecuador. Adult pygmy marmosets measure about 5.5 to 6.3 inches (14 to 16 centimeters) in body length, with a tail length of about 7 to 8 inches (18 to 20 centimeters). They weigh only around 3 to 5 ounces (85 to 140 grams).
These tiny primates have distinctive features, including large ears, sharp claws, and specialized teeth for feeding on gum exudates from trees. They are highly social animals that live in family groups and communicate through a variety of vocalizations, body postures, and scent marking. Despite their small size, pygmy marmosets are active and agile, capable of leaping between trees with great dexterity.