The black-tailed marmoset (Mico melanurus) is a species of New World monkey from central South America, where ranging from the south-central Amazon in Brazil, south through the Pantanal and eastern Bolivia, to the Chaco in far northern Paraguay. It is the southernmost member of the genus Mico and the only where most of its range is outside the Amazon. The diet of the black-tailed marmoset predominantly consists of tree sap. To a lesser extent, they also eat bird eggs, fruits, insects, and small vertebrates.