The Roosmalens' dwarf marmoset, also known as the black-crowned dwarf marmoset, is a small New World monkey native to the Amazon rainforest, on the east bank of the lower Madeira River, and the west bank of the Aripuanã River, in Brazil. It has the smallest distribution of any primate in Amazonia. This marmoset has several unique attributes, which has resulted in it sometimes being placed in the monotypic genus Callibella. However, genetic analysis has subsequently resulted in its being classified within the genus Mico.