Abstract
Currently, 15 species of Amazon marmosets (genus Mico) are known to science. The Amazon marmosets occur primarily in southern Brazilian Amazonia, the arc of deforestation, and are among the least studied primates of the neotropics. This is particularly the case for M. acariensis and M. chrysoleucos, both endemic to the Aripuanã-Sucundurí interfluve, south-central Amazonia. Mico acariensis was not studied beyond the species description, and the only information currently available is the pelage colouration of the holotype, inferred coordinates of the type locality, and a field report with two additional localities of occurrence. Regarding M. chrysoleucos, in addition to the species description, there are taxonomic reviews, the report of a second occurrence record, and a study on the species range. We provide here new occurrence records that extend the distribution of M. chrysoleucos; provide new records for and update the distribution of M. acariensis; and propose the existence of a hybrid zone in the Aripuanã-Sucundurí interfluve, i.e. around the known distribution boundaries of M. acariensis, M. chrysoleucos, and M. melanurus, and we also discuss habitat use patterns of Amazon marmosets.