- black-tailed marmoset Mico melanurus
- Paraguay ()
The most southerly marmoset is the black-tailed marmoset Mico melanurus. Whereas all other marmosets are confined to the Amazon rainforest, the distribution range of this particular species extends southwards from the south-central Amazon in Brazil through the Pantanal and eastern Bolivia to the Chaco in northern Paraguay. The Pantanal is a region encompassing the world's largest wetland area.
This species was originally an inhabitant of rainforests like other marmosets, but the proliferation of plantations has encouraged it to extend its range beyond its traditional location. The Chaco in particular, a hot and semi-arid region of the Rio de la Plata basin, is a very different environment from humid tropical rainforests, but this species has clearly adapted well because it is common and deemed to be of Least Concern by the IUCN.