The black-tailed marmoset (Mico melanurus) was first described by É. Geoffroy in Humboldt, 1812. He provided a brief description of the species but only noted Brazil as the type locality. Alien (1916, in Vivo, 1991) later determined the type locality to be Cuiabá, in the state of Mato Grosso. Mico melanurus was considered part of the group Callithrix argentata sensu Hershkovitz (1977) and Vivo (1988, 1991), and associated with the bareeared marmosets Mico saterei and M. acariensis. Diagnostic characters include pigmented ears and ear-surfaces, an absence of ear tufts, white or yellowish-white spots on the upper thighs, and a completely black tail (Vivo, 1991). Vivo (1991) noted color variations among the different individuals collected. Specimens from Cárceres, Palmeiras, Rio Aricád, Santo Antônio do Leverger, Chapada dos Guimarães, Aripuanã and Água Dulce (Chaco-Paraguay) were very similar, with brown torsos and anterior limbs, while those collected in Corumbá and a specimen from the Rio Paraguay were noticeably lighter.

The black-tailed marmoset has an ample geographic range, extending from the headwaters of the Rios Madeira, Mamoré and Guaporé, to the Rios Aripuanã and Juruena (van Roosmalen et al., 2000). Prior to this study, the species was only known to occur in Bolivia, Paraguay and the states of Mato Grosso and Mato Grosso do Sul in Brazil. Fonseca et al. (1994) predicted that the northernmost limit of the species' range would probably occur in the area between the Rios Aripuanã and Juruena, near the Serra do Sucundurí or the headwaters of the Rio Sucundurí at 8°S, in the Brazilian state of Amazonas.

Figure 1.

Geographic range of Mico melanurus, based on Vivo (1991) and records from this study: (1) N. Chiquitos, Rio Quiser, Santa Cruz, Bolivia; (2) Aripuanã, Mato Grosso, Brazil; (3) Cáceres, Mato Grosso; (4) Chapada dos Guimarães, Mato Grosso; (5) Rio Aricá, Mato Grosso; (6) Santo Antônio do Leverger, Mato Grosso; (7) Palmeiras, Mato Grosso; (8) Corumbá, Mato Grosso do Sul; (9) Urucum, Mato Grosso do Sul; (10) 48 km E de Água Dulce, Chaco, Paraguay; (11) Floresta Estadual do Sucundurí, right bank of the Rio Sucundurí, Amazonas, Brazil (08°34'S, 59°08'W); and (12) Parque Estadual do Sucundurí, right bank of the Rio Bararati, Amazonas (08°21'S, 58°37'W).

During a recent (June and July, 2006) primate survey of the Aripuanã-Juruena interfluve in the state of Amazonas, we observed the brown form of Mico melanurus in both terra firme and campinarana forests at two locations near the Serra do Sucundurí. At the first site, three groups were spotted on the right bank of the Rio Sucundurí in the Floresta Estadual do Sucundurí (08°34'S, 59°08'W). A specimen was collected and deposited in the vertebrate collection of the National Institute of Amazonian Research (INPA- lote 2002). At the second site, a troop was seen on the right bank of the Rio Bararati, a left bank tributary of the Rio Tapajós, in the Parque Estadual do Sucundurí (08°21'S, 58°37'W). These new records confirm the northern limit of the species' range proposed by Fonseca et al. (1994) (Fig. 1.), and if predicted geographic ranges for the species M. acariensis (van Roosmalen et al., 2000) and M. mauesi are correct, indicate possible contact zones with these species further north, on the left and right banks of the Rio Sucundurí, respectively.