The black tamarin (Saguinus niger) or western black-handed tamarin, is a species of tamarin endemic to Brazil. Taxonomy Based on mitochondrial DNA analysis, black tamarins were found to be more closely related to populations on the same side of the Tocantins River than on the other, showing that the river constitutes an effective gene flow barrier. As a consequence of the genetic divergence, as well as minor differences in pelage color, some recent authorities have argued for recognizing the population east of the Tocantins River as S. ursulus (eastern black-handed tamarin), leaving the "true" S. niger for the population west of this river. The closest living relative of the black tamarin is thought to be the golden-handed tamarin (S. midas). Description Black-handed tamarins are among the smallest primates, weighing approximately 500 grams. As with other tamarins, the hind limbs are longer than the forelimbs and the thumbs are not opposable. With the exception of the big toe, there are claws on all fingers and toes, as well as two molars on each side of the jaw. The face of the black tamarin is generally hairless. The fur is blackish-brown with lighter markings on the back, similar to the golden-handed tamarin but without the golden-orange feet and hands of that species. Distribution and habitat The geographic range of black-handed tamarins, which are endemic to Pará, Brazil, is limited by the Rio Amazonas (Amazon River) to the North, the Rio Tocantins (Tocantins River) to the East, the Rio Xingu (Xingu River) to the West, and until recently, the Rio Gradaus (Gradaus River) to the South. Photographic evidence of a black-handed tamarin in Confresa, a town in the northeastern region of the state of Mato Grosso, indicates an increase in the species' geographic range to the South. Some marmosets occupy small areas of forest in the Tapajós and Madeira Basins, but the black-handed tamarin is absent from these regions due to lack of food resources. However, this species is considered to be more tolerant of habitat disturbances than other Callitrichides. Black-handed tamarins are arboreal primates that prefer semi-deciduous forest for ease of foraging and thick growth as cover from aerial and terrestrial predators. Due to deforestation in eastern Brazil, black-handed tamarins regularly rely on fragmented and disturbed secondary forest habitats. Although much of the forest canopy has been destroyed, and black-handed tamarins have been seen moving through all levels of the forest, they