Graells's tamarin, Leontocebus nigricollis graellsi, is a subspecies of the black-mantled tamarin from the northwestern Amazon in southeastern Colombia, eastern Ecuador and northeastern Peru. It differs from other black-mantled tamarins in having a dull olive-brown (no reddish-orange) lower back, rump and thighs.Rylands, Mittermeier, Coimbra-Filho, Heymann, de la Torre, Silva Jr., Kierulff, Noronha and Röhe (2008). Marmosets and Tamarins: Pocket Identification Guide. Conservation International. Defler, T. (2004). Primates of Colombia. Conservation International. However, molecular genetic analysis does not support treating Graell's tamarin as a separate species from the black-mantled tamarin.
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