Callicebus discolor is the species of titi monkey about which there is always much confusion. People often believe that this is the white-browed species commonly seen in southern Colombia, Ecuador and Peru. However, according to the original description and the type specimens, the species has no white band on the forehead!
Callicebus discolor was described in 1848 Isodore Geoffroy Saint-Hilaire and Émille Deville from animals collected in Peru. The species was described as having the ” pelage speckled grey above and on the outer side of the arms and thighs; grey-whitish on the front of the head; a vivid red-brown on the underside and almost the entire limbs. Tail ashy-grey, with the tip of the hairs white. Related, but different on several characteristics, especially the colour of the forehead and a shape of the inferior mandible, to a species of the same region that we include, not without doubts, to C. cupreus“.
From this description one could indeed conclude that the species has a white band on the forehead. However, in 1851 Geoffroy Saint-Hilaire published a more extensive description of his species, with a coloured plate. The plate leaves no doubt that this species is a junior synonym of Callicebus cupreus. The specimens mentioned by Geoffroy Saint-Hilaire, collected in 1847 by Castelnau and Deville along the Amazon River (Peru and Brazil) and Sarayacu at the Ucayali River (Peru) are still present in the collection of the National Natural History Museum of Paris. None of them has a white band on the forehead.
If the white-browed titi monkeys in southern Colombia, Ecuador and Peru are not Callicebus discolor, how should we name them? Assuming that all these animals belong to the same species, the first available name would be Callicebus leucometopus (Cabrera, 1900). I will therefore sum up all information on the white-browed titi monkeys, whatever name they were given, under Callicebus leucometopus.