Atrato River
This species of white-headed tamarin is thought to have diverged from the other Amazonian forms such as "S. leucopus". This is supported by morphological considerations of the transition from juvenile to adulthood, during which the fur coloration patterns change. significantly and are similar between the two species. Hershkovitz proposed that the separation of the two species happened in the Pleistocene at the height of the Atrato River, where it intersected the Cauca-Magdalena. At that time, the area was covered by a sea, which created a geographic barrier that caused the species to diverge through the process of allopatric speciation. Today, the two species are principally separated by the Atrato River.