Pygoscelis contains species with a fairly simple black-and-white head pattern; their distribution is intermediate, centered on Antarctic coasts but extending somewhat northwards from there. In external morphology, these apparently still resemble the common ancestor of the Spheniscinae, as Aptenodytes' autapomorphies are in most cases fairly pronounced adaptations related to that genus' extreme habitat conditions. As the former genus, Pygoscelis seems to have diverged during the Bartonian[8], but the range expansion and radiation which led to the present-day diversity probably did not occur until much later, around the Burdigalian stage of the Early Miocene, roughly 20-15 mya (Baker et al. 2006).