Hyperbrachycephaly is characterised by the skull width reaching at least 85.5 percent of the skull breadth. The highest population means ever measured reach values close to 90 (e.g. in Sumo of Central America). On the individual level, ultrabrachycephaly may appear with a cephalic index of at least 91. In evolutionary terms, such round skulls are a relatively recent phenomenon in humans. It seems to appear in different climate zones, e.g. in Europe among French Alpines, Montenegrin Dinarics, and Scandinavian Saami, in the Central Asian steppes among some Turkic people, and Armenoids of Turkey and the Caucasus. In tropical regions, hyperbrachycephals are found in Lao and Thai of the plains as well as Central Americans (Sumo, Paya, Cuna, Totonachi...). In North America, hyperbrachycephals have been identified in Pueblids (e.g. Mohave) as well as Pacifids (e.g. Chilcotin). They may also have been typical for some extinct Patagonians.