Brain evolution in extinct South American ungulates.

Endocasts of 27 genera of extinct South American ungulates are known from a time span of almost 55 million years. They provide evidence of two major evolutionary trends, increase in relative brain size and expansion of the neocortex, both of which reached advanced levels by about 35 million years ago. Characteristic patterns of neocortical folding distinguished brains of the two major groups of South American ungulates, the notoungulates and litopterns, from each other and from those of the Holarctic artiodactyls and perissodactyls. Relative brain size in the South American ungulates was comparable to that of the northern ungulates, which reached modern levels by about 30 million years ago, and which shows a wide range, both than and now.