Radinsky L
Brain Behav Evol. 1981;18(4):169-87. doi: 10.1159/000121785.
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.
已知在近5500万年的时间跨度里，有27个已灭绝的南美洲有蹄类动物的脑腔模型。它们提供了两个主要进化趋势的证据，即相对脑容量增加和新皮层扩张，这两者在大约3500万年前都达到了高级水平。南美洲有蹄类动物的两大主要类群，即南方有蹄目动物和滑距骨目动物，其新皮层折叠的特征模式使它们彼此区分开来，也与全北区偶蹄目动物和奇蹄目动物的新皮层折叠特征模式不同。南美洲有蹄类动物的相对脑容量与北方有蹄类动物相当，北方有蹄类动物在大约3000万年前达到了现代水平，并且无论在当时还是现在都显示出很大的范围。
