Endocranial casts of 12 genera of extinctcanids, covering a time span of 30 million years, and of all living canid genera provide information on brain evolution in that carnivoran family. The oldest canid brains had only suprasylvian and coronolateral sulci, a widely exposed cerebellum with a straight posterior vermis, a high rhinal fissure and a strikingly undeveloped frontal lobe. By 25 million years ago, ectosylvian, ectolateral and presylvian sulci had appeared, and by about 12 million years ago, a Sylvian sulcus had developed, expansion of the temporal lobe and of orbital and sigmoid gyri was noticeable, and lobule VII of the cerebellar vermis had enlarged and twisted in the line leading to modern canids. Ansate, postcruciate and cruciate sulci developed along with the expansion of the sigmoid gyri. Canid brains 15–30 million years old average slightly smaller relative to body size than do modern canid brains, while later fossil canid brains are about the same relative size as modern ones. Modern canid brains are relatively uniform in external morphology, differing mainly in the relative size of the prorean gyru