40 A Short History of The World That unusual growth of brain which is the central fact of Cainozoic times marks a new communication and interdependence of individuals. It foresliadows the development of human societies of which we shall soon be telling. As the Cainozoic Period unrolled, the resemblance of its flora and fauna to the plants and animals that inhabit the world to-day in- creased. The l^ig elums^• Uintatheres and Titanotheres, Ijig clumsy "~^> 'mm' "w^wsgwaas .,/,'. ///.. .1/.*. COMPARATIVE SIZES OF BRAINS OF THE LIVING RHINOCEROS AND OF THE DINOCERAS. AN EARLY CAINOZOIC PREDECESSOR OF THE RHINOCEROS (showing the mental advance, even in the ca^c of *uch a stupid type as the rhinoceros) lu-utes like nothing li^'iIlg, disappeared. On the other hand a series of forms led up by steady degrees from grotesque and clumsy predecessors to the giraffes, camels, horses, elephants, deer, dogs and lions and tigers of the existing world. The evolution of the horse is particularly legible upon the geological record. We have a fairly complete series of ffirms froni a small tapir-like ancestor in the early Cainozoic. Another line of development that has now been pieced together with some precision is that of the llamas and camels.
