Later on the horse developed in America, growing larger till it was first as big as a collie-dog, with signs of being more adapted for speed. It then had four toes on its foot. It continued, though very gradually, to grow larger, and even more gradually its unnecessary toes grew fewer and fewer till at last they disappeared.
At length appeared the horse which had only one toe. This type, that of the modern horse, first becomes known in the Upper Pliocene beds of Europe, and represents the culmination of the race. The completeness of the record of the evolution of the horse tells us something of the enormous numbers of ancestral forms which must have existed in the more than two million years that have elapsed since the first diminutive horse appeared in North America. While not strongly given to migration, in the course of time these animals wandered over the entire world, with the exception of such inaccessible places as Australia and the Oceanic Islands.... It would seem that the original stock was of Eurasian derivation, though the great theatre of the evolutionary drama was soon transferred to North America, the Eurasian, African, and South American horses which appear from time to time being in all probability of North American origin. The ultimate fate of the horses in both North and South America was extinction, all wild horses of our own time, including the asses and zebras, being confined to Asia and Africa. The apparently wild bands of the American western plains, and those which roam over the pampas of South America, are the descendants of domestic horses that have escaped from human bondage, largely from the early Spanish explorers.
The rhinoceroses of to-day, the one-horned Indian variety and the two-horned African rhinoceros, were preceded by a whole regiment of rhinoceroses in the Tertiary period. One such was dug out in Fleet Street during the excavation for the _Daily Chronicle_ office. This rhinoceros had a hairy coat like the Mammoth which lived much later, and in Siberia is found sometimes side by side with the later quadruped. Many of the extinct rhinoceroses had two horns like the African square-mouthed rhinoceros, which is sometimes misleadingly called the white rhinoceros. One great extinct beast, the _Elasmotherium_, allied to them, had a great horn carried on a huge boss in the middle of its head instead of on the nose, while another still huger animal called the _Titanotherium_ and found in North America had a pair of horns perched on either side of its nose. As large as the rhinoceros but having a very different arrangement of the bones of its ankles and wrists and very different teeth and horns are the extraordinary creatures known as _Dinoceras_, whole skeletons of which have been disinterred from the Eocene strata of Wyoming in the United States by Professor Marsh. These creatures had three pairs of horns on the top of the head and a pair of great tusks as well. Nearly all these animals, though they were more brainy than the reptiles, had much smaller brains in proportion to their size than the bulk of the animals which now roam the earth, from which we may surmise that though a small brain suffices to guide a great animal machine in established ways, yet in order to learn new things in its lifetime an animal must have a big brain.