THE EVOLUTION OF THE HORSE AND THE ELEPHANT
By Frederic Brewster Loomis
Professor of Geology, Amherst College
The horse and the elephant are so well known and their characteristic features are so striking that a study of the changes which have taken place in their ancestors to bring them to their present forms should be of general interest. The horse and his associates, unlike other animals, has on each foot only a single toe—the hoof—and the elephant is unique in possessing that wonderful organ, the trunk, which is adapted to so many uses. In our study of the evolution of these animals we shall have to turn to the geologist for the evidence, which consists of bones entombed in beds of sand and clay, most of them now hardened to rock, laid down in different parts of the world during what is called the Tertiary period (see the accompanying geologic time table) and part of the succeeding Quaternary period, in which we are now living. The order of succession of the animals whose forms are thus revealed must be determined by the order of the deposition of the beds in which the bones are found. In a series of such beds the one at the bottom was laid down first and the overlying beds were laid down in the order in which they appear, one above another. The bones found in these beds belonged to animals that lived and died about the time the beds were formed. Each bone found occupied a certain known position in the skeleton of the animal, had certain
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