Evolution / by Patrick Geddes and J. Arthur Thomson.

  • Patrick Geddes
Date:
[1911?]
Catalogue details

Licence: Public Domain Mark

Credit: Evolution / by Patrick Geddes and J. Arthur Thomson. Source: Wellcome Collection.

    30/264 (page 26)
    Also in the Eocene there was Protorohippus, with four toes in front and three behind, the side ones behind touching the ground. It seems to have been about fourteen inches high, and the evolution of speed had begun. During the Eocene times North America was in great part forest-clad, but “ the moist climate gave rise to many streams and lakes, along the shores of which grew sedgy meadows that in turn gave rise to grassy plains. These were the conditions under which the horses made their first appearance, and the increasing development of grass lands gave the initial trend to their evolution.” Somewhat later, in the Oligocene, Meso- hippus makes its appearance, the hind-foot with three toes as before, but the fore-foot with the little toe reduced to a splint, so that only three remain, the side ones just touching the ground. The middle or third toe is now much larger than the side toes, which no longer bear much of the weight of the animal, save on marshy ground. The grinding teeth have become more complex. One of the species of Mesohippus was about the size of a sheep, and one of the treasures in the Yale Museum that brings the past very vividly back to us is the nearly perfect skull of its new-born foal. Of the physical conditions of the Oli-