WHEN THE WORLD WAS YOUNG 187
banks of Siberian rivers, the stupid, awkward animals should have been unable to place themselves in safety, and got swallowed up in the mud of the lake.
Then, too, but much later in date, the great pampas or plains of South America were the home of the ances≠tors of the Sloth tribeóMegatheria by nameóanimals eighteen feet in length, whose bones are found in the river deposits. As in all animals that can stand on their hind legs, the lower limbs and back were immensely strong, while the thick tail acted as ballast; the very thigh bone is three times as thick as that of an elephant. Like the modern Sloth, the Megatherium had no teeth in front, but it probably possessed a long and flexible tongue, which it used to curl round branches of trees and tear them down. It was also able to dig its sharp, powerful claws into the trunk of a tree, and with a mighty heave of its body to loosen the roots, and by repeating this process three or four times the tree would fall to the ground, and the particular morsel on which the Megatherium had set its heart would be within its reach.
Further back still we find that birds and mammals have not yet come into being, but, instead, their places are taken by a strange kind of flying reptile, whose wings were more like those of a bat than a bird, and often measured twenty-five feet. The name of Pterodactyl has been given to this extraordinary creature, which resembles some of the queer fancies men used to carve on churches rather than anything we ever see now. The pterodactyl had teeth, but no feathers, and could swim as well as fly. As to its food, we guess from its teeth that it lived chiefly upon fish, though it may sometimes have swooped down, when flying, on little animals, or even have pecked at fruit.
But besides the pterodactyls, there existed at the same period, which has been called the Age of the Eeptiles, vast swarms of creatures whose forms seemed to be made up of a large number of other species. In many ways