monsters had legs, and they are usually figured as standing up on them; but it is very doubtful if they could have supported their weight in this way, out of water. Buoyed up by water or mud, they may have got along. Another noteworthy type we have figured is the Triceratops. There were also a number of great flesh-eaters who preyed upon these herbivores. Of these, Tyrannosaurus seems almost the last word in "frightfulness" among living things. Some species of this genus measured forty feet from snout to tail. Apparently it carried this vast body kangaroo fashion on its tail and hind legs. Probably it reared itself up. Some authorities even suppose that it leapt through the air. If so, it possessed muscles of a quite miraculous quality. A leaping elephant would be a far less astounding idea. Much more probably it waded half submerged in pursuit of the herbivorous river saurians.
§ 2
One special development of the dinosaurian type of reptile was a light, hopping, climbing group of creatures which developed a bat-like web between the fifth finger and the side of the body, which was used in gliding from tree to tree after the fashion of the flying squirrels. These bat-lizards were the Pterodactyls. They are often described as flying reptiles, and pictures are drawn of Mesozoic scenery in which they are seen soaring and swooping about. But their breastbone has no keel such as the breastbone of a bird has for the attachment of muscles strong enough for long-sustained flying. They must have flitted about like bats. They must have had a grotesque resemblance to heraldic dragons, and they played the part of bat-like birds in the Mesozoic jungles. But bird-like though they were, they were not birds nor the ancestors of birds. The structure of their wings was altogether different from that of birds. The structure of their wings was that of a hand with one long finger and a web; the wing of a bird is like an arm with feathers projecting from its hind edge. And these Pterodactyls had no feathers.
§ 3
Far less prevalent at this time were certain other truly bird-
