The _Jurassic_ period showed a continuance of the reptilian splendour. They radiated in many directions, becoming adapted to many haunts. Thus there were many Fish Lizards paddling in the seas, many types of terrestrial dragons stalking about on land, many swiftly gliding alligator-like forms, and the Flying Dragons which began in the Triassic attained to remarkable success and variety. Their wing was formed by the extension of a great fold of skin on the enormously elongated outermost finger, and they varied from the size of a sparrow to a spread of over five feet. A soldering of the dorsal vertebrae as in our Flying Birds was an adaptation to striking the air with some force, but as there is not more than a slight keel, if any, on the breast-bone, it is unlikely that they could fly far. For we know from our modern birds that the power of flight may be to some extent gauged from the degree of development of the keel, which is simply a great ridge for the better insertion of the muscles of flight. It is absent, of course, in the Running Birds, like the ostrich, and it has degenerated in an interesting way in the burrowing parrot (_Stringops_) and a few other birds that have "gone back." The First Known Bird But the Jurassic is particularly memorable because its strata have yielded two fine specimens of the first known bird, _Archaeopteryx_. These were entombed in the deposits which formed the fine-grained lithographic stones of Bavaria, and practically every bone in the body is preserved except the breast-bone. Even the feathers have left their marks with distinctness. This oldest known bird--too far advanced to be the first bird--was about the size of a crow and was probably of arboreal habits. Of great interest are its reptilian features, so pronounced that one cannot evade the evolutionist suggestion. It had teeth in both jaws, which no modern bird has; it had a long lizard-like tail, which no modern bird has; it had claws on three fingers, and a sort of half-made wing. That is to say, it does not show, what all modern birds show, a fusion of half the wrist-bones with the whole of the palm-bones, the well-known carpo-metacarpus bone which forms a basis for the longest pinions. In many reptiles, such as Crocodiles, there are peculiar bones running across the abdomen beneath the skin, the so-called "abdominal ribs," and it seems an eloquent detail to find these represented in _Archaeopteryx_, the earliest known bird. No modern bird shows any trace of them. [Illustration: SKELETON OF AN EXTINCT FLIGHTLESS TOOTHED BIRD, HESPERORNIS (_After Marsh._) The bird was five or six feet high, something like a swimming ostrich, with a very powerful leg but only a vestige of a wing. There were sharp teeth in a groove. The modern divers come nearest to this ancient type.] [Illustration: SIX STAGES IN THE EVOLUTION OF THE HORSE, SHOWING GRADUAL INCREASE IN SIZE (_After Lull and Matthew._)