Page:Popular Science Monthly Volume 22.djvu/765

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PROGRESS OF THE BACKBONED FAMILY.

types—tortoises, lizards, crocodiles, and snakes—should have managed to find room to live among the myriads of warm-blooded animals which have filled the earth. These four groups have made a good fight of it, and many of them even make use of warm-blooded animals as food. The tortoises, it is true, feed upon plants, except those that live in fresh water, and feed chiefly on fish, snakes, and frogs, while most of the lizards are insect-feeders. But the crocodile, as he lurks near the river's edge, and the snake, when he fastens his glittering eye on a mouse or bird, are both on the lookout for animals higher in the world than themselves.

We come now into quite a new life, for we are going to wander among the conquerors of the air, who have learned to rise far beyond our solid ground, and to soar, like the lark, into the clouds, or, like the eagle, to sail over the topmost crags of the mountains, there to build his solitary eyrie.

In those far by-gone times, when the huge land-lizards browsed upon the trees, the birds living among them were much more like them in many ways than they are now. Of water-birds there were some about the size of small gulls, which flew with strong wings and had fan-shaped tails, but had teeth in their horny jaws, set in sockets like those of the crocodile, while their backbones had joints like those of fishes rather than birds; and with them were other and wingless birds rather larger than our swans, but more like swimming, fish-eating ostriches.

In these and many other points the early birds came very near to the reptiles—not to the flying ones, but to those which walked on the land. And now, perhaps you will ask, Did reptiles, then, turn into birds? No, since they were both living at the same time, and those reptiles which flew did so like bats, and not in any way like the birds which were their companions. To explain the facts, we must go much further back than this. If any one were to ask us whether the Australian colonists came from the white Americans or the Americans from the Australians, we should answer, "Neither the one nor the other, and yet they are related, for both have sprung from the English race." In the same way, when we see how like the ancient birds and reptiles were to each other, so that it is very difficult to say which were bird-like reptiles and which were reptile-like birds, we can only conclude that they, too, once branched off from some older race which had that bone between the jaws, that single neck-joint, and the other characters which birds and reptiles have in common.

But where have the feathers come from—those wonderful, beautiful appendages without which the bird could not fly? They are growths of his skin, of the same nature as the scales of reptiles, or those on the bird's own feet and legs; and on some low birds, such as the penguins, they are so stiff and scale-like that it is often difficult to say where the scales end and the feathers begin. All feathers, even