Page:Popular Science Monthly Volume 24.djvu/625

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607
THE ANCESTRY OF BIRDS.

Provençal summits some nameless calamity overtook him, from greedy kestrel or from native sportsman, and left him here, a sheer hulk, for the future contemplation of a wandering and lazy field-naturalist. Fit text, truly, for a sermon on the ancestry of birds; for this solid tail-bone of his tells more strangely than any other part of his whole anatomy the curious story of his evolution from some primitive lizard-like progenitor. Close by here, among the dry rosemary and large-leaved cistus by my side, a few weathered tips of naked basking limestone are peeping thirstily through the arid soil; and on one of these gray lichen-covered masses a motionless gray lizard sits sunning his limbs, in hue and spots just like the lichen itself, so that none but a sharp eye could detect his presence, or distinguish his little curling body from the jutting angles of the rock, to which it adapts itself with such marvelous accuracy. Only the restless sidelong glance from the quick upturned eye suffices to tell one that this is a living animal and not a piece of the lifeless stone on which it "rests like a shadow." A very snake the lizard looks in outline, with only a pair of sprawling fore-legs and a pair of sprawling hind-legs to distinguish him outwardly from his serpentine kin. Yet from some such lizard as this, my swallow and all other birds are ultimately descended; and from such a little creeping four-legged reptile science has to undertake the evolutionary pedigree of the powerful eagle or the broad-winged albatross.

Reptiles are at present a small and dying race. They have seen their best days. But in the great secondary age, as Tennyson graphically puts it, "A monstrous eft was of old the lord and master of earth." At the beginning of that time the mammals had not been developed at all; and even at its close they were but a feeble folk, represented only by weak creatures like the smaller pouched animals of Australia and Tasmania. Accordingly, during the secondary period, the reptiles had things everywhere pretty much their own way, ruling over the earth as absolutely as man and the mammals do now. Like all dominant types for the time being, they split up into many and various forms. In the sea, they became huge paddling enaliosaurians; on the dry land, they became great erect dinosaurians; in the air, they became terrible flying pterodactyls. For a vast epoch they inherited the earth; and then at last they began to fail, in competition with their own more developed descendants, the birds and mammals. One by one they died out before the face of the younger fauna, until at last only a few crocodiles and alligators, a few great snakes, and a few big turtles, remain among the wee skulking lizards and geckos to remind us of the enormous reptilian types that crowded the surface of the liassic oceans.

Long before the actual arrival of true birds upon the scene, however, sundry branches of the reptilian class had been gradually approximating to and foreshadowing the future flying things. Indeed, one