Fig. 147.—Restoration of Rhamphorhyncus Bucklandi. Jurassic of England.—After Phillips.
a, One of the teeth. Natural size.
Perhaps the most extraordinary of all the Mesozoic modifications of the reptilian type was that of the flying reptiles, or Pterodactyls. These were, in short, lizards modified for flight, somewhat in the same manner with the bats among the mammals. If the bat may be likened to a flying shrew-mouse, a Pterodactyl may in like manner be compared to a flying lizard; but the modification in the latter case is by much the more remarkable, inasmuch as the lizard is a cold-blooded animal, and far less likely to be endowed with the active circulation and muscular power necessary to flight than is the mouse. In point of fact, there can be no doubt that the Pterodactyls must have been provided with some approach to a mammalian or ornithic heart, as they certainly were with great breast-muscles attached to a keel in the breast-bone for working their large membranous wings. These wings were also somewhat original in their construction. They were not furnished with pinions, like those of the bird, but with a membrane like that of the bat, and this, instead of being stretched over four enormously lengthened fingers, as in that quadruped, was supported on a single elongated finger, corresponding, singularly enough, to the little finger, which usually inconspicuous member constituted in some of these strange creatures a limb longer than the whole body ([Figs. 146, 147].) The other fingers of the hand were left free for walking or grasping. They are thus believed to have been able to walk as well as to fly, and even in case of need, to swim; while they could probably perch like birds on rocks and trees. Their heads, though very lightly framed, were large and reptilian in aspect, and furnished with sharp teeth, and sometimes probably with a beak as well. Few creatures of the old world are of more hideous and sinister aspect. Yet some of them must have been as light and graceful on the wing as swallows or sea-gulls. There are many species, most of them small, but some of those in the later Mesozoic attained to so great a size that the expanse of their wings must have exceeded twenty feet, making them veritable flying dragons, probably formidable to all the smaller animals of their time. Though these animals were strictly reptiles, they combined in their structures contrivances for aërial locomotion now distributed between the bats and the birds. They had bat-like wings and bird-like chests. Some had horny beaks. All had hollow limb bones, and air cavities to give lightness to the skull. Their brains approach to those of birds, and, as already stated, their respiration and circulation must have been of a high order. These facts are very suggestive, and perhaps in no point is the imagination or the faith of the devout evolutionist more severely tested than in realising the spontaneous assumption of these characters by reptiles, and their subsequent distribution between the very dissimilar types in which they are now continued.
Fig. 148.—A Jurassic Bird (Archæopteryx macroura).—After Owen.
