Page:Evolution of Life (Henry Cadwalader Chapman, 1873).djvu/86

62 The Reptiles of the present day include, 1st, the Lacertilia (Monitors, Chameleons, Wall-lizards); 2d, the Ophidia (Snakes); 3d, the Crocodilia (Crocodile, Alligator); 4th, the Chelonia (Turtles); and numerous extinct forms. As the reptiles that live at the present day are but a small portion left of those that have once lived, and as these extinct forms are not always entirely preserved, and from the nature of petrifaction very little of their soft parts can be known except from analogy, naturally the ancestors of the reptilian class have not been positively determined. Premising that the tree of the Reptiles, like all other such trees, is only a provisional one, the following line of descent is offered with diffidence. As long ago as 1710 the Proterosaurus—which, when translated, means "first lizard"—was described by Spener, a physician of Berlin. Since that time other reptiles, allied to Proterosaurus, have been discovered, as Belodon, Paleosaurus, etc., which have been classed together as Thecodonts. The skeleton of Proterosaurus resembles most closely, among living reptiles, that of the Varanus, the large African lizard; but among the Thecodonts have been found also scales of a crocodilian nature, so that the Thecodont group seems to be the forerunner in the Proterosaurus of the lizards and crocodiles, while the Paleosaurus and Belodon are the first of a series leading to the Dinosauria. The Snakes are probably an offshoot of the Lizard, to which they are closely allied; the Sepidae (Fig. 68), among the Lacertilia, leading to the Anguidae (Fig. 67) among the Snakes. The Anemodonts, of which the Pterodactyle is a remarkable representative, lead to the Turtles through forms like Rhynchosaurus. The Dinosauria were represented by huge reptiles like Iguanodon and Hadrosaurus, of which some were more than thirty feet long. They are very interesting on account of their affinities to birds. The different orders of Reptiles seem to have branched off from a common stock represented by Thecodont forms, which are allied to the Salamanders among the Batrachia. Until some better theory of the origin of Reptiles is offered, this one will be provisionally accepted.