62 EVOLUTION OF LIFE. 
The Reptiles of the present day include, Ist, the Lacer- 
tilia (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 Prote- 
rosaurus—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 Prote- 
rosaurus 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 fore- 
runner 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 
Sepide (Fig. 68), among the Lacertilia, leading to the 
Anguidz (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 Iguano- 
don 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 
