274 



VERTEBRATE ANIMALS. 



EXTINCT ORDERS OF REPTILES. 



Order Y. Ichthtopterygia. 



In this order are included a number of gigantic fish-like Reptiles, which are 

 all extinct, and are characteristic of the Secondary period of geology, and 

 especially of the formation known as the Lias. The chief characters by which 

 they are distinguished have reference to their purely aquatic life, for there can 

 be no doiibt that they were inhabitants of the sea. Thus the body was fish- 

 like, without any distinct neck. The vertebree were hollow at both ends 

 {amphiccelous), and the spine thus possessed the flexibility and power of motion 

 so characteristic of the true Fishes. The limbs also constituted powerful swim- 

 ming-paddles, and it is probable that there was a vertical tail-fin. 



Much has been gathered from various sources as to the habits of the Ichthy- 

 osauri, and their history is one of the most interesting chapters iu the geo- 

 logical record. That they chiefly kept to open seas may be inferred from their 



Fig. 198.— Skull oi Ichthyosaurus, sho-wiiig the sclerotic plates. 



strong and well-developed swimming apparatus ; but the presence of a powerful 

 bony arch supporting the fore-limbs proves that they must occasionally have 

 betaken themselves to the land. That they were tenants of stormy waters, or 

 were in the habit of diving in search of prey, has been inferred from the fact 

 that the eyeball is protected from pressure by a ring of bony plates. That 

 they possessed great powers of vision, especially in the dusk, seems to be 

 rendered certain from the size of the pupil and the enormous width of the 

 bony cavities (orbits) which contained the eyes. Lastly, that they were car- 

 nivorous and predaceous in the highest degree is shown by their wide mouths, 

 long jaws, and numerous powerful and pointed teeth. This is also proved by 

 an examination of their petrified droppings, which are kno\vn as " coprolites," 

 and which contain in abundance undigested fragments of fishes and other 

 marine animals. 



Order VL Sauropterygia. 



The Reptiles bielonging to this order agree with the last in being all extinct, 

 and in being confined to the Secondary period of geology. The best known 

 are the Plesiosauri, which resembled the Ichthyosauri in having all the limbs 

 converted into swimming-paddles, but difl'ered in several respects, of which the 

 most obvious is the great elongation of the neck (fig. 199). The Plesiosaur 



