THE PLESIOSAUR8. 



513 



Another form was still more like the turtles, the jaws being 

 toothless and enclosed in a nipping, horny beak. In Lys- 

 trosaurus (Fig. 450) the head was blunt, the jaws armed in 

 front with stout teeth, and behind with canine teeth ; and 

 these animals, anticipating in their dentition the lions and 

 tigers, were called by Owen Theriodonts (beast-toothed). 

 These forms lived during the Permian and Triassic times.* 

 Order 8. Sauropterygia. The Plesiosaurus is the type 



Prf 



--.I/a; 



An 



Fig. 450. Skull of LystrosaurusfrontosusfTomCeapeCoAouy, Profile. Lettering 

 as in Fifr. 443 and 444, with the following additions : Etnom, ethmovonierine ; x/>/i, 

 sphenoid; pro. Prootic; Pt-er, Pterygoid ; Col, Columella ; JSctp, Ectopterygoid ; 

 Subart, subarticular bone. From Cope. 



of this extinct order. The Plesiosaurs were somewhat like 

 the Ichthyosaurs, swimming by paddle-like feet, but the neck 

 was very long, and the head rather small. The largest true 

 Plesiosaur was about nine metres in length. They ahounded 

 during the Jurassic and Cretaceous period. During the lat- 

 ter period off the coast of New Jersey and in the seas of 

 Kansas nourished huge Plesiosaurian reptiles, such as Elax- 

 mosaurus, which had an enormous compressed tail. The 

 * The Theromorphs were the earliest, most generalized reptiles. 



