452 MESOZOIC TIME — REPTILIAN AGE. 



The Plcsiosaur (figs. 712, 715) had a long, snake-like neck consist- 

 ing of twenty to forty vertebrre, a small head, short body, paddles, 

 and biconcave vertebrae differing little in length and breadth. P. 

 dolichodeirus (fig. 712) was 25 to 30 feet long. P. macrocephalus is 

 represented in fig. 715 just as it lay in the rocks. The British 

 rocks of the Jurassic and Cretaceous periods have afforded sixteen 

 species of Plesiosaurs ; and in all twenty-one are known, of which 

 twelve were found in the Lias and seven in the Oolite. The 

 Pliosaur is another swimming Saurian, near the Plesiosaur: some 

 individuals were 30 to 40 feet long. Eemains of more than fifty 

 species of Jurassic Enaliosaurs have been found in the rocks. 



Many of the Crocodilians were of the Teleosaur type, having 

 slender jaws like the Gavial, and also biconcave vertebrae, — the 

 latter a mark both of antiquity and inferiority. Fig. 714 represents 

 the skull of one of these species, the. Mystriosaur. 



The Dinosaurs (p. 34G) attained in some species a length of 50 

 or 60 feet. Unlike all other Eeptiles, the sacrum corresponded 

 to five combined vertebrae, as in the higher Mammals. The Megalo- 

 saurus Bucklandi was about 30 feet long ; the teeth were flattened 

 and curved, with trenchant edges, and were set in sockets : a 

 horizontal section of one is shown in fig. 740. It was a terrestrial 

 carnivorous Saurian. 



The Tguanodon of Mantell was an herbivorous Dinosaur, and had 

 the habit of a Hippopotamus. It was 30 feet long, and of great 

 bulk : the femur, or thigh-bone, in a large individual was about 

 33 inches long, and the humerus 19 inches ; the teeth (fig. 745) were 

 flat, and had a serrated cutting edge like the teeth of the Iguana; 

 and the jaws had some lateral motion, — indicative of its herbivo- 

 rous character. Many of the teeth from old animals are worn off 

 short. The remains occur in the Wealden of Tilgate Forest, and 

 in the Kentish Kag near Maidstone. 



The Hylceosaur, another Tilgate Forest Dinosaur, had its skin 

 covered with circular or elliptical plates, and was 20 to 22 feet 

 long. 



The Pterosaurs belong mostly to the genus Pterodactyl. Fig. 739 re- 

 presents the skeleton (reduced in size) of P. crassirostris, showing the 

 forearm, with the outer finger excessively prolonged for supporting 

 the wing, while the other fingers are free for clinging or grasping. 

 The species was a foot in length, and the spread of the wings was 

 about three feet. As in birds, the bones of Pterodactyls are 

 hollow to fit them for flying ; but, unlike birds, they had the skin, 

 claws, and teeth of reptiles. Their habits were probably those of 

 bats rather than birds. They are found mostly in the Oolite and 



