xi THE GEOLOGICAL RECORD 207 



in appearance from the various crocodiles and alligators 

 now living in the tropics they need only be mentioned. 

 But besides these there were true Dinosaurs of similar 

 shape to the Iguanodon, but of rather less massive form 

 and with strong teeth curved backward, which with their 

 wide-opening jaws evidently adapted them to seize and 

 prey upon the larger land-reptiles. These form the Sub- 

 order Theropoda, or beast-footed Dinosaurs. The skull of one 

 of these here shown (Fig. 59) is more than 2. feet long, but 

 no complete skeleton has been yet discovered. The allied 

 Megalosaurus was found by Dr. Buckland in the Wealden 

 beds in such abundance that he was able to piece together 

 enough of the skeleton to show its affinity to the Iguanodon. 



Order Sauropterygia 



We now come to the group of aquatic lizards which 

 abounded in all the seas of the Mesozoic period from the 

 Trias to the Chalk. They had lizard-like heads, powerful 

 teeth, both fore and hind limbs converted into paddles, and 

 often with a dilated swimming tail. They varied much in 

 size, but were often very large. Plesiosaurus cramptoni, from 

 the Upper Lias of Whitby, was 22 feet long, but some 

 species from the Chalk formation were from 30 to 40 feet 

 long. A skull and jaws of P. grandts, from the Kimmeridge 

 clay, is 6 feet long, which, if the proportions were the same 

 as those of the species here represented (Fig. 60), would 

 have belonged to an animal nearly 50 feet long. The 

 whole group was extremely varied in form and structure, 

 but all were adapted for preying upon such aquatic or 

 marsh-frequenting animals as abounded during the same 

 period. 



Order Ichthyopterygia 



All the members of the preceding order have the paddles 

 supported by a complete bony foot or hand composed of 

 five separate fingers and connecting wrist-bones. But in the 

 present order the adaptation to marine life is more perfect, 

 a dorsal fin and bi-forked tail having been developed (Fig. 61), 

 while the bony skeleton of the four limbs often consists of 

 seven or eight rows of polygonal bones closely fitted together 



