THE GEOLOGICAL RECORD 299 



Wealden deposits of Europe, was a huge herbivore, which seems to 

 have supported its massive body, chiefly at any rate, on its hind 

 limbs, which were much more strongly developed than the front 

 pair. The American Brontosaurus (Fig. 144) and Diplodocus 

 walked on all fours, and the latter attained a length of 80 feet, 

 but a large proportion of this was taken up by the enormously 

 long neck and tail. In both these forms the head was of 

 astonishingly small dimensions in proportion to the rest of the 

 body. Other Dinosaurs, such as Stegosaurus (Fig. 145) and 

 Triceratops (Fig. 146), developed an extraordinary dermal 

 armature of bony plates or spines. 



Perhaps the most remarkable of all the extinct reptiles of 

 the Secondary period, however, were the Ornithosauria (Ptero- 

 sauria or pterodactyls), which at that time occupied the place now 



FIG. 147. Skeleton and Outline of Pteranodon occidentals, from the Upper 

 Cretaceous of Kansas, U.S.A. ; X 5%- (From British Museum Guide.) 



filled by the birds and bats. These animals were very perfectly 

 adapted for flight, the wing being formed, as already described in 

 Chapter XVII, by an extension of the skin supported by the arms, 

 legs and tail, and especially by the enormously elongated fifth digit 

 (Fig. 99). Some of these flying reptiles attained a very large 

 size, the total expanse of the wings in Pteranodon (Fig. 147) 

 being about eighteen feet. 



The origin of birds from reptilian ancestors has been quite 

 conclusively demonstrated on anatomical and embryological 



FIG. 144. Skeleton of Brontosaurus excelsus, from the Upper Jurassic of 



Wyoming, U.S.A.; x T ^. (From British Museum Guide, after O. C. 



Marsh.) 

 FIG. 145. Skeleton of Stegosaurus urtyulatus, from Jurassic of Wyoming ; 



X aV (From Smith Woodward's "Vertebrate Palaeontology," after 



O. C. Marsh.) 

 FIG. 146. Skeleton of Triceratops prorsus, from Cretaceous of Wyoming; 



X S V (From British Museum Guide, after 0. C. Marsh.) 



