ORDER IX 



PTEROSAURIA 



255 



Ornithostoma, Seeley, from the Cambridge Greensand, presents no generic 

 differences from Pteranodon so far as known, and may prove to be identical. 



Ornithocheirus, Seeley. Similar in all essential respects to Ptercmodon, 

 except for the presence of well-developed teeth in both jaws. Pelvis and hind 

 limbs imperfectly known. Cambridge Greensand ; England. 



Kg*© 



Fig. 361. 

 Nyctodaetylus gracilis, Marsh. Niobrara Cretaceous ; Kansas. 1/9 (after Williston). 



Ornithodesmus, Boratorhynchus, Seeley ; Palaeornis, Mantell. Founded on 

 fragmentary remains from the "Weald en and Purbeck of England. 



Range and Phylogeny of the Pterosauria. 



The earliest undoubted remains of Pterosaurs occur in the Lower Lias of 

 England, from which horizon the history of the group is traceable to near the 

 close of the Mesozoic era. Regarding its origin and evolution very little can 

 be affirmed. Dimorphodon, the oldest known genus, appears suddenly and fully 

 differentiated in the same manner as do the earliest Chelonians ; nor are there 

 any essential modifications to be observed among its successors throughout the 

 Jura and Cretaceous, except that some of the latest survivors were toothless 

 and of gigantic size. The group attained its maximum development during 

 the Upper Cretaceous, and passed away with the Dinosaurs, Pythonomorphs, 

 and Plesiosaurs towards the close of this period. 



Although Pterosaurs exhibit a number of avian resemblances, they can in 

 no sense be regarded as the ancestors of birds, and are in fact even more widely 

 separated from them than from other orders of reptiles. They are known to us 

 simply as a race of peculiarly modified Arcliusauria, or reptiles with two temporal 

 arches, whose origin is as yet mysterious, and whose hypertropic specialisation 

 precipitated their decline, and finally swept them from off the face of the earth. 



[The text for the preceding chapter on Pterosauria has been revised by Dr. S. W. Williston, 

 of the University of Kansas, who has also put the chapters on Pythonomorphs and Plesiosaurs 

 in their present shape. — Editoi;.] 





