224 REPTILIA. 



Middle Eocene of Bracklesham, Sussex (Gavialis dixoni). 

 Crocodiles and Alligators are found extensively both in Europe 

 and North America, and they appear not to have become 

 completely extinct in Europe before the Pliocene period. 

 Diplocynodon is an interesting extinct generalized Alligator, 

 characterized by the third lower tooth as large as the fourth, 

 and a strong ventral armour. D. hantoniensis is well known in 

 the Upper Eocene sands of Hordwell, Hampshire ; other 

 species occur in the London Clay ; and others are found in the 

 Lower Tertiaries of France and Germany as late as the Miocene. 

 It is also worthy of note that the Alligator-like character of 

 the lower teeth biting entirely within the upper teeth, is 

 observable in a gigantic Gavial, Rhamphosuchus crassidens, 

 known only by fragments from the Pliocene of the Siwalik 

 Hills, India. This is probably the largest known crocodilian, 

 and cannot have attained a length of less than fifteen metres. 



ORDER 9. ORNITHOSAURIA. 



Reptiles with hollow bones, well-formed articulations, and 

 fore limbs adapted for flight, occur throughout all Mesozoic 

 formations from the Lower Lias upwards. They are completely 

 evolved at their earliest known appearance (Dimorphodon) ; 

 and they exhibit little essential change as they are traced 

 through the successive deposits in which they occur. It can 

 only be said that some of these reptiles become toothless and 

 attain enormous dimensions in the Cretaceous ; the wings 

 eventually becoming so large, that the scapula articulates 

 directly and firmly with the neural arches of some dorsal 

 vertebrae fused together for support. 



These flying reptiles are grouped in an order variously 

 termed ORNITHOSAURIA or PTEROSAURIA. The skull is large, 

 remarkably bird-like in shape, and its constituent bones are 

 fused together in the adult. The single occipital condyle is 

 fixed on the base of the skull, so that the long axis of the head 

 is approximately at right angles to that of the neck ; the en- 

 larged premaxillse form the greater part of the upper jaw ; and 

 the two rami of the mandible are fused together at the 



