390 



PTEROSAURIA. 



but some genera are without them, in which case the jaws may have 

 possessed horny beaks. The quadrates slope forward. The pterygoids 

 enclose an interpterygoid vacuity and extend forwards to the vomers 

 between the palatines. 



The shoulder girdle is avine, and in some of the larger forms the scapula 

 is attached to some of the dorsal vertebrae. The hand has four separate 

 metacarpals and four digits (probably 1-4) of which the first three are 

 clawed, the last enormously elongated and without a claw. The phalangeal 

 formula is 2. 3. 4. 4. A splint-like bone is sometimes attached to the 

 radial side of the carpus. 



The pelvis is small and not at all avine. The ilia are expanded antero- 

 posteriorly, and the ventral part consists of broad ischia meeting in a 

 ventral symphysis and pierced by a small foramen. The pubis is 

 separate and excluded from the acetabulum (as in crocodiles). The fibula 

 is small and splint-like. There are two proximal and two distal tarsals, 

 of which the proximal are sometimes fused with the tibia. The pes pos- 

 sesses five separate toes, of which four bear claws. The fifth digit is often 

 shorter than the rest and is sometimes divaricated from them as 



FIG. 216. RhampJtorhynchus phyllvrus restored by Marsh x }. U. Jura (from Woodward). 



though it assisted in the support of the patagium. There was no dermal 

 armour, but abdominal ribs were present. 



From this account it is clear that the Pterosauria resemble birds in the 

 structure of the shoulder girdle, in certain features of the skull, but they 

 differ from them completely in the structure of the organ of flight and of 

 the limbs, in the presence of postfrontal bones, and of both temporal 

 arcades in the skull, and in the structure of the vertebral column and 

 pelvis. 



They make their appearance in the Lower Lias, and the earliest known 

 genus Dimorphodon (Fig. 215) presents all the features of specialisation of 

 the group. 



Dimorphodon Owen (Fig. 215) with teeth and long tail, Lower Lias, 

 England. Rhamphorhynchus v. Meyr (Fig. 216) with teeth and long tail, 

 U. Jura (Lithographic Slate). Pterodactylus Cuvier, with teeth, tail 

 short, Lithographic Slate. Pteranodon Marsh, contains the largest form 

 (skull to 2 feet, wing spread to 20 feet), without teeth, tail short, Creta- 

 ceous, U. S. Ornithochirus Seeley, similar to last but with teeth, Cam- 

 bridge Greensand. 



