FLYING-DRAGONS. 171 



the Lithographic Stone of Bavaria, differed from 

 Dimorphodon chiefly in that the head was long 

 and pointed, and that the tail, which was of great 

 length, terminated in a leaf -like expansion. 



Side by side with these long-tailed, tooth- 

 bearing forms there lived numerous short-tailed 

 types, which exhibit evidences of increasing 

 specialisation in the gradual decline of the teeth 

 and the evolution of toothless types, whose jaws 

 were either encased in horn or a thin leathery 

 skin as in birds. These new types are repre- 

 sented by the species of the genus Ptertdadylus. 

 In Pterodadylus antiquus, for example, we find 

 only a few small teeth confined to the anterior 

 end of the jaws, whilst in P. spectabilis they have 

 completely disappeared. Curiosity is naturally 

 stimulated to account for this loss of the teeth, 

 but so far, no explanation appears to be forth- 

 coming. Assuming them to have preyed upon 

 fish, as is generally believed, the advantage of 

 such weapons seems obvious, for fish are pro- 

 verbially slippery creatures. Nevertheless, we 

 find indubitable evidence, if we turn to the birds, 

 that toothless jaws are by no means incompatible 

 with a fish diet, as witness the Corrnorants and 

 Kingfishers, Herons, Divers and Grebes, and 

 Penguins, for example. Among the fish-eating 

 birds, however, we must not forget that some 

 seem to have had to make shift to replace the 

 lost teeth of their ancestors by developing tooth- 

 like processes on the edges of the horny jaws, as 

 in the case of the Mergansers among the Drakes, 

 and in the Darters, allies of the Cormorants. 



Further evidence of specialisation in the form 



