14 S. W. WILLISTON 



ious, animals is scarcely open to doubt, and all are agreed that the phyto- 

 saurs were not this ancestral type. That they should have become more 



aquatic in habit than are 

 any now living, and again 

 reverted to a subterrestrial 

 habit, as in the modern 

 alligators, is difficult, if not 

 impossible, to believe. The 

 true teleosaurs, Hke the 

 thalattosaurs, were a short- 

 hved branch of which no 

 modern descendants have 

 survived. Owen has 

 thought^ that the introduc- 

 tion and development of 

 the small mammals was a 

 cause of the evolution of 

 the small, brevirostrate 

 crocodiles, the Atoposauridae 

 and Goniopholididae ; but 

 I doubt this very much, 

 though they may have been 

 the inciting cause of the 

 evolution of such diminu- 

 / "^x\ ^^^^ forms as Alligatorellus 



I . , - i and Atoposaurus. Were 



/ -' >. more extensive land faunae 



^' \ to be discovered in the 



/ } ""''^ middle and lower Jura, I 



^^ I, t believe that we should 



^^''''*^:^,^, _^^^ J find the remains of real 



-'■-^-■^..^^^i.^....^^^- ' amphibious brachystomous 



Fig. ^.—Coelosuchus reedii. Right coracoid, crocodiles, mUch leSS like 

 one-half natural size. , r n-i 7 



the structure of Teieosaurus 

 than is Teleidosaurus even. It is hard to believe that the littoral 

 reptiles, or semiaquatic forms, like Pleurosaurus, Acrosaurus, etc., 



I Owen, Quarterly Journal of the Geological Society, February, 1879, p. 148. 



