536 HISTORICAL GEOLOGY 



the seas of the whole world. Most of the ganoids became extinct, 

 either because of their inability to compete with the teleosts in the 

 search for food, or because of climatic and other conditions. 



REFERENCES FOR FISHES 



Oean, B., — Fishes, Living and Fossil. 



Eastman, C. R., — Ann. Rept. New Jersey Geol. Surv. for 1904. 



Woodward, A. S., — Vertebrate P alee ontology. 



Zittel- Eastman, — Textbook of Paleontology. 



Amphibians. — The amphibians reached their greatest develop- 

 ment in the Permian, but were present in considerable numbers in 

 the Triassic, after which their remains are seldom found. Individ- 

 uals of this class attained their greatest size in the Triassic, Masto- 

 donsaurus (so-called because of its bulk) having a skull four feet long 

 and probably attaining a length of 15 or 20 feet. Although large 

 for an amphibian, the size is not great as compared with some modern 

 crocodiles. In general appearance, Mastodonsaurus resembled the 

 modern salamander, but it differed in several essential points of struc- 

 ture. Its teeth were of the complicated labyrinthine type (p. 485), 

 and the skull was roofed over with bony plates (Stegocephalia). 

 It is possible that bony plates protected the chest, but if so, positive 

 proof is lacking. The Stegocephalia became extinct before the close 

 of the Triassic, and thus far with the exception of two specimens of 

 frogs from Wyoming no amphibian remains have been found in 

 Jurassic rocks. The cause of the extinction of this great amphibian 

 order is probably to be found in the highly developed reptiles, large 

 and small, with which they had to compete. A few specimens of 

 salamanders of modern type, differing little in general appearance from 

 the salamander of to-day, though of a different genus, have been found 

 in the Cretaceous. Because of the lack of fossil evidence, the an- 

 cestry of the modern amphibians is not known. 



Reptiles 



Reptiles with Mammalian Characters. — The reptiles with mam- 

 malian characters, as far as fossil evidence shows, began, and were 

 represented by many genera in the Permian (p. 490), but, since 

 they apparently attained their greatest development in the Triassic, 

 their discussion has been postponed to this chapter. This group 

 of reptiles is included under the term Theromorpha (Greek, ther, 



