42 



GEOLOGY. 



borders and the adjacent lowlands where alone relics were usually 

 preserved by sedimentation. 



Though the amphibians had lost the foremost place in the Permian, 

 they still formed a notable element in the European and American 

 Triassic faunas. More than twenty-two genera have been described, 

 all belonging to the Temnospondyli and Stereospondyli, or true laby- 

 rinthodonts. During the period, however, they entered upon a rapid 

 decline, and by its close had ceased to be a prominent feature of the 

 land life, a decline from which they have never recovered. Ancestors 

 of the whole tribe of terrestrial vertebrates, they soon became its most 

 insignificant representatives. None of the modern amphibians had 

 yet appeared. 



The strange ancestral reptiles rapidly evolved into higher forms. 

 The branch with the mammalian strain (Synapsida) seems to have 

 been left far behind by the more distinctively reptilian branch 

 (Diapsida). The latter developed prodigiously in the closing stages 

 of the period, when the conditions were ameliorated and vegetation 

 began again to flourish and furnish a better basis for animal life. Every 

 chief group of reptiles had its representatives before the close of the 



Fig. 339. — Oudenodon trijoniceps. An anamodont (or Dicynodont) from the Karoo 

 formation of South Africa, so similar to forms of the Trias in Wyoming as to be 

 distinguished from them with difficulty. (After Broom.) 



period, Rhynchocephalia (including the Proterosauria and Gnathosauria) , 

 Crocodilia (including Phytosauria) , Thalattosauria, Ichthyosauria, 

 Squamata, Dinosauria and Pterosauria, of the cliapsidan group, and 

 Theromorpha (Anomodontia) , Chelonia and Sauropterygia (Notho- 

 sauria and Plesiosauria) of the synapsidan group. As the reverse side 

 of this remarkable development, some of the older types, as Protero- 

 sauria, Phytosauria, Theromorpha and Nothosauria, disappeared with 



