328 



HISTORICAL GEOLOGY. 



Amphibians. Labyrinthodonts, introduced in the 

 Coal, continue and culminate here (Fig. 260), and soon 

 become extinct. 



Reptiles. Reptiles were introduced in the Permian 

 but did not become dominant until the Mesozoic. Cer- 

 tain forms, of which we shall speak hereafter, commence 

 here, but culminate in the Jurassic. But there are also 

 some curious transitional forms entirely characteristic 

 of this period. The Anomodonts (lawless-toothed) were 

 beaked like a turtle, and either toothless or else with 



long tusks only (Fig. 

 261), but crocodilian in 

 form. The Therodonts 

 (beast-toothed) were so 

 called because their teeth 

 were in three groups, 

 corresponding to inci- 

 sors, canines, and molars 

 of mammals (Fig. 262). 

 Both of these curious 

 families had many char- 

 acters allying them with 

 the lowest mammals, i. e., Monotremes (Ornithorhynchus, 

 Echidna, etc.), now found only in Australia. They have 

 been fitly called, by Cope, Theromorpha (beast-like). 

 These beast-like reptiles seem to have been introduced 

 first in the Permian. 



Mammals. If beast-like reptiles are found here, we 

 might naturally expect also the lower forms of beasts 

 themselves. In the uppermost Triassic, both of Europe 

 and America, remains of small marsupial mammals have 

 indeed been found ; but as only a feiv have been found, 

 and these in the uppermost Triassic, almost passing into 

 the Jurassic, and as similar remains are far more abun- 

 dant in the Jurassic, we shall put off their description 

 until that time. 



FIG. 262. Lycosaurtis. 



