THE CARBONIFEROUS PERIODS 491 



Triassic and also because they were the probable ancestors of the mam- 

 mals. They were small reptiles with short but strong legs and large 

 heads. The mammalian characters are to be seen in the skull, the 



j 



[ SJvyrmu 



Fig. 467. — Faranops, a Permian reptile forty-tour inches long, on a Sigillaria 

 log. (After Prof. S. W. Williston.) 



teeth, and other parts of the skeleton. This important group is de- 

 scribed more fully in the following chapter (p. 536). 



Rise of Reptiles. — The rise of reptiles from amphibians was a logi- 

 cal sequence. On account of their aquatic larval life, amphibians 

 were restricted to the vicinity of the water, while reptiles, because of 

 the development of a firm eggshell and the omission of the aquatic 

 stage of the young, were able to populate the dry lands and thus to 

 take advantage of many kinds of food. Amphibians may indeed be 

 considered as transitional forms by which reptiles were evolved from 

 fishes. 



The rapid development of this class after it was once well-started 

 was probably due to its higher organization, to the lack of competition 

 in the new surroundings, and to the abundance of food. It has been 

 suggested that the purification of the air as a result of the withdrawal 

 of carbon dioxide in the formation of coal produced an atmosphere 

 which was more favorable for the development of air-breathing ani- 

 mals, but the amount of carbon dioxide withdrawn does not seem to 

 have been sufficient to have made a great difference. 



Carboniferous Plants 



The forests of the Carboniferous were very different in appearance 

 from those of to-day. None of the trees common at present in the for- 

 ests and swamps were in existence, flowering plants were conspicuous 



