THE PENNSYLVANIAN PERIOD 



653 



gation of their bodies involved a notable multiplication of the 

 vertebrae, one form having no less than 150. In places, their 



tracks are so abundant as to imply 

 great numbers of individuals, at 

 least locally. 



The predominant forms were 

 branchiosaurs and microsaurs. In 

 size and in habits, the branchiosaurs 

 at least were comparable to the sala- 

 manders of to-day. The microsaurs, 

 on the other hand, had made distinct 

 advance, both toward higher types, 

 and away from water, in and about 

 which the branchiosaurs lived. Some 

 of the microsaurs lost their dermal 

 armor, and became fleet, like modern 

 lizards. Before the close of the 

 period, some of them were probably 

 inhabitants of dry lands where fleet- 

 ness, rather than protective armor, 

 preserved them from their enemies. 

 Differentiation went so far before 

 the close of the period that some of 

 them were limbless and snake-like, 

 crawling reptiles in everything 

 except certain technical details of 

 their palates. 



Two other types, Temnospondyli 

 (African) and Stereo spondyli, either 

 persisted from unknown ancestors, 

 or made their advent at this time. 

 The temnospondylous branch, which reached its highest develop- 

 ment in the Permian, is supposed by some paleontologists to 

 be the ancestral line of all modern reptiles, and by others to be the 

 ancestral stock from which mammals arose. The stereospondylous 

 branch, which included the labyrinthodonts, is the only group of 

 Pennsylvanian air-breathing vertebrates which left no descendants. 



Fig. 453. Carboniferous am- 

 phibian Lepterpeton dobbsi 

 Huxley: a microsaurian from 

 Kilkenny, Ireland, about % 

 natural size. (Zittel.) 



