LIFE 



465 



systems have bones of these animals been found in America, and 

 only imperfect ones in Europe. Fossils of amphibians first appear 

 in abundance in the later Coal Measures, and in such variety as 

 to imply a long antecedent existence. Most of them were rather 

 primitive in structure, but they were 

 genuine amphibians, not transition 

 types. All of them seem to have 

 had elongate forms, and their heads 

 were well roofed over by the bony 

 plates of the skull. On account of 

 this last feature they are called 

 stegocephalians (roof headed). Some 

 of them have also been named laby- 

 rint/iodonts, from the intricate infold- 

 ing of the dentine of their teeth. 

 Labyrinthodonts were doubtless the 

 largest amphibia of the period, some 

 of their skulls reaching a length of 

 half a meter. 



The amphibia varied in length 

 and strength of limb, in agility, 

 ability to climb, etc. The elonga- 

 tion of their bodies involved a nota- 

 ble multiplication of the vertebrae, 

 one form having no less than 150. 

 Before the close of the period, prob- 

 ably some of them lived on dry land 

 where fleetness, rather than protect- 

 ive armor, preserved them from their 

 enemies. Others were limbless and 

 snake-like, crawling reptiles in every- 

 thing except certain technical details 

 of their palates. 



One branch of the amphibia 

 which reached its highest develop- 

 ment in the Permian is supposed by some paleontologists to be the 

 ancestral stock from which mammals arose. The other branch, 

 which included the labyrinthodonts, is the only group of Pennsyl- 

 vanian air-breathing vertebrates which left no descendants. 



Not much is known of the habits of the amphibia, but from their 



Fig. 401. A CARBONIFEROUS AM- 

 PHIBIAN; Lepterpdon dobbsi Hux- 

 ley. A microsaurian from Kil 

 kenny, Ireland, about 3/5 natural 

 size. (Zittel.) 



