THE GEOLOGICAL RECORD 



293 



The earliest known amphibians are the Stegocephalia, so- 

 called on account of the strongly developed bony armour 

 which covered the head and formed the roof of the skull, as it 

 did already in many of the earlier fishes. These Stegocephalia 

 included both small, salamander-like forms such as Branchio- 

 saurus (Fig. 139) and large crocodile-like creatures the 

 labyrinthodonts. Some of them survived into the j-Triassic 



FIG. 139. Branchiosaurus amblystomus ; restoration of Skeleton (A) and 

 ventral Armour (B) by II. Credner, nat. size. Lower Permian. (From 

 Smith Woodward's " Vertebrate Palaeontology.") 



epoch, after which they appear to have become entirely extinct, 

 and although a fair number of Amphibia still exist at the present 

 day, the group must be regarded as having attained its maximum 

 of development in late Palaeozoic and early Mesozoic times. The 

 existing frogs and toads are very highly specialized forms, 

 completely adapted to a terrestrial life in the adult condition but 

 for the most part resorting to water to deposit their eggs, which 

 hatch out in the form of aquatic fish-like larvae or tadpoles, 



