PALEOZOIC AGE 



PERMIAN PERIOD 



Many new species of stegocephs were now to be seen amphibians 



swimming the rivers, and crawling the marshes. Some were (stegocephs) 



becoming of decidedly crocodiHan aspect ; but, so far as is 



known, they presented no essential differences from the types 



of the preceding Period. Forms, however, much larger than 



those of Carboniferous date were certainly abroad, especially 



among those with teeth of " labyrinthine " structure (Labyrin- 



thodonts). Some of these animals attained a length of nine 



feet (Cricotus) ; whilst others with broad skulls of two feet 



in length must have been of colossal proportions (Eryops). 



These monsters were inhabitants of North American swamps 



and rivers. The largest European stegoceph — a creature of 



crocodiUan appearance — was hardly as big as a monitor 



lizard (Archegosaurus). 



Some stegocephs with teeth of simpler construction 

 possessed what are known as abdominal ribs, i.e. transverse 

 fibres of ventral tissue faced with a bony substance (Petro- 

 bates). A protective development of this description is 

 characteristic of many reptiles. 



But whatever may have been the reptilian tendencies reptiles 

 disclosed by some amphibians, a distinct divergence from the 

 ranks of the latter had taken place, for primitive reptiles 

 were now on the scene. 



Most of these new leaders of life differed notably from 

 the " roofed-head " amphibians owing to cranial modifica- 

 tions. Their skulls were not of the blocky type, but had 

 been hollowed out in parts, and made lighter and more refined. 

 These modifications had, no doubt, been accompanied by other 

 important changes, mental as well as physical. 



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