THE GEOLOGICAL EECOKD. 97 



Labyrinthodonts ; others remained small, and were prob- 

 ably harmless herbivores ; some became elongated, lost 

 their limbs, and were adapted to an eel- or snake-like 

 mode of progression (Aistopoda) ; while others (Braii- 

 chiosauria), losing the original scaly covering of the fish- 

 like ancestor, gave rise to the modern groups (the frogs 

 and toads, or Anura, and the salamanders and newts, 

 or Urodela). These latter are all specialised forms, the 

 existing Urodela being only the degenerate remnants of 

 a once flourishing class which have become more or less 

 completely readapted to an aquatic life. In fact, the 

 Anura are the only order which has succeeded and ex- 

 panded in recent times. 



The Amphibian was the dominant type in Carbonif- 

 erous times ; it now occupies a very subordinate place. 

 But from some unspecialised branch of it arose the more 

 thoroughly terrestrial Reptilia towards the end of the 

 Carboniferous or beginning of the Permian epoch. The 

 class Reptilia reached a higher grade of structure, and 

 soon almost completely superseded the Amphibia on 

 dry land. So successful were the reptiles that already in 

 Permian and Triassic times they had spread over the 

 whole earth, becoming adapted in various directions to 

 all sorts of life (Fig. 4). The earliest reptiles known so 

 closely resemble the primitive Amphibia that it is diflicult 

 to say where one class begins and the other ends ; but 

 these undifferentiated reptiles soon gave way to more 

 specialised successors. The Theromorpha gave rise to 

 remarkable forms : some with large flat grinding teeth 

 (Placodontia) ; others active, vigorous creatures with a 

 formidable carnivorous dentition (Therocephalia and 

 Therodontia) ; while the highly-specialised Dicynodoutia 

 retained only two huge tusks. None of these specialised 

 reptiles survived beyond the Trias. Other lines of dif- 

 ferentiation lead toward a return to aquatic life. 

 Plesiosaurs and Ichthyosaurs quite independently took 

 to marine life, and their limbs became transformed into 



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