434 



THE CHANGING GENERATIONS 



Carboniferous, and culminated in heavy-bodied, 5-foot long predators 

 during the Permian, only to decline until their last Triassic survivors were 

 small degenerate forms incapable of leaving the water. The reptiles are 

 believed to have evolved from primitive labyrinthodonts, and it is possi- 

 ble that the frogs and toads are a surviving offshoot from this stock. The 



Fig. 27.20. Eryops, a primitive Carboniferous amphibian. This labyrinthodont "stego- 

 cephalian" lived in the coal swamps of Pennsylvania. The trees in the background are 

 Calamites, Sigillaria, and Cordaites; the herbaceous plants in the foreground are Spheno- 

 phyllum. (Courtesy Carnegie Museum, Pittsburgh.) 



salamanders (Fig. B. 31), however, are descended from some other group 

 of stegocephalians. 



The winged insects of the coal forests. Although our account of the 

 evolutionary history of animals centers around the vertebrates, we must 

 occasionally take note of developments in other groups which were im- 

 portant for life as a whole. One such event was the appearance of winged 

 insects, the descendants of which were destined to play a major role in 

 the evolution of the flowering plants, and which today share dominance 



