480 



THE PERMIAN PERIOD 



Fresh-water life. Besides the amphibians and some of the 

 reptiles which constituted, in a sense, a portion of the fresh-water 

 life, fishes were abundant. On the whole they had a rather modern 

 aspect. There were fresh-water mollusks, some of which resembled 

 unios. 



Marine life. The withdrawal of the epicontinental seas from 

 considerable portions of the continents reduced the area available 



Fig. 410. Pareiasaurus serridens, Karroo formation, Cape Colony, S. Africa; 

 about 1/25 natural size. (After Broom.) 



for shallow-water sea life, and so reduced its amount. It is to be 

 noted that this reduction came at a time when conditions were 

 unfavorable for land life. In North America the restricted marine 

 faunas were lineal descendants of ancestors occupying the same 

 area. At first, many of the species were the same as those of the 

 preceding period, and hence there has always been difficulty in 

 drawing a dividing line between the systems. The known species 

 of the marine Permian of the Great Plains are only about 70, and 

 of these about half are pelecypods. 



The increasing complexity of the sutures of the coiled cephalopods 

 has been noted in previous chapters. By the close of the Permian, 

 the complexity (Fig. 411), foreshadowed that of the Mesozoic 

 ammonites, though older types (goniatites and nautiloids) still 

 lived. The ancient straight form (Orthoceras,/, Fig. 411), was in the 

 last stage of its long career. The contrast between the disap- 

 pearing straight type, in its depauperate form, and the robust youth- 

 ful ammonites (a and b, Fig. 411), about to become a ruling 

 dynasty, is marked. 



