i8o 



THE ORIGIN AND EVOLUTION OF LIFE 



Recent researches in this country, chiefly by WilHston, 

 Case, and Moodie, indicate that the soKd-headed Amphibia 

 (Stegocephaha) and primary forms of the ReptiKa chiefly be- 

 long to late Carboniferous (Pennsylvania) and early Permian 

 time. They are found abundantly in ancient pool deposits, 

 which are now widespread over the southwestern United States 



and Europe deposited in 

 rocks of a reddish color. 

 This reddish color points 

 to aridity of climate in 

 the northern hemis- 

 phere during the period 

 in which the terrestrial 

 adaptive radiation of the 

 Amphibia occurred. 

 These arid conditions 

 continued during the 

 greater part of Permian 

 time, especially in the 

 northern hemisphere. 

 In the southern hemisphere there is evidence, on the con- 

 trary, of a period of humidity, cold, and extensive glaciaticn, 

 which was accompanied by the disappearance of the old lyco- 

 pod flora (club-mosses) and arrival of the cool fern flora (GIos- 

 sopteris), which appeared simultaneously in South America, 

 South Africa, Australia, Tasmania, and southern India. The 

 widespread distribution of this flora in the southern hemisphere 

 furnishes one of the arguments for the existence of the great 

 South Atlantic continent Goudwana, a transatlantic land bridge 

 of animal and plant migration, postulated by Suess and sup- 

 ported by the palaeogeographic studies of Schuchert. In 

 North America the glaciation of Permian time is believed to 



Fig. 6i. Skull and Vertebral Column of 



Diplocaidus. 



A typical solid-, broad-headed amphibian from the 

 Permian of northern Texas. Specimen in the 

 American Museum of Natural History. (Com- 

 pare Fig. 60.) 



