THE TRIASSIC PERIOD 695 



The Marine Life 



The. reduction of marine life of the shallow-water type during 

 the Permian (p. 673) was continued into the Triassic period, and 

 since its remains are in sediments now buried, such record as it 

 made is mainly concealed. This was especially true of North 

 America. To trace the shallow-water marine life of the Permian 

 into that of the next period, it is necessary to bring together evidence 

 from different continents. The question of supreme interest is the 

 way in which the epicontinental sea life, crowded to a minimum 



Fig. 472. A Triassic sauropterygian, Lariosaurus balsami, restored; about 

 ^ii natural size; from the Muschelkalk, Lombardy, Italy. (After 

 Woodward.) 



habitat between the land and the deep sea, maintained its con- 

 tinuity, transformed its species, and later re-peopled the shallow 

 waters when they again became more extensive in the closing 

 stages of the Trias and later. 



When the sea readvanced on the North American continent, it 

 was chiefly from the Pacific, but there were also incursions up the 

 MacKenzie Valley and from the Gulf of Mexico. It is not clear that 

 the sea completely withdrew from the present land area on the 

 Pacific coast after the Permian; but the fossils so far recovered 

 from the Trias of this region do not give clear evidence of continuous 

 submergence of an area such as to allow the development of a 

 definite provincial fauna. 



The transition tracts. It was otherwise on the Eurasian con- 

 tinent. While the sea withdrew from the northwestern part of 



