THE TRIASSIC PERIOD 



399 



Mt. Holyoke in Massachusetts are merely the outcropping 

 edges of hard Triassic lava sheets, formed during this epoch 

 of volcanic activity, the last in the history of the eastern 

 portion of North America. 



FIG. 416. A Triassic 

 brachiopod (Terebrat- 

 ula). The majority 

 of Mesozoic brachio- 

 pods have this general 

 form. 



LIFE OF THE TRIASSIC 



New aspect of the marine invertebrates. Although the 

 lower animals of the Triassic seas resemble the Paleozoic 

 types in many ways, the differences are 

 nevertheless very distinct. Not only 

 had some of the Paleozoic groups, such 

 as the trilobites, wholly disappeared, 

 but others, as the brachiopods (Fig. 

 416), had been relegated to an inferior 

 station. 



The mollusks became the most abun- 

 dant and conspicuous of the shelled ani- 

 mals, and among them the group of 

 coiled cephalopods had a remarkable 

 development during the Triassic and 

 later Mesozoic periods. From the simple 

 types with straight sutures, they had 



advanced 

 later in the 

 Paleozoic to 

 the posses- 

 sion of lobed 



or wavy sutures. In the Mesozoic 

 era the folding of the partitions 

 became most intricate (Figs. 418 

 and 419), producing equally com- 

 plicated suture patterns. 

 FIG. 418. An ammonite with Reptiles overreach the amphib- 

 part of the outer shell re- i ans ._The brief supremacy of 



moved to show the complexly . 



folded sutures. the clumsy amphibians had now 



FIG. 417. A small pele- 

 cypod from the Triassic 

 limestone of Europe. 



