46 



GEOLOGY. 



developed limbs how certainly it had been a land form. In later forms, 

 the limbs were modified into paddles, and all adaptation to locomotion 

 on land was lost. The ancestral affinities of the order are with the 

 anomodonts. The eighteen Triassic genera that have already been 



, Fig. 341. Fig. 342. 



Fig. 341. — A Triassic sauropterygian, Lariosaurus balsami, restored; about one-tenth 

 natural size; from the Muschelkalk, Lombardy, Italy. (After Woodward.) 



Fig. 342. — A primitive ichthyosaurian limb from the Middle Triassic of Nevada, 

 showing the elongation of the arm bones (H, humerus; R, radius; U, ulna) 

 characteristic of land animals. The structure is in contrast with that of the later 

 ichthyosaurs. (After Merriam.) 



described show the great progress in evolution the order had made 

 before the close of the period. 



Numerous primitive forms of ichthyopterygians (fish-limbed rep- 

 tiles) have recently been discovered by Merriam in the Trias of Cali- 



