I20 WATER REPTILES OF THE PAST AND PRESENT 



of the fishes as they were universally thought to have been at that 

 time. As Professor Baur very pertinently said, if the ichthyosaurs 

 were descended from the fishes directly, the earliest forms should 

 be more nearly like the fishes than the later ones, whereas just the 

 opposite was the real fact. The arguments which he gave in sup- 

 port of his contention were so convincing that they found imme- 

 diate acceptance among all naturalists. Fortunately within the 

 past fifteen years many other remains of early ichthyosaurs from 

 the Triassic rocks of Cahfornia have been brought to light by Pro- 

 fessor Merriam, remains which throw a flood of Hght upon the early, 

 though not the earhest, history of these strange reptiles. He has 

 recognized among the forms he has discovered, not only ' new 

 species, but several new genera, and perhaps new famiUes of ichthyo- 

 saurs. His studies have demonstrated so well the stages of evolu- 

 tion between the early ichthyosaurs and the later ones in their 

 progressive adaptation to water life that it will be of interest to 

 summarize them here. 



In the early ichthyosaurs locomotion was largely by the aid of 

 the limbs; in the later ones almost exclusively by the aid of the 

 caudal fin. In the former the paddles were larger and the bones 

 longer, more hke those of land animals; in the latter they were rela- 

 tively smaller and shorter, and more fin-like. In the digits of the 

 early forms the finger and toe bones were more elongated and fewer 

 in number. The hind limbs were nearly as large as the front ones 

 in the Triassic, often very much smaller in the later ichthyosaurs; 

 and the increased number of digits occurs only in the later forms. 



In the Triassic ichthyosaurs, all classed in the family Mixo- 

 sauridae, the pelvis was larger and more firmly connected with the 

 body than in the later forms. 



The skull of the early forms was relatively shorter, as com- 

 pared with the trunk, the jaws shorter as compared with the head, 

 the eyes were relatively small, the teeth in some less numerous, and 

 set in distinct sockets like those of land reptiles; the vertebrae 

 were relatively longer and less fish-like, and their articulations more 

 like those of land reptiles. 



The distal part of the tail was not bent downward so sharply, 

 that is, the terminal fin was smaller, or the tail may have been 



