112 WATER REPTILES OF THE PAST AND PRESENT 



profusion. His researches, and those of several authors since then, 

 supplementing and confirming or disproving those of the many 

 observers made during the preceding seventy years, have finally 

 determined almost perfectly the complete structure of the more 

 typical ichthyosaurs, enabling us to infer not a little as to their 

 habits and distribution in the old Jurassic oceans. Within the 

 past few years the discoveries. of Professor J. C. Merriam of Cali- 

 fornia have likewise added greatly to our knowledge of the earlier 

 ichthyosaurs. It may now truthfully be said that of no group of 

 extinct reptiles do we have a more complete and satisfactory knowl- 

 edge than of the ichthyosaurs. 



Nevertheless we have yet very much more to learn about the 

 order Ichthyosauria as a whole — whence they came and how they 



Fio. 52. — Ichthyosaurus quadricissus. Photograph of specimen in Senckenberg 

 museum, from Dr. Dreverman. 



originated; what their nearest kin were among other reptiles; and 

 especially, more about the connecting links between them and 

 terrestrial reptiles. They have, as an order, so isolated a position, 

 are so widely separated from all other reptiles in structure, that they 

 have long been a puzzle to paleontologists. Like the whales and 

 other cetaceans among mammals, we know the ichthyosaurs well 

 in the plenitude of their power and the fulness of their development, 

 but have yet only an imperfect knowledge of their earlier history, 

 and none whatever of their earliest. However, as will be seen 

 farther on, the recent discoveries by Merriam have shed much light 

 on some of the stages of their evolution. So nearly perfectly were 

 all the later ichthyosaurs adapted to their life in the water that it 

 was beheved by nearly all paleontologists until about a score of years 



