CHAPTER XII 

 THALATTOSAURIA 



Millions of years before the first appearance of the mosasaurs 

 in geological history, another group of reptiles showing many 

 curious resemblances to them attempted a rather precarious exist- 

 ence in the water. Its members survived long enough to acquire 

 many structural adaptations to a water life, long enough to become 

 diversely modified, but not long enough, apparently, to wander far 

 from their birthplace, not long enough to attain that security from 

 their enemies and more ambitious competitors, the early ichthyo- 

 saurs and plesiosaurs, to insure them a long existence. They were 

 only a partial success as water reptiles. 



It has been only within a few years that we have had any 

 knowledge whatever of them, and that knowledge is still very 

 incomplete, too incomplete to justify any attempt to picture them 

 as living animals, even though we take the liberties that some of 

 our illustrators of extinct animals feel warranted in assuming. 

 The first known specimens of these "sea-reptiles" —for that is the 

 meaning of the word Thalattosauria — were discovered and described 

 by Professor J. C. Merriam less than ten years ago, and all our 

 knowledge of these animals is due to the same author, who has 

 studied attentively the known specimens, all of which are pre- 

 served in the museum of the University of California. The first 

 discovered fragmentary specimens were confounded with those of 

 early ichthyosaurs, from the Upper Triassic rocks of northern Cali- 

 fornia with which they were associated. No specimen has yet been 

 found that is even approximately complete; some parts of the 

 skeleton are not yet known, even from fragmentary remains, and 

 not till other and more complete specimens have been found will 

 it be possible to determine the real form of the living animals or to 

 decide what their nearest relationships with other reptiles were. 

 Professor Merriam thinks that they were related most closely with 



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