68 ANIMALS OF THE PAST 



not know. Did they devour everything large 

 enough to be eaten throughout their habitat, 

 and then fall to eating one another ? Again, 

 we do not know. But perish they did, while 

 the smaller white shark, which came into being 

 at the same time, still lives, as if to emphasize 

 the fact that it is best not to overdo things, 

 and that in the long run the victory is not 

 always to the largest. 



REFERENCES 



The finest Mosasaur skeleton ever discovered, an 

 almost complete skeleton of Tylosaurus dyspelor, 29 feet 

 in length, may be seen at the head of the staircase lead- 

 ing to the Hall of Paleontology, in the American Museum 

 of Natural History, New York. Another good specimen 

 may be seen in the Yale University Museum, which prob- 

 ably has the largest collection of Mosasaurs in existence. 

 Another fine collection is in the Museum of the State 

 University of Kansas, at Lawrence. 



The best Zeuglodon, the first to show the vestigial hind 

 legs and to make clear other portions of the structure, is 

 in the United States National Museum. 



The great sharks are known in this country by their 

 teeth only, and, as these are common in the phosphate 



