RULERS OF THE ANCIENT SEAS 49 



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 com- 

 plete skeleton of Tylosaurus dyspelor, 29 feet in length, may he 

 seen at the head of the staircase leading to the Hall of Paleon- 

 tology, in the American Museum of Natural History, New York. 

 Another good specimen may he seen in the Yale University 

 Museum, which prohably has the largest collection of Mosa- 

 saurs in existence. Another fine collection is in the Museum of 

 the State University of Kansas, at Lawrence. These animals 

 are described in Water Reptiles of the Past and Present by S. 

 W. Williston 



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 beds, specimens may 

 be seen in almost any collection. In the United States National 

 Museum, the jaws of a twelve-foot blue shark are shown for 

 comparison. The largest tooth in that collection is 5% inches 

 high and 5 inches across the base. It takes five teeth of the blue 

 shark to fill the same number of inches. 



There is a technical — and, consequently, uninteresting — ac- 

 count of Zeuglodon in Vol. XXIII of the "Proceedings of the 

 United States National Museum," page 327, and a full account 

 of the skeleton, illustrated is given by Mr. Gidley in the Proceed- 

 ings of "the U. S. National Museum for 1913, Volume 44; 

 pages 6 49-6 5 4- 



