252 THE MAMMALIA. 



seals and whales, the shape of the skull and 

 the strong nasal bones covering the nasal cavity 

 having been thought to indicate this. Their length 

 varies between twelve to seventy feet. They belong 

 in America to the Eocene, in Europe to the Mio- 

 cene period. 



Squalodon approaches closer to. the Dolphins 

 than does Zeuglodon, more particularly by the 

 position of the nasal bones and the corresponding 

 displacement of the other bones. Its teeth (Fig. 

 47), like those of the Zeuglodonta, remind one of 



31 4 

 the Seals. The dental formula is : i -, c -, pm . 



17 



m -. The compressed molars, which are pyra- 



midical in form, show a certain external resemblance 

 to the teeth of the Sharks. 



As the Zeuglodonta including the Squalodonta 

 are not yet as far advanced in the transformation 

 of their skull as the Delphinidae, it has never oc- 

 curred to anyone to regard the Dolphins as ances- 

 tors of the Zeuglodonta. Such a supposition would 

 be as irrational as if we were to imagine the 

 Antelopes descended from Oxen. On the other 

 hand, however, as great a difficulty would have to 

 be faced were we to suppose that animals of the 

 Squalodon species had left descendants of the 



