MARINE MAMMALS 199 



vailing one at present, although opinions are not entirely unanimous. 

 The origin of the whalebone whales is not known, though it is recognized 

 that their ancestors were toothed forms. 



The notion, recently promulgated, that the large whales are direct de- 

 scendants of large marine reptiles of similar form is treated somewhat in 

 the light of a paleontological jest. 



The idea that the Cetacea are. derived from pig-like mammals is, 1 be- 

 lieve, no longer entertained. 



That the existing Sirenia were derived from forms with four func- 

 tional legs has been demonstrated, and that the group had common ances- 

 tors with the Proboscidea seems to be generally accepted at present. 



Hypotheses on Trial 



It has been shown that cetaceans have some resemblances to edentates, 

 but there are no known fossil forms, I believe, that strengthen the idea 

 that these similarities are genetic. 



As to the zeuglodonts, the weight of opinion seems to be that they are 

 descendants of creodonts, but some consider that they actually are aquatic 

 creodonts. This view is opposed by others, who think that the zeuglo- 

 donts may quite as well be descendants of insectivores. 



Two hypotheses regarding the origin of the pinnipeds find adherents. 

 The one most strongly advocated is that they are descended from creo- 

 donts. The other is that they are derived from bear-like fissiped car- 

 nivora. 



The hypothesis that the cetaceans, or some groups of them,, were pro- 

 tected by an armor of bony scales, and that Zeuglodon had such an armor 

 is at present in controversy. It has been demonstrated that some recent 

 porpoises have such scales on the dorsal fin and some fossil species had 

 them on the flippers. 



It has been inferred, but not demonstrated, that the walruses are de- 

 rived from some primitive form of sea-lion. 



Important Investigations and Explorations which should be 



MADE 



It is very desirable that further collections of the American zeuglo- 

 donts should be made, and that a full and well illustrated description of 

 Z. cetoides should be pu])lished. 



It is especially important tliat the Oligocene formation of the south- 

 eastern United States, and particularly certain areas in South Carolina, 

 should be searched for primitive cetaceans, which will quite surely be 



