MARINE MAMMALS 197 



MARINE MAMMALS 



BY FREDERICK W. TRUE ^ 



CONTENTS 



Page 



Progress made during the past decade 197 



Theories accepted and rejected in recent years 198 



Hypotheses on trial 199 



Imiwrtant investigations and explorations which should be made 199 



Progress made during the past Decade 



The term Marine Mammals is ecological rather than systematic. 

 Under it are usually comprised several quite distinct groups of animals — 

 the whales and porpoises, or Cetacea; the sea-cows, or Sirenia; the zeu- 

 glodonts, or Zeuglodontia ; and the seals, walruses, and sea-lions, or 

 Pinnipedia. 



While the investigations of the last decade relative to these animals 

 have been extensive and important — on the whole, more so than those of 

 any comparable preceding period — it can not be said that the present 

 knowledge of the fossil representation of any of the groups is fairly 

 complete. 



The greatest progress, on the whole, has been made with regard to 

 cetaceans, closely followed by the zeuglodonts and sirenians, while the 

 knowledge of the seals and walruses has advanced but little, and that of 

 the sea-lions still less. I speak now both with reference to the forms 

 which actually inhabited the earth in former epochs and with reference 

 to the ancestry of existing forms. 



As regards cetaceans, the number of forms represented by names in 

 printed lists is very large, but many of these are based on inadequate 

 material, and on that account they can not be said to be well known. 

 Their osteology can not be completely worked out, and their relation- 

 ships are a matter of surmise rather than of demonstration. Nevertheless, 

 chiefly through the investigations of the last decade, the families of 

 toothed whales have been delimited with a considerable degree of ac- 

 curacy, and their relations to each other and their phylogeny have been 

 measurably determined. The same can not be said regarding the whale- 

 bone whales. Although the European material, at least, is extensive and- 

 is of a character which has permitted the quite complete description and 

 illustration of the osteology of different forms, their relationships and 



* Introduced by C. D. Walcott. 



