EXTINCT PLATANISTIDS 305 



Cetacean life does not enter. It is often held that 

 the original terrestrial ancestors of the whales 

 gradually adopted the marine life by first taking to 

 rivers and then gradually passing through estuaries 

 to the sea. It is alleged that these very Platanistids, 

 being largely fresh water in range themselves, furnish 

 such a proof of the way in which the ancestors of 

 the whales changed to an aquatic from a land life. 

 For they present, as has been pointed out, certain 

 archaic points of structure, and are fresh water in 

 habitat. There is, however, no a priori reason why 

 the original whale should not have boldly plunged 

 into salt water at once without gradually accustoming 

 himself to the change. For we have the sea otter 

 as an instance of a land animal frequenting the waters 

 of the sea. And, furthermore, the remains of extinct 

 Platanistids are from definitely marine strata. The 

 question, indeed, is one upon which guesses alone are 

 possible. 



Seeing that the Platanistids (represented at any 

 rate by the genus Iniopsis) go back as far in time 

 as the Zeuglodonts, we might expect to find some 

 approximation in structure between these two tribes, 

 nearer than that which obtains between the Zeuglo- 

 donts and others. There are, however, so few 

 apparent points at which the two groups touch that 

 it seems necessary to look upon the two as in- 

 dependently evolved from some more ancient form, 

 and to regard the Zeuglodont type as having 

 culminated in the later Squalodonts (see p. 307) and 

 then to have become extinct. There are, however, 



