492 University of California Publications in Geology [Vol. 7 



event its teeth might attain a form more like those of a seal (i.e., 

 approach the conical type), its cranium might increase still 

 further in size, its neck become shorter, the tail be reduced, and 

 other changes in the skeleton take place. 



Plwca evidently represents a considerably more advanced 

 stage of adaptation to aquatic life than Latax, for it has devel- 

 oped the habits and corresponding adaptive characters whereby 

 it may live at times in the open seas independent of shore forms. 

 As has been suggested, there is some evidence that Latax also 

 has the ability to live far from land. 



The following characters are illustrative of the sort of modi- 

 fication which is shown particularly well by the seal, adaptation 

 of its teeth to a piscivorous diet, modification of its fore and hind 

 feet to serve as paddles, abbreviation of the tail, and flexibility 

 of the vertebral column. Modification in form of almost every 

 bone in the skeleton has taken place so as to carry on with greater 

 efficiency some new function in the new environmental medium. 

 The same statement is true of the sea-otter, though, of course, 

 the modification is less in amount. 



PALAEONTOLOGIC EVIDENCE BEARING ON PROBLEM OF 

 ORIGIN OF SEA-OTTER 



Our knowledge of the history of the Mustelidae in general and 

 the Lutrinae in particular is so limited that it is impossible to 

 point out at this time where the sea-otter first appeared. 



Lydekker has remarked 38 that the distribution of fossil Mus- 

 telinae accords well with present-day distribution of the living 

 species. So far as is known to the writer, this may be said of 

 the lutrine division of the Mustelidae also. It is therefore not 

 improbable that Latax is descended from some primitive form 

 that lived in North America or Asia, since Latax is found at 

 present in the waters of the Pacific Ocean only. 



The evident agreement in skeleton between Latax and Lutra 

 suggests that the sea-otter is an offshoot from the lutrine stock 

 after it had become differentiated as such. The fundamental 

 consonance of characters, as illustrated especially in the denti- 



38 Lydekker. R., "Siwalik and Narbada carnivora. " Palae. Ind., Cal- 

 cutta, series 10, vol. 2 (1884), p. 179. 



