1914] Taylor: Aquatic Adaptation in the Carnivora 493 



tion, militates against the idea that Latax is of independent origin. 

 If the sea-otter is derived from some form of otter immediately 

 ancestral to the Recent Lutra, it would presumably not date back 

 earlier than Pliocene or late Miocene time. As the genus Lutra 

 is known to have occurred in North America as early as the 

 Miocene, it may easily be the parent stock. 



EnJiydridon 30 or Enhydriodon from the Lower Pliocene of 

 Asia (Siwalik beds, India) possesses teeth which are interme- 

 diate in their crowns between Lutra and Latax. The superior- 

 tooth formula is the same as in Latax. Enhydriodon may lie 

 somewhere near the line of ancestry of this genus, although its 

 geographic location might argue against its actually being ances- 

 tral to the sea-otter. It may represent a form which, in another 

 part of the world, had started to specialize in the same direction 

 as that followed by the sea-otter. 



VARIATION IN LATAX 

 Under this head two conclusions seem obvious : ( 1 ) The 

 variation in the sea-otter has been away from Lutra; (2) The 

 variation in the sea-otter is intimately related to aquatic 

 adaptation. 



It will be remembered that 69.6 per cent of the most im- 

 portant differences between Latax and Lutra are shown to be 

 related to aquatic adaptation. Doubtless, if our knowledge were 

 greater, other characters would be seen to be so related also. 



In general a slow change through continuous variations is seem- 

 ingly indicated both by the nature of the characters separating 

 the sea-otter from the terrestrial form, and by probable analogies 

 with the development of other species of mammals as appre- 

 hended through a contemplation of certain palaeontologic phyla. 

 The differently shaped skull in Latax, such that the anterior ends 

 of the nasals are almost directly above the anterior ends of the 

 premaxillaries, the different degree of development of the para- 

 conid of the lower carnassial, the modification in the form of 

 the zygapophyses, and the slightly different size of the olecranon, 

 are some of the characters which would seem to indicate this 



39 Beddard, F. E., "Mammalia," in Cambridge Natural History (New 

 York and London, The Macmillan Company, 1902), vol. 10, p. 439. 



