1922] Kellogg: Pinnipeds from Miocene and Pleistocene Deposits 89 



swollen, the basicranial region approaches that of the felid type, and 

 the astragalus has a ealcanear process. On the whole the Monachinae 

 appear to be more closely allied with the Lobodoninae than with the 

 Phocinae. 



LOBODONINAE 



As already remarked, the Antarctic Lobodoninae appear to be very 

 closely allied to the Monachinae. In considering the relationships of 

 the Lobodoninae with the Holarctic Phocinae, it is at once evident 

 that many great difficulties yet remain to be settled. This subfamily, 

 as a whole, differs considerably from any known fossil or living form 

 of the Holarctic Phocinae. 



It is difficult, however, to draw the exact differences that exist 

 between the Monachinae and the Lobodoninae. With the exception 

 of certain American writers, all other previous investigators, including 

 Sir William Turner, placed the genus Monachus in the Lobodoninae. 

 If Monachus is a member of this subfamily, then the affinities of a 

 large number of fossil pinnipeds are diverted to it. 



In regard to aquatic modifications, it has been found that the most 

 perfectly adapted marine mammals possess an exceedingly flexible 

 thoracic wall, and associated with it certain peculiarities in the affected 

 muscles. This condition is probably better developed in Leptonychotes 

 than in any other member of the Lobodoninae. The anatomy of this 

 seal was carefully studied by Hepburn, 179 and as a result of his studies 

 he came to the conclusion that pelagic mammals require a more flexible 

 chest than do terrestrial mammals. This flexibility, however, becomes 

 a source of danger to such a highly specialized marine mammal when 

 it comes ashore. In the case of the cetaceans, death is caused as much 

 by suffocation as by starvation. According to the observations of 

 Wilson, 180 few seals are more fully adapted to pelagic life than 

 Leptonychotes. This seal is an excellent swimmer, though landing is 

 very difficult for it to accomplish. After it has succeeded in landing, 

 its gait is exceedingly clumsy. Thus it would appear that a long 

 period must have elapsed since it enjoyed the power of using its limbs 

 as an ordinary terrestrial mammal, for it has almost entirely lost the 

 use of its limbs on land or ice. 



179 Hepburn, D., Observations on the anatomy of the Weddell Seal (Leptony- 

 chotes weddelli). Trans. Eov. Soc. Edinburgh, vol. 47, pp. 57-63, 191-194, 321- 

 332, pi. 4. 1909. 



180 Wilson, E. A., National Antarctic Expedition, 1901-1904, Mammalia. Publ. 

 Brit. Mus., vol. 2, pp. 23-24. London, 1907. 



