1922] Kellogg: Pinnipeds from Miocene and Pleistocene Deposits 97 



on "gut-patterns" also indicate that the similarities observed in the 

 long intestine may also be a case of convergence. The bears differ from 

 all other Carnivora in the possession of an ansa coli dextra and the 

 lack of a caecum. 



At present we may say that the verdict is not proven for any of 

 the hypotheses that have been offered. 



CONCLUSIONS 



Aquatic adaptation has undoubtedly masked many changes in 

 structure in the evolution of the Pinnipedia and these changes have 

 profoundly affected the whole internal as well as external organiza- 

 tion of the various members of the group. The most obvious changes 

 relate largely to those of the limbs and skull. The vertebrae of most 

 fossil pinnipeds are very imperfectly known. We can only surmise 

 the incipient transformations that marked the transformation of some 

 member of the land carnivora into a pelagic pinniped. 



According to the theory proposed by Kiikenthal 1 " 4 we may assign 

 the relationships of aquatic animals in proportion to the length of time 

 that has elapsed since their separation from their terrestrial relatives. 

 Also that the amount of adaptation is intimately connected with the 

 length of time that has elapsed since they were subjected to the 

 influence of the water and with the degree of connection that they 

 have retained with the land. This theory explains, to some extent, 

 why the pinnipeds have not been so strongly modified as either the 

 whales or sirenians, for they are dependent upon land to bring forth 

 their young. 



In course of time, aquatic adaptation has brought about a shorten- 

 ing of the fore limbs and a lengthening of the hind pes. At the same 

 time there has been a marked change in the nature of the molariform 

 teeth. The reduction of the angular tuberosities, as pointed out by 

 Osburn 195 is generally indicative of aquatic adaptation, for water does 

 not require the development of such heavy muscles as are needed 

 for progression on land or for support. There is also an increased 

 flexibility of the vertebral column, along with the reduction of the 

 interlocking processes, a shortening and a heightening of the centra 



is* Kiikenthal, W., Ueber die Anpassung von Saugethieren an das Leben im 

 Wasser. Zool. Jahrb., vol. 5. 1890. 



195 Osburn, R. 0., Adaptation to aquatic, arboreal, fossorial and cursorial habits 

 in mammals, aquatic adaptations. Am. Nat., vol. 37, no. 442, pp. 651-665. Adap- 

 tive modifications of the limb skeleton in aquatic reptiles and mammals. Ann. 

 Acad. Sci. New York, vol. 16, p. 449. 1906. 



