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University of California Publications in Geology [Vol. 13 



appear to be closely allied with Phoca, so much so, that for many 

 years the remains of the first two mentioned were attributed to Phoca 

 vituUna. Little change appears among the Phocidae since the Upper 

 Miocene, so that the divergence into racial lines must have taken place 

 during a considerable period subsequent to this stage. 



Again in the Middle Pliocene we find that there were present a 

 relatively large number of phocid genera in the North Atlantic region. 

 Most of these appear to be intimately related with or were, at least, 

 forbears of our existing genera. In this estimate, as previously pointed 

 out, the passage of time has not resulted so much in the extinction of 

 aberrant types, as in the increased divergence or accentuation of racial 

 peculiarities in the types already in existence during the Middle 

 Pliocene. In support of this, it should be remembered that Callophoca 

 is allied to Pagophoca, Platyphoca with Erignathits, Gryphoca with 

 Ilalichoerus, Phocanella with Pagomys, and Phoca vitulinoides with 

 Phoca vitulma. 



A review of the Pleistocene phocicls shows that there is a surprising 

 similarity between them and their existing representatives. In fact, in 

 respect to some of the forms of this stage, many investigators have 

 concluded that there were no points of difference as the fossil remains 

 agreed in every particular with similar skeletal parts of living phocids. 

 Among these are Phoca groenlandica, Phoca vitulina, Phoca hispida, 

 and Erignathus barbatus. 



Thus the belief seems to be confirmed that the phocidae are a very 

 old group and their specialization and adaptation to a pelagic life have 

 proceeded along somewhat different lines than those of the Sirenia 

 and Cetacea. The most specialized seals have been commonly assumed 

 to be those that are the least dependent upon land for any part of 

 their existence. Conversely, the most generalized would be those 

 that are confined to the vicinity of or dependent upon land or ice. 

 The most specialized should show the most marked structural and 

 anatomical changes. 



Starting with the most generalized we may be able to observe some 

 structural indications as to how specialization has proceeded. Seals 

 have not as yet reached the stage, like whales and sirenians, of being 

 able to bring forth their j^oung in the water. The period that elapses 

 between birth and the time they take to water has been thought by 

 some to be one indication of their degree of adaptation. According 

 to Lloyd, 162 the young of Phoca vitulina may take to water at birth 



i 62 Lloyd, L., The game birds and wild fowl of Sweden and Norway, p. 381. 

 London, 1867. 



