92 University of California Publications in Geology [Vol. 13 



PALEONTOLOGIC EVIDENCE BEARING ON THE ORIGIN OP THE 



PINNIPEDIA 



Among living Mammalia the seals, sea lions and walruses comprise 

 a group whose ancestry has so far been shrouded in mystery. Even 

 if one were not familiar with the relative scarcity of known specimens 

 from the Tertiary marine beds of this and other countries he would 

 be justified, from the highly specialized aquatic adaptations of this 

 group, in placing their origin far back in the Tertiary, at a time 

 when the primitive divergence of the various lines of Carnivora was 

 taking place. 



The ancestry of the Pinnipedia has been the subject of investi- 

 gation by many of our foremost paleontologists. The subject is 

 especially interesting, for these men have not succeeded in convincing 

 each other as to the correct interpretation of the evidence which they 

 had at hand. Anyone who has had occasion to look up information 

 concerning this group is no doubt aware that of the two best and latest 

 books on fossil mammals, one contains an incidental mention of but 

 two species, while the other contains the statement that, since so little 

 is known concerning the pinnipeds, they will not be dealt with at all. 



In dealing with such a controversial subject as the ancestry of the 

 pinnipeds, it seems advisable to consider briefly, at least, the essential 

 criteria on which the interpretation of the various factors concerned 

 must depend. A consideration of the genealogy of this group involves 

 not only the morphologic evidence but also the stratigraphic occur- 

 rence, and the nature of the deposit as well, whether fresh-water or 

 marine. Morphologically, we are confronted with the problem of dis- 

 tinguishing between characteristics which would theoretically belong 

 to a definite stage in evolution and those due possibly to retrogression 

 or to other causes that must be taken into account. These morphologic 

 criteria, while of prime importance, are frequently masked by aquatic 

 adaptations. In general, to establish beyond doubt the geological 

 antiquity of the pinnipeds, it must be shown that the characters pos- 

 sessed by the earliest known forms are considerably more specialized 

 than those possessed by their assumed terrestrial relatives. 



Unfortunately the known fossils are not as yet sufficiently com- 

 plete to enable one to trace the history of the group below the Lower 

 Miocene or Temblor stage. From this stage on to the present time, 

 while there is much to be desired in the way of intermediate forms 

 to establish a closely connected series extending to modern types, yet 



