1922] Kellogg: Pinnipeds from Miocene and Pleistocene Deposits !)3 



those that are known furnish some clews as to how specialization has 

 proceeded. The early history of this group has long been a subject of 

 much controversy and will likely remain so until a series of connect- 

 ing forms is discovered to unite the known Miocene forms with their 

 ancestral group. However, what now remains is to direct attention 

 to the marine beds preceding the Temblor stage with the hope that 

 such connecting forms will be found and to ascertain if possible the 

 various points which will clear up the ancestry of this very interest- 

 ing group. While many writers have expressed opinions as to the 

 ancestry of this group, none of them have successfully traced the 

 origin of the group back to any particular genus, or even to any 

 particular family. This is largely due to the fact that, while quite 

 a number of forms have been described, most of the descriptions were 

 based on scanty material. 



Evolutionary changes have not progressed equally in all the families 

 of the Pinnipedia. These changes may be progressive in one direction 

 or retrogressive along another. There may be an apparent standstill, 

 as in the case of Phoca, or even a complete disappearance of one or 

 more lines. Such considerations complicate very much the problem 

 of following out the lines of descent of any group. At each period 

 some individuals were doubtless more advanced than others. Numer- 

 ous changes have taken place in the structural organization of the 

 different members of the three families of pinnipeds and these changes 

 may appear more pronounced in one part of the body than in others. 



In considering the evolution of the Pinnipedia it has to be admitted 

 that the earliest forms of this group of which we have any knowledge 

 were even then somewhat highly modified for aquatic life. The pinni- 

 peds were well specialized in the Miocene for a pelagic life and the 

 distribution of the fossil forms corresponds very well, in most respects, 

 with the present distribution of their living representatives. There 

 are some doubtful exceptions to this statement which have as yet to 

 be confirmed by future exploration. 



The earliest forms, as already mentioned, of which we have any 

 knowledge, are found in the Lower Miocene ; at the same time it is 

 certain that the group was detached from the main stem of the Gar- 

 ni vora at a much earlier date. Several theories at wide variance with 

 each other have been proposed to explain the origin of this group. 

 Their relationships with Pantolestes, Smilodon, Patriofclis, Cynarctus, 

 and Synoplotherium have been discussed by various writers. The 

 derivation of the Pinnipeds from the arctoid Fissipedia has been sup- 

 ported by George Mivart, Thomas Huxley, W. H. Flower, and more 



