310 University, of California Publications. [Geology 



species represented. Despite the fact that eagles are known to 

 resort to carrion diet at times, the great preponderance of this 

 bird's remains over those of other avian species is surprising. 

 Was the golden eagle numerically so much more abundant than 

 any of the vultures as to have outnumbered all species of that 

 group despite its less habitual resort to carrion? Was its feeding 

 upon carrion a matter of more common occurence then than 

 now? A greater numerical abundance owing to the absence of 

 man, one of its chief enemies, may have sharpened competition 

 to such a degree as to compel it oftener to resort to such a habit. 

 Again, was the submersion of the carcass of the entrapped mam- 

 mal more rapid than we have hitherto considered so that it re- 

 mained attractive to the predatory form almost as long as it was 

 exposed to view? 



HALIAeTUS LEUCOCEPHALUS (Linnaeus) 



This species is represented by a series of thirteen tarsometa- 

 tarsi from the asphalt and by Recent specimens of the two sub- 

 species at present recognized by American ornithologists. The 

 largest of the fossil series exceeds both in length and in robust- 

 ness the large female of H. I. alascanus at hand, while the small- 

 est specimen is quite noticeably less than the Recent //. /. leuco- 

 cephalus taken at Long Island. The. intergradation in size and 

 the homogeneity of characters is perfect throughout the series. 



There seems to have existed in Southern California during 

 the Pleistocene a generalized stock of this species which was sub- 

 ject to a wide range of variation on either side of a norm lying 

 intermediate between the varieties at present recognized as H. 

 leucocephalus and H. alascanus. In the series of fossil tarsometa- 

 tarsi at hand, there appears no suggestion of a splitting of the 

 species by a grouping about two norms. Alascanus and leuco- 

 cephalus are at present separated geographically by a somewhat 

 elastic barrier of temperature corresponding almost exactly with 

 the northern limit of the Sonoran region of Arctogaea as deter- 

 mined by the distribution of Recent Mammalia. There appears 

 to have occurred in the species since Pleistocene time a selec- 

 tion based upon adaptation to climatic conditions causing the 

 retraction of a larger phase to the northward and a smaller to 



