1911 J Miller: Eagle Tarsi from Kancho La Brea. 



307 



Description op Species 



AQUILA CHRYSAETOS (Linnaeus) 



Twenty-nine almost perfect tarsi represent this existing 

 species. Except in the matter of size there is almost no per- 

 ceptible variation in the specimens of the entire series. A greater 

 or less distinctness in the rugosities about the head of the bone 

 to which the articular ligaments attach is here ascribed to age 

 of the individual. The positions of these rugosities are very 

 constant and form one of the bases of distinction between the 

 genera Aquila and Haliaetus. Differences in size of the two 

 extremes of the series are cpiite noticeable ; there is, however, a 

 complete intergradation in this respect. This variation is, in all 

 probability, due to sex and individuality combined, large males 

 intergrading with the smaller females in regard to size of tarso- 

 metatarsus. 



The most noticeable differences between this series and the Haliaetus 

 series lie in the characters of the head region of the bone. When viewed 

 from the front, the depression into which the two proximal foramina open 

 is deep and sharply delineated on all sides except the distal side. The 

 inner margin of this depression just even with or but slightly above the 

 internal, proximal foramen is marked by an elongate, ridge-like papilla 

 which is the outer attachment of the ligamentous supratendinal bridge. 

 In the genus Haliaetus, the proximal depression is very shallow and ill 

 defined and the outer attachment of the ligamentous bridge lies almost 

 directly above the interior proximal foramen. The tubercle of the tibialis 

 anticus is much the same except that it is placed further down the shaft 

 in Aquila. On viewing the bones from their proximal articular faces, the 

 two species are at once distinguishable by the much greater development in 

 Aquila of the outer ridge of the hypotarsus. In Haliaetus this portion 

 appears as a rounded hillock, whereas in Aquila it is developed into a 

 strong unciform process. 



Minor differences lie in the positions of the proximal foramina. These 

 are placed close together in Haliaetus and the outer is almost invariably 

 raised appreciably above the inner. The reverse is true of the foramina 

 in Aquila. In the latter genus the inner attachment of the ligamentous 

 bridge is usually less distinct and less elongate than in the former. The 

 length of the bone in Aquila averages greater and the robustness less. The 

 inner trochlea is larger in every respect, the outer trochlea is more com- 

 pressed laterally. 



None of the bones in the large series of Aquila surpasses in 

 size the single specimen of the Recent phase which is at hand. 

 The evidence furnished by the group of fossil tarsometatarsi is 



