1922] Kellogg: Pinnipeds from Miocene and Pleistocene Deposits 65 



The successive cranial changes of Callotaria alascana have been 

 well figured in the last report on the fur seal. 82 A glance at these 

 plates will show what changes take place as an animal approaches 

 maturity, and also, which is more interesting, that an individual with 

 a fully developed sagittal crest is nearly twelve years old. With each 

 succeeding year the lambdoidal crests became more prominent and 

 the relative length of the interorbital region increases, while the con- 

 dyles become more visible when the skull is viewed from above. The 

 sagittal crest is conspicuous on males over ten years old. 



Those types of pinnipeds which are best adapted for walking on 

 land, such as the eared seals or Otariidae, and which are the least 

 adapted to life in the water or have adopted an acpiatic life later than 

 the Phocidae or Odobenidae, have an astragalar foramen or at least 

 a vestigial one. Primitive plantigrade Arctoidea also have an astraga- 

 lar foramen according to Matthew. 83 This may indicate another point 

 of resemblance of the pinnipeds to the bears. On the other hand, it 

 appears that the increased adaptation to the life in the water, as 

 exhibited by the stages of which Zalophits, Eumetopias, the Odobeni- 

 dae, and the Phocidae may be taken as respective representatives, has 

 brought about in the elapsing time a gradual constriction and a final 

 abortion of this peroneal artery by the pinching in of the tibia against 

 the astragalus, and by the increased flexibility of the limbs as they 

 were developed to their efficiency as paddles, along with the eversion 

 of the pes. Thus aquatic adaptation may also cause a closure of the 

 astragalar foramen, as well as digitigradism, which Matthew sug- 

 gested. 84 Matthew, in an earlier paper, however, states that Professor 

 Osborn has suggested that this astragalar foramen in the creodonts 

 may have held the extension of the interosseous ligament, instead of 

 the peroneal artery. 85 



A study of the known fossil otarids shows, then, that the origin 

 of this family is as yet completely unknown. This is more apparent 

 when one learns that the earliest known members were already quite 

 specialized for their aquatic mode of living. The best concrete evi- 

 dence of this is furnished by their possession of a single haplodont 



82 Osgood, W. H., Preble, E. A., and Parker, G. H., The fur seals and other life 

 of the Pribilof Islands, Alaska, in 1914. Bull. U. S. Bur. Fish., vol. 34, no. 820, 

 pis. 9-10. 1915. 



83 Matthew, W. D., The carnivora and insectivora of the Bridger Basin, Middle 

 Eocene. Mem. Am. Mus. Nat. Hist., vol. 9, pt. (i, p. 551. 1909. 



s* Matthew, W. D., op. cit. 



ss Matthew, W. D., Additional observations on the creodonta. Bull. Am. Mus. 

 Nat. Hist., vol. 14, p. 16 (footnote). 1901. 



