1922] Kellogg: Pinnipeds from Miocene and Pleistocene Deposits 57 



Matthew 50 has discussed the supposed analogy of the walrus with 

 Smilodon and has also pointed out the features of the skull and 

 skeleton of Pantolestes 51 which agree more closely with those of the 

 walruses than with those of the remainder of the Pinnipedia. Most 

 of these may, as he states, be due to parallel adaptation. The follow- 

 ing citation is taken from his memoir : 



On the whole Pantolestes appears to be an aquatic Inseetivore of predatory 

 habits, with marked analogy and some degree of affinity to the Pinnipedia. Its 

 food may have been fish or turtles, or with a closer analogy to the walrus, fresh 

 water clams ; but was more probably an admixture of the three, as far as can 

 be inferred from the characters of the teeth. 



Dr. Murie 58 in his comprehensive treatise on the myology of the 

 walrus mentioned several points wherein walruses differ from the 

 other pinnipeds. He also showed that the resemblances between the 

 Odobenidae and the Otariidae are closer than are the resemblances of 

 either with the Phocidae. 



It is a question of much interest today whether or not the environ- 

 ment can influence or control variations in form and whether or not 

 gradual quantitative racial changes are matters of much importance 

 in evolution. That the influence of temperature shocks on the germ 

 plasm during the maturation stages is a factor in evolution is strongly 

 upheld by some workers in the field of biology. If temperature, along 

 with humidity and aridity, may be said to be a factor in evolution as 

 Tower 59 has shown, then there will be adequate grounds for the belief 

 that, as a factor in evolution, the entrance upon an aquatic mode of 

 life might act in a somewhat similar fashion. The main question as 

 regards this seems to be whether this adaptation has been a gradual 

 one or an abrupt saltation. Castle 00 in his experiments on the hooded 

 rats has demonstrated that selection may be effective in changing 

 racial characters gradually; that these changes are permanent, and 

 that selection is an agency capable of producing progressive racial 

 evolution. 



50 Matthew, W. D., Fossil mammals of the Tertiary of northeastern Colorado. 

 Mem. Am, Mus. Nat. Hist,, vol. 1, pt. 7, pp. 385-386. New York, 1901. 



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

 Eocene. Ibid., vol. 9, pt. 6, pp. 531-532. New York, 1909. 



Murie, J., Proe. Zool. Soe. London, vol. 7, pp. 411-464, pis. 51-55. 1871. 



59 Tower, "W. L., An investigation of evolution in chrysomelid beetles of the 

 genus Leptinotarsa. Carnegie Inst. Washington, Publ. no. 48, x + 321 pp., 30 pis., 

 31 text figs. 1906. 



60 Castle, W. E., Genetics and eugenics, vi+353 pp., 135 text figs., 2 pis. 

 Harvard Univ. Press, Cambridge, 1916. 



