36 



CENOZOIC MAMMAL HORIZONS 



fauna. It must be remembered that while there is no evidence of a 

 ''Hoi arctic a," or north polar continent, similar to the ''Antarctica" 

 in the south, there was certainly a great American-Asiatic land mass 

 to the north, of temperate climate, favorable to the evolution of mam- 

 malian life. The vast region between parallels 50° and 70° is also a 

 terra incognita until the mid-Pleistocene. There is every reason to 

 believe that even to the north this region was through the whole 

 pre-Pleistocene Tertiary highly favorable to mammalian life, other- 

 wise the faunal continuity between Europe and western America 

 could not have been sustained by constant intermigration. Wort- 

 man" and others have especially advocated the theory of a northerly 

 or Arctic Circle land mass as a source of evolution and southward 

 migration. 



The actual origin of this modernized fauna which suddenly appears 

 in North America and Europe is, however, hypothetical and will not 

 be determined until Eocene fossil mammal beds in northern portions 

 of America and Asia shall have been discovered. 



LOWER EOCENE (EUROPE, ETAGES SPARNACIEN, YPRESIEN). 

 3. WASATCH FORMATION; CORYPHODON ZONE. 

 (Figs. 1-4; PI. I.) 

 HOMOTAXIS. 



North America.-^l , Typical Wasatch (in part), Knight formation, 

 Veatch (1,750 feet), western Wyoming. 2, Wasatch near Black 

 Buttes, Washakie basin, Wyoming. 3, Wasatch of the San Juan 

 basin of northern New Mexico (1,500 feet). 4, Wasatch of the Big- 

 horn Basin of northern Wyoming (2,391 feet, Loomis). 5, Lower 

 portion of the Huerfano formation near Spanish Peaks, Colorado. 



South America. — No South American affinities are known. 



Europe. — Strong affinities with the fauna of the etage Sparnacien 

 and especially with that of the etage Ypresien (Londinien) of France 

 are found in the evolution of the archaic and in the sudden appear- 

 ance of the modernized Mammalia of this period. 



The Sparnacien (Soissonais inferieur) includes in France the 

 deposits of Soissons, Meudon, and Vaugirard ; in Englaijd, the Wool- 

 wich beds and lower Ijondon clay. The Ypresien (or Soissonais 

 superieur) of France includes deposits of Ay and Cuis. It is in this 

 stage that the European modernization becomes marked by the 

 sudden appearance of Primates, Rodentia, 2 families, Perissodactyla- 

 Lophiodontidse and Artiod^^^la-Dichobunidae. The Lutetien infe- 

 rieur of France corresponds^^proximately with the American upper 

 part of the Wind River. 



a Wortman, J. L., Studies of Eocene Mammalia in the Marsh collection, Peabody Museum; Part II, 

 Primates: Am. Jour. Sci., June, 1903, 4th ser., vol. 1.5, pp. 419-436. 



