OF WESTERN NORTH AMERICA. 



43 



appeared (Wind River), namely, the Titanotheriidae, possibly entering 

 from the Great Plains Region to the east; 1 new family related to the 

 Edentata-Dasypoda, or armadillos, appeared (Bridger), probably 

 from the southern Great Plains Region and originally of South 

 American origin before the Cretaceous land connection was inter- 

 rupted. 



.LOWER TO MIDDLE EOCENE (EUROPE, ETAGES YPRESIEN, LTTTETTEN 



INFERIEITR). 



4. WIND RIVER FORMATION; « LAMBDOTHERIUM AND BATHYOPSIS ZONES . 



(Figs. 1-2, 5; PI. L) 

 HOMOTAXIS. 



North America. — 1, Wind River formation. Hay den, of northern 

 Wyoming (1,200-1,400 feet). 2, Upper half of the Wasatch of the 

 Bighorn Basin. 3, Lower part of Huerfano formation, Hills, of 

 Colorado (200? feet). 



Europe (provisional), — The lower part of the Wind River is partly 

 equivalent to the Ypresien of France. The upper part of the Wind 

 River is approximately equivalent to the Lutetien inferieur of France. 



FAUNA. ^ 



The mammals of the Wind River deposition are less fully known 

 than those of either the Wasatch or the Bridger. So far as these 

 three faunse can be separated at present, the lower Wind River pre- 

 sents closer afhnities to the Wasatch, while the upper Wind River 

 presents closer affinities to the Bridger. The balance of life between 

 the archaic and the modernized mammals continues to be nearly 

 even. 



Summary of genera. 



Archaic or Cretaceous mammals 17 



Modernized or Tertiary mammals 17 



34 



Faunal sequence to the Wasatch. — Partial faunal continuity with, 

 and partial sequence in time to, the Wasatch is sustained (1) by the' 

 presence of 19 genera in common with the Wasatch, (2) by the rarity 

 or absence of a few Wasatch animals, (3) by the occurrence of more 

 advanced (or post-Wasatch) stages of evolution in a large number 

 of descendants of animals which persist from the Wasatch, (4) by 



«This section has been revised by Prof. F. B. Loomis, the most recent explorer of this basin. 



b Loomis, F. B.. Origin ot the Wasatch deposits: Am. Jour. Sci. May, 1907, 4th ser. vol. 23. pp. 356-364 

 Cope, E. D. , The badlands of the Wind River and their fauna: Am. Naturalist, vol. 14, 1880, pp. 745-748. 

 See Appendix, p. 91. 



