OF WESTERN NOPtTH AMERICA. 



85 



19. EQUUS ZONE. 

 HOMOTAXIS. 



America. — Plains and border fauna. 1, '^Sheridan formation" 

 (Scott ^) or, 2, Equus zone, Hay Springs, northwestern Nebraska. 

 3, "Rock Creek beds" (Gidley^), Tule Canyon, Llano Estacado, 

 Texas. Widely scattered and numerous deposits in Great Plains and 

 Mountain regions, some of which have received distinct formation 

 names. 



Europe. — Preglacial. Forest beds of Norfolk (England) ; St. Prest 

 (Eure-et-Loire) ; Durfort (Gard), containing Elephas meridionalis (its 

 last appearance). The European fauna of this period includes 

 (Osborn,*^ 1900) 12 Pliocene species, 32 Pleistocene species and races, 

 now extinct, and 17 living species (7 Insectivora, 1 Cheiroptera.) 



FAUNA. 



It is noteworthy (Matthew,^ 1902) that chiefly the Plains fauna 

 and no purely forest fauna of this phase is known, a fact which may 

 account for the nonappearance of certain forest-living types. There 

 is some evidence of increasing moisture and of the renewal of streams 

 and of forests; for example, at Hay Springs, northwestern Nebraska 

 (a slightly earlier phase), the presence of streams is indicated by 

 Fiber, '0^ wooded rivers by Castoroides. In Silver Lake, Oregon (a 

 slightly more recent phase), a partly fluviatile and wooded country is 

 indicated by Fiber, Lutra, Castor, and Castoroides. 



The mammal fauna ^ is characterized negatively (1) by the absence 

 or disappearance of Perissodactyla-Ilhinocerotidae, (2) by the non- 

 appearance of Bovidse or Ursidse. It is characterized positively by 

 the first appearance (3) among Equidse, of Equus (3 species); (4) 

 among Proboscidea, of Elephas (2 species), E. columbi, E. imperator/ 

 (5) among Artiodactyla, of the distinctively American genus Antilo- 

 capra; among Camelidse, of Camelus; among Rodentia, of 6 new 

 modern genera and the first appearance of the extinct Castoroides. 



More in detail, among Rodentia of Nebraska and Oregon occur 8 

 existing genera of the same region, Arvicola, Fiber, Thomomys, 

 Geomys, Cynomys, Castor, Lepus, and Castoroides; among Carnivora- 

 Canidse, Canis (3 species) ; among Mustelidse, Lutra; among Felidse, 

 Felis; among Edentata, Mylodon and Paramylodon^ (plains or river- 



o Bull. Geol. Soc. America, vol. 9, 1898, p. 406. 



?>The fresh-water Tertiary of northwestern Texas: Bull. Am. Mus. Nat. Hist., vol. 19, 1903, p. 622. 

 c Correlation, etc.: Ann. New York Acad. Sci., vol. 13, 1900, p. 38. 

 d See Appendix, p. 91. 



« Matthew, W. D., List of the Pleistocene fauna from Hay Springs, Nebraska: Bull. Am. Mus. Nat. 

 Hist., vol. 16, art. 24, Sept. 25, 1902, pp. 317-322. Cope, E. D., The Silver Lake of Oregon and its region: 

 Am. NaturaUst, vol. 23, 1889, pp. 970-982. 



/ As noted on p. 83, E. imperator may represent a late Pliocene phase. 



g Brown,, Bamum, Bull. Am. Mus. Nat. Hist., vol. 19. 1903. no. .'^(i9-583. 



