OF WESTERN NORTH AMERICA. 



79 



UPPER MIOCENE (EUROPE, ETAGE PONTIEN). 

 15. OGALALLA FORMATION (IN PART); PROCAMELUS ZONE. 

 (Figs. 1, 10; PL I.) 

 HOMOTAXIS AND SYNONYMY. 



North America. — This includes the ''Loup Fork" of Leidy, Marshy 

 also of Scott and Osborn, in part. 1, ''Nebraska" of Scott, 1894, 

 western Nebraska.^ 2, Cosorijx zone, Scott, ^ 1894. (The genus 

 Cosoryx is preoccupied by Merycodus, so it appears that this name 

 can not be used.) 3, Ogalalla and Arikaree of Darton (in part), 

 1899, western Nebraska. 4, ProtoJiippus zone of Osborn, 1907. 5, 

 "Santa Fe marls" of Cope, New Mexico. 6, "Clarendon beds" of Gid- 

 ley, Llano Estacado, northwestern Texas (75 feet). Northern Plains: 

 7, "Madison Valley beds" of Douglass, Montana (1,200 feet). 



Europe. — Etage Pontien, Pikermi, Eppelsheim. The so-called 

 "Loup Fork mammals," although including Hipparion, are not quite 

 so modernized as those of Eppelsheim and Pikermi, which should be 

 regarded as lower Pliocene. 



This fauna has become universally known as the "Loup Fork 

 fauna" (Cope, 1877), owing to errors on the part of Hayden, Leidy, 

 Cope, and their successors, arising from the confusion of late Miocene 

 and upper Pliocene faunae. But, as shown fully on page 84, the term 

 "Loup Fork" is equivalent to "Loup River," and the latter term 

 was originally applied so as to include an upper Pliocene or lower 

 Pleistocene formation containing Elephas imiJerator. 



FAUNA. ^ 



This is one of the best known, most widely distributed, and 

 most characteristic faunae in all the Tertiary series. There is no 

 evidence of a fresh Eurasiatic migration, but rather of rapid local 

 evolution. The genus Protohippus distinguishes it clearly from the 

 middle Miocene, which contains MerycJiippus only. Other new dis- 

 tinctive genera are the camels Procamelus and PliaucTienia, the 

 horse Neohipparion, and the rhinoceros Peraceras. The wide distri- 

 bution of a similar fauna at this stage indicates widespread condi- 

 tions of aridity and a uniformly favorable environment, summer 

 droughts probably lengthening and eolian deposits increasing. From 

 Montana on the northwest and Texas on the southwest to Nebraska 

 in the central west we find a very similar list of animals; so the homo- 



a Bull. Geol. Soc. America, vol. 5, 1894, p. 595. 



h Under a misapprehension as to Scott's definition of the term " Nebraska," both Hatcher and Peter- 

 son first applied this term to a part of the lower Arikaree or lower Miocene. 



c Matthew, W. D., and Gidley, J W., New or little known mammals from the Miocene of South Dakota^ 

 etc.: Bull. Am. Mus. Nat. Hist., vol. 2d, 1904, pp 241-2G8, See Appendix, p. 91. 



