OF WESTERN NORTH AMERICA. 



81 



FAUNA/' 



From our present knowledge, the close of the Miocene or advent of 

 the Pliocene may be characterized: Negatively, (1) by the absence of 

 Artiodactyla-Oreodontidse and the rarity of Merychyus, Meryco- 

 choerus, etc., which thus far are represented only by fragmentary 

 specimens; (2) by some reduction in the number of Camelidse (in this 

 family PliaucJienia is now the characteristic genus) ; (3) by the rarity 

 of the browsing horses (HypoMjppus) ; (4) by the disappearance of the 

 Perissodactyla-Chalicotheriidse. Probably some of these absent 

 forms will be unearthed by future exploration. Positively, (1) by 

 the more advanced evolution of the Rhinocerotidse in progressive 

 species of Teleoceras, Peraceras, and ApTielops; (2) by more progress- 

 ive but still long-jawed forms of Proboscidea-Mastodontidse, with 

 four or more crests on the molar teeth. 



Characteristic animals are: Among Rodentia-Mylagaulidse, Myla- 

 gaulus, also a new and more specialized genus, Epigaulus Gidley; 

 among Castoridge, Dipoides; among Carnivora, both Felina? and 

 Machaerodontinse ; among Canidse, jElurodon, fDinocyon; among 

 Rhinocerotidse, Teleoceras, Peraceras, Aplielops, including the pro- 

 gressive species A. malacorJiinus; among Equidse, Protohippus ; 

 among Artiodactyla, 4 families, (a) Dicotylidse, Prosthenops; (Jb) Cam- 

 elidsB, Procamelus , PliaucJienia (a large form), Alticamelus (typical 

 in the Rattlesnake formation, Oregon); (c) Merycodontinse, Mery- 

 codus; (d) Cervidse, Blastomeryx; among Proboscidea, Trilophodon 

 campester and T. euJiypodon are recorded, both with long jaws. 



16a. RATTLESNAKE FORMATION (200 FEET) OF JOHN DAY VALLEY, OREGON. 



(Figs. 1, 10; PI. I.) 



The sparsely known fauna of this formation, as determined by 

 Merriam,^ Sinclair, and Gidley, contains the tortoise Clemmys 

 Jiesperia Hay. Among mammals: Perissodactyla, (a) Equidse, Plio- 

 Mppus supremus, (b) Rhinocerotidse-^Teleocerinse, indet.; Artiodac- 

 tyla, (a) Dicotylidse, indet., (h) Camelidje, Alticamelus alius (the 

 typical form), also PliaucJienia; large species of Procamelus still 

 survive. 



PLIOCENE. 



Homotaxis, — Pliocene homotaxis must be prefaced by the state- 

 ment that the American fauna is sparsely and imperfectly known as 

 yet, and that correlations with Europe (etages Messinien, Plaisancien, 

 Astien) are very provisional. The gaps will undoubtedly be filled 

 eventually. 



n Sec Appendix, p. 115. 



J> A contribution to the geology of the John Day basin: Bull. Dept. Geology, Univ. California, 

 vol. 2, 1901, pp. 310-312. 



56092— Bull. 361—09 6 



