OF WESTERN XORI'IT A:\lKKTrA. 



57 



reference uncertain); among Perissodactyla-Tilanotheriidse, Doliclio- 

 rliinus cornutus. Creodonta-^Iesonycliida* (last appearance). Closely 

 ecjiiivalent to upper part of ''Washakie" (B). 



A. Lower beds of Uinta Basin, later Eocene, 800 feet, bro^vn beds. 

 ^rintatherium zone, approximately equivalent to upper part of the 

 Bridger (C-D) and to corresponding beds in Washakie Basin (A). 



Of archaic mammals the Carnivora-Creodonta include 2 families, 

 Mesonychidae (last appearance) and Oxyjenid^e (last appearance); 

 the Hysenodontidse, if existent, have not been discovered. The 

 Eohasileus zone contains the last of the Amblypoda-Uintatheriidae. 

 Of modern mammals (Uinta) the Primates are little known as yet. 

 Among Rodent ia 2 families, (a) Isch}Tomyid8e {Paramys, Pseu- 

 dotomus), (b) Heteromyidse (Protoptyclius). Among Pro-Carnivora, 

 Miacidje, also true Carnivora" (Cynodictis). Of Ungulata-Perisso- 

 dactyla, 6 families: (a) Titanotheriidse, horned animals of much 

 greater size, especially increasing after the extinction of the huge 

 Dinocerata, (b) Equidse, (c) Lophiodontidae (still to be discovered), 

 (d) Tapiridae, (e) Hyracodontidae, (/) Amynodontidse. Xo true 

 Rhinocerotidse. Ungulata-Artiodactyla now assume the five divi- 

 sions or families which are found in the American Oligocene, namely: 

 (a) Elotheriidae-Achaenodontinae, mammals of large size; (b) Homa- 

 codontidae (Dichobunidae ?); (c) Oreodontidae, Xorth America only; 

 (d) Hypertragulidae, Xorth America only; (e) Camelidae, the- first 

 definite recognition of this family, Xorth America exclusively until 

 the Pliocene. The Uinta selenodonts ^ are all brachyodont and 

 much alike in dentition; they are much less abundant than in the 

 lower Oligocene. 



OLIGOCEXE. 



IV. FOURTH FAUNAL PHASE. 



Second modernization — First knowledge of the Great Plains fauna — 

 Absence of all archaic mammals except Hyaenodontidae — Reestabhsh- 

 ment of faunal resemblance with western Europe, followed by a long 

 period of independent evolution and partial extinction of the same 

 fauna to the close of the lower Miocene. 



Environment; dry-land conditions in the Great Plains. — In addition 

 to the geologic and faunistic evidence above cited we find collateral 

 evidence from herpetology. The Testudinata, as analyzed by Dr. 

 O. P. Hay,<^ furnish important proofs of prevailing dry-land conditions 



a A rather arbitrary distinction, founded on the union of the scapholunar bones, which first occurs 

 in certain Bridger species of the Miacidae; the union is exceptional in the Bridger, presumably common 

 in the Uinta, and universal in the White River. More essential distinctions are the small size of the 

 brain and the absence of tympanic bullae. 



Scott, W. B., The selenodont artiodactyls of the Uinta Eocene: Trans. Wagner Free Inst. Sci., 

 Philadelphia, vol. 6, 1899, pp. ix-xiii, 1-121. 



c In his monograph on the fossil turtles of North America, published l)y the Carnegie Institution. 



