ENVIRONMENT OF THE TITANOTHEEES 



99 



therium and of doubtful relationship both to earlier 

 or to later titanotheres, although it was possibly 

 derived from Manteoceras. Of the same phylum is 

 Protitanotherium swperhum, a gigantic animal, with a 

 jaw 24 inches long and premolars and molars of very 

 progressive type. It is much larger than the smaller 

 titanotheres of the lower Oligocene. 



Another titanothere of uncertain relationship is 

 BrachydiasUmatherium from Transylvania, eastern 

 Hungary (now Rumania). The geologic age of this 

 animal is not certain, but it is in an upper Eocene 

 stage of evolution as compared with the titanotheres 

 of America. 



FAUNA UNREPRESENTED 



The sequence of titanothere species in the Uinta 

 Basin illustrates the vagaries of the fossil records of 

 the Rocky Mountain basin region caused by local 

 physiographic changes; each kind of sedimentation 

 exhibits only a part of the fauna. For the entire 

 period covered by the lower sediments of the Uinta 



Basin little or no knowledge of the small terrestrial 

 fauna has come to light, none of the arboreal fauna, 

 and none of the plains and upland fauna, in contrast 

 with the surprisingly extensive knowledge of the 

 fluviatile and the swamp-dwelling fauna. Gradually 

 conditions changed, and Uinta B 2, as we ascend, 

 affords an increasing knowledge of the cursorial 

 meadow fauna; but it is not until Uinta C (true Uinta) 

 that local conditions became favorable to the pres- 

 ervation and fossilization of the small cursorial mam- 

 mals of the artiodactyl and perissodactyl divisions 

 of the ungulates. The sudden appearance of these 

 animals might be attributed to immigration, but it 

 is equally probable that they were all evolving in the 

 same region or in the adjacent Plains region. Thus 

 the data do not necessarily suggest immigration or 

 migration; these animals may have been brought into 

 the field of observation by changing conditions of 

 fossilization. The manner in which these numerous 

 phyla of titanotheres enter this field is shown in the 

 following table: 



Geologic and geographic range of phyla {here "subfamilies" and certain genera) of titanotheres 



[Showing their successive immigration from the north and their evolution in their i 

 column; the later immigrants are named in order from bottom to top. 



ew habitat. The earliest immigrants are those named at the bottom ot the first 

 The difference in the length of the blaclc bars has no significance] 



» Wind River B = Huerfano A. 

 I Bridger A = Huerfano B. 



■ Bridger and D = Washakie A. 

 ' Washakie A = Bridger C and D. 



• Uinta B = Washakie B. 



'Diplacodon, Eotitanotherium, Protitanotherium. 



ZONE 16: THEORETIC UINTA C 2 



Titanotheres have thus far been determined from 

 only the lower 100 feet of Uinta C. They are at 

 present only partly known. When fully known we 

 shall probably find close generic if not specific corre- 

 lation between the upper fauna (now unknown) of 

 Uinta C and the fauna of the lower levels (Chadron 

 A) of the White River group. The passage from 

 Eocene to Oligocene time probably occurs within the 

 period of Uinta C (true Uinta) deposition. Scott is 

 disposed to put all of Uinta C in the Oligocene. 



COMPOSITE EOCENE AND LOWER OIIGOCENE SECTION AT BEAVER 

 DIVIDE, WIND RIVER BASIN, WYO. 



Most of the Oligocene sediments in the Rocky 

 Mountain basin region have been eroded away. The 

 only locality where fossil-bearing lower Oligocene sedi- 

 ments still overlie those of the upper Eocene is on the 

 southern border of the Wind River Basin, Wyo., 

 where the true Titanotherium zone overlies sediments 

 containing a fauna similar to that of the Diplacodon 

 zone (Uinta C). The geologic section observed at this 

 point by the American Museum expedition of 1909 



