EOCENE AND OLIGOCENE TITANOTHERES OF MONGOLIA 



943 



andrewsi revealed this wide contrast between Emholo- 

 therium and Brontotherium. 



The subfanuly Embolotheriinae, typified by the 

 characters observed in three distinct species of Enibolo- 

 iherium, probably represents a purely Asiatic phylum, 

 no members of which have thus far been discovered in 

 North America; nor do the three species of Erribolo- 

 therium from the Ulan Gochu formation here described 



seem to be related to the titanotheres discovered in the 

 three older geologic formations described above (pp. 

 903-941, figs. 773-795) ; they appear rather to represent 

 immigrants into the central Gobi region, whose ances- 

 tors lived farther north in central Asia. The geologic 

 age of the Ulan Gochu formation is probably lower to 

 middle Oligocene. It is intercalated between the 

 Tertiary formations shown on page 903 as follows : 



New theoretic sequence (1929) oj middle Oligocene to ujpiper Eocene formations 



[Compare p. 903] 



Geographic region 



Probable or estimated age 



Baron Sog__- 

 Hsanda Gol, 



Houldjin 



Ulan Gochu - 



Ardyn Obo 



Shara Murun_. 

 Irdin Manha. . 



Feet 



35 



3,000 



30 



132-195 



500 



500 



40-100 



Uliassutai trail 



Eastern Altai 



Iren Dabasu Basin.., 

 Uliassutai trail 



do 



do 



Iren Dabasu Basin. .. 



Baluchitherium n. sp J 



Baluchitherium grangeri zone 



Baluchitherium grangeri? zone 



Embolotherium andrewsi zone; E. loucksii 



E. grangeri. 

 Brontops gobiensis zone; Menodus mongol- 



iensis. 

 Protitanotherium mongoliense zone; Doli- 



chorhinus, Telmatherium, Manteoceras. 

 Protitanotherium grangeri zone. Dolicho 



rhinus olseni, Telmatherium berkeyi. 



Lower and middle Oligocene. 



Do. 



Do. 

 Extinction of titanotheres. 



Lower Oligocene. 



Summit of Eocene. Titano- 

 theres very abundant. 



Upper Eocene. Titanotheres 

 present. 



Materials. — In all 14 individual specimens of Embo- 

 lotherium were found in the Ulan Gochu formation 

 associated with the remains of lagomorphs and other 

 rodents, carnivores, creodonts, hyaenodonts, rhino- 

 cerids, lophiodonts, entelodonts, characteristic of lower 

 to middle Oligocene age. As exposed in three sections 

 (north of the bluffs on the Sair Usu-Kalgan trail, lat. 

 42° 31' N.) by Granger and Spock, the Ulan Gochu 

 formation shows a thickness of 132 feet at Twin 

 Oboes, 195 feet at Urtyn Obo, and 190 feet at Holy 

 Mesa, thus representing along period of geologic time. 



Genus EMBOLOTHERITTM Osborn, 1929 



Genotypic species Embolotherium andrewsi Osborn, 1929 



Generic characters. — PremaxUlaries elongate {Em- 

 bolotherium grangeri), reduced {E. andrewsi); elevated 

 anterior bony protuberances or nasal horns expanded 

 at the summits, moderately broad (E. loucTcsii), 

 extremely broad {E. andrewsi); frontals normal, not 

 entering into nasal protuberances. Broad postorbital 

 expansion of vertex; zygomata extremely broad. 

 Premolars with prominent tetartocones and partly 

 separate metalophs; M 3 with prominent hypocone 

 {E. andrewsi). 



Embolotherium loucksii Osborn, 1929 



Type: Am. Mus. 21610, Figure 797, A. Premaxilla 

 elongate, nasal protuberance with upward and forward 

 curvature arising from middle portion of vertex and 

 directly above orbit, straight superior border relatively 

 narrow at summit. Known from type specimen only. 



Figure 796. — Restoration of Emholotheriam andrewsi, the giant 

 single-horned titanothere of the lower to middle Oligocene 

 of the Gobi Desert, Mongolia. Reconstructed from three 

 crania, without knowledge of the limb skeleton. About one- 

 thirtieth natural size 



