EOCENE AND OLIGOCENE TITANOTHERES OF MONGOLIA 



901 



Eocene time by the agile lophiodonts of the family 

 Lophiodontidae. The tapirs (Tapuidae) are also 

 absent; these forest-living animals are rare in all 

 flood-plain formations. 



CARNIVORA 



True Carnivora are first known in the upper Eocene 

 (Miacidae). They are found also in the middle and 

 lower Oligocene (Canidae, Viverridae). The rhinoc- 



OLDER FORMATIONS 



Below these formations is the little-known Arshanto 

 formation, of middle (?) Eocene age, and far below 

 is the Gashato formation, of basal Eocene or Upper 

 Cretaceous age. Above the Ardyn Obo there have 

 been discovered the Houldjin and Hsanda Gol for- 

 mations, very rich in fossil mammalian life, probably 

 representing lower and middle Oligocene time. 



Former land areas Former migration areas Known fossil areas 



Figure 762. — Chief centers of the known zoogeographio distribution of the titanotheres 



Rocky Mountain region; Balkan region; Burma region; Gobi Desert of Mongolia. 



eroses are represented by three families, members of 

 all of which are rather rare — first, the amphibious 

 Amynodontidae ; second, the small, swift, cursorial 

 Hyracodontidae ; third, the large, tall, and slender- 

 limbed Baluchitheriinae. 



TITANOTHERES 



The titanothere family (Brontotheriidae) flourished 

 in upper Eocene time and was the dominant element 

 in the Mongolian fauna. The titanotheres were 

 extremely numerous in Mongolia during the deposi- 

 tion of the upper Eocene Irdin Manha and Shara 

 Murun formations. They also appear in the lower 

 Oligocene Ardyn Obo formation and then apparently 

 disappear. The Oligocene formations Hsanda Gol 

 and Houldjin contain no trace of titanotheres. The 

 dominating hoofed mammals of the middle Oligocene 

 are the great baluchitheres, of the species Baluchi- 

 therium grangeri. The upper Eocene titanotheres are 

 as large as the existing rhinoceroses, fully twice the 

 size of their American Eocene relatives. Three titano- 

 there life zones have been discovered in the flood- 

 plain formations, known as the Irdin Manha, Shara 

 Murun, and Ardyn Obo; they correspond, respectively, 

 to our Bridger (upper part) and Uinta formations 

 (Eocene) of Wyoming and Utah and the White River 

 group (Oligocene) of Wyoming and South Dakota. 



THE TERTIARY FORMATIONS OF MONGOLIA AND 

 THEIR FAUNAS 



NAMES, NAMES OF SUBDIVISIONS, AND THICKNESS 



The oldest name applied to the continental sedi- 

 mentary deposits of the Gobi Basin is the Khan-Khai 

 of Von Richthofen, who used it (1877) with the sig- 

 nificance of "deposits of an evaporating sea." No 

 one of these deposits, however, is caused by evapora- 

 tion; all are strictly continental in origin, and for this 

 reason Obruchev's term Gobi series (1892-1894) is 

 preferable. Gobi means desert basin, and Gobi series 

 is a suitable name for these scattered desert-basin 

 deposits. The name Gobi series was used by Obru- 

 chev to include the whole series of late sedimentary 

 beds, without distinction as to age. Obruchev's term 

 is therefore chosen, although Von Richthofen's has 

 priority. 



Some of these continental formations may over- 

 lap in time, so that the sum of all the thicknesses 

 may not afford an accurate statement of the total 

 column. Making all due allowance, however, for 

 possible overlap, no less than 6,000 to 8,000 feet of 

 Tertiary sedimentary strata have thus far been 

 discovered (1922, 1923) above the post-Jurassic 

 unconformity in the Gobi Desert of Mongolia. 



