EOCENE AND OLIGOCENE TITANOTHERES OF MONGOLIA 



939 



Menodus mongoliensis Osborn, 1925 



Original reference.- — Osborn, H. F., Upper Eocene 

 and lower Oligocene titanotheres of Mongolia: Am. 

 Mus. Novitates No. 202, 1925. 



Type locality and geologic level. — The type of 

 Menodus mongoliensis is from the Ardyn Obo forma- 

 tion, Brontops goliensis life zone, collected on the 

 Kalgan-Uliassutai trail, southeastern Gobi, Mongolia. 



Specific cJiaracters. — The type of Menodus mon- 

 goliensis (Am. Mus. 20351) is a second right inferior 

 molar in which the second lobe is perfect and the first 

 lobe is broken in front. This fractured molar (fig. 

 792, B, Bi, B2) corresponds best in size and character 

 with the two lobes of the second inferior molar of the 

 right side, of a large male of Menodus ( = Titano- 

 therium) giganteus of the lower Oligocene Chadron 



80 millimeters of the two lobes of 1x13 in Marsh's type 

 of Brontops rohustus. The width of the anterior lobe 

 of this type molar of M. mongoliensis is 40 millimeters, 

 as compared with a width of 52 millimeters in the 

 corresponding lobe of B. roiustus and of 42 millimeters 

 in M. giganteus (Am. Mus. 1007). Height of unworn 

 second lobe 53 millimeters. Other specific characters 

 are the elevation or subhypsodonty of the anterior 

 lobe (53 mm.) prominent postero-external cingulum; 

 also elevated and serrated crest extending backward 

 from the metaconid; prominent posterior cingula on 

 metaconid and hypoconid ; internal valleys of trigonid 

 and talonid widely open, shallow character of the 

 internal valleys; molar proportions similar to those 

 of Menodus, indicating a long-headed rather than a 

 broad-headed animal. 



Figure 793. — Type jaw of Manieoceras? irdinensis (Am. Mus. 20111), Irdin Manha formation 



(upper Eocene) 



A, Eight lateral aspect of jaw with crowns of premolar teeth and canine teeth restored in outline; Ai, inferior aspect of symphysis of 

 same specimen; A2, superior aspect of symphysis and alveoli of anterior teeth; As, superior aspect of third inferior molar. All 

 one-third natural size. 



formation (horizon B) of South Dakota; in fact, these 

 lobes exceed in length those of the largest specimens 

 of the true female Menodus giganteus in the American 

 Museum collection. Consequently, we refer this 

 tooth not to any species of Brontops, in which the 

 second lower molars are relatively broad, low-crowned, 

 and less elongate anteroposteriorly, but to a gigantic 

 species of Menodus, to which the name Menodus 

 mongoliensis has been provisionally assigned. The 

 specific characters are as follows: 



A large menodont equal in size to the largest 

 Menodus giganteus of South Dakota; second inferior 

 molars relatively elongate, narrow, with elevated 

 crowns. Estimated length of two lobes 93 millimeters, 

 as compared with 83 millimeters in a large female 

 Menodus giganteus (Am. Mus. 506), and also as 

 compared with the corresponding measurement of 



MONGOLIAN TITANOTHERES OF UNCERTAIN 

 GENERIC REFERENCE 



SUBFAMILY MANTEOCERATINAE (BRONTOPINAE) 



Manteoceras Hatcher- Wortman, 1895 



The species described herewith as Manteoceras? 

 irdinensis is of doubtful generic reference to the 

 "prophet-horned" genus Manteoceras, so highly char- 

 acteristic of the upper levels of the Bridger formation 

 of the Bridger and Washakie Basins of Wyoming and 

 of levels A and B of the Bridger formation of the 

 Uinta Basin of Utah. The type jaw (Am. Mus. 

 20111), from the Irdin Manha formation of Mongolia, 

 is a titanothere clearly distinguishable both specifically 

 and generically from other Irdin Manha species; it 

 certainly does not belong either to ProtitanotTierium 

 or to Dolichorhinus. Although on the whole it pre- 



