EOCENE AND OLIGOCENE TITANOTHERES OP MONGOLIA 



941 



Metarhinus, an animal highly characteristic of the 

 fluviatile deposits of levels A and B (Bridger forma- 

 tion) of the Uinta Basin, Utah. The reference to 

 Metarhinus, however, is still very doubtful, so that 

 for the generic reference of this jaw, as for that of the 

 imperfect jaw referred to Manteoceras, we must await 

 the evidence that may be afforded by more perfectly 

 preserved material. 



Metarhinus? 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 jaw 

 (fragment) of MeiarTiinus? mongoliensis (Am. Mus. 



20167) was picked up in the Irdin Manha formation, 

 but the exact locality was not recorded. Figure 794 

 shows the type specimen in comparison with a small 

 individual of Protitanotherium grangeri (Am. Mus. 



20168) from the Irdin Manha formation. Although 

 the teeth of M. mongoliensis (p4, nii) are only slightly 

 less elongate (ap. 43 mm.) than the corresponding 

 teeth of P. grangeri (ap. 45 mm.), the transverse 

 measurements shown in Figure 794, A, B, indicate 

 that the M. mongoliensis type belongs to a relatively 

 longer and narrower dental series than that of P. 

 grangeri. This elongation of the grinding teeth is one 

 ground for the reference of this diminutive specimen 

 to the Dolichorhininae. More detailed comparative 

 measurements are as follows: 



Comparative measurements of species of Metarhinus and 

 Protitanotherium, in millimeters 



Linear space occupied by fourth inferior 



premolar and first molar (pi, mi) 



P4, ap. by tr 



P4, index 



Mi, ap. by tr 



Ml, index 



M.? mon- 

 goliensis, 

 Am. Mus. 

 20167 

 (type, 

 fragnient 

 of jaw) 



43 

 19X11 



58 

 24X14 



58 



P. grangeri 

 Am. Mus. 



20168 



(fragment 



of jaw, 



referred) 



45 

 21X14 



67 

 24X17 



70 



Specific characters. — Of smaller size than Proti- 

 tanotherium grangeri; inferior grinders relatively longer 

 and narrower; valleys of posterior lobes of mi deeply 

 cupped, with elevated internal border; valleys of 

 anterior lobes open, without internal cingulum; 

 entoconid of p4 depressed, of mi elevated; depth of 

 mandibular ramus, at interval between p4 and mi, 

 46 millimeters; thickness of mandibular ramus below 

 same interval, 26 millimeters. 



TITANOTHERES OF EASTERN EUROPE 



The above description of upper Eocene and lower 

 Oligocene titanotheres discovered in Mongolia suggests 



comparison with the three species of titanotheres 

 described from eastern Europe, as follows: 



1876. Brachydiastematherium transilvanicum Bockh and 

 Maty, found in the neighborhood of Andrashdza 

 (Siebenbiirgen) , Transylvania, southeastern Hun- 

 gary, "am linken Ufer des Nddosbaches." 

 Resembles Protitanotherium in size. 



1892. Menodusf rumelicus Toula, Kajali, found northwest 

 of Burgas on the Jambol-Burgas Railroad, eastern 

 Rumelia. Resembles Protitanotherium or Brontops 

 in size. 



1913. Titanotherium bohemicum Kiernik, locality somewhat 

 doubtful, attributed to " Siisswasserkalke von 

 Tuchofitz Oder diesen entsprechende Bildungen." 

 Resembles MIenodus {= Titanotherium) giganteus 

 in size. 



Brachydiastematherium transilvanicum BocTch and 

 Maty. — In the main part of this monograph, relating 

 to the upper Eocene titanotheres of the Eocky Moun- 

 tains, Brachydiastematherium transilvanicum has 

 already been compared with Protitanotherium super- 

 hum of the Uinta formation (Diplacodon zone or 

 level C) of Utah. There is nothing new to be added 

 as to this Transylvanian species, which is fully figured 

 and described therein. 



Menodusf rumelicus Toula. — The type of this 

 Rumelian species (cast Am. Mus. 17602 from original 

 in the National Museum of Vienna) is probably 

 referable to Protitanotherium or to Brontops rather 

 than to any species of Menodus. This new generic 

 reference is based on the relatively short and broad 

 measurements of the third inferior molar of the right 

 side, which constitutes the type, namely, antero- 

 posterior, 94 millimeters; transverse, 44 millimeters; 

 index, 47; accordingly the breadth-length index of ma 

 is much greater than that of the typical Menodus. 



Corresponding with the short, broad proportions 

 and closed valleys of the type molar of M. rumelicus 

 is the paratype second inferior molar m2 (cast Am. 

 Mus. 17603, from original in the Vienna Museum), 

 in which the measurements are as follows: Antero- 

 posterior, 79 millimeters; transverse, 44 millimeters; 

 index 56. We are therefore inclined to refer the 

 Menodus? rumelicus of Toula either to Protitanotherium 

 or to Brontops rumelicus; the latter generic reference 

 being made more probable by the discovery of the 

 brachycephalic Brontops gohiensis. 



Titanotherium iohemicum Kiernik. — The type of this 

 Bohemian species (fig. 795, C), represented in the 

 American Museum collection by a cast (Am. Mus. 

 14449), is possibly referable to Menodus {= Titano- 

 therium), although the molar proportions of the third 

 inferior molar are intermediate between those charac- 

 teristic of the brachycephalic Brontops and of the 

 true dolichocephalic Menodus. The imperfect third 

 inferior molar of the right side, which constitutes the 

 type of Menodus ( = Titanotherium) lohemicum, is 



