EOCENE AND OLIGOCENE TITANOTHERES OF MONGOLIA 



927 



elongate horns, the broad, shovel-shaped nasals, the 

 broad sweep of the zygomatic arches, and the saddle- 

 shaped cranial top; also, in the dentition, by the 

 sharply incurved canines, the enlarged lateral superior 

 and inferior third incisors, and the diminishing second 

 and first incisors, which in this species retain their 

 pointed, postcingulate form. 



Dentition. — The ancestral or primitive character of 

 the grinding teeth of P. grangeri, as compared with 

 the more progressive grinders of Protitanotherium mon- 

 goliense and of P. andrewsi, is seen in the absolutely 



lobe is broadened with a more or less prominent ento- 

 conid rudiment. (See figs. 777, 778, 779.) 



Cranium. — The type of P. grangeri is a female skull 

 with small, sharply recm-ved canines, whereas the males 

 of P. grangeri (Am. Mus. 20112) have relatively 

 prominent, lanceolate canines, suggesting those of the 

 true Menodus (= Titanotherium), but the broadened 

 sub-brachycephalic cranium and shallow jaws do not 

 resemble those of the true Menodus. 



Our conclusion is that the female type cranium of 

 Protitanotherium grangeri exhibits the following dis- 





Figure 783. — Type right ramus, fragment, with six grinding teeth, of Protitanotherium mongoliense Osborn (Am. Mus. 18653) 



from the Shara Murun formation 



A, Internal aspect of type right grinding series, p2-m3. Rectigradations indicated as follows: pa<^ = paraconid, me*^=metaconid, mts'i = metastylid, hyd=hypoconid 

 pr^=protoconid, en''=entoconid. Ai, External aspect of the type grinding teeth showing relative elevation (hypsodonty) of the crowns and characters of the 

 cingula. A2, Superior aspect of the type grinding teeth showing relative proportions of the molars and relative development of the talonid or posterior lobe of the 

 premolars. All one-half natural size. 



simple internal deuterocones without even a rudiment 

 of the tetartocones. The ancestral character is ob- 

 served also in the absence of any trace of a hypocone 

 in m' (compare type Am. Mus. 20103, also referred 

 Am. Mus. 20114, 20108, and 20120). These non- 

 progressive superior grinders indicate that Proti- 

 tanotherium grangeri is geologically far more ancient 

 than the P. mongoliense and the P. andrewsi of the 

 Shara Murun. The inferior premolars are correspond- 

 ingly simple (type Am. Mus. 20103, referred Am. Mus. 

 20112, 20126); there is barely a rudiment of the 

 entoconid, or entoconid shelf, on the inner side of the 

 narrow posterior lobe, whereas in P. mongoliense this 



tinctive characters: (1) Concave postpalatal border 

 (2) basipresphenoidal pits, (3) subangulate characters 

 of the suborbital borders of the zygoma, (4) slender, 

 angulate zygoma. These characters show that P. 

 grangeri is not directly or typically ancestral to the 

 P. mongoliense of the Shara Murun formation. 



Mandible. — The contrast between the female type 

 jaw, with its small canines (Am. Mus. 20103), and the 

 male jaw of the same species (Am. Mus. 20110) is very 

 marked. In the latter the canines are decidedly 

 larger, the lower lateral incisors, is, are not greatly 

 enlarged, the second incisors are somewhat larger, 

 the median incisors are missing; in the same specimen 



