EOCENE AND OLIGOCENE TITANOTHERES OF MONGOLIA 



919 



Measurements oj lower jaw and teeth oj two species of Dolicho- 

 rhinus, in millimeters 



Vi-THz 



Mi-ms 



Mi-m^ 



P4, ap. by tr 



Pi, index 



M3, ap. by tr 



Mj, index 



Basilar length of skull, 

 condyles to premaxil- 



lae 



Total length of jaw, con- 

 dyles to incisive bor- 

 der 



P2-m3 



Pz-ms 



D. olseni, type jaw 

 (Am. Mus. 20109) 



258 



182 



(?) 



28X20 



71 



88X32 



36 



256 



175 



(?) 



28X20 



71 



86X35 



41 



536-538 

 256-258 



D.kaiseni, referred jaw 

 (Am. Mus. 20260) and 

 type jaw (Am. Mus. 

 20262) 



276 



190 



164 



31X22 



71 



85X39 



46 



277 



190 



162 



29X26 



90 



"83X40 



48 



660-695 



555-580 

 230-262 

 265-277 



Dolichorhinus olseni Osborn, 1925 



Original rejerence. — Osborn, H. F., Upper Eocene 

 and lower Oligocene titanotheres of Mongolia: Am. 

 Mus. Novitates No. 202, 1925. 



Tyfe locality and geologic level. — Half a mile north 

 of the Kalgan-Urga telegraph line, southeastern Gobi, 

 Mongolia; Irdin Manha formation (upper Eocene). 



Materials. — This species is based upon a fine pair 

 of jaws, the type of Dolichorhinus olseni Osborn (Am. 

 Mus. 20109, fig. 774, E), found half a mile north of the 

 Kalgan-Urga telegraph line. Species of this genus 

 appear to be relatively rare in the Irdin Manha, 

 whereas the more progressive species Dolichorhinus 

 Icaiseni is quite abundant in the overlying Shara 

 Murun formation. 



Specific characters. — The measurements given above 

 show that the type jaw of Dolichorhinus olseni is 

 throughout inferior in size to the referred jaw (Am. 

 Mus. 20260) and to the type jaw (Am. Mus. 20252) of 

 Dolichorhinus Icaiseni, as shown by the type figure 

 of D. olseni (fig. 774) and more clearly in a compari- 

 son of the type specimen of D. olseni itself with the 

 three jaws of D. Icaiseni (Am. Mus. 20257, 20255, and 

 20260). 



We observe the following less progressive characters ; 

 (1) Canines narrow and sharply pointed; (2) lateral 

 first and second incisors more pointed, less broadly 

 cupped or cingulate posteriorly; (3) first premolars 

 small, single-fanged, pointed; second and third pre- 

 molars, p2_3, lacking cup-shaped concavity of talonid 

 which is present only in pi — that is, all rudiments of 

 entoconid and all evidence of broadening of talonid are 

 lacking in D. olseni in P2-3; these teeth are far more 

 primitive than the corresponding teeth of D. Icaiseni; 

 101959— 29— VOL 2 38 



(4) the fourth inferior premolar still very primitive, 

 exhibiting a shallow concavity of the trigonid, a rela- 

 tively broad, slightly concave talonid. 



Dolichorhinus Icaiseni 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. — Near Ula Usu on 

 the Kalgan-Uliassutai trail, southeastern Gobi, Mon- 

 golia; Shara Murun formation (uppermost Eocene). 



Materials. — This species is based upon the type (Am. 

 Mus. 20252), a male skull and jaws, nearly complete 

 dentition, and the paratype (Am. Mus. 20257), a 

 palate and basicranium, complete dentition. There 

 are also two referred specimens, namely. Am. Mus. 

 20255, a female skull and jaws, nearly complete den- 

 tition, and Am. Mus. 20260, a male skull and jaws, 

 complete dentition. Because of the tubular air spaces 

 filling the arched cranium, the three crania were se- 

 verely crushed, and the broken parts, assembled 

 through most careful field collecting, were pieced 

 together with great skill by Mr. George Olsen. The 

 cream-white external appearance of the skull is quite 

 different from the rust-brown color of the Irdin 

 Manha specimens. 



Specific characters. — As shown in the comparative 

 series of measurements above, Dolichorhinus Icaiseni is 

 superior in length of jaw and in all its dental measure- 

 ments to Dolichorhinus olseni; the breadth-length 

 indices of the fourth inferior premolar, p^, and of the 

 third inferior molar, ma, are approximately the same 

 in the two species. These relatively long, narrow 

 indices are harmonic with the extremely dolichoce- 

 phalic, elongate cranium and jaws. As in several of the 

 Wyoming and Utah species of this genus, the small 

 canines, even in the males, are in compensation for the 

 precociously developed horn swellings; these bony 

 horns are relatively much more prominent than in 

 Dolichorhinus hyognathus ( = cornutus) of the uppermost 

 part of the Bridger formation of the Washakie Basin, 

 Wyoming, and the Uinta Basin, Utah. 



The type cranium (Am. Mus. 20252), the paratype 

 cranium (Am. Mus. 20257), the fine referred cranium 

 (Am. Mus. 20260), and the more mature referred 

 cranium (Am. Mus. 20255) are singularly uniform in 

 their characters and apparently represent different 

 stages of growth rather than different phases of evolu- 

 tionary progress. Although the canines are relatively 

 small as compared with the robust canines of Proti- 

 tanotherium, we judge that these four crania belong to 

 male individuals because of the uniform size of the 

 canines and of the uniform development of the tuber- 

 ous bony horns. These horns project outward rather 

 than upward; the fore-and-aft diameter of the horn base 

 is short as compared with the elongate horns of Pro- 

 titanotherium. Below them are the flaring sides of the 



