EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



295 



widely separate from orbit (closer to orbits in Eocene 

 forms); (3) malars gently rounded, and zygomata 

 moderately projecting; (4) superior profile believed 

 to be plane or gently convex, slightly convex above 

 the orbits; (5) greatest width of skull opposite glenoid 

 fossae; (6) temporal fossae deep, brain case small, sur- 

 mounted by high, thin parietal crest; (7) occipital 

 crest overhanging condyle superiorly, deeply indented 

 in median line; (8) postglenoid and post-tympanic open 

 below auditory meatus; (9) small exposure of the 

 mastoid between the post-tympanic and paroccipital 

 process; (10) in occipital view (fig. 251) the parietal 

 crest is narrow and flaring superiorly; (11) in palatal 

 view basioccipital and basisphenoid keeled or com- 

 pressed; (12) typical perissodactyl foramina separate^ 

 namely, condylar, lacerum medium and posterius, 

 ovale, and alisphenoid; (13) posterior nares deeply 

 inclosed by pterygoids and 

 pterygoid wings of alisphe- 

 noids; (14) posterior borders 

 of palatines not preserved; 

 (15) palate relatively elon- 

 gate, narrow and arched 

 from side to side; (16) post- 

 glenoid process narrow, 

 internal in position ; (17) 

 occipital condyles sharply 

 convex, prominent, sepa- 

 rated in median line. 



ing behind ms; symphysis moderately elongate, gently 

 convex, incisive alveoli, indicating progressive increase 

 of size from ii to is and semiprocumbent position of the 

 incisors. 



Eotitanops prlnceps Osborn 



Plates XXVI, LIV; text figures 27, 33, 143, 144, 231, 246, 252, 

 407, 408, 483, 484, 490, 492-494, 496, 498-500, 512, 661, 

 686, 692, 700, 704, 709, 724 



[For original description and type references see p. 193. For sljeletal characters 

 see p. 690] 



Type locality and geologic 

 horizon. — Wind River Basin, 

 Wyo. ; Wind River formation, 

 Lambdotherium-E otitanops- 

 CorypJiodon zone (Wind River 

 B, "Lost Cabin"). 



Measurements of Eotitanops borealis and E. princeps, in milli- 

 meters 



Basilar length, premaxillaries to con- 

 dyles (estimated) 



Zygomatic or transverse width (esti- 

 mated) 



Width across occipital condyles 



Cranial length, postorbital process to 



occipital condyles 



Facial length, postorbital process to 



maxillary symphysis 



Length of lower jaw, symphysis to 



condyles (estimated) 



Height of jaw, condyle to bottom of 



angle 



Lower jaw, depth behind ma 



E. borealis. 



Am. Mus. 



14887 (neo- 



type) 



E. princeps, 

 Am. Mus. 

 296 (type) 



The jaws are well displayed in the neotype (Am. 

 Mus. 14887) and in the referred specimens, especiaUy 

 in the well-preserved jaw shown in Figure 248 (Am. 

 Mus. 14891). 



The chief characters are the following: Ramus 

 elongate, gently convex in vertical section, expanding 

 toward symphysis; lower border suddenly compressed 

 and descending below angle, thin posterior border; 

 delicately retroverted coronoid, ramus slowly ascend- 

 101959— 29— VOL 1 22 



riGTTHB 252. — Lower jaw of Eotitanops princeps 

 One-halt natural size. Am. Mus. 296 (type), reversed. Wind River Basin; Wind River formation. 



Specific cJiaracters. — Of still larger size; Pa-ms, 105 

 millimeters (estimated). Inferior premolar teeth some- 

 what more complicated, as shown in the type specimen; 

 P2 with elevated, distinct, but very rudimentary para- 

 conid and metastylid, entoconid very rudimentary if 

 present, talonid narrow; ps, paraconid quite distinct, 

 elevated, metastylid small, distinct, entoconid rudi- 

 mentary, talonid broad; p4 submolariform, talonid 

 broad, entoconid shelf distinct. Hypoconulid of ma 

 rounded, more robust. Ramus larger and more robust. 



The more advanced development of the premolar 

 rectigradations, the increased size of the teeth and of 

 the jaw, the larger size of the hind feet in the referred 

 specimen (Am. Mus. 4902) combine to distinguish 

 this specimen as a mutation or subspecific stage 

 between E. borealis and E. major. 



Lower jaw of type. — The weU-preserved jaw (fig. 

 252) of the type specimen (Am. Mus. 296) measures 

 253 millimeters from the back of the condyle to the 

 symphysis, 99 from the condyle to the bottom of the 

 angle, and 53 vertical depth of the ramus just behind 

 ms. Its distinguishing features are (1) the elevation 

 of the condyle above the grinders; (2) the rather 

 slender, recurved coronoid with sharply angulated 

 and flattened anterior border, which reminds us of the 

 coronoid of the middle Eocene Mesatirhinus and 

 DolichorJiinus rather than of that of Palaeosyops; 

 (3) the well-defined superior fossa between the angle 

 and the coronoid; (4) the depressed or delicate incurved 



513 



162 

 52 



128 



245 



97 



