EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



289 



E. borealis (Cope), 14890, portions of right and left jaws. 



E. borealis (Cope), 14891, complete jaws (figs. 231, 248, 249). 



E. borealis (Cope), 4886, anterior portion of jaw (figs. 246, 

 249). 



E. borealis (Cope), 14895, caleaneum, astragalus (reference 

 doubtful) (figs. 503, 505, 522). 



E. borealis (Cope), 14888, jaws and fragments of skeleton 

 and feet, right pes (figs. 246, 249, 494, 501-503, 521, 701). 



E. brownianus (Cope), 4885 (type), jaw fragment (figs. 104, 

 231, 246, 247). 



E. gregoryi Osborn, 14889 (type), jaws, also m'-s (figs. 142, 

 231, 245-247; PI. LIV). 



E. gregoryi Osborn, 14933 (referred) , portions of pes and tibia 

 (fig. 503). 



The specimens listed above are arranged not in the 

 ascending geologic order but according to size, E. 

 gregoryi being the smallest and E. major the largest 



Manus numerically tetradactyl but functionally tri- 

 dactyl, with a tendency to mesaxonic structure. 



This animal is separated generically from Larnbdo- 

 therium by the possession of full eutherian dentition, 

 including p|. The fact that the face is longer than 

 the cranium constitutes its principal generic distinction 

 from the middle Eocene titanotheres (fig. 256). As 

 has been shown above, the genus is represented by 

 five specific stages or mutations, which are distin- 

 guished partly by size but more clearly, at least in 

 four species, by the development of cuspules on the 

 inferior premolar teeth, as follows : 



E. major Osborn, distinguished only by its large size. 

 . E. princeps Osborn, distinguished by size and premolar com- 

 plication. 



Figure 243. — Restoration of Eotitanops borealis, of the Wind River formation (Eocene) 

 About one-twelfth natural size. Made by E. S. Christman in 1917 under the direction of W. K. Gregory. 



of the animals represented by these types and other 

 specimens. The specific reference of the separate 

 foot bones (Nos. 14893, 4902, 14895, 14933) is doubtful. 



Eotitanops Osborn 

 Plates XXVI, LIV; text figures 10, 21, 25, 27, 28, 29, 33 142- 

 145, 155, 210, 212, 219, 229-232,243-253,405-408,482-485, 

 490, 492-503, 505-507, 512, 515, 521-523, 646, 648, 649, 

 661, 686, 688, 690, 692, 694, 695, 700, 701, 704, 709, 711, 717, 

 721-727, 733, 740, 742, 745 



[For original description and type references see p. 179; for skeletal characters see 

 p. 591] 



Generic characters. — Skull of proopic dolichoceph- 

 aly. Incisor series obliquely anteroposterior. Pj 

 with small, compressed single fang; p^-p* with single 

 internal cusps; p'-p* with rudimentary lophoid proto- 

 conules; p4 rather progressive. Superior molars sub- 

 quadrate and rounded in form; protoconules small; 

 metaconules wanting or rudimentary; inferior molars 

 without metastylids; hypoconulid of ms subconic. 



E. borealis (Cope), distinguished by intermediate size and 

 premolar simplicity. 



E. brownianus (Cope), distinguished by smaller size and 

 premolar simplicity. 



E. gregoryi Osborn, distinguished by the smallest size and 

 extreme premolar simplicity. 



The range of measurement in the species and muta- 

 tions is shown in the following tables : 



Comparative measurements of Eotitanops, in millimeters 

 [All specimens in American Museum] 



