294 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



strongly concave and incurved as in the Bridger 

 titanotheres; the protoconule is distinct, the meta- 



FiGURE 249. — Lower teeth of Eotitanops borealis 



Natural size. A, Crown view of left lower premolars and molars (P2--m3); Am. Mus. 1488S; Alkali 

 Creek, Davis's ranch, Wind Hiver. B, Crown view of molars (mj-ms); Am. Mus. 14891; west 

 bank of Wind River, 3 miles above canyon (top of banded beds). C, Crown view of premolars 

 Cp!-P4); Am. Mus. 4886; Wind River valley, Wind River formation. 



Figure 250. — Skull of Eotitanops borealis 



One-fourth natural size. Am. Mus. 14887, Dry Muddy Creek 12 miles above mouth; 

 Wind River formation. Ai, Palatal view of crushed specimen; Az, As, recon- 

 struction of the palatal and side views of the same skull made by L. M. Sterling 

 under the direction of W. K. Gregory. 



conule is faint. In m' similar characters are observed 

 on the anterior half of the crown; the posterior half 

 is broken away. 



The lower molars exhibit low brachyodont crowns, 



the crescentic external cusps alternating with the 

 subconic internal cusps; extremely rudi- 

 mentary hypoconulids, metastylids, and 

 vestigial paraconids are observed; external 

 cingula rudimentary, internal cingula en- 

 tirely wanting, as in all titanotheres; hypo- 

 conulid of m^ central, small, sublophoid. 



Slcull.—The discovery of the skull of E. 

 borealis (Am. Mus. 14887, neotype) was an 

 important event in the work of determining 

 the morphology of the titanotheres because 

 it connected these mammals closely with 

 other early Eocene perissodactyls and sepa- 

 rated them from the middle Eocene forms. 



The chief feature of the 



skull is that the proopic or 



facial region is longer than 



the opisthopic or cranial 



region, whereas in all the 



middle Eocene titanothere 



skulls yet known the face is 



shorter than the cranium 



and becoming progres- 

 sively shorter throughout 



Eocene and lower Oligo- 



cene time. The skull is 



also relatively long and 



narrow, and the true molar 



series is relatively short as 



compared with the total 



length of the skull. These 



characters are well shown 



in the reconstruction of the 



skull (figs. 250, 251) and 



in the model of the head 



(figs. 646, 648, 649); they are 



expressed in the following 



indices, which are estimates 



only, because the skull is 



considerably crushed : 



Cephalic index 50 (vs^idth 



across zygomata -=- basal 



length = 160 millimeters h- Figure 251. — Skull of Eotitan- 



313 [estimated]). 

 Faciocephalio index 56 (length 



of face -;- basal length = 



185-^313). 

 Molar index 17 (length m"- 



m^ -^ basal length of skull = 



54 -H 313). 



These fundamental proportions give the skull of 

 Eotitanops (fig. 250) a striking resemblance to that 

 of other lower Eocene perissodactyls. The type is 

 technically known as proopic dolichocephaly. 



Attention may be called to the following details: 

 (1) Premaxillaries slender, symphyseal union very 

 slight, indicating feeble use of superior incisors, pre- 

 maxillaries joining nasals superiorly, a primitive fea- 

 ture; (2) infraorbital foramen placed above p'-p*, 



ops borealis 



A I, Top view; A2, occipital view. One- 

 fourth natural size. Am. Mus. 14887, 

 Dry Muddy Creek 12 miles above 

 mouth; Wind River formation. Re- 

 construction made by L. M. Sterling 

 under the direction of W. K. Gregory. 



