EVOLUTION OF THE SKULL AND TEETH OP EOCENE TITANOTHERES 



435 



Eotitanotherium Peterson 



[Diploceras Peterson; cf. Diplacodon Marsh] 



Plate LXXXI; text figures 148, 149, 365-367, 372, 598-605, 647 



[For original description and type references see p. 196. For skeletal characters see 

 p. 656] 



Geologic Tiorizon. — Uinta B 2. In 1913 Peterson 

 (1914.1) announced the surprising discovery, in the 

 middle levels of the Uinta Basin, Utah, of a large 

 titanothere having a pair of prominent bony out- 

 growths above the orbits, which he proposed to name 

 Diploceras. Peterson later gave it the name Eotitano- 

 therium to replace Diploceras, which was preoccupied. 



Generic characters. — Large upper Eocene dolicho- 

 cephalic titanotheres with very long, decurved nasals 

 and well-developed, anteroposteriorly oval horns. 

 Premolars decidedly progressive. P^, p* with large 

 distinct tetartocones and reduced external and inter- 

 nal cingula. The type of Eotitanotherium oshorni 

 Peterson (Carnegie Mus. 2859), so far as known, 

 conforms with the definition of Diplacodon as given 

 below: 



Skull mesatlcephalic to dolichocephalic, zygomatic arches 

 slender; superior premolars with flattened ectolophs and double 

 convexities, p^-p"* progressive, quadritubercular — that is, with 

 tetartocones; molars of elongate or dolichocephalic type — 

 that is, laterally compressed. 



E. oshorni Peterson further agrees with Diplacodon 

 elatus Marsh in the general small, obtuse form of the 

 canine and in the presence of a wide post canine 

 diastema. 



On the other hand, the type of E. oshorni appears to 

 represent a distinct species or even a different genus 

 from D. elatus, for although it comes from a lower 

 geologic level (Uinta B 2) its premolars are decidedly 

 more progressive in character, p', p* having the 

 tetartocones larger and more separate from the deu- 

 terocones, the external and internal cingula reduced, 

 and the whole appearance of the crown more molari- 

 form than in D. elatus. 



Comparative measurements of the two species are 

 given below. 



Comparative measurements of Eotitanotherium and Diplacodon, 



P>-m3 



Pi-p4 



M'-m' 



P^, ap. by tr 



M', ap. by tr 



M2, ap. by tr_ .. 



M', ap. by tr 



Canine, vertical 



Canine, anteroposterior 



Postoanine diastema 



Nasals, length 



Comparative measurements of Eotitanotherium and Diplacodon, 

 in millimeters — Continued 



Pi-ma 



Pi-P4 



P2-P4 



Mi-ms 



Postcanine to hyloid of ms 



Postcanine diastema . 



Depth below ms . 



E. osborni, 



Carnegie Mus 



2859 (type) 



255 

 95 

 79 

 158 

 283 

 34 

 93 



D. elatus, Yale 



Mus. 10320 



(type) 



Whether the paratype skull (Peterson, Carnegie 

 Mus. 2858) belongs with this species is somewhat 

 doubtful. The greater size of the horns and the asso- 

 ciated widening of the nasals in the paratype may 

 well be a sexual difference, the paratype being possibly 

 a male, the type a female. On the other hand, the 

 paratype differs radically from the type in having 

 the tetartocone of p* feebly developed, thus approach- 

 ing D. elatus. 



Although Eotitanotherium, from Uinta B 2, is prob- 

 ably allied to the somewhat later Diplacodon (Uinta 

 C 1), it seems best to let it stand provisionally as a 

 distinct genus, especially in view of the progressive 

 character of p^ and p* in this older stage. 



Eotitanotherium osborni Peterson 



[Diploceras osborni Peterson] 



[For original description and type reference see p. 195. For skeletal characters 

 see p. 656] 



Type locality and geologic horizon. — Duchesne River, 

 near My ton, Uinta County, Utah; Eohasileus-Doli- 

 chorinus zone (Uinta B 2). 



Specific characters. — P'-m^ 240 millimeters; m'-m^, 

 145. Median and lateral incisors small and "round- 

 topped," approaching Oligocene type, with heavy 

 posterior cingulum; lateral incisors more massive. 

 Canines short, subconic, without cingula, postcanine 

 diastema 28 millimeters. Premolars and molars with 

 little or no external cingula; internal cingula reduced; 

 p', p* highly progressive, submolariform, with large 

 tetartocones (type) and two well-marked external con- 

 vexities; dimensions of p* (ap. by tr.) 29 by 37 milli- 

 meters. Upper molars wider than in D. elatus, 

 m' with incipient tetartocones. Nasals long, tapering, 

 decurved. Horn swellings low, elongate, oval in basal 

 section. Lower jaw with deep ramus and deep 

 symphysis. 



The type and paratype skulls of Eotitanotherium 

 {Diploceras) oshorni were thus described by Peterson 

 (1914.1, pp. 30-37): 



SKULL 

 [Fig. 366] 



In comparing the recently discovered material with the best 

 preserved remains of Protitanotherium (P. emarginatum Hatcher) 

 a number of important differences are at once observed. The 



