98 



TITANOTHEEES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



B 2. The allied D. cornutus is believed to be specifi- 

 cally identical with D. hyognathus of Washakie B. 

 In Uinta B 1 remains of Dolicliorliinus, as noted by 

 Riggs, are frequently found associated with those of 

 Metarhinus in coarse pebbly sandstone laid down in 

 rapid streams; but in Uinta B 2 they are frequently 

 found in lenticular sandstones, which were apparently 

 deposited in quiet water, for they show little evidence 

 of water currents, and which yield skulls associated 

 with mandibles and parts of skeletons. Riggs accord- 

 ingly infers that Dolichorliinus inhabited the low 

 grounds near quiet waters rather than the swift 

 currents preferred by Metarhinus. 



Contrasting with the elongate and straight-sided 

 skull of Bolichorhinus is the broad, robust skull of 

 StJienodedes incisivus (Douglass), a titano there with 

 exceptionally massive incisor and canine teeth and 

 broad, low-crowned upper molars. The type skull 

 was found by Douglass in a thick deposit of sandstone 

 and small gravel, evidently of stream origin, near the 

 middle of Uinta B 2, whereas Riggs's specimen was 

 found in lenticular sandstones at about the same level. 

 Sthenodectes shares many characters in common with 

 the Bridger genera Manteoceras and Telmaiherium and 

 appears to be an advanced member of that macrodont 

 group. 



With the possible exception of Rhadinorhinus all 

 the titanotheres so far noted from Uinta B 1 and B 2 

 belonged to aberrantly specialized side lines, which 

 are not found in later formations and apparently 

 became extinct. 



One titanothere recorded from near the summit of 

 Uinta B 2, namely, Eotitanoiherium osborni Peterson 

 (1914.1 ; 1914.4), is highly progressive toward the giant 

 plains-living types of the uppermost Eocene (Uinta C) 

 and of the lower Oligocene. This animal, represented 

 by parts of two skeletons in the Carnegie Museum, 

 surpasses even ProtitanotTierium of Uinta C in the 

 development of a pair of large oval bony protuber- 

 ances above the eyes. One of the most remarkable 

 features of Eotitanotherium is the progressive sub- 

 molariform character of its third and fourth upper 

 molars, which are, indeed, slightly more advanced in 

 type than those of certain lower Oligocene titano- 

 theres. The animal was about as large as a rhinoceros, 

 and throughout the skeleton are mingled the earlier 

 characters of its Eocene predecessors with progressive, 

 plains-living adaptations prophetic of some of the 

 Oligocene titanotheres, especially those of the meno- 

 dontine group. 



The titanothere fauna of the true Uinta (Uinta C), 

 though less extensive in genera and species than that 

 of Uinta B 1 and B 2, is none the less of prime impor- 

 tance to the historian of the family. Thus the titano- 

 theres of the true Uinta include, first, certain conserva- 

 tive phyla {Manteoceras, Telmatherium) , which repre- 

 sent the little-altered descendants of genera either of 



Uinta B 1 and B 2 or of Washakie and Bridger types; 

 second, two very progressive and different phyla, 

 Diplacodon and ProtitanotTierium, of uncertain relation- 

 ships, which appear to be immigrants from other 

 localities. 



ADAPTIVE RADIATION OF PHYLA 



There seem to be at least four contemporary phyla, 

 representing wide local adaptive radiation : 



First, the robust, short-limbed forms, one of which, 

 Manteoceras uintensis Douglass, found in gray sand- 

 stone in the red beds of the lower portion of Uinta C, 

 is considerably larger than the more primitive species 

 of Manteoceras in the upper Bridger and Washakie A 

 but is little modified otherwise. Its horn swellings, 

 if developed at all, were not large, and it is strongly 

 macrodont in type, like Telmatherium and Sthenodectes. 



Second, the long-limbed, long-headed, relatively 

 hornless Telmatherium, which is distinguished espe- 

 cially by its deep malar bones and the high sagittal 

 crest and is represented in Uinta C by the great 

 Telmatherium ultimum and the gigantic T. altidens. 

 T. ultimum is practically hornless, having only the 

 slightest rugosity at the naso-frontal junction in the 

 type skull. Accordingly the species Manteoceras 

 uintensis and Telmatherium ultimum and the genus 

 Sthenodectes, while advancing in the direction of the 

 Oligocene type in various characters, are apparently 

 excluded from direct ancestry to the later types by 

 certain specializations, such as marked enlargement 

 of the incisors and canines, and by the lack of develop- 

 ment of effective horn swellings. 



Third, Diplacodon elatus Marsh of Uinta C, a 

 progressive titanothere, which is known chiefly from 

 the upper dentition and takes its generic name from 

 its submolariform third and fourth premolars. The 

 precise relations of this animal are still in doubt. 

 The premolars and molars may have been derived 

 from the type represented by Rhadinorhinus diploconus 

 of Uinta B 2, which is the only one of the older titano- 

 theres that has the dentition and skull at all like 

 those of Diplacodon. In other respects the Diplacodon 

 dentition suggests that of the lower Oligocene titano- 

 there Menodus trigonoceras , and in still another respect 

 it resembles that of Eotitanotherium of Uinta B 2, though 

 it differs from that genus in the more molariform con- 

 dition of the third upper molar. 



Fourth, Protitanotherium emarginatum Hatcher, 

 which is known from the facial part of the skull and 

 the lower jaw of the type specimen. It is a large 

 animal, which, so far as Imown, approaches the 

 Oligocene type of Brontops. It has oval horn swellings 

 which are less protruding than those of the type of 

 Eotitanotherium; its nasals are wide distally, in con- 

 trast to the tapering nasals of Eotitanotherium; its 

 canines are very stout and acutely conical; its stout 

 upper incisors form a flattened arch. Altogether it 

 seems to represent a phylum distinct from Eotitano- 



