572 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



On the other hand, the specimen differs from male 

 brontotheres and resembles the Menodontinae, espe- 

 cially Dijjloclonus amplus, in the following features: 

 (1) The narrow well-defined 

 internal cingula; (2) the 

 dimensions of p* (ap. by 

 tr., 40 by 61 mm.) and m^ 

 (84 by 82) are closer to 

 those of a skull referred to 

 Diploclonus amplus (Nat. 

 Mus. 4710), which are re- 

 spectively 42 by 61 and 

 82 by 81 millimeters, 

 than they are to those of 

 male brontotheres, which 

 usually have larger p* and 

 wider m'; (3) the canine 

 (PI. CXC) is not of the 

 swollen Brontotherium 

 type; by analogy with 

 Menodus the female canine 

 in Brontotherium should 

 be somewhat like that of 

 the male, only much more 

 slender; (4) the cranial 

 vertex lacks the midpa- 

 rietal convexity or emi- 

 nence of BrontotJierium and 

 Megacerops. The antero- 

 posterior measurements of 

 the dentition (see above) do 

 not offer decisive evidence 

 of relationship with Bronto- 

 tJierium. In brief, the sys- 

 tematic position of this 

 skull at present appears 

 doubtful and it may pos- 

 sibly belong near Diploclonus amplus. (See fig. 472.) 



Figure 472. — Sections and 

 contours of skull of Bronto- 

 therium gigas? 

 Am. Mus. 1006, 9, referred to B. gigas on 

 account of the characteristic form of 

 these sections. It seems, however, to 

 be too small to be a female of that 

 species (W. E. Gregory). One-eighth 

 natural size. 



Brontotherium dolichoceras (Scott and Osborn) 



{Menodus dolichoceras Scott and Osborn, 1887; 

 "Brontotherium dolichoceras" Osborn, 1902) 



Plate CLXXXVI; text figures 177, 473, 474 



[For original description and type references see p. 220J 



Geologic horizon. — TitanotJierium zone 

 of South Dakota, level not recorded. 



Specific characters. — Nasals, free length' 

 49 millimeters, breadth 90 millimeters — 

 that is, more reduced than in B. gigas, 

 less reduced than in B. curtum. Horns 

 elongate (310 mm.), about as in B. gigas; 

 horn section transversely oval, more progressive than 

 in B. gigas, with anterolateral depression and incipient 

 external ridge. Size of skull about as in B. hatcheri. 

 Premolar cingula reduced, which perhaps is an indi- 

 vidual variation. 



"^■■^ 



As described the type of this species is an adult, 

 not aged male preserved in the Museum of Compara- 

 tive Zoology at Harvard. It is in the seventh stage of 

 growth, with the internal 

 cones of p^ completely worn 

 and the protocone and hy- 

 pocone of m' worn. As 

 shown by the measurements 

 given below, the skxill was 

 of medium size, or about as 

 large as the type skull of B. 

 hatcheri. 



This species, named "the 

 long-horned brontothere " by 

 Scott and Osborn, repre- 

 sents a next higher stage in 

 the evolution of the bron- 

 tothere phylum, although it 

 appears rather as a collat- 

 eral branch than as a mem- 

 ber of the main line of as- 

 cent. The type skull is the 

 only material that can be re- 

 ferred certainly to this spe- 

 cies. The nasals now project 

 only 49 millimeters in front 

 of the anterior bases of the 

 horns, and in sagittal section (fig. 473) there is a uniformly 

 convex curve from the summit of the connecting crest to 



Figure 473. — Sections and 

 contours of skull of Bron- 

 totherium dolichoceras 



Harvard Mus. (type) elongate horns 

 subo val in basal section, nasals short. 

 One-ninth natural size. 



Figure 474. — Skull of Brontotherium dolichoceras 



Harvard Mus. (type). The right horn is longer and more slender than the left, possibly an effect of 

 crushing. (See PI. CLXXXVI, C.) One-eighth natural size. 



the tips of the nasals, as in the fine specimen of B. curtum 

 (Nat. Mus. 4946) described below. The horn section 

 on the right side is the more perfect, that on the left 

 being crushed laterally; the horns are crushed in upon 

 the antero-external faces, a feature which exaggerates 



