EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



671 



As mounted with great skill by Mr. Adam Hermann, 

 the skeleton is about 14 feet long, 8 feet high, and 4 

 feet broad. The sex can not be positively determined, 

 as the canine teeth were wanting and are restored in 

 plaster. The teeth are well worn, the protocones of 

 m", m' being slightly abraded. The animal was 

 therefore in the tenth stage of growth, as defined 

 below, a fairly old adult. 



An interesting feature of the skeleton, which may 

 bear upon the question of the sex, is the exostosis and 

 false joint in the center of the seventh rib on the right 

 side (fig. 606); this was undoubtedly an after repair of 

 a fracture, which may have been incurred in fighting. 

 This would support the idea that the skeleton is that 

 of a male, although it is known that the bulls of larger 

 quadrupeds sometimes charge upon females which 

 refuse their advances. As the cranial characters are 

 decidedly those of a female the latter supposition is 

 more probably the correct one. 



The generic and specific determination of this skele- 

 ton is extremely difficult. It was originally referred by 

 Osborn to Titanotherium (Brontops) robustum, but 

 later he referred it to Brontotherium gigas, 9 , chiefly 

 because the carpus (Am. Mus. 518) diff'ers in important 

 characters from that of Marsh's type of Bronto-ps 

 robustus. 



Unfortunately the specimen lacks all the front teeth, 

 as far back as p^ and pa. The upper premolars have 

 the tetartocones retarded and well constricted, as in 

 Brontops, and very difi'erent from the progressive cir- 

 cular tetartocones of male brontotheres. A supposed 

 female of Brontotherium gigas (Am. Mus. 1006) also 

 has the tetartocones much constricted, but the refer- 

 ence of this specimen is very doubtful. The external 

 cingulum of the upper premolars and molars is absent, 

 as it is in both Brontops robustus and Brontotheriwn, so 

 this character is not decisive. The external cingulum 

 of the lower premolars is reduced. On the whole the 

 molar-premolar dentition appears closer to that of 

 B. robustus than to that of Brontotherium. 



The lower jaw as a whole presents no close resem- 

 blance to the jaws of brontotheres; from the type of 

 Brontops robustus it differs in minor characters; per- 

 haps its nearest resemblance is to the type of Diplo- 

 clonus tyleri. The significant measurements of the 

 skull and dentition, though few, are nearer to those of 

 the type and referred Brontops robustus (especially 

 Am. Mus. 1069) than to those of large male bronto- 

 theres. The skull is relatively larger than those of the 

 supposed female brontotheres of Brontotherium curium 

 and B. gigas and differs from them in many characters. 



The sections and contours of the horns and nasals are 

 certainly different from those of the supposed female 

 brontotheres and still more from those of the male 

 brontotheres. The cranial sections are, in fact, closer 

 to those of Diploclonus tyleri and Brontops robustus 

 (especially Am. Mus. 1083). 



101959— 29— VOL 1 46 



The manus has the magnum much broader, more 

 angulate than that of B. robustus as figured by Marsh. 

 The lunar and magnum are also wider and more 

 angulate than in the supposed Brontotherium gigas 

 manus in the National Museum (No. 4262). 



Figure 607. — Three views of mounted skeleton of 

 Brontops robustus, female 



Chiefly Am. Mus. 518. After Osborn and Wortman (1895.105). The 

 skull and whole anterior part of the skeleton as far back as the pelvis 

 belong to one individual. The pelvis and hind limbs are supplied 

 from other specimens. (See fig. 606.) 



As the hind limbs mounted with this skeleton belong 

 to other individuals they do not assist in the deter- 

 mination of the principal specimen. 



On the whole, the evidence indicates that the 

 mounted skeleton is not that of a female brontothere 

 but is a member of the brontopine group, probably a 

 phase in the evolution of Brontops. 



