EVOLUTION OF THE SKULL AND DENTITION OF OLIGOCENE TITANOTHERES 



553 



Sexual characters of brontotheres 



Horns elongate. 

 Connecting crest very high. 

 Occiput very robust and back- 



wardly produced. 

 Zygomatic arches very broad. 

 Incisors persistent. 

 Canines larger. 



Horns abbreviate. 



Crest less developed. 



Occiput less robust and less 



produced backwardly. 

 Zygomatic arches less broad. 

 ?Incisors less persistent. 

 Canines two-thirds size of 



male canines. 



The contrast between the males and females gener- 

 ally is well brought out in the accompanying figures 

 of the male and female skulls of B. gigas. It is obvi- 

 ous that a number of correlated characters disappear 

 in the nondevelopment of the horns in the females, 

 especially the marked width of the zygomatic arches, 

 which may have been partly defensive structures, and 

 the nonextension of the occiput posteriorly, which was 

 probably designed in the males for the support of the 

 great muscles of the neck. 



Standard measurements in the BrontotJierium 'phylum, in millimeters 



