EVOLUTION OF THE SKULL AND DENTITION OF OLIGOCENE TITANOTHBRES 



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Diploclonus amplus 



Allops serotinus 



Menodus giganteus 



Allops walcotti 



Allops marshi 



Brontops brachycephalus Brontops dispar 



FiGUBB 391. — Skulls of the menodontine group 



Top view. One-twelfth natural size. 



Subfamily Brontopinae: A, Brontops brachtjcephalus, a primitive stage witli horns very short and nasals long and tapering. The specimen is a 

 female, and the zygomata are not much expanded; the skull top is rather slender, although the skull as a whole Is broad. B, BToniops 

 dispar, an intermediate stage with short horns rounded in section, nasals and frontals broad, and zygomata expanded. The midparietal 

 crest is constricted, as in many other members of this family. C, Diploclonus amplus, a highly specialized brachycephalic stage, resembling 

 Brontops robustus in general proportions. The horns are w ide and flattened at the base and pointed at the tips and bear accessory hornlets 

 on the antero-internal portion. The nasals are wide and short. 



Subfamily Menodontinae: D, Allops walcotti, a primitive dolichocephalic type (thought to be ancestral to the Allops phylum) with small horns 

 elongate oval in section, nasals long and tapering, zygomata slender, and skull top narrow. E, Allops marshi, horns widely trihedral in 

 basal section and directed outward and upward, skull top fairly broad, zygomata gently expanded. F, Allops serotinus, a specialized stage 

 with long outward-directed horns, wide, short nasals, wide frontals, and moderately stout zygomata. G, Menodus giganteus, the terminal 

 stage of the Menodus phylum, with skull dolichocephalic, skull top long, zygomatic expansion moderate, nasals long and distally wide, 

 horns sharply trihedral in basal section, the connecting crest lying in the plane of the posterior face of the horns. 



