358 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



Suhdiinsions of the Manteoceras-JDolicJiorMnus group 

 Subfamilies 



Genera 



Protitanotherium (Eocene) . 

 Manteoceras (Eocene) . 



Mesatirhinus (Eocene). 

 Dolichorhinus (Eocene) . 

 Metarhinus (Eocene) . 

 ?Sphenocoelus (Eocene) . 

 Eonietarhinus (Eocene) . 



Rhadinorhinus (Eocene) . 



The phyletic position of the recently discovered 

 Eometarhinus, from Huerfano B ( = Bridger A), is 

 ancestral either to Metarhinus or to Rhadinorhinus. 



Of these genera Manteoceras and Mesatirhinus rep- 

 resent phyla which appear contemporaneously in the 

 upper Bridger but which have already diverged from 

 each other toward brachycephaly and dolichocephaly, 

 respectively. As these subphyla diverge more and 

 more the resemblances which are observed between 

 the lower members of each series become fewer, and 

 the differences become greater. Thus Manteoceras 

 and Mesatirhinus are much nearer each other than the 

 forms to which they respectively gave rise, namely, 

 Protitanotherium and Dolichorhinus. The Rhadino- 

 rhinus phylum may prove to be a distinct one, and in 

 some characters it points toward the Oligocene Mega- 

 cerops (Symhorodon) . 



SUBFAMILY MANTEOCERATINAE {=BRONTOPINAE) OSBOEN, EOCENE 

 ANCESTOES 



A branch of the same stock as that of Mesatirhinus 

 and Dolichorhinus. Precociously horned animals, 

 known from the upper deposits of the Bridger Basin, 

 from the Washakie Basin, and from the Uinta Basin. 

 First referred to Telmatherium and subsequently de- 

 scribed as Manteoceras, or "prophet horn." In all 

 known characters more nearly central or ancestral to 

 the Oligocene titanotheres of the genus Brontops than 

 any of the Eocene forms thus far discovered. 



Manteoceras 



General structure and habits.- — The presence of the 

 rudiment of a horn above and in front of the eyes is 

 the most distinctive and interesting feature of the 

 middle Eocene Manteoceras, which is the earliest known 

 member of this subfamily. Many more characters 

 both of the skull and the teeth make this a prophetic 

 or ancestral form of great significance and interest, 

 worthy of the most thorough, detailed study. Alto- 

 gether more than fourteen such prophetic characters 



have been found in these animals. In point of size 

 the known individuals are intermediate between the 

 largest tapirs and the smaller rhinoceroses, such as 

 Rhinoceros (Dicerorhinus) sumatrensis. 



The skull in these animals is moderately elongate, 

 or mesaticephalic. The fluctuations are between 

 mesaticephalic and brachycephalic types. Female 

 skulls tend to be somewhat more long and narrow; 

 aged male skulls tend to be broader and more robust. 



The parts of the limbs and feet which signify speed, 

 especially the humerus, femur, and manus, indicate 

 that the quadrupeds belonging to this genus were 

 swifter than Palaeosyops but slower than Mesati- 

 rhinus. They were brachypodal as compared with 

 Mesatirhinus but considerably longer footed than 

 Palaeosyops. The large tusks of the males and the 

 earlier development of horn rudiments as compared 

 with the palaeosyopine group indicate that these 

 quadrupeds were vigorous fighters. In a large per- 

 centage of the adult specimens the teeth are much 

 worn, indicating that the food was somewhat harder 

 and drier than that of Palaeosyops. As feeders these 

 animals were better equipped than the members of 

 the Palaeosyops and Limnohyops series, for their 

 grinding teeth were decidedly more trenchant or cut- 

 ting, but even in the later members of Manteoceras 

 the grinding teeth are somewhat less efficient than 

 those of the contemporary telmatheres, because the 

 molar ectolophs are a little shorter and the premolars 

 are less advanced in evolution. 



History of discovery. — The discovery of these animals 

 was one of the turning points in the history of the evo- 

 lution of the titanotheres. In 1894 the American 

 Museum expedition was working under the direction 

 of Dr. J. L. Wortman in a layer of brown sandstone 3 

 miles north of the base of Haystack Mounain, in what 

 is now loaown as the Washakie A level. Here two 

 skulls (Am. Mus. 1569, 1570) were found, and as 

 partly exposed in the field they attracted the attention 



