South Dakota School of Mines 99 



ed from the Big Badlands, and called it a Paleotherium (see Fig- 

 ure 2) . Later the true character of the specimen was recognized, 

 a new name was necessitated, and Titanotherium (Titan-beast), 

 suggested by Dr. Leidy in 1852, came into use. Since the find- 

 ing of the earliest specimen many species have been described, 

 representing according to present usage, five genera. In con- 

 sequence of the readjustment required by the rules governing 

 paleontological nomenclature, Titanotherium, as originally used, 

 is now recognized as co-equal with the several other genera, 

 namely, Megacerops, Allops, Symborodon, and Brontotherium, 

 •while the term Titanothere, by reason of its significance and 

 usefulness, is recognized as the general term under which the 

 various subdivisions are placed. Anyone wishing to trace in 

 detail the history of the development of Titanothere names 

 should consult Prof. Osborn's Titanothere Contributions No. 3, 

 and No. 4, in the Bulletin of the American Museum of Natural 

 History, 1896 and 1902.* 



The genera are distinguished from each other chiefly by 

 differences in tooth and horn structure and by differences in the 

 shape of the head. Osborn indicates the characters as follows : 

 The species of Titanotherium have long skulls (dolichocephalic), 

 persistently long and broad nasals, short triangular horns placed 

 slightly in front of the eyes, vestigial incisors ranging from two 

 to none above and below, and large canine teeth. Megacerops 

 species have broad skulls (brachycephalic), nasals progressively 

 shortening, short horns rounded or oval in section, shifting an- 

 teriorly, one or two pairs of incisor teeth above and below, and 

 medium sized canine teeth. Symborodon species have skulls of 

 varying proportion, horns elongate and peculiar in being placed 

 above the eyes instead of shifting forwards, incisors vestigial, 

 two to none above and below and canines small. Brontother- 

 ium includes the largest Titanotheres. They have very broad 

 zygomatic arches, nasals shortening while horns elongate and 

 shift forwards; incisors persistent, in the males two above and 

 two below, canines short and obtuse. Allops is closely related 

 10 Megacerops, but differs from it in horn characters. The fol- 

 lowing species, all from the Lower Oligocene, have been identi- 

 fied from the Black Hills region : 



Titanotheriidae (Brontotheriidae) . 

 Titanotherium prouti Leidy. 



*It may be of interest here to state that since 1900, Prof. Osborn 

 •has had in preparation a special Monograph on the Titanotheres. 

 This is to he published 1 by the United States Geological Survey. 



