152 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



advanced stage which in 1895 (1895.1) he described 

 as Diplacodon ejnarginatus. In a brief postscript 

 to this description he noted the wide range of forms 

 that had been erroneously grouped by Osborn under 

 the genus " TelmatotTierium," and he formally proposed 

 the generic names Manteoceras for the "prophet- 

 horn" and Dolichorhinus for the long-skulled form. 



Figure 87. — Four stages in the origin and evolution of tlie 

 horns in titanotheres 



After Hatcher's original plate (1895). A, Palaeosyops laiiceps (= Limnohyops lali- 

 ceps), after Earle; B, Telmatotherium vallidens ( = Manteoceras manteoceras), after Os- 

 born; C, Diplacodon emarginatus (,= PTOtitanotherium emarginatum), after Hatcher; 

 D, Titanotherium varians (= Bronioihermin leidyi), after Marsh. One-eighth 

 natural size. 



Both these terms, as well as the name Protitanotherium 

 of Hatcher, have proved to be valid. Hatcher's separa- 

 tion of these genera was a very important move toward 

 a correct understanding of their phylogenetic rela- 

 tions. He also figured a series of four stages ranging 

 from the middle Eocene to the lower Oligocene, inclu- 

 sive, showing the origin of the "horns." (See fig. 87.) 



INVESTIGATIONS AND EXPLORATIONS MADE IN PREPARA- 

 TION FOR THE PRESENT MONOGRAPH (1900-1919) 



Between 1895 and 1900 no very important work on 

 the Eocene titanotheres was done. By the end of the 

 nineteenth century some 12 nominal genera and 25 

 nominal species of the titanotheres had been proposed, 

 but many of the real generic limits and phyloge- 

 netic relations were still obscure except for the preg- 

 nant suggestions of Hatcher. In 1900 Professor 

 Osborn, at the invitation of Director Charles D. 

 Walcott, undertook to revise and monograph the 

 Eocene titanotheres in connection with the United 

 States Geological Survey monograph on the Oligocene 

 titanotheres that had been begun by Professor Marsh. 

 The work on the Eocene titanotheres has proved to be 

 by far the most difficult and most extensive part of 

 this task. During the last 28 years Professor Osborn, 

 with the assistance of Dr. W. K. Gregory, has studied 

 the great and growing collection in the American 

 Museum of Natural History and in other institutions 

 and has set forth the results in several prelimmary 

 articles and more fully in the present work. 



A long series of parties of exploration, beginnLng in 

 1903, sent out from the American Museum by Osborn 

 (1909.321) and conducted chiefly by Mr. Walter 

 Granger, have carefully examined the various lower, 

 middle, and upper Eocene basins of the West with 

 special reference to the exact succession of species. 

 This very precise work has shown that the Bridger 

 and other formations are divided into a succession of 

 zonal levels characterized by the remains of titano- 

 theres and other mammals in different generic and 

 specific stages of evolution. The stratigraphic rela- 

 tions of the Eocene to the Oligocene deposits have also 

 been in part explored. The results are fully set forth 

 in this monograph. Although this work in the 

 Eocene basins has been carried on chiefly by the Ameri- 

 can Museum of Natural History, the Carnegie and 

 Field Museums have sent expeditions into the Uinta 

 Basin under Douglass (1909.1) and under Riggs 

 (1912.1), which have yielded similar results as to 

 specific and generic succession. 



The distinction of numerous independent Eocene 

 phyla by Osborn has followed the discovery of the 

 Oligocene phyla, some of which arise from those of the 

 Eocene. 



Thus have been established secure bases of fact, 

 first, for a general history of the early Tertiary faunas 

 of the West; second, for a demonstration of the evolu- 

 tion of certain phyla of titanotheres through long 

 periods of time; and, third, for a consideration of the 

 modes and factors of evolution of titanotheres in par- 

 ticular and of mammals in general. 



