LETTER OF TRANSMITTAL 



Dr. George Otis Smith, 



Director United States Geological Survey, 



Washington, D. C. 



Dear Sir: I have the honor to transmit herewith 

 a monograph on the evolution of a pecuharly American 

 family of quadrupeds known as the titanotheres. 

 This designation was given to them in 1852 by Joseph 

 Leidy while he was employed as vertebrate paleon- 

 tologist in David Dale Owen's survey of a part of 

 the ancient territory of Nebraska. This family is 

 one of a group of vertebrate animals whose fossil 

 remains, found in the western United States, were 

 long studied by Othniel Charles Marsh, my distin- 

 guished predecessor in this work in the United States 

 Geological Survey. Early in the eighties Professor 

 Marsh projected a monograph on the Brontotheridae 

 (here called the titanotheres), and subsequently he 

 made the largest and most valuable contributions to 

 our knowledge of this family and of its evolution. He 

 planned the monumental field work of John Bell 

 Hatcher, by which the great collection for the United 

 States National Museum was made, and he super- 

 vised the preparation of sixty lithographic plates, 

 which are here reproduced. Unfortunately he died 

 before he had even begun to prepare the manuscript. 

 The duty of continuing his work was intrusted to me 

 June 30, 1900, by your predecessor, Charles D. Wal- 

 cott. During this period of nearly 20 years I have 

 supervised the preparation of the monograph on the 

 Ceratopsia by Hatcher and Lull and have half com- 

 pleted the monograph on the Sauropoda. The mono- 

 graph on the Stegosauria has not yet been prepared. 



The task of preparing the present monograph has 

 been long and difficult. First, it proved necessary 

 to reexplore the entire Eocene and lower Oligocene 

 series of rocks in Wyoming, Colorado, and South 

 Dakota, where the fossilized remains of titanotheres 

 are found, both to determine precisely their geologic 

 succession and to close up gaps in the stages of evolu- 

 tion; second, it proved necessary to examine and com- 

 pare the titanotheres of these geologic epochs in all 

 the museums of this country and in several museums 

 abroad; third, it pi-oved necessary, in order thoroughly 

 to understand the titanotheres, to discover and to 

 follow many side lines of investigation that have not 

 hitherto been followed in vertebrate paleontology. 



This work has been done with the aid of many 

 specialists, foremost among whom is my junior col- 

 league Prof. William K. Gregory, without whose in- 



telligent and unremitting cooperation the monograph 

 could never have been completed. 



It is perhaps not too much to say that this work 

 has transformed our knowledge of the early Tertiary 

 geology of the Rocky Mountain basin region. First, 

 the six life periods recognized by Marsh and his no 

 less distinguished contemporary Edward Drinker Cope 

 may now be replaced by sixteen life periods, which may 

 be clearly defined and separated and certain of which 

 may be more or less precisely correlated with life 

 periods established for western Europe. Second, a 

 much clearer notion has been gained of the changing 

 geographic, physiographic, climatic, and volcanic con- 

 ditions in Wyoming and Dakota and of their influence 

 on the migration and succession of forms of life. 

 Third, the whole method of attack on problems of 

 vertebrate paleontology has been developed; we seek 

 to know the entire living animal, its musculature, its 

 mode of locomotion, and its feeding habits, in order 

 to insure the complete restoration of the body. Fourth, 

 the study of the many branches of this group has given 

 the most convincing demonstration that evolution, 

 even in any one geographic region, seldom moves along 

 a single line of descent ; more frequently it moves along 

 many lines — it is polyphyletic; in other words, it 

 radiates, following the principles of local adaptive 

 radiation. Finally, the history of the titanothere 

 family in its evolution from very small and relatively 

 weak forms into titanic quadrupeds, second in size 

 only to the elephants, has afforded us a unique oppor- 

 tunity to enlarge our previous knowledge of the actual 

 modes of evolution as well as to revise our theories as 

 to the causes of evolution and of extinction. 



I desire to express my appreciation of the support 

 given by the Geological Survey under your direction 

 in the completion and publication of this work. 



With the aid of many coworkers I have endeavored 

 to set a new standard of broad, thorough, and ex- 

 haustive research in vertebrate paleontology which 

 shall be worthy of the great geologic traditions of our 

 national Geological Survey. I trust that this mono- 

 graph, like Leidy's classic memoir of 1869, may ex- 

 ercise a permanent influence upon future studies of 

 the geologic history of the great West. 



Henry Fairfield Osborn, 



Vertebrate Paleontologist. 



American Museum of Natural History, 

 December 19, 1919. 



