TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



in scientific method — in the constant union of paleon- 

 tologic with geologic evidence in the reconstruction of 

 the slow succession of events in the wonderful history 

 of this western resion. 



ROCKY 

 MOUNTAIN 



LARAMIDE 



SIERRA NEVADA 



APPALACHIAN 



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/PENNSYLVANjAN 



/ ' MISSfeSIPPlKN^ / 

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? PRE-CAMBRIAN 



? ARCHEAN 



FiGtTRE 3. — Geologic ages and orogenic 

 periods in North America 



Age of mammals, stipple; age of reptiles, vertical lines; 

 age of amphibians and fishes, oblique lines. The peri- 

 ods of the birth and elevation of the chief American 

 mountain systems, notably the Rocky Mountains 

 (including the Laramide revolution), are indicated 

 approximately by incisions on the right. Modified 

 from diagram by Henry Shaler Williams. 



The present monograph is made up of this introduc- 

 tory chapter and of ten other chapters, covering the 

 following six main lines of exploration and research 



that have been followed in order to restore, at least 

 in part, the life and times of the titanotheres : 



1. Geologic, physiographic, climatic, and faunal 

 environmental conditions of the titanothere epoch — • 

 the Eocene and lower Oligocene divisions of the 

 Tertiary. Principles of adaptive radiation in animals 

 as explaining the variation of the titanotheres. 

 (Chap. II.) 



2. History of the discoveries of the remains of 

 titanotheres, the original published descriptions, and 

 the previous and present classification of genera and 

 species. (Chaps. Ill and IV.) 



3. Systematic study of the titanotheres: Eocene 

 and lower Oligocene subfamilies, genera, and species. 

 Characters of the skull, dentition, and postcranial 

 skeleton. (Chaps. V, VI, and VII.) 



4. Muscular anatomy of the titanotheres: Princi- 

 ples of locomotion and evolution of limb structure in 

 the hoofed mammals (Ungulata) in relation to habits. 

 (Chaps. VIII and IX.) 



5. Origin, ancestry, and adaptive radiations of the 

 titanotheres and other odd-toed ungulates. (Chap. X.) 



6. Evolution and extinction of the titanotheres: 

 Evidence regarding modes and causes of evolutionary 

 development and decline in mammals. (Chap. XI.) 



SECTION 2. PRELIMINARY SURVEY OF THE MONO- 

 GRAPH AND OF THE CONCLUSIONS PRESENTED 



RANGE OF THE TITANOTHERES IN GEOLOGIC TIME 



Geographic distribution. — The earliest known titano- 

 theres lived near the end of early Eocene time, after 

 the appearance in the Rocky Mountain region of 

 three kinds of quadrupeds — the horses, the related 

 forest-living tapirs, and the more remotely related 

 rhinoceroses, which still exist elsewhere. 



The successive immigrations of related odd-toed 

 ungulates are recorded in the Eocene deposits of the 

 region now included in the State of Wyoming, which 

 during Eocene time was a fertile land inhabited by 

 an abundant fauna. The Eocene titanothere epoch 

 in northern Utah, south of the great Uinta Mountain 

 range, which, according to Powell, rose to majestic 

 heights, ended in late Eocene time. 



In lower Oligocene time the titanotheres had 

 seemingly become the largest mammals in North 

 America. They were second in size to the existing 

 elephants only, but recent paleontologic evidence 

 indicates the existence in Oligocene time in India of 

 mammals that exceeded in size both the titanotheres 

 and the elephants. In 1913 Mr. C. Forster-Cooper 

 (1913. 1) described a new genus of perissodactyls from 

 the upper Oligocene deposits of the Bugti Hills of 

 Baluchistan, BalucTiiiherium (Thaumastotherium) os- 

 borni, an animal of proportions so gigantic that it 

 dwarfs the largest known titanothere. 



Sedimentary divisions and faunal life zones. — The 

 lower Eocene to lower Oligocene sediments in which 

 titanothere remains have been found occur here and 



