ENVIRONMENT OF THE TITANOTHERES 



45 



tion of Depgret in France and of Matthew, Merriam, 

 Granger, Brown, Peterson, Douglass, Riggs, Darton, 

 Stanton, Berry, Knowlton, and others in this country. 

 The theoretic correlations reached are shown in the 

 accompanying tables (pp. 43, 48). The comparison of 

 similar stages in the evolution and migration of floras 

 and faunas is partly independent of changes in the 

 surface of the earth and in climate and is partly 

 related to them. The general succession (Osborn and 

 Matthew, 1909.321; Osborn, 1910.346) of the four 

 Eocene and Oligocene life phases of North America is 

 as follows: 



Phase IV (lower Oligocene) , approximation. — A similar mam- 

 mal fauna in western America and western Europe. Extinction 

 of archaic fauna and invasion of modern fauna. 



Phase III {upper and middle Eocene), estrangement. — Inde- 

 pendent mammal fauna of western America and western Europe; 

 gradual diminution of archaic fauna. 



Phase II (lower Eocene), approximation. — Closely allied and 

 similar fauna of western America and western Europe; first 

 invasion of modernized fauna. 



place this after the first Rocky Mountain (Laramide) 

 revolution in post-Laramie time — that is, after the 

 end of typical Laramie deposition in Colorado. 

 Others, among them the author of this monograph, 

 place it at the time of the extinction of the great land 

 and marine reptiles of Europe and America — that is, 

 after Lance time.'' The Fox Hills formation, which 

 underlies the Lance, represents the end of uniform 

 widespread marine sedimentation. At some places 

 the Fox Hills is continuous with overlying fresh- 

 water deposits laiown as Laramie; at others it is con- 

 tinuous with overlying deposits known as the Lance. 

 Thus Laramie time and Lance time, in our opinion, 

 are in part the same — that is, they overlap at some 

 places. 



Lance and Fort Union flora. — New physiographic 

 and climatic conditions arose during the initial period 

 of the Rocky Mountain uplift, when uplands and 

 plateaus were formed. Knowlton and Berry have 

 shown that the Fort Union flora extends back into 



land areas 



Forme 



Known fossil areas 



iigration areas 



Figure 34. — Map showing the known areas (black) and the hypothetical areas (oblique lines) 

 of titanothere migration and habitat 



Phase I (basal Eocene) , approximation. — Partly similar archaic 

 mammal fauna of western America and western Europe. 



Final Mesozoic phase. — Gradual extinction of the upper 

 Cretaceous dinosaur fauna and appearance of ancestors of the 

 archaic Eocene fauna. 



This alternate approximation and estrangement of 

 the mammal life of western America and western 

 Europe points to periods during which conditions 

 favored intermigration and intervening periods when 

 geographic, climatic, or forest barriers may have stood 

 between these widely separated regions. The basal 

 Eocene American forests — those of the Fort Union 

 epoch, for example — were very luxuriant and were 

 unfavorable to migration. 



lATE CRETACEOUS AND EARLY TERTIARY CLIMATES 



End of the Cretaceous period. — The initial point in 

 the correlation of geologic time in both the Eastern 

 and the Western Hemisphere is-the end of Cretaceous 

 deposition. (See table on p. 48.) Some geologists 



Lance dinosaur time, regarded by the author as late 

 Cretaceous. The Lance flora is prevailingly a rela- 

 tively warm temperate flora as compared with the 

 antecedent Laramie and other Upper Cretaceous 

 floras in the same region, and the climate in Lance 

 time was about like that of the present Atlantic Coast 

 States from North Carolina southward. In the Rocky 

 Mountain province (Berry, 1914.1, pp. 153-154), in 

 the zone of transition from the Cretaceous to the 

 Eocene, a large number of local floras appear, such 

 as those in the Arapahoe and Denver formations of 

 Colorado, the Livingston formation and the Lance 

 formation ("Hell Creek beds") of Montana, and the 

 typical Lance formation of Wyoming. The forma- 

 tions in which they occur consist of lacustrine, 

 fluviatfle, and terrestrial deposits eroded from the 

 rising land area of the Rocky Mountain province. 

 These early so-called post-Laramie floras are said to 



8 The United States Geological Survey classifies the Lance formation as Terti- 

 I ary (?). The author of this monograph regards it as Cretaceous. 



