12 



TITANOTHEEES OF ANCIENT WYOMING, DAKOTA, AND NEBKASKA 



mammalian life during lower Eocene time, so that we 

 shall probably discover a similar Coryphodon fauna 

 in the intermediate regions of eastern Europe, northern 

 Asia, and British Columbia. 



COMPARISON OF THE FOUE LIFE PHASES IN EUROPE 

 AND IN NORTH AMERICA DURING EOCENE AND EARIY 

 OLIGOCENE TIME 



Length of Eocene time. — It is the comparison of the 

 ancient life of the Old and the New World, especially 

 by means of the results of the successive studies of 

 Cope, Filhol, Deperet, Osborn, and Matthew, that 

 has led to the demonstration by Osborn of four great 

 continental faunal phases in Eocene and lower Oligo- 

 cene time — phases that probably extended over the 

 entire Northern Hemisphere and that were separated 

 by the rise and fall of the archaic forms of life, by the 

 union or separation of western Europe and western 

 America into one single or two distinct centers of mam- 

 malian life, and by the severance of all connection be- 



tween North and South America. Together these 

 three series of events form a sequence that affords evi- 

 dence of the great length of Eocene time. In other 

 words, the biologic evidences of very marked evolution 

 in single families like the titanotheres, of the zoogeo- 

 graphic events of migration, and of the succession and 

 extinction of faunas together indicate that the Eocene 

 epoch alone may have been longer than the 600,000 to 

 1,000,000 years allotted to the titanothere epoch in 

 accordance with Walcott's estimates of Tertiary time 

 based upon purely geologic data. 



The archaic succeeded hy the modernized mammals. — 

 The long duration of Eocene time is further indicated 

 by the subdivision of the Wasatch {Coryphodon) epoch 

 (the "Coryphodon beds" of Marsh and Cope) into 

 five lesser time divisions. Thus the term Coryphodon 

 alone no longer serves as the designation of a life zone, 

 because Coryphodon is now known to have survived 

 through at least five life zones, Nos. 5-9 in the 

 zonal series (p. 57), as follows: 



"Coryphodon beds" oj Marsh and Cope 

 9. Lambdotherium-Eotitanops-Coryphodon zone o( Osborn 



8. Heptodon-Coryphodon-Eohippus zone 



7. Systemodon-Coryphodon-Eohippus zone__ 

 6. Eohippus-Coryphodon zone 



5. Phenacodus-Nothodedes-Coryphodon zone. 



The modernized mammals in the series tabulated 

 above are the titanotheres, lophiodonts, tapirs, horses; 

 the archaic mammals are the condylarths (Phenacodus) 

 and amblypods (Coryphodon). 



As remarked above, no single biologic phenomenon 

 affords stronger evidence of the long duration of 

 Eocene time than the complete replacement of the 

 archaic fauna of North America, which exclusively 

 held the stage during basal Eocene time, in itself a 

 very long epoch, by the ancestors of modern mam- 

 mals, as shown in the accompanying diagram (fig. 12) 

 and indicated precisely in the transition between the 

 Phenacodus and Eohippus zones. The modernized 

 mammals came in not suddenly or en masse, as we 

 formerly supposed, but gradually, family by family, 

 the first apparently being the swiftest and most vita- 

 tive family — the horses (Eohippus). 



We infer that western Eiu-ope witnessed a similar 

 replacement, for, although sparsely loiown, the basal 

 Eocene life of western Europe was broadly similar to 

 that of western North America. 



The archaic life of American basal Eocene time, 

 first made known by Cope, then studied by Osborn 

 and Earle, and finally given very full and precise 

 geologic and zoologic determinations by Matthew, 



_ First appearance of the titanotheres in America. " Wind 

 River" fauna of Cope. 



.First appearance of lophiodonts in America. "Lysite" 

 fauna of Granger. 



.First appearance of tapirs in America. "Gray Bull" fauna 

 of Granger. 



.First appearance of horses in America. "Sand Coulee" 

 fauna of Granger. 



_ Phenacodus extremely abundant. "Clark Forli" and "Tif- 

 fany" fauna of Granger. The closing phase of the reign of 

 the archaic mammals of North America, Pantolambda, Cory- 

 phodon, Phenacodus. 



Granger, and Gidley, affords the basis of our present 

 knowledge of the wonderfully rich and varied fauna 

 embraced within the four basal Eocene life zones. 



The precision with which we are now able to note 

 the extinction or disappearance of the archaic mam- 

 mals and their replacement, one by one, by members 

 of modernized families is due especially to the ex- 

 plorations of the American Museum of Natural His- 

 tory, led by Granger with the assistance of Sinclair, 

 and to the analyses of the fauna by Matthew and 

 Granger in a series of researches which are classic not 

 only for their precision but for the revelation of new 

 and hitherto unsuspected affinities of the mammals 

 of North America with those of South America and 

 with the existing mammals of the oriental region of 

 the Old World. 



Relation of the titanotheres to other quadrupeds. — In 

 their broadest relations the titanotheres were mam- 

 mals of the cohort Ungulata, which possess hoofs as 

 distinguished from claws. We know that eleven great 

 orders of ungulates (see accompanying table) were 

 distributed through different parts of the earth during 

 ancient and modern time. Of these eleven orders, 

 which were the sources of the herbivorous quadrupeds 

 of the world, only five have survived to the present 

 time. 



