OF WESTERN NORTH AMERICA. 



59 



Faunistic reunion with western Europe in the Oligocene. 



Order. 



Edentata 



Rodentia 



Insectivora 



Creodonta 



Marsupialia. . . 



Carnivora 



Artiodactyla. . 

 Perissodactyla 



a Subfamily. 



b The Titanotheriidse found in central Europe are included in this number. Dr. 11. G. Stehlin detter, 

 April 15, 1907?) regards the geologic level of these animals as Oligocene. They closely resemble cer- 

 tain of our titanotheres. 



Thus (1) the faunal community with western Europe becomes 

 much closer than in the upper Eocene (see p. 56) ; (2) it is important 

 to note that many American lower Oligocene types are represented 

 by more primitive forms of European upper Eocene types and partly 

 of north African types, namely, Hysenodon, Hyopotamus, Elotherium, 

 and Suoidea-Dicotylidge; (3) the strongest community is among the 

 Perissodactyla, with 7 families out of 9 in common; (4) the least 

 community is among the Artiodactyla, with only 2 families out of 1 1 

 in common. 



As above noted, this momentous faunal change in North America 

 may be more apparent than real, because attributable to various 

 causes: (1) Partly to the fact that this is our first glimpse of the 

 western portion of the Great Plains fauna; (2) partly to fresh migra- 

 tion from the northerly or North American-Eurasiatic region. The 

 apparent sharp distinctions of this phase from the Uinta faunal phase 

 will probably be partly lessened when a fuller knowledge of the Uinta 

 mammals shall have been gained. 



There are many distinctive characters of this North American 

 faunistic stage, as follows: (1) First appearance of Marsupialia- 

 Didelphyidae and of Rhinocerotidse-Diceratheriinae ; (2) sudden dis- 

 appearance of all Primates, which do not again appear in North 

 America; (3) continued evolution of certain of the North Aixierican 

 families of mammals derived from the first modernization, 4-toed 

 horses replaced by 3-toed horses, advanced evolution of American 

 Eocene Rodentia {Paramys, Sciuravus), appearance of Eurasiatic 

 Rodentia; (4) extinction of other modernized North American fami- 

 lies, including especially 4 families of Perissodactyla, also, Insectivora- 

 Hyopsodontidae ; (5) migration, probably from Eurasia, of some new 



North 

 American 

 families 

 not found 

 in western 

 European 

 Oligocene, 



