32 VERTEBRATA OF THE TERTIARY. 



raiy period appears to have been different. In America, the changes of 

 evel appear to liave been more uniform in character over large areas. 

 Each deposit has a wider geographical extent, and the fauna presents less 

 rregular variation. In Europe we have a great number of comparatively 

 estricted deposits, each of wliich differs from the others in possessing more 

 or less peculiarity of fauna. After a study of these faunae, their natural 

 arrangement in Europe into three series — Eocene, Miocene, and Pliocene — 

 does not appear to rest on any solid basis. This is especially true of the 

 distinction between the first two; and authors are at variance as to the 

 point of demarkation between the last two. Thus, the Tongrian is the 

 summit of the Eocene according to Renevier, while Gaudry, with Filhol 

 and others, places it at the base of the Miocene. One opinion is as well 

 supported by facts, as now interpreted, as the other. 



As an essential aid in the estimation of the Hmits of the formations, I 

 appeal to the criterion adopted at the opening of this chapter, viz, the 

 period of extinction of animal groups. 



If we take a general view of the Tertiary faun£E, we find that the fol- 

 lowing well-marked types representing famiUes and higher groups have 

 become extinct, and have left no living descendants or successors : Among 

 Bunotheria, the American groups Tceniodonta and Tillodonta ; also the Meso- 

 donta of both continents; of Edentata, Macrotherium, and Ancyhtherium in 

 Europe, and the 3IegatJieriidce in North America; among the Carnivora, the 

 Eyanodons and Proviverrce, with the Drepanodons ; of Ungidata, the entire 

 order of Amhlypoda, which, however, doubtless disappeared in some of its 

 members by modification ; but its only known suborders, the Pantodonta 

 and the Dinocerata, become absolutely extinct. Among Perissodactyla, both 

 continents lost by extinction the ChaUcotheriidcB, which terminated in a 

 great development in North America; and the Bhinocerida. Of Artiodactyla, 

 two great divisions, representative of each other in the two continents, 

 totally disappeared, viz, the OreodontidcB and the Anoplotheriida ; to which 

 must be added the Hyopotamidfc. Of true ruminants, the most important 

 type which has disappeared from both continents is that of the Cameltda, 

 Oi 8u\\\hw gauera, Anthracotherium and Elotherium may be looked upon as 



