THE MIOCENE PERIOD. 285 



classification. The forms found in Eurasia in the Miocene are Dino- 

 therium and Tetrabelodon; those found in the Upper Miocene in North 

 America are Tetrabelodon and Dibelodon. The Dinotherium, which 

 was distinguished by downward curved tusks in the lower jaw, seems 

 never to have reached America. This, together with the simplicity 

 of the teeth of the American Tetrabelodon, has suggested that the latter 

 may have reached America by some other than the European route, 

 perhaps via eastern Asia. 



Fig. 454. — A Miocene Mastodon, Tetrabelodon angustidens Cuvier. (Restoration by 



Gaudry.) 



The immigration of the ruminants. — Much more important in 

 ulterior results was the immigration of the modern ruminants. Cer- 

 tain branches of the ruminants had been represented previously by 

 the Tragulidw, Camelidw, and perhaps other groups now extinct, but 

 the great ruminant group that later formed so important a part of 

 the fauna does not seem to have been derived from these, but to have 

 immigrated from Eurasia. They are first recorded in the Loup Fork 

 beds. The first immigrants belonged to the deer and ox families. 

 The earliest known deer (not including Protoceras) are first known in 

 Europe. They were hornless, as are their surviving relatives in Asia, 

 the musk-deer and the Chinese water-deer. 1 By the middle of the 

 Miocene period certain male forms had acquired small two-pronged 

 deciduous antlers, fixed on long bone pedicles. About the close of 



1 Vert. Pal., Woodward, p. 365. 



