SUCCESSIVE MAMMALIAN FAUNAS 281 



Of equal significance for the future was the arrival of the 

 Artiodactyla, of which there were members of three famiUes 

 in the Wasatch, though individually they were much less 

 common than the horses. These were geologically the oldest 

 known artiodactyls, Europe having yielded none of this date, 

 and are still too imperfectly known to justify any very positive 

 statements about them. One genus, however {\Trigono- 

 lestes), tiny little creatures, like rabbits in size, would seem to 

 represent the beginnings of the great ruminant tribe, now so 

 very important a factor in the life of the world. A second 

 genus {^Eohyus), considerably larger, is very doubtfully refer- 

 able to the pigs; while a third {^Parahyus), still larger, was 

 the first in the short-faced series of the fentelodonts, which 

 persisted in ever increasing size through the whole Eocene, 

 but could hardly have been ancestral to the true fentelodonts, 

 or fgiant-pigs, of the Oligocene, the place and time of whose 

 origin are unknown. 



Another immigrant order of great interest, since we our- 

 selves belong to it, the Primates, made its first appearance in 

 North America in the Wasatch, but was not destined to long 

 life or great importance in this continent, where it did not 

 survive the Eocene. Several different kinds of small, lemur- 

 like and monkey-like creatures dwelt in the tree-tops of the 

 Wasatch forests. One genus {^Anaptomorphus) had a remark- 

 able likeness to the modern Tarsier {Tarsius spectrum) of the 

 Malay peninsula and islands. 



South America. — The Eocene of South America, referred 

 by some writers to the upper Cretaceous, is very incompletely 

 and unsatisfactorily known. The Casa Mayor formation 

 (or Notostylops Beds), which has yielded a great variety of 

 mammals, for the most part very fragmentary, probably 

 contains not one but several successive faunas which have 

 not yet been fully discriminated, and that of the next succeed- 

 ing Astraponotus Beds is still but a scanty list. This list, 

 however, includes the most ancient fgiyptodonts yet discovered 



