134 THE AGE OF MAMMALS 



The Rodentia are represented by the bunodont squirrel-like Paramys, 

 surviving from the Wasatch, and the somewhat more rare Sciuravus of the 

 primitive family Ischyromyidse. 



To be ranged among the ancient Creodonta or among the more modern 

 pro-Carnivora is the family Miacidse, which is now becoming higlily diver- 

 sified. It includes a variety of species which belong to the surviving Wa- 

 satch genera Didymictis, Miacis, and Vulpavus, as well as to the higher 

 genera Viverravus and Oodedes. These animals are analogous in dental 

 structure, in size, and in proportions to the civets and to the South American 

 procyonids (Bassariscus, Cercoleptes) rather than to the dogs. The reten- 

 tion of the last lower molar is the only especial cynoid feature. 



Similarly the Primates begin to take on a slightly more modernized form. 

 There are the highly specialized T'arsms-like anaptomorphids, including 

 two species, Anaptomorphus spierianus Cope, A. abboti Loomis, as well as a 

 third representative of a new anaptomorphid genus. Related to the same 

 family are diminutive monkeys allied to the Omomys and Washakius of the 

 Bridger. We discover also the lemuroid or insectivoroid microsyopsids, 

 including the Wasatch genus Cynodontomys, as well as the Bridger genus 

 Microsyops. Similarly monkeys or lemurs of larger size represent the fam- 

 ily Notharctidse, which now includes not only the smaller Wasatch Pelycodus, 

 but the more progressive Nothardus, a primate appearing here for the first 

 time which becomes especially characteristic of the Bridger. 



Of the cursorial Herbivora the odd-toed ungulates (Perissodactyla) 

 are now enriched by the newly appearing family of Titanotheriidae, both 

 by the light-limbed Lambdotherium and the larger and more central Eoti- 

 tanops. Lambdotherium is especially abundant, and characteristic of rocks 

 of Wind River age wherever found. The prevailing species, L. popoagicum 

 (named after a local stream, the Popoagie River), is an animal of the size 

 of a coyote (Canis latrans), with a slender, elongate muzzle, and laterally 

 compressed digits which suggest those of the contemporary equines; it 

 was evidently a cursorial, or slender-footed form adapted to the open basins 

 of the mountain region. The larger Wind River titanothere (Eotitanops 

 borealis) is now about the size of a two-thirds grown tapir, and appears 

 to possess all the characters which justify our regarding it as ancestral to 

 certain of the Bridger and Upper Eocene titanotheres ; whereas Lambdo- 

 therium belongs to a dying-out phylum. It is noteworthy that these mem- 

 bers of the titanothere family, which is destined to become the dominant 

 perissodactyl family of the remainder of the Eocene, are already dominant 

 in size among the modernized herbivores of Wind River times, although in- 

 ferior to the coryphodonts and uintatheres. 



The horses are represented by the persisting Wasatch genus Eohippus, 

 in which the hind feet retain the vestigial fifth digit, and there is little ad- 

 vance in the complication of the grinding teeth. The famous skeleton of 

 Eohippus venticolus, discovered by Wortman and fully described and figured 



