276 LAND MAMMALS IN THE WESTERN HEMISPHERE 



isolated character than that of the Bridger as to suggest 

 a connection with the eastern hemisphere, a suggestion which 

 is strengthened by the unheralded appearance of the ftitano- 

 theres and fhyracodonts, of which no forerunners have been 

 found in the Wasatch. 



The lowest and most ancient of the Eocene faunas is that 

 of the Wasatch formation, which is extensively developed 

 in central and southern Wyoming, Utah and New Mexico. 

 The fauna of this stage is plainly divisible into two groups : 



(1) those types which were the descendants of American 

 Paleocene mammals and were therefore indigenous, and 



(2) the immigrants from other continents. The indigenous 

 mammals, which almost all belonged to orders now extinct, 

 few of which survived later than the Eocene, must have given 

 a very bizarre appearance to the assemblage, especially as 

 they were more numerous, varied and, for the most part, 

 larger and more conspicuous than the newcomers. Marsupials 

 have not yet been found, but the occurrence of opossums in the 

 Bridger and probably in the Wind River gives some reason to 

 believe that they were in North America during Wasatch 

 times also. The fTseniodontia, which bore a certain resem- 

 blance to South American edentates, had one pair of incisor 

 teeth above and below enlarged and chisel-shaped, somewhat 

 like those of rodents. The fTillodontia were much smaller than 

 those of the Bridger, and their incisors were only beginning to 

 take on the chisel-like form. Insectivora were quite abundant, 

 and three, or perhaps four, families were represented in the 

 Wasatch ; some of these resembled the modern aquatic in- 

 sectivores of the west African rivers and others were more 

 like European hedgehogs. 



The flesh-eaters all belonged to the fCreodonta, and, 

 though rather less diversified than those of the Bridger, were 

 yet relatively abundant. In size, they ranged from little 

 creatures not larger than a weasel up to truly enormous beasts, 

 and differed, no doubt, largely in habits and manner of life. 



