OF WESTERN NORTH AMERICA. 85 



tions in surviving types are the pro-Carnivora-Miacidae, which first 

 appear at this stage. Others will be discovered. 



Mammals of larger size, mostly evolved from the Puerco mammals. 

 Last survivors of the Multituberculata. Edentata-Tseniodonta of 

 larger size. Of archaic Ungulata, 2 orders and 3 families: (1) Con- 

 dylarthra-Phenacodontidae, (2) Amblypoda-Periptychidse, (3) Ambly- 

 poda-Pantolambdidae. Of the latter, Pantolamhda is supposed to be 

 ancestral to the Coryphodontidse of the Wasatch. Carnivora-Creo- 

 donta, 4 families: (1) Mesonjchidse- Triisodon and Dissacus, (2) Oxy- 

 claenidse, (3) Arctocyonidae, (4) pro-Carnivora-Miacidse. The primate- 

 like Indrodon and aberrant Mixodectes are of unknown relationships; 

 they are possibly Insectivora. 



Summary of genera and species. 



Genera. Species. 



Archaic Triassic stock 3 4 



Archaic Cretaceous stock 21 36 



Total archaic stock 24 40 



Modernized Tertiary stock 1 1 



II. SECOND FAUNAL PHASE. 



First modernization — Invasion of the archaic by the modern fauna — South 

 American land connection interrupted — Close faunal connection with west- 

 em Europe — Initial eUmination of the archaic fauna in competition with 

 the modem. 



In the period of the deposition of the Wasatch formation, inde- 

 pendent deposits were formed in western Wyoming, northern Wyo- 

 ming, and New Mexico. A momentous change occurs, namely, the 

 sudden modernization of the mammalian fauna of the Mountain 

 Region. 



In the San Juan basin of northwestern New Mexico, after a barren 

 deposition interval of only a few hundred feet between fossiliferous 

 Torre j on and Wasatch levels (see fig. 1), there appear represent- 

 atives of ancestors of 4 or 5 modern orders, including 1 1 new families, 

 2 of which persist to the present time. European paleontologists 

 usually attribute the origin of this modernized fauna to North Amer- 

 ica, but this is without evidence; it is certain that it originated 

 neither in South America nor in Africa. There remain four possible 

 sources; these animals may have entered the central Mountain 

 Region by migration (1) from the Great Plains Region, or (2) from 

 the more northerly American Mountain Region, or (3) from the 

 northerly Eurasiatic Region, or (4) from the northerly American- 

 Asiatic land mass. 



In the writer's judgment, the simultaneous and sudden appearance 

 in North America, latitude 40°, and in western Europe, latitude 

 50°, of a similar fauna favors the fourth theory, namely, that of the 

 intermediate or North American-Asiatic or Holarctic origin of this 



