SUCCESSIVE MAMMALIAN FAUNAS 249 



3. Oligocene 



North America. — The John Day formation of eastern Oregon 

 represents the upper OUgocene and has yielded a very extensive 

 series of mammals, though with some obvious gaps that remain 

 to be filled by future work. The land-connection with the 

 Old World which had existed in the lower Oligocene and was 

 restored in the lower, or at latest in the middle, Miocene, was 

 interrupted in John Day times, and so the mammals assumed 

 a purely indigenous character. 



No opossums or other marsupials have been found, and 

 nothing is known of the Insectivora. Of the Carnivora, there 

 were but three families, and one of these, the mustelines, was 

 represented but scantily by a few small species. Cats of the 

 fsabre-tooth subfamily were common and one species was 

 quite large, almost equalling the Jaguar in length ; but most of 

 the species were small, much smaller than the Pleistocene 

 members of the group. True cats are not definitely known 

 to have been present, but there were two genera {^Nimravus 

 and ^Archcelurus) which have been called the "false fsabre- 

 tooths," which may prove to be referable to that series. The 

 dogs, on the other hand, were remarkably numerous and 

 diversified, more so than ever before or since ; none of them 

 was very large, the largest but little exceeding the Timber 

 Wolf in size, and some were extremely small ; but the number 

 of distinct genera and species and the differences among them 

 are quite remarkable. Both long and short-faced forms 

 and early stages of the f" bear-dogs," and f hyena-dogs," 

 and ancestral forms of the wolves and dholes may be distin- 

 guished, a truly wonderful assemblage. The rodents also 

 were numerous and varied, including ancient and extinct 

 genera of the beavers, squirrels, mice, pocket-gophers and 

 hares and the earliest distinguishable ancestors of the sewellels 

 (Aplodontiidfp). 



The remainder of the known John Day fauna was composed 



