. The age of mammals in Europe, Asia and North America. Mammals, Fossil; Paleontology. 232 THE AGE OF MAMMALS conditions of deposition are more fully discussed under the Miocene, p. 278. As soon as fossils become abundant it is evident that we are in the Promerycochoerus Zone, because, while the entire assemblage of mammals is, on the whole, similar generically to that of the Upper John Day, the specific stages are regarded as type for type more recent than those either of the Middle or even of the Upper John Day, or of the Aquitanian or St. Gerand-le-Puy of France. The peccaries afford simila
. The age of mammals in Europe, Asia and North America. Mammals, Fossil; Paleontology. 232 THE AGE OF MAMMALS conditions of deposition are more fully discussed under the Miocene, p. 278. As soon as fossils become abundant it is evident that we are in the Promerycochoerus Zone, because, while the entire assemblage of mammals is, on the whole, similar generically to that of the Upper John Day, the specific stages are regarded as type for type more recent than those either of the Middle or even of the Upper John Day, or of the Aquitanian or St. Gerand-le-Puy of France. The peccaries afford similar testimony. Thi- nohyus siouxensis is more modified than any of the species of the John Day.^ It is interesting to note that these peccaries, like those of the John. Fig. 116. — Upper John Day Formation, Oregon ; Promerycochoerus Zone. Photograph by the University of California expedition of 1900. Day, fall into two phyla, a dolichocephalic and a brachycephalic. This more recent character and the presence in these lower Arikaree deposits of the plains of several new genera of mammals may justify the placing of these formations in the Lower Miocene (Peterson, Matthew). We are certainly in the presence of a transition. As compared with the Old World, however, it would appear that this mammalian assemblage of the Upper John Day, Lower Arikaree, Lower Harrison, and Lower Rosebud is still characteristically Oligocene rather than Miocene, as shown in the accompanying list. 1 Peterson, O. A., New Suilline Remains from the Miocene of Nebraska. Mem. Carnegie. Mus., Pittsburg, Vol. II, no. 8, 1906, pp. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Osborn, Henry Fairfield, 1857-1935. New York, The Macmillan Company
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