298 ORIGIN AND DISTRIBUTION OF MAMMALS 



of sirenians — Halitherium — while cetaceans are very rare, and represented only 

 by Squalodontidae, mingled with which occur isolated remains of land mammals 

 — Apterodon, Anthracotherium and j)rimitive rhinoceroses. 



Miocene. 



In North America the Miocene begins with the John Day beds of Oregon, 

 which are characterised especially by the abundance of rodents and by 

 the presence of Diceratherium and Promenjcochoerus. From the White Eiver 

 Oligocene there pass upwards the perissodactyls Aceratherium, Protapirus and 

 Mesohippus, and the artiodactyls Elothermm, Perchoerus, Agriochoerus, Paratylopus 

 and Hypertragidus ; but with the former are newly associated the first Dicera- 

 therium, Miohippus, and the chalicothere Moropus, with the latter, Eporeodon and 

 Promerycochoerus. The numei'ous carnivores are distributed among the genera 

 Nothocyon, Mesocyon, Temnocyon, Enhydrocyon, Nimravus, Pogonodon, and Hoplo- 

 phoneus ; the rodents, among the genera Prosciurus, Steneofiber, Entoptychus, 

 PleuroUcus, Meniscomys, Mylagaulodon, Pacicalus, Peromyscus, and Lepus. The 

 somewhat younger faunas of the Harrison beds of Montana, the Kosebud beds 

 of South Dakota, the Monroe Creek beds of Nebraska, etc., are on the whole 

 rather poor in species and genera. As characteristic and at the same time new 

 types there are of interest the carnivore genera Phlaocyon, Cynodes7nus, OUgobunis, 

 Megalictis and Aelurocyon, the perissodactyls Parahippus, Anchitherium and 

 Miohippus, and the artiodactyls Dinohyus, Desmathyus, Mesoreodon, Merycodtoerus, 

 Merychyus, Leptauchenia, Stenomylus, Protomeryx, Oxydadylus, and especially the 

 genus Blastomeryx, a Hypertragulid. The immediately succeeding faunas of the 

 Deep River and Flint Creek in Montana, of Pawnee Creek in Colorado, and 

 the Mascall beds in Oregon, exhibit no such diversitj^ as that of the North 

 American Oligocene. They comprise essentially only the successors of the 

 earlier Canidae, Rhinoceridae, Equidae, A griochoeridae, Camelidae and Suidae, but 

 they have almost all so much changed that the recognition of many new genera 

 seems necessary. Of Canidae may be mentioned Tephrocyon, CynardxhS, Amphi- 

 cyon and Canis ; of Felidae, Pseudaelurus ; of Bhinoceridae, Caenopus, Aphelops 

 and Teleoceras ; of Equidae, Merydiippus, Hypohippus and Parahippus ; of Suidae 

 a dicotyline, Hesperhyus ; of Agriodioeridae, Merycodioerus, Promerycochoerus, Meso- 

 reodon, Merychjua and Cydojndius ; and of Camelidae, Miolabis, Procamelus, 

 Profolabis and Aliicamelus. The rodents are represented almost entirely by 

 Mylagaidus-V\ke forms. The first appearance of Proboscidea — Tetrabelodon 

 (Trilophodon) — in North America, however, gives to these younger faunas special 

 importance. They also appear strange from the occurrence of the rhinoceroses 

 Aphelops and Teleoceras, of Palacomerycinae, and of the Mustelidae, Potamotherium 

 and Mustela, which are reminiscent of European conditions. Blastomeryx and 

 Merycodus on the other hand are certainly autochthonous. 



While the composition of the fauna just described certainly indicates 

 an immigration of Old World elements, the next younger fauna is evidently 

 the product of the quiet further development of the types already present 

 without any foreign intrusion. Unfortunately, it is far behind the older North 

 American faunas in variety, but this is partly compensated for by a remarkable 

 abundance of individuals. The somewhat older Arikaree stage has apparently 

 a wider distribution — Nebraska (Niobrara), South Dakota, Montana, New 

 Mexico and Texas — than the younger Olagalla stage in Kansas and Nebraska, 



