Preliminary report on the American Clark Fork mammal fauna, and its correlation with similar faunas in Europe and Asia

On the basis of collections made during the past two summers (1975, 1976), the Clarkforkian appears to be a valid and important land mammal age in North America. Comparing the Clarkforkian mammal fauna to the sequence of mammal faunas spanning the Paleocene-Eocene boundary in Europe, the Clarkforkian fauna is most similar to the basal Sparnacian fauna from Meudon. Thus the Clarkforkian is regarded as the earliest Eocene land mammal age in North America. The stratigraphic and geographic distribution of notoungulates, together with the climatic history of the Paleocene and Eocene, makes it probable that notougulates originated in Central or South America, reached North America early in the Clarkforkian, and reached Asia in the Clarkforkian or early Wasatchian. The age of the Mongolian Gashato and Naran Bulak mammal faunas is thus regarded as early Eocene rather than late Paleocene.