Clarkforkian

The Clarkforkian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 56,800,000 to 55,400,000 years BP lasting 1.4 million years.

It is usually considered to be within the Paleocene, more specifically the Late Paleocene. The Clarkforkian shares its upper boundary with the Thanetian.

The Clarkforkian is preceded by the Tiffanian and followed by the Wasatchian NALMA stages.

It is considered to contain the following substages:

...
Wikipedia