 "D. hartshornianus" fossils found in Oligocene Orellan rocks in the Lower Nodular Zone, Pennington County, South Dakota are dated at ~33.4 Ma.Other sites include the Prairie Dog Creek Site and Warbonnet Creek Site, Sioux County, Nebraska ~33.4 Ma., Bartlett High Site, Dawes County, Nebraska ~33.2 Ma., Babby Butte Site, Oglala Lakota County, South Dakota ~33.4 Ma—33.2 Ma."D.