Terrestrial mammal fossils from the Wildcat Creek Beds (Paleogene),
Tieton River Area, south-central Washington, USA
Fossil mammals from two units of the Wildcat Creek beds, a distal facies of the volcanogenic Ohanapecosh Formation in the Tieton River area, 30 miles southeast of Mount Rainier are described. A tooth fragment of a rhinocerotid or hyracodontid from the Milk Creek tuff is suggestive of a post middle Chadronian age and is supported by a published zircon fission track age of 34 Ma. This date places the fossil as the oldest terrestrial mammal recovered from Washington. Isolated elements collected from the overlying upper Wildcat Creek beds belong to Cormocyon copei, Enhydrocyon sp., Parenhydrocyon josephi, a cricetid rodent, cf. Palaeolagus sp., ?Miohippus equinanus, Miohippus equiceps, Diceratherium annectens, Promerycochoerus superbus, Eporeodon sp., Merycoides sp., Mesoreodon sp., Hypertragulus sp., and a tayassuid. These taxa comprise the Wildcat Creek local fauna and represent a biogeographic extension of the middle John Day fauna of eastern Oregon of late early Arikareean age. This biochronology is supported by 40Ar/39Ar radiometric ages of 27.16 ± 0.19 and 26.97 ± 0.30 Ma from beds constraining the upper Wildcat Creek beds. The Wildcat Creek local fauna lived in a moist seasonal environment, indicated by a Goshen-type paleoflora in the lower Ohanapecosh Formation and supported by a succession of Argillisols and Gleysols to gleyed Protosols.
KEY WORDS: Paleogene; North America; mammals; sedimentology; faunal composition; geochronology
PE Article Number: 14.3.24A
Copyright: Society of
Vertebrate Paleontology November 2011
Submission: 15 June 2007. Acceptance: 27 August 2011