Eocene bird, reptile, and mammal tracks from the Chuckanut Formation, northwest Washington

The diversity and abundance of bird and animal tracks preserved in Eocene strata of the Chuckanut Formation in Washington contrasts to the scarcity of body fossils. These ichnofossils were made by vertebrates that inhabited river margins, the only depositional environment favorable for track preservation. Three of the four localities described herein contain tracks from at least two different types of animals. Site SM-6 contains approximately 200 shallow circular plantigrade footprints, perhaps made by a type of archaic mammal of the Orders Pantodonta or Dinocerata. Site RU-1 yielded footprints from a small shorebird and tracks from an early equid or tapiroid. The same type of perissodactyl tracks were preserved at Site KC-1, along with a single webbed bird track, and trackways from a large heron-like bird and a turtle. Site SM-9.5 contained multiple bird tracks of a type not found at the other localities. The discovery of tracks only at Chuckanut Formation sites that expose large bedding planes indicates the importance of considering outcrop architecture during the search for vertebrate ichnofossils, and inspires the hope that similar fossils may eventually be found in correlative formations in the Pacific Northwest.