A Probable Diatryma Track from the Eocene of Washington: An Intriguing Case of Controversy and Skepticism

Abstract

A large tridactyl track from the Franklin Series of the Eocene Puget Group has been named Ornithoformipes controversus ichnogen et ichnosp. nov. and is attributed to a large ground-dwelling Diatryma or a Diatryma-like bird. The isolated footprint clearly shows that the trackmaker had broad semi-circular unguals and feet that show several correspondences with the foot morphology inferred for Diatryma and related forms. The age of the footprint is estimated at about 45 million years, which is about 5 million years younger than known Diatryma body fossils. The sedimentary geology context of the track is consistent with an interpretation of the trackmaker as a large herbivore that lived in well-vegetated areas.

Keywords:

• Eocene
• bird tracks
• Diatryma

ACKNOWLEDGEMENTS

We thank Spencer Lucas, New Mexico Museum of Natural History and Science, for his helpful review. Emma Rainforth, Mesalands College, Tucumcari, New Mexico, also provided challenging comments. We also thank George Mustoe, Department of Geology, Western Washington University, for his comments on an earlier version of this manuscript. Peter Murray kindly provided useful observations and illustrations of dromornithid feet.