Vickers-Rich, Patricia and Bohaska, David J. 1976. "The World’s Oldest Owl: A New Strigiform from the Paleocene of Southwestern Colorado." In Collected papers in avian paleontology honoring the 90th birthday of Alexander Wetmore. 87–93. Washington, D.C.: Smithsonian Institution Press. In Smithsonian Contributions to Paleobiology, 27. https://doi.org/10.5479/si.00810266.27.87.