Willwood Formation

Radiometric dating of volcanic tuffs, combined with comparisons with other formations using magnetostratigraphy, using numerous samples from various levels of the formation suggest an age range of 55 - 52 million years ago, placing the Paleocene-Eocene boundary near the base of the formation.[4]

Trace fossils have been found in the Willwood Formation.[5] Fossil birds include Gastornis, Neocathartes and Paracathartes. A fossil alligatorid, namely Orthogenysuchus, was also found in this formation.

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• Clyde, W. C. 1997. Stratigraphy and mammalian paleontology of the McCullough Peaks, northern Bighorn Basin, Wyoming: Implications for biochronology, basin development, and community reorganization across the Paleocene-Eocene boundary - PhD thesis, .. University of Michigan.
• Polly, P. D. 1997. Ancestry and Species Definition in Paleontology: A Stratocladistic Analysis of Paleocene-Eocene Viverravidae (Mammalia, Carnivora) from Wyoming. Contributions from the Museum of Paleontology, University of Michigan 30. 1–53.
• Redline, A. D. 1997. Revision of the Wind River faunas, early Eocene of central Wyoming. Part 13. Systematics and phylogenetic pattern of early Eocene Hyopsodus (Mammalia: Condylarthra). Annals of Carnegie Museum 66. 1–81.
• Maas, M. C., and M. O'Leary. 1996. Evolution of molar enamel microstructure in North American Notharctidae (primates). Journal of Human Evolution 31. ..
• O'Leary, M. A., and K. D. Rose. 1995. New mesonychian dentitions from the Paleocene of the Bighorn Basin, Wyoming. Annals of Carnegie Museum 64. 147–172.
• Wing, S. L.; J. Alroy, and L. J. Hickey. 1995. Plant and mammal diversity in the Paleocene to Early Eocene of the Bighorn Basin. Palaeogeography, Palaeoclimatology, Palaeoecology 115. 117–155.
• Bown, T. M.; K. D. Rose; E. L. Simons, and S. L. Wing. 1994. Distribution and stratigraphic correlation of upper Paleocene and lower Eocene fossil mammal and plant localities of the Fort Union, Willwood, and Tatman formations, southern Bighorn Basin, Wyoming. United States Geological Survey Professional Paper 1540. 1–103.
• Tauxe, L.; J. Gee; Y. Gallet; T. Pick, and T. Bown. 1994. Magnetostratigraphy of the Willwood Formation, Bighorn Basin, Wyoming: new constraints on the location of Paleocene/Eocene boundary. Earth and Planetary Science Letters 125. 159–172.
• Gunnell, G. F., and P. D. Gingerich. 1991. Systematics and Evolution of Late Paleocene and Early Eocene Oxyaenidae (Mammalia, Creodonta) in the Clarks Fork Basin, Wyoming. Contributions from the Museum of Paleontology, University of Michigan 28. 141–180.
• Zhou, X., and P. D. Gingerich. 1991. New Species of Hapalodectes (Mammalia, Mesonychia) from the Early Wasatchian, Early Eocene of Northwestern Wyoming. Contributions from the Museum of Paleontology, University of Michigan 28. 215–220.
• Ivy, L. D. 1990. Systematics of Late Paleocene and Early Eocene Rodentia (Mammalia) from the Clarks Fork Basin, Wyoming. Contributions from the Museum of Paleontology, University of Michigan 28. 21–70.
• Gingerich, P. D., and H. A. Deutsch. 1989. Systematics and Evolution of Early Eocene Hyaenodontidae (Mammalia, Creodonta) in the Clarks Fork Basin, Wyoming. Contributions from the Museum of Paleontology, University of Michigan 27. 327–391.
• Thewissen, J. G. M., and P. D. Gingerich. 1989. Skull and Endocranial Cast of Eoructes melanus, a New Palaeoryctid (Mammalia: Insectivora) from the Early Eocene of Western North America. Journal of Vertebrate Paleontology 9. 459–470.
• Bown, T. M., and K. D. Rose. 1987. Patterns of Dental Evolution in Early Eocene Anaptomorphine Primates (Omomyidae) from the Bighorn Basin, Wyoming. Paleontological Society Memoir 23. 1–162.
• Gingerich, P. D. 1987. Early Eocene bats (Mammalia, Chiroptera) and other vertebrates in freshwater limestones of the Willlwood Formation, Clark's Fork Basin, Wyoming. Contributions from the Museum of Paleontology, University of Michigan 27. 275–320.
• Gunnell, G. F. 1985. Systematics of Early Eocene Microsyopinae (Mammalia, Primates) in the Clark's Fork Basin, Wyoming. Contributions from the Museum of Paleontology, University of Michigan 27. 51–71.
• Bown, Thomas M., and Mary J. Kraus. 1983. Ichnofossils of the alluvial Willwood Formation (lower Eocene), Bighorn Basin, northwest Wyoming, U.S.A. Palaeogeography, Palaeoclimatology, Palaeoecology 43. 95–128. doi:10.1016/0031-0182(83)90050-0
• Winkler, D. A. 1983. Paleoecology of an Early Eocene mammalian fauna from paleosols in the Clarks Fork Basin, northwestern Wyoming (U.S.A.).. Palaeogeography, Palaeoclimatology, Palaeoecology 43. 261–298.
• Krause, D. W. 1982. Multituberculates from the Wasatchian Land-Mammal Age, Early Eocene, of Western North America. Journal of Paleontology 56. 271–294.
• Rose, K. D. 1981. The Clarkforkian Land-Mammal Age and Mammalian Faunal Composition Across the Paleocene-Eocene Boundary. University of Michigan Papers on Paleontology 26. 1–197.
• Bown, Thomas M. 1979. New Omomyid Primates (Haplorhini, Tarsiiformes) from Middle Eocene Rocks of West-Central Hot Springs County, Wyoming. Folia Primatologica 31. ..
• Harrison, C. J. O. 1979. A new cathartid vulture from the lower Eocene of Wyoming. In C. J. O Harrison, C. A. Walker (eds.), 7–10. Studies in Tertiary Avian Palaeontology.
• Neasham, John W., and Carl F. Vondra. 1972. Stratigraphy and Petrology of the Lower Eocene Willwood Formation, Bighorn Basin, Wyoming. . _. .. doi:10.1130/0016-7606(1972)83[267:SAPOTL]2.0.CO;2