Theodore Roosevelt National Park: Paleontological resource inventory (public version)

Abstract

Theodore Roosevelt National Park (THRO) in western North Dakota was established for its historical connections with President Theodore Roosevelt. It contains not only historical and cultural resources, but abundant natural resources as well. Among these is one of the best geological and paleontological records of the Paleocene Epoch (66 to 56 million years ago) of any park in the National Park System. The Paleocene Epoch is of great scientific interest due to the great mass extinction that occurred at its opening (the Cretaceous–Paleogene extinction event), and the unusual climatic event that began at the end of the epoch (the Paleocene–Eocene Thermal Maximum, an anomalous global temperature spike). It is during the Paleocene that mammals began to diversify and move into the large-bodied niches vacated by dinosaurs. The rocks exposed at THRO preserve the latter part of the Paleocene, when mammals were proliferating and crocodiles were the largest predators. Western North Dakota was warmer and wetter with swampy forests; today these are preserved as the “petrified forests” that are one of THRO’s notable features. Despite abundant fossil resources, THRO has not historically been a scene of significant paleontological exploration. For example, the fossil forests have only had one published scientific description, and that report focused on the associated paleosols (“fossil soils”). The widespread petrified wood of the area has been known since at least the 19th century and was considered significant enough to be a tourist draw in the decades leading up to the establishment of THRO in 1947. Paleontologists occasionally collected and described fossil specimens from the park over the next few decades, but the true extent of paleontological resources was not realized until a joint North Dakota Geological Survey–NPS investigation under John Hoganson and Johnathan Campbell between 1994–1996. This survey uncovered 400 paleontological localities within the park representing a variety of plant, invertebrate, vertebrate, and trace fossils. Limited investigation and occasional collection of noteworthy specimens took place over the next two decades. In 2020, a new two-year initiative to further document the park’s paleontological resources began. This inventory, which was the basis for this report, identified another 158 fossil localities, some yielding taxa not recorded by the previous survey. Additional specimens were collected from the surface, among them a partial skeleton of a choristodere (an extinct aquatic reptile), dental material of two mammal taxa not previously recorded at THRO, and the first bird track found at the park. The inventory also provided an assessment of an area scheduled for ground-disturbing maintenance. This inventory is intended to inform future paleontological resource research, management, protection, and interpretation at THRO. THRO’s bedrock geology is dominated by two Paleocene rock formations: the Bullion Creek Formation and the overlying Sentinel Butte Formation of the Fort Union Group. Weathering of these formations has produced the distinctive banded badlands seen in THRO today. These two formations were deposited under very different conditions than the current conditions of western North Dakota. In the Paleocene, the region was warm and wet, with a landscape dominated by swamps, lakes, and rivers. Great forests now represented by petrified wood grew throughout the area. Freshwater mollusks, fish, amphibians (including giant salamanders), turtles, choristoderes, and crocodilians abounded in the ancient wetlands, while a variety of mammals representing either extinct lineages or the early forebearers of modern groups inhabited the land. There is little representation of the next 56 million years at THRO. The only evidence we have of events in the park for most of these millions of years is isolated Neogene lag deposits and terrace gravel. Quaternary surficial deposits have yielded a few fossils...