Colorado National Monument: Paleontological resource inventory (public version)

Abstract

Colorado National Monument (COLM) in western Colorado was established on May 24, 1911 with the purpose of preserving, understanding, and enjoying the natural and cultural resources of the landscape, focusing on the history, erosional processes, and geology present. Although not explicitly mentioned in the monument?s purpose statement, the paleontological resources of COLM are nevertheless important. Significant fossils have been known from the area since the late 19th and early 20th centuries, and from COLM specifically within a few decades of the monument?s founding. The direct urban interface of COLM with Colorado?s Grand Valley provides unique management concerns for fossils and other resources of the monument. While COLM preserves a long geologic history (roughly 1.7 billion years ago to the present), the fossils preserved at the monument mostly come from sedimentary rocks of the Mesozoic Era. The paleontological resources of COLM include both body fossils and trace fossils of a wide variety of organisms (e.g., freshwater mussels, dinosaurs, plants) representing diverse paleoenvironments. In order to assess the paleontological resources of COLM, a field inventory was conducted from April to November 2023, visiting all previously reported fossil sites and documenting new localities. A total of 226 paleontological localities were verified during this fieldwork, of which nearly two-thirds (146 sites) were newly documented. Two more were discovered in March 2024. These 228 localities are distributed throughout much of the monument and many of the geologic units, with higher concentrations present in certain units (e.g., the Morrison Formation). Fieldwork was supplemented by the review of published and gray literature and assessment of COLM paleontological collections. A number of significant paleontological discoveries were made during this inventory, including the first documented fossils (dinosaur tracks, plant fossils, and dinosaur skin) from the Naturita Formation within COLM and multiple novel fossil occurrences (e.g., likely the oldest-known fish otoliths in North America and possibly one of the only Jurassic ankylosaur tracks known globally). When considered alongside previously identified significant fossil finds from COLM (e.g., one of only three known turtle tracksites in the Morrison Formation and potentially one of the only known lizard trackways in the same unit), the paleontological resources of the monument are of high scientific importance. Future research on the paleontological resources of COLM has a high potential for identifying important fossil specimens and/or describing new species. This report provides foundational data on the scope, significance, and distribution of paleontological resources at COLM and provides recommendations to support the management, interpretation, and research of these resources.