Distribution and Significance of Mesozoic Vertebrate Trace Fossils in Dinosaur National Monument

Abstract

Search for new tracksites has now revealed a total of 25 localities in the older Mesozoic sedimentary rocks of Dinosaur National Monument (DNM). To date, the most productive units have proved to be the Late Triassic Chinle Group and the mainly Early Jurassic Glen Canyon Group in the western part of DNM. In addition several sites, that are an integral part of the overall paleontological picture, have been found just outside the boundaries of DNM. All these sites (and stratigraphic levels) add up to a total of about 45 tracksites in the DNM area. Chinle sites have now yielded dozens of trackways of theropod dinosaurs, ?prosauropod dinosaurs, mammal-like reptiles, ?phytosaurs, aetosaurs, lepidosaurs and tanystropheids, producing one of the most diverse Late Triassic track assemblages known anywhere. The ?prosauropod tracks are the first Late Triassic examples ever reported from the North American continent. The Lower Jurassic has also yielded theropod and prosauropod dinosaur tracks. These tracks are useful for correlation with other Early Mesozoic tracksites around the world and can be used to help construct a series of track zones (or Palichnostratigraphy) for the western United States. The discovery of prosauropod tracks (Pseudotetrasauropus) in the Chinle Group and in the lower part of Glen Canyon Group (Otozoum) points to a much wider distribution of prosauropod tracks in the western United States than previously supposed, and the need for a thorough study of these and similar track types. Further examination of the Jurassic Cannel Formation close to the DNM boundaries, reveals several tracksites that require further study.