A large assemblage of tetrapod tracks from the Cretaceous Naturita Formation, Cedar Canyon region, southwestern Utah

Abstract

A large assemblage of more than 100 archosaur tracks was recovered from the Cretaceous “Dakota Formation” (Naturita Formation) at a high elevation site on private land in the Cedar Canyon area of southwestern Utah. The assemblage is notable for several reasons. It consists exclusively of large, deep, and well preserved natural casts. All three major groups of archosaurs are represented: dinosaurs, pterosaurs and crocodylians. Non-avian theropod (Magnoavipes), ankylosaurian (Tetrapodosaurus), ornithopod (Caririchnium) and crocodylian swim tracks are all represented abundantly, in similar proportions. Both swim tracks and crocodilian walking tracks are represented, the former assigned to Hatcherichnus are common, but the latter assigned to Mehliella are rare. The assemblage also contains a few pterosaur tracks (Pteraichnus). The composition of the assemblage is very similar to that found in the Naturita Formation in western Colorado, where a Cenomanian age is reported. This is the most westerly occurrence of an assemblage with this distinctive composition, and suggests a vast paleogeographical extension of the so called Dakota megatracksite or dinosaur freeway.