A survey of fossil footprint sites at glen canyon national recreation area (western USA): A case study in documentation of trace fossil resources at a national preserve

Abstract

Fossil footprints are very widespread in the Late Paleozoic and Mesozoic rocks of eastern Utah, but until recently have not been studied in detail. This is surprising in light of the fact that skeletal remains of fossils in this area are generally rare, whereas footprints are common and very informative about the distribution and behavior of ancient vertebrates. In this report we describe more than three dozen tracksites in the Glen Canyon National Recreation Area (GCNRA) and immediate vicinity, from eight formations (Cedar Mesa, Moenkopi, Chinle, Wingate, Kayenta, Navajo, Summerville, and Morrison) that range in age from Permian through Jurassic. Tracks in the Permian, cf. Anomalopus (or Chelichnus) and Stenichnus, represent at least two types of pre‐archosaurian reptiles, and reveal evidence of predator–prey interaction and digging activity. Footprints in the Moenkopi include a large number of swim traces attributable to amphibians, and horseshoe crabs. Footprints in the Chinle Group include the first example of Atreipus from the western United States–a track attributed to an early, turkey–sized bipedal dinosaur. Footprints in the Wingate and Kayenta Formations are assigned to Grallator and Eubrontes and represent theropod dinosaurs. One Kayenta occurrence of theropod tracks resembles the famous so‐called “man tracks” of Texas. The Navajo Formation has produced a large number of track‐bearing localities including sites that reveal theropod footprints (Grallator and Eubrontes), mammal‐like reptile footprints (cf. Brasilichnium), tracks probably attributable to prosauropods, or thyreophorans (Otozoum) and ornithopods (cf. Anomoepus). Footprints from the Summerville and Morrison Formations include the first brontosaur ichnites (cf. Brontopodus) with skin impressions and well‐preserved digit impressions, and pterosaur tracks (Pteraichnus). Fossil footprints are an important, non‐renewable resource in this area, that provide special management challenges. Part of these challenges involve a dialogue between paleontologists and land management authorities that permits an understanding of the resource and promotes the use of non‐technical terminology. To this end, this manuscript is written with both audiences in mind. Both groups are responsible for distinguishing between more‐ and less‐important sites and guiding or prioritizing conservation, collection and public education/ viewing policies. Tracksites can not all be removed to museums for safekeeping. Similarly they can not all be made available for public viewing, nor can they be completely protected from weathering and vandalism.