IN SEARCH OF FERDINAND V. HAYDEN'S 1868 “LOST” TRACKS: NEW FIELD EVIDENCE FOR THE LOCATION AND DESCRIPTION OF THE FIRST DINOSAUR FOSSIL DISCOVERY IN WYOMING

Traveling by horse along the Overland Trail during September 9-25, 1868; Ferdinand V. Hayden and his lone assistant James Stevenson discovered the first dinosaur fossils in the Wyoming Territory while conducting the Geological Survey of the Territories. The fossils were large animal tracks briefly described in his Second Annual Report as tracks “that seem to belong to a huge bird” and other associated tracks that resemble those made by “mules” and a “four-toed pachydermatous animal.” These tracks were reported to occur in hard, flat table-rocks with wave-ripple marks at one location between Black Buttes and Point of Rocks stations in southwestern Wyoming. The strata in this region are Late Cretaceous which suggest the huge bird tracks were likely produced by dinosaurs and therefore Hayden is credited with the first dinosaur discovery in Wyoming. Hayden's field notes, sketches, and samples of the tracks have apparently been “lost” over time and the exact stratigraphic and geographic location has been unknown, as well as any detailed description of the tracks. Our reconnaissance fieldwork searching for these tracks indicates they are located in the lower part of the Campanian Almond Formation approximately 7 km southeast of Point of Rocks. At this location, a few large (60 cm-long) three-toed tracks are present in wave-rippled sandstone beds. In addition, many circular features (10-15 cm in diameter) were found that could be attributed to Hayden's “mule” tracks, suggesting this location is the site of Hayden's track discovery. The large tridactyl tracks are interpreted as hadrosaurian dinosaur footprints. The tracks occur 52 m stratigraphically above the base of the Almond Formation and lie within coastal and barrier plain deposits. Specifically, the tracks occur in a laterally continuous, 25-70 cm-thick, fine-grained sandstone bed with extensive wave-ripple cross-laminations and minor bioturbation. The sandstone bed is interpreted to be a distributary crevasse splay that prograded into a salt marsh or bay. The rediscovery of these tracks is important for its historical value. Future detailed work on these tracks will be important in understanding Campanian dinosaurs in Wyoming because very few dinosaur fossils of this age have been found in the state.