The Mill Canyon Dinosaur Tracksite: North America’s First Dromaeosaurid Trackway
Executive Summary
The Mill Canyon Dinosaur Tracksite is the largest and most diverse dinosaur tracksite documented in the Lower Cretaceous Cedar Mountain Formation. The locality has yielded multiple theropod, sauropod, and ornithischian trackways, alongside the significant discovery of the first dromaeosaurid trackway in North America.
Introduction and Geologic Context
The Mill Canyon Dinosaur Tracksite (MCDT), the eighth reported tracksite from the Lower Cretaceous Cedar Mountain Formation of eastern Utah, was discovered south of the Moab airport and formally documented in 2009 under BLM permit UT 09-006S. Geologically, it occurs in the Ruby Ranch Member and preserves exceptionally well-preserved dinosaur tracks and the first-known dromaeosaurid trackways in North America.
Methods and Materials
Initial documentation employed compass and tape mapping, clear acetate tracings, and silicon rubber molds (now cataloged as UCM 199.67–199.75). Photogrammetric imaging of the main exposure and selected tracks was utilized to ensure digital preservation. These methods were supplemented by thin section petrographic analysis of the silica-rich, microcrystalline track-bearing substrate.
Ichnological Results
At least 45 discrete tracks form multiple trackways on a northeast-southwest trending surface. Theropod ichnotaxa include large Irenesauripus tracks inferred to reflect Acrocanthosaurus-type producers, a medium-sized tridactyl morphotype resembling Carmelopodus, and a didactyl dromaeosaurid trackway (cf. Dromaeopodus).
Sauropod traces occur as manus-only and manus-pes configurations, with some specimens showing postero-lateral digit V impressions. Ornithopod (iguanodontian) trackways display bipedal progression. Additional enigmatic paired traces and elongate swimming-style grooves suggest crocodilian or other vertebrate activity in shallow water environments.
Site Importance and Management
MCDT represents the largest Cedar Mountain Formation tracksite with the highest ichnodiversity, presenting significant research opportunities while requiring protective measures against erosion, livestock, and vandalism. A protective fence was installed in 2011, and further excavation in 2013 expanded the documented area.
References
Lockley MG, Gierlinski GD, Dubicka Z, Breithaupt BH, Matthews NA. 2014. A preliminary report on a new dinosaur tracksite in the Cedar Mountain Formation (Cretaceous) of eastern Utah. In: Lockley MG, Lucas SG, editors. Fossil footprints of western North America. NMMNHS Bulletin 62.
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- Hero Image: Photogrammetric rendering of a large Irenesauripus theropod footprint adjacent to a didactyl dromaeosaurid trackway on the main exposure at Mill Canyon, Utah.