Recognizing primary palaeotopography utilizing ichnofossils and 3D models: Mill Canyon Dinosaur Tracksite, Utah

Preservation and recognition of primary palaeotopography along a bedding surface is often a neglected component in palaeogeographic reconstruction. The Mill Canyon Dinosaur Tracksite (MCDT) is a spectacular bedding plane exposure with a diverse assemblage of vertebrate ichnnofauna. Small-scale 3D photogrammetric and ichnofossil analyses of two areas on the periphery of the MCDT surface demonstrate the presence of preserved primary palaeotopography. The first area consists of a palaeotopographic bench that drops off to a minimum of c. 0.5–0.6 m. On this bench is at least one resting trace analogous to modern traces of crocodiles documented from topographic highs along rivers and lakes. At the second locality, systematic variations in track morphology indicate that the trackmaker gait was influenced by changes in surface elevation with movement across the ridge, thus affirming that palaeorelief is preserved. The ichnofossils on this Cretaceous bedding surface likely represent months- to years-worth of biological activity.