AN UNUSUAL THEROPOD TRACKSITE IN THE CRETACEOUS DAKOTA GROUP, WESTERN COLORADO: IMPLICATIONS FOR ICHNODIVERSITY

At least 80 dinosaur tracksites are known from the Dakota Group on the Eastern Slope of Colorado: i.e., east of the continental divide (Lockley et al., 1992). Here we capitalize “Eastern Slope” and “Western Slope” in accordance with conventions used by the Colorado Geological Survey. As discussed elsewhere in this volume, the first of these sites was discovered in 1902, and since then all others have been reported with increasing frequency through the end of the 20 and into the 21 centuries (Kukihara and Lockley, 2012; Matsukawa et al., 1999, 2001). In contrast, about 40 tracksites have been discovered in the Dakota Group on the Western Slope in the last three years (2011-2013 inclusive). As also noted elsewhere in this volume, the Western Slope ichnofauna is significantly different from the Eastern Slope ichnofauna with respect to the high proportion of anklylosaur and pterosaur tracks (Lockley et al., this volume). The discovery of a new theropod tracksite, here referred to as the Escalante Rim site (Fig. 1) indicates that the theropod ichnofauna is different from anything yet reported from the Eastern Slope. We here describe the site in detail and discuss the ichnotaxonomy of the theropod tracks and the implications for ichnodiversity and regional paleoecology.