At the Top of the Grand Staircase: The Late Cretaceous of Southern Utah

24 First Report of Probable Therizinosaur (cf. Macropodosaurus) Tracks from North America, with Notes on the Neglected Vertebrate Ichnofauna of the Ferron Sandstone (Late Cretaceous) of Central Utah

530 24 First Report of Probable Therizinosaur (cf. Macropodosaurus) Tracks from North America, with Notes on the Neglected Vertebrate Ichnofauna of the Ferron Sandstone (Late Cretaceous) of Central Utah Gerard Gierlinski and Martin Lockley Although known for some years, vertebrate tracks from the Ferron Sandstone in the San Rafael Swell (Emery County, Utah) have never been described in detail. A new find attributed to cf. Macropodosaurus, one of the least known dinosaur tracks, is the first report of the ichnogenus from North America. Macropodosaurus is otherwise known only from the type locality in central Asia and a recently reported site in Poland. Recent studies suggest that the distinctive tetradactyl tracks may represent the aberrant theropodan group known as the Therizinosauroidea. We also reinterpret the so-called Moore Trackway as that of a quadrupedal rather than a bipedal ornithopod. Introduction The purpose of this chapter is to report on two dinosaur tracksites in the Ferron Sandstone Coal Cliffs region of Emery County, Utah (Fig. 24.1). The first site, alongside 803 Road about 6 km east-southeast of Moore, was previously reported by DeCourten (1998) and referred to by Jones (2001) as the Moore Trackway at the Moore Tracksite. Cassingham (2005) referred to the locality as the Moore Cutoff Road site. Although previously described by Jones (2001), the tracks need interpretation in detail and herein are attributed to a quadrupedal ornithopod with an unusual gait. The second site, which yields cf. Macropodosaurus, is in Muddy Creek Canyon ~6 km south southeast of the town of Emery, and was only recently discovered by one of us (G.G.) in 2008. This find is significant because Macropodosaurus has not been previously reported from North America, and it adds to the known Late Cretaceous vertebrate ichnodiversity of the region. It is outside the scope of this short report to describe the geology of these two sites in detail. The Mesozoic vertebrate ichnology of parts of Utah is well known. For example, in Grand County to the east, many vertebrate tracksites have been documented in the Moab region (Lockley and Hunt, 1995). The situation is somewhat different in the San Rafael Swell region of Emery County. Vertebrate tracksites are known at a few scattered locations, including a famous Early Jurassic (Navajo Formation) theropod site in Buckhorn Draw reported in various field guides (Massey and Wilson, 2006). Likewise, Mickelson et al. (2004) reported an important pterosaur tracksite ~16 km east of Ferron. Various tracksites are also known from the Upper Cretaceous Mesaverde Group in the Price-Castle Dale region (Robinson, 1991; Lockley and Hunt, 1995; Lockley, 1999). The most accessible collections of Upper Cretaceous tracks are those held in the College of Eastern Utah Museum in Price. These specimens, some of which have been known since the 1930s (Strevell, 1932), mostly originate from coal mines (Parker and Rowley, 1989). Although scattered sites are known from the Lower Cretaceous Cedar Mountain Formation of eastern and central Utah (Lockley et al., 1999, 2004), there is a significant ichnological gap between this unit and the Mesaverde Group (Wolfe, 2006). The present report is a preliminary step toward filling in this gap. Undoubtedly, there is great potential for further vertebrate trackway discoveries in this region. Institutional Abbreviations CU, Dinosaur Tracks Museum , University of Colorado, Denver, Colorado; Muz.PIG, Geological Museum of the Polish Geological Institute, Warsaw. Moore Tr acksite at the 803 Road Localit y As shown in Fig. 24.1, this locality consists of a large fallen block close to the north side of the road (803) that connects the Interstate 70 corridor with the small, near-abandoned settlement of Moore. The site is well known because it is adjacent to spectacular petroglyphs (Cassingham, 2005) and is just east of the large water gap that cuts through the Coal Cliffs to the west. The exact point of origin of the fallen block is not known, but it must have originated from the Probable Therizinosaur (cf. Macropodosaurus) Tracks 531 24.1. Locality map showing two Ferron Sandstone localities mentioned in this chapter. Map modified after Gani, Bhattachaerya, and MacEachern (2008). Gierlinski and Lockley 532 cliff-forming sandstone sequence at the top of the shale slope (Fig. 24.1). Jones (2001) described the tracks, briefly inferring that the block originated from the very top of the Ferron Sandstone escarpment. Herein we offer our interpretations. The tracks appear to comprise a single trackway consisting of nine poorly preserved natural casts...