287 Lockley, M.G. & Lucas, S.G., eds., 2014, Fossil footprints of western North America: NMMNHS Bulletin 62 NEW EXCAVATIONS AT THE MILL CANYON DINOSAUR TRACK SITE (CEDAR MOUNTAIN FORMATION, LOWER CRETACEOUS) OF EASTERN UTAH MARTIN G. LOCKLEY 1 , GERARD D. GIERLINSKI 2,3 , KAREN HOUCK 1 , JONG-DEOCK LIM 4 , KYUNG SOO KIM 5 , DAL-YONG KIM 4 , TAE HYEONG KIM 4 , SEUNG-HYEOP KANG 5 , REBECCA HUNT FOSTER 6 , RIHUI LI 7 , CHRISTOPHER CHESSSER 6 , ROB GAY 6 , ZOFIA DUBICKA 2, 8 , KEN CART 9 AND CHRISTY WRIGHT 9 1 Dinosaur Tracks Museum, University of Colorado at Denver, PO Box 173364, Denver, Colorado, 80217. Martin.Lockley@UCDenver.edu; 2 JuraPark, ul. Sandomierska 4, 27-400 Ostrowiec Swiztokrzyski, Poland; 3 Moab Giants, PO Box 573, Moab, Utah 84532; 4 Natural Heritage Center, National Research Institute of Cultural Heritage, 927 Yudeng-ro, Seo-gu, Daejon, 302-834, Korea; 5 Department of Science Education, Chinju National University of Education, Jinju, Kyungnam, 660-756, Korea; 6 Moab District Field Ofice, Bureau of Land Management, Moab, Utah; 7 Qingdao Institute of Marine Geology, Qingdao, China; 8 Faculty of Geology, University of Warsaw, Al. Zwirki i Wigury 93, PL-02-089 Warsaw, Poland; 9 3072 Bison Avenue, Grand Junction, Colorado 81504 INTRODUCTION Despite being well known for its vertebrate fauna, the Lower Cretaceous Cedar Mountain Formation has until recently yielded relatively few dinosaur tracksites (Lockley et al., 1999) among which the sixth site (in Arches National Park) and the seventh, a bird tracksite, are particularly note- worthy (Lockley et al., 2004, 2013; Foster et al., in prep). However, together with the important report of the bird tracksite, the eighth discovery, that of the Mill Canyon Dinosaur Tracksite (MCDT) in 2009, has added a signiicant new chapter to vertebrate tracks research in the Cedar Mountain For- mation. The site is located in the Ruby Ranch Member, which is the same member in which the Arches National Park site occurs. Here we demonstrate that the MCDT (Figs. 1-2) is by far the largest and most diverse hither- to known from the Cedar Mountain Formation. To date ~170 tracks have been mapped in an area of ~500 m 2 , while it can be shown unequivocally that there is potential to expose at least 5,000 m 2 (~100 x 50 m) of track-bearing surface, which would make the site one of the world’s largest known from the Lower Cretaceous. METHODS, MATERIALS AND PREVIOUS WORK As reported by Lockley et al. (2014, this volume) the senior authors and Bureau of Land Management (BLM) survey permit holders (MGL and GDG) used traditional compass and tape mapping methods, and tracings of repre- sentative tracks on clear acetate ilm to document the largest natural exposure at the site. We also obtained and cataloged 9 specimens for the University of Colorado Denver, Dino- saur Tracks Museum (now re-cat- aloged in the University of Colo- rado Museum of Natural History as UCM 199.67-75). Preliminary survey activity was reported to the BLM in 2009, stressing the importance and vulnerability of the site (cf. Cowen et al., 2010). As a result, in 2011 a fence was put around the site to keep out cattle and off-road vehicles. Subsequently the site was visited by two BLM research- ers (Brent Breithaupt and Nef- fra Matthews) in order to obtain photogrammetric images of part Abstract—The discovery of the Mill Canyon Dinosaur Tracksite (MCDT) in the Cedar Mountain Formation (Ruby Ranch Member), near Moab in eastern Utah, has generated considerable interest. Following the completion of a preliminary study of natural exposures, reported elsewhere in this volume, an international team was assembled to excavate the site in 2013. Complementary to the preliminary report published elsewhere in this volume, we here outline the initial cartographic results of the 2013 excavation in order to show the extent of the exposed track-bearing surface, the diversity of track types and the excellent potential for further development of the site. Results of the excavation indicate a diverse vertebrate ichnofauna with a minimum diversity of at least 10 named ichnotaxa, including three distinct theropod tracks morphotypes identiied as Irenesauriopus, a Dromaeosaurpus-like form and an un-named ichnite. Poorly preserved bird tracks have also been identiied. Sauropod tracks include Brontopodus and another morphotype of probable titanosaurid afinity. Ornithopod tracks resemble Caririchnium. Footprint density and preservation quality varies across the site and is evidently controlled by variations in the original topography of the site as well as by variation in the substrate and the direction of progression of the trackmakers. Novel sedimentological evidence demonstrates that some manus-only sauropod trackways are undertracks, thereby providing new lines of evidence to weaken the once-popular swimming sauropod scenario. The tracks occur in the upper part of the Ruby Ranch Member, which consists mostly of gray, calcareous mudstone with micritic limestone beds and nodules. However, the track bed is a light gray, impure chert. It is interpreted as a lacustrine or palustrine deposit that was originally limestone, and was later siliciied. A large coprolite was found on the track bed; it is composed of plant fragments cemented by calcite and silica, so was probably produced by a large, herbivorous animal, presumably a dinosaur. FIGURE 1. Location of Mill Canyon Dino- saur Tracksite, after Lockley et al. (2013)