DISCOVERY AND EXCAVATION OF A THERIZINOSAURID DINOSAUR FROM THE UPPER CRETACEOUS TROPIC SHALE (EARLY TURONIAN), KANE COUNTY, UTAH

In 2000 and 2001 the Museum of Northern Arizona excavated the partial skeleton of a large therizinosaurid dinosaur from the Upper Cretaceous Tropic Shale, a marine formation that otherwise has not yielded fossils of terrestrial origin. The site is in Kane County, Utah, immediately south of the southern boundary of the Grand Staircase-Escalante National Monument. The skeleton consists of one front limb including most of the manus, complete pelvis, both rear limbs including partial pes, dorsal vertebrae, complete sacrum and sacral vertebrae, and caudal vertebrae. To date, no skull elements or cervical vertebrae have been recognized. The skeleton occurred in open marine sediments in association with ammonoids of the upper Watinoceras coloradoense-lower Mammites nodosoides biozone interval of late early Turonian age. Some elements were compressed by compaction, and the skeleton was slightly disarticulated owing to settling after coming to rest in the soft marine sediments. The manus possesses at least three compressed, oversized ungual phalanges. The characteristically opisthopubic pelvis and tetradactyl pes with blunt ungual phalanges confirm identification as a therizinosaurid dinosaur, but its taxonomic position remains uncertain. It seems to be related to the recently described therizinosaurid dinosaur Nothronychus mckinleyi Kirkland and Wolfe 2001 from the Middle Turonian of southwestern New Mexico. Because these two occurrences are separated stratigraphically by at least a million years, they are probably different species, if not different genera. Phylogenetic assessment of the new specimen must await full preparation of the skeleton.