504 22 Late Cretaceous Theropod Dinosaurs of Southern Utah Lindsay E. Zanno, Mark A. Loewen, Andrew A. Farke, Gy-Su Kim, Leon P. A. M. Claessens, and Christopher T. McGarrity Recent interest in Upper Cretaceous formations of southern Utah including intense collection efforts by the Kaiparowits Basin Project – a joint collaboration between the Utah Museum of Natural History, the University of Utah, and the Bureau of Land Management – has added consider- ably to our understanding of dinosaur diversity in the West- ern Interior Basin. These taxonomically unique and histori- cally underrepresented ecosystems document a relatively high diversity of theropods, including a minimum of seven taxa known from the Kaiparowits Formation alone. Recent discoveries include at least five new taxa: Hagryphus gigan- teus, the first diagnostic North American oviraptorosaurian south of Montana; a new species of troodontid paravian; Nothronychus graffami, the most complete therizinosaurid skeleton yet discovered; and two new tyrannosaurid taxa, including Teratophoneus curriei and an undescribed taxon that represents the oldest North American tyrannosaurid recovered to date. Presently, data-rich paleobiogeographical comparison of latitudinally arrayed, coeval Western Interior Basin formations can only be made for a short temporal win- dow that includes the upper Campanian Kaiparowits Forma- tion. These investigations reveal that theropod diversity is relatively homogenous at higher taxonomic levels. Yet new discoveries also demonstrate a high degree of interforma- tional, species-level endemism, indicating that the south- ern Utah theropod fauna is surprisingly unique and that theropod ranges in the upper Campanian Western Interior Basin were more restricted than previously understood. On the basis of these data, we argue against the referral of frag- mentary dinosaur remains and teeth recovered from upper Campanian strata of the Western Interior Basin to taxa from other Western Interior Basin formations without substantial morphological evidence. Introduction In 2000, field crews of the Utah Museum of Natural History, the University of Utah, and the Bureau of Land Manage- ment embarked on an exhaustive research project to survey and document the Late Cretaceous dinosaur fauna of the Kaiparowits Basin, southern Utah, with a focus on upper Campanian exposures of the Wahweap and Kaiparowits for- mations of Grand Staircase–Escalante National Monument. This collaborative effort – known as the Kaiparowits Basin Project (KBP) – has documented at least 11 definitively new dinosaur taxa (with many more currently under study) that are challenging previous ideas regarding Late Cretaceous di- nosaur evolution and diversity within Western Interior Basin. Although the recent work undertaken by the KBP along with several other institutions, including the Raymond M. Alf Museum of Paleontology (R AM) and the Utah Geologi- cal Survey, represents the first concerted effort to collect and research the dinosaurian fauna of the Kaiparowits Basin, decades of microvertebrate studies were conducted in this and other areas of southern Utah by Richard Cifelli, Jeffrey Eaton, and their colleagues, who were studying the region’s mammalian fauna before the project’s initiation (Eaton and Cifelli, 1988; Eaton, Munk, and Hardman, 1998; Eaton, 1999; Eaton, Cifelli, et al., 1999; Eaton, Diem, et al., 1999). Con- comitant fieldwork by J. Howard Hutchison and colleagues (Hutchison et al., 1997) involved surface reconnaissance in addition to microvertebrate screening and a greater focus on identifying the lower vertebrate fauna, including dinosaurs. Such early studies provided the first insight into the dino- saurian fauna of the region and the first (and in some cases only) comprehensive faunal lists for the formations reviewed here (Tables 22.1–22.5). These foundational contributions notwithstanding, the dinosaurian identifications generated by these studies are restricted almost entirely to surface float and isolated teeth, which recent discoveries indicate to be of limited taxonomic utility for theropods. Table 22.1. Historical survey of the theropod fauna of the Iron Springs Formation derived from the literature Taxon Reference Theropoda Theropoda indet. Eaton, 1999 Paraves ?Dromeosauridae ?Dromeosauridae indet. Eaton, 1999 Troodontidae Troodontidae indet. Eaton, 1999 ©2013 by Indiana University Press. All rights reserved. Do not reproduce.