GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association ISSN 2380-7601 Volume 4 2017 FIRST UNAMBIGUOUS DINOSAUR SPECIMEN FROM THE UPPER TRIASSIC CHINLE FORMATION IN UTAH Xavier A. Jenkins, John R. Foster, and Robert J. Gay © 2017 Utah Geological Association. All rights reserved. For permission to copy and distribute, see the following page or visit the UGA website at www.utahgeology.org for information. Email inquiries to [email protected]. GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association Volume 4 2017 Editors UGA Board Douglas A. 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If you would like to participate please contact the current are not noted as copyrighted, provided the original president or committee member corresponding with the area in which you would author and source are credited. like to volunteer. Utah Geological Association formed in 1970 from a merger of the Utah Geological Society, founded in 1946, and the Intermountain Association of Geologists, founded in 1949. Aliated with the American Association of Petroleum Geologists. i GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association Volume 4 2017 First Unambiguous Dinosaur Specimen from the Upper Triassic Chinle Formation in Utah Xavier A. Jenkins1, John R. Foster2, and Robert J. Gay3 1College of Liberal Arts and Sciences, Arizona State University, Tempe, AZ 85281; [email protected] 2Museum of Moab, Moab, UT 84532; [email protected] 3Colorado Canyons Association, Grand Junction, CO 81501; [email protected] ABSTRACT Triassic dinosaurs represent relatively rare but important components of terrestrial faunas across Pan- gea. Whereas this record has been well studied at various locales across the American West, there has been no previous systematic review of Triassic material assigned to Dinosauria from Utah. Here, we critically examine the published body fossil and footprint record of Triassic dinosaurs from Utah and revise their record from the state. In addition, we describe a sacrum from a locality within the Upper Triassic Chinle Formation of southeastern Utah. is specimen represents the only unambiguous Triassic dinosaur body fossil from Utah. MWC 5627 falls within the range of variation known for sacrum morphology from Coe- lophysis bauri. Based on a literature review and examination of specimens available to us, we restrict the Triassic Utah dinosaurian record to eropoda from the Chinle Formation. Preliminary reports of Triassic dinosaurs from other clades and formations in Utah are unsubstantiated. INTRODUCTION crosbyensis (Long and Murry, 1995) present in Texas. e same study found only two theropods, C. bryans- eropod dinosaurs are an important but rare com- malli (Long and Murry, 1995) and a coelophysoid (Pa- ponent in terrestrial faunas from the Triassic of western dian, 1986) from Arizona. Nesbitt and others (2007) did North America (Nesbitt and others, 2007). Although not nd references to Triassic theropods in Colorado several taxa have been identied from New Mexico, in- and Utah. Unfortunately, that review did not assess re- cluding Coelophysis bauri (Colbert, 1989; Rinehart and ported dinosaurian remains from the Four Aces mine others, 2009), Gojirasaurus quayi (Carpenter, 1997), locality near the Glen Canyon National Recreation Area Chindesaurus bryansmalli (Irmis and others, 2007), in southeastern Utah (Parrish, 1999) (gure 1). In a re- Tawa hallae (Nesbitt and others, 2009), and Daemon- lated study, Irmis and others (2007) found reports that osaurus chauliodus (Sues and others, 2011), the sur- described ornithischian dinosaurs from the Triassic of rounding continental deposits have produced little North America had been misinterpreted, although this in the way of dinosaurian body fossils. In contrast, an study also overlooked the Parrish (1999) report from apomorphy-based study by Nesbitt and others (2007) southeastern Utah. examined all referred dinosaurs from the Triassic of Various methods have been proposed to explain western North America and found only Caseosaurus the distribution of dinosaurs in North America. e Citation for this article. Jenkins, X.A., Foster, J.R., and Gay, R.J., 2017, First unambiguous dinosaur specimen from the Upper Triassic Chinle Formation in Utah: Geology of the Intermountain West, v. 4, p. 231–242. © 2017 Utah Geological Association. All rights reserved. For permission to use, copy, or distribute see the preceeding page or the UGA website, www.utahgeology.org, for information. Email inquiries to [email protected]. 231 First Unambiguous Dinosaur Specimen from the Upper Triassic Chinle Formation in Utah Jenkins, X.A., Foster, J.R., and Gay, R.J. 2001; Gaston and others, 2003; Santucci and others, 2006; Hunt and Lucas, 2007; Martz and others, 2014), and some preserving the purported prosauropod track Pseudotetrasauropus (Lockley and Hunt, 1995; Foster and others, 2001). Recent work by other authors has raised questions about the reliability of identifying di- nosaurs from ichnological evidence alone (Olsen and others, 1998; Marsicano and others, 2007; Brusatte and others, 2011; Niedźwiedzki, and others, 2013; Farlow and others, 2014). Although a poposauroid footprint reconstruction based on an articulated specimen of Po- posaurus gracilis from the Circle Clis of southern Utah (Farlow and others, 2014) is somewhat similar to Gral- lator, it is only so if the rst digit never impressed. ere are a number of Grallator specimens from the Chinle Formation in Utah and western Colorado that look rather dierent at least from hypothetical tracks of po- posauroids, and the fact that the ichnogenus continues upward through the Wingate, Kayenta, and Navajo For- mations (by which time poposauroids and other con- vergent non-dinosaurs were extinct) suggests that many tracks assigned to Grallator (though not necessarily all) were likely made by theropods. e dinosaurian anity Figure 1. Map of Utah's Triassic dinosaur occurrences. of Pseudotetrasauropus is perhaps a bit more tenuous, as CC = Corral Canyon, FA = Four Aces. the morphology of these tracks can overlap to some de- gree with those of several other tetradactyl ichnogenera current consensus is that the radiation of Dinosauria attributed to non-dinosaurian archosaurs known from across the globe was diachronous (Nesbitt and others, the Late Triassic (Lucas and Heckert, 2000). us, the 2009; Irmis and others, 2011; Kent and others, 2014; see ichnological evidence for the presence of dinosaurs in Ramezani and others, 2011, for a dissenting view). e what is now the state of Utah during the Triassic Period earliest records of all major dinosaurian clades came is to some degree ambiguous. ere may likely be many from southern Pangaea in the Carnian Stage of the Late dinosaurian tracks among the specimens assigned to Triassic Epoch, followed by later appearances in the Grallator and Pseudotetrasauropus, but it is possible that Norian and Rhaetian Stages in the north of the super- some