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UC Berkeley Paleobios UC Berkeley PaleoBios Title New insights into Late Triassic dinosauromorph-bearing assemblages from Texas using apomorphy-based identifications Permalink https://escholarship.org/uc/item/4ht19712 Journal PaleoBios, 35(0) ISSN 0031-0298 Authors Lessner, Emily J. Parker, William G. Marsh, Adam D. et al. Publication Date 2018-07-21 DOI 10.5070/P9351039960 Peer reviewed eScholarship.org Powered by the California Digital Library University of California PaleoBios 35: 1–41, July 21, 2018 PaleoBios OFFICIAL PUBLICATION OF THE UNIVERSITY OF CALIFORNIA MUSEUM OF PALEONTOLOGY ctf mc A C E G I J lc L lc cn ctf mc lc mc lc ctf ctf B D F H K M mc lc cn mfe mc amt pmt amt pmt lc lc Q R S N mc cn O cn lc cn mfe lc lc ap Y T P 1 cm cn mc AA lc dp ap ctf mc U W Z lc r ap mc dp ctf ap AB V X ap lc mc ctf cn ap dp AE AG cn AC AD mc ctf lc lc lc AF AH mc cn mc mc cn ctf lc lc EMILY J. LESSNER, WILLIAM G. PARKER, ADAM D. MARSH, STERLING J. NESBITT, RANDALL B. IRMIS & BILL D. MUELLER (2018). New insights into Late Triassic dinosauromorph-bearing assemblages from Texas using apomorphy-based iden- tifications. Cover illustration: Dinosauromorph limb bones from the Late Triassic Dockum Group of Texas. See Figure 10 for details. Citation: Lessner, E.J., W.G. Parker, A.D. Marsh, S.J. Nesbitt, R.B. Irmis, and B.D. Mueller. New insights into Late Triassic dinosauromorph- PaleoBios, 35.ucmp_paleobios_39960. bearing assemblages from Texas using apomorphy-based identifications. New insights into Late Triassic dinosauromorph-bearing assemblages from Texas using apomorphy-based identifications EMILY J. LESSNER1*, WILLIAM G. PARKER1, ADAM D. MARSH1, STERLING J. NESBITT2, RANDALL B. IRMIS3, AND BILL D. MUELLER4 1 AZ 86028 U.S.A., [email protected]; [email protected] 2DepartmentDivision of Geosciences, of Resource Virginia Management, Tech, 926 Petrified West Campus Forest National Dr., Blacksburg, Park, Box VA 2217, 24061 Petrified U.S.A., [email protected] Forest, ; 3Natural History Museum of Utah and Department of Geology & Geophysics, University of Utah, Salt Lake City, UT 84108-1214, U.S.A., [email protected]; 4The Museum of Texas Tech University, Box 43191, Lubbock, TX 79409 U.S.A., [email protected] The Upper Triassic Dockum Group of Garza County, Texas (lower, middle, and upper Cooper Canyon Forma- tion) captures the radiation of Triassic non-marine tetrapods by preserving a variety of Late Triassic taxa from the southwestern United States. Our understanding of the vertebrate assemblage from these strata largely comes from a single site, the Post Quarry (lower Cooper Canyon Formation), with previous research documenting a variety of temnospondyls, sphenodontians, non-archosauriform archosauromorphs, and archosauriforms including a phytosaur, three species of aetosaurs, a poposauroid, a rauisuchid, a crocodylomorph, and several dinosauromorphs. To more completely reconstruct the vertebrate assemblage of the Dockum Group of Garza County we use an apomorphy-based approach to identify morphologically similar disarticulated and fragmen- tary elements from a variety of localities that span the entire Cooper Canyon Formation (Norian-Rhaetian), allowing assignments from the large clade level to the species level. Many skeletal elements are incomplete yet diagnostic and are assigned to the least inclusive clade if discrete character states do not allow for an un- ambiguous species-level identification. We identify new specimens referable to numerous clades including Tanystropheidae, Allokotosauria + Prolacerta + Archosauriformes, Vancleavea + Litorosuchus, Phytosauria, Paracrocodylomorpha, Dinosauriformes, and Saurischia, in addition to additional species identifications of the aetosaur Scutarx deltatlyus, and the dinosauromorph Dromomeron gregorii. Our study of this material demonstrates the utility of an apomorphy-based approach in making testable and repeatable observations for identifying small, isolated fragmentary fossil tetrapod material to reconstruct a more accurate faunal hypothesis for a portion of the Late Triassic of Texas. Previous claims of the earliest dinosaurs from near the base of the Dockum Group do not pass the apomorphy-based identification test, and the question of whether the oldest known North American dinosaurs are present in the Chinle Formation or Dockum Group can be resolved by utilizing vertebrate biostratigraphic correlation. Our revision of these fossil assemblages supports the hypoth- esis that early diapsids, early archosauromorphs, and non-dinosaurian dinosauromorphs were more common, diverse, and widespread in low latitudes during this time than previously thought. Keywords: Upper Triassic, Dockum Group, Diapsida, Archosauromorpha, Dinosauromorpha INTRODUCTION 2015, Pritchard et al. 2015), shuvosaurid poposauroids - (Long and Murry 1995, Nesbitt and Norell 2006, Nes- sids during the Triassic Period led to the appearance of bitt, 2007), as well as the discovery of abundant non- taxaThe characterized radiation and by diversification unique suites ofof morphologiesterrestrial diap in dinosaurian dinosauromorphs and dinosauriforms from addition to the emergence of present-day clades (Fra- Upper Triassic strata (Dzik 2003, Ferigolo and Langer ser and Sues 2010). Key discoveries emphasizing the 2007, Irmis et al. 2007a, Nesbitt et al. 2007, 2009c, diversity of Late Triassic taxa include the recognition of 2010, Kammerer et al. 2012, Martinez et al. 2016). What small diapsids (Senter 2004, Pritchard et al. 2016), early archosauromorphs (Murry 1986, 1989a, b, Nesbitt et al. material prompted workers to re-evaluate specimens is significant is that discovery of relatively complete clades in material collected over the past seven decades. *Author for correspondence: [email protected] already in collections, allowing the identification of these Citation: Lessner, E.J., W.G. Parker, A.D. Marsh, S.J. Nesbitt, R.B. Irmis, and B.D. Mueller. New insights into Late Triassic dinosauromorph- PaleoBios, 35.ucmp_paleobios_39960. Permalink: https://escholarship.org/uc/item/4ht19712 Copyright:bearing assemblages Items in eScholarship from Texas using are protected apomorphy-based by copyright, identifications. with all rights reserved, unless otherwise indicated. 2 PALEOBIOS, VOL. 35, JULY 2018 For example, the description of the non-dinosaurian Voucher specimens with discrete apomorphic character dinosauriform Silesaurus opolensis Dzik, 2003 resulted in a paradigm shift towards the discoveries of large, when describing vertebrate faunal assemblages (Nesbitt possibly globally-distributed dinosauriforms with un- andstates Stocker allow for 2008 the, verificationBell et al. 2010 of taxonomic). This paper assignments follows expected morphologies, which was needed to highlight those recommendations and demonstrates the utility of an apomorphy-based approach in identifying isolated material. Along with the subsequent discovery of skel- and fragmentary small limb material from a variety of etalthe significancematerial that of could less complete,unambiguously previously be assigned collected to sites from the Dockum Group of Texas to report a tetra- the tooth-taxon Revueltosaurus callenderi Hunt, 1989, pod assemblage whose taxonomy is both testable and this spurred apomorphy-based investigations (Parker repeatable. 2005b, Irmis et al. 2007b, Nesbitt et al. 2007) of the Late Triassic dinosaur record of North America. These studies GEOLOGIC SETTING AND AGE found that many of the Late Triassic fossils previously All of the specimens discussed here were collected assigned to the Dinosauria were not referable to that from localities within the Upper Triassic Dockum clade based on discrete character states present in the specimens and that Triassic dinosaurs in North America University (Table 1, 2). The stratigraphic relationships were rarer and less diverse than previously hypothesized. andGroup nomenclature of western Texas of the by Dockum field crews Group from has Texas been Tech the A similar apomorphy-based study provided critical new subject of debate (Chatterjee 1986a, Lucas 1993, 1994, paleoecological insights by overturning the long standing Lehman 1994a, b, Lucas et al. 1994, Long and Murry hypothesis that juvenile dinosaurian gut contents in an 1995, Carpenter 1997, Lehman and Chatterjee 2005); adult specimen of Coelophysis bauri Colbert, 1989 was evidence for cannibalism (e. g., Colbert 1989, 1995) by the stratigraphic relationships between many of the determining that the gut contents belonged instead to a vertebratehowever, subsequent quarries from detailed the type fieldwork section has of theelucidated Cooper pseudosuchian archosaur (Nesbitt et al. 2006). Canyon Formation of the Dockum Group in southern Such studies have illuminated that although avemeta- Garza County, Texas (Martz 2007, 2008, Martz et al. 2013, tarsalians and pseudosuchians are distinct phylo- Martz and Parker 2017; Fig. 1). Those studies divided the genetically, their postcrania can be morphologically type section of the Cooper Canyon Formation (Lehman similar, anatomical convergence is common, and that 1992) into three units that correlate with formations in eastern New Mexico: a lower mudstone unit that is cor- state distributions from up-to-date phylogenetic analy- related with the Tecovas Formation, a middle unit that is ses,apomorphy-based is essential to determining identification, taxonomic utilizing assignments character correlated with the Trujillo Formation, and an upper unit (Nesbitt and Stocker 2008, Nesbitt et al. 2017b). A that is correlated
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