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Osteology of the Middle Triassic Archosaur Lewisuchus Admixtus

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Osteology of the Middle Triassic Archosaur Lewisuchus Admixtus This article was downloaded by: [Sistema Integrado de Bibliotecas USP], [Jonathas Souza Bittencourt] On: 16 February 2015, At: 08:09 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Journal of Systematic Palaeontology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tjsp20 Osteology of the Middle Triassic archosaur Lewisuchus admixtus Romer (Chañares Formation, Argentina), its inclusivity, and relationships amongst early dinosauromorphs Jonathas S. Bittencourta, Andrea B. Arcuccib, Claudia A. Marsicanoc & Max C. Langerd a Departamento de Geologia, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6670, 31270901, Belo Horizonte, Brazil b Area de Zoologia, Universidad Nacional de San Luis, Chacabuco 917, 5700, San Luis, Argentina c Click for updates Departamento de Ciencias Geológicas, Universidad de Buenos Aires, IDEAN-CONICET, Ciudad Universitaria, Pab. II, C1428 DHE, Ciudad Autónoma de Buenos Aires, Argentina d Laboratório de Paleontologia, Departamento de Biologia, Universidade de São Paulo, Av. Bandeirantes 3900, 1404901, Ribeirão Preto, Brazil Published online: 31 Mar 2014. To cite this article: Jonathas S. Bittencourt, Andrea B. Arcucci, Claudia A. Marsicano & Max C. Langer (2015) Osteology of the Middle Triassic archosaur Lewisuchus admixtus Romer (Chañares Formation, Argentina), its inclusivity, and relationships amongst early dinosauromorphs, Journal of Systematic Palaeontology, 13:3, 189-219, DOI: 10.1080/14772019.2013.878758 To link to this article: http://dx.doi.org/10.1080/14772019.2013.878758 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions Journal of Systematic Palaeontology, 2015 Vol. 13, No. 3, 189–219, http://dx.doi.org/10.1080/14772019.2013.878758 Osteology of the Middle Triassic archosaur Lewisuchus admixtus Romer (Chanares~ Formation, Argentina), its inclusivity, and relationships amongst early dinosauromorphs Jonathas S. Bittencourta*, Andrea B. Arcuccib, Claudia A. Marsicanoc and Max C. Langerd aDepartamento de Geologia, Universidade Federal de Minas Gerais, Av. Antonio^ Carlos 6670, 31270901, Belo Horizonte, Brazil; bArea de Zoologia, Universidad Nacional de San Luis, Chacabuco 917, 5700, San Luis, Argentina; cDepartamento de Ciencias Geologicas, Universidad de Buenos Aires, IDEAN-CONICET, Ciudad Universitaria, Pab. II, C1428 DHE, Ciudad Autonoma de Buenos Aires, Argentina; dLaboratorio de Paleontologia, Departamento de Biologia, Universidade de Sao~ Paulo, Av. Bandeirantes 3900, 1404901, Ribeirao~ Preto, Brazil (Received 6 March 2013; accepted 13 October 2013; first published online 31 March 2014) Lewisuchus admixtus is an enigmatic early dinosauriform from the Chanares~ Formation, Ladinian of Argentina, which has been recently considered a member of Silesauridae. Yet, it differs markedly from Late Triassic silesaurids in dental and vertebral anatomy. Indeed, a detailed redescription of its holotype allowed the identification of several features of the skeleton previously unrecognized amongst silesaurids. These include pterygoid teeth, a dorsomedial posttemporal opening on the otoccipital, foramina associated with cranial nerves X–XII on the caudal region of the prootic–otoccipital, and postaxial neck/trunk vertebrae with craniocaudally expanded neural spines. The presence of a single row of presacral scutes was also confirmed. Some elements previously referred to, or found associated with, the holotype, including a lower jaw, pedal elements and an astragalus, more probably correspond to proterochampsid remains. The anatomical information available for the holotype of L. admixtus was rescored into a new phylogenetic dataset for dinosauromorphs, mostly based on previous works. Lewisuchus admixtus and Pseudolagosuchus major are treated as distinct OTUs because their preserved skeletons mostly lack overlapping parts. The parsimony analysis supports the basal position of L. admixtus within dinosauriforms, prior to the silesaurid–dinosaur split, rather than at the base of Silesauridae. This suggests that a higher number of early dinosauriform clades branched in the Middle and Late Triassic than previously suggested. Keywords: Lewisuchus; Pseudolagosuchus; basal dinosauromorphs; Middle Triassic; silesaurids Introduction 1994a; Irmis et al. 2007a; Nesbitt et al. 2009a). Marasu- chus is monoespecific (M. lilloensis), and restricted to the Archosaur remains discovered from the Middle to Late Chanares~ Formation (Sereno & Arcucci 1994b). Silesaur- Triassic of Europe (Dzik 2003; Dzik & Sulej 2007), North ids are minimally known from Anisian to Norian strata in America (Ezcurra 2006; Nesbitt et al. 2007; Nesbitt et al. Poland, Brazil, Argentina, United States, Tanzania, 2010), Brazil (Ferigolo & Langer 2007) and Africa Morocco and Zambia (Dzik 2003; Ferigolo & Langer (Nesbitt et al. 2010; Kammerer et al. 2012; Peecook et al. 2007; Nesbitt et al. 2010; Kammerer et al. 2012; Peecook 2013) have improved the record of lightly built dinosaur et al. 2013). Some authors support the position of silesaur- precursors (Bakker & Galton 1974; Bonaparte 1978; ids as basal ornithischians (Ferigolo & Langer 2007; Sereno 1991a; Novas 1996), until recently known only Langer et al. 2007b; Langer & Ferigolo 2013), but this from the Ladinian of the Chanares~ Formation, in Argen- hypothesis has been disputed (Irmis et al. 2007b; Nesbitt tina (Romer 1971, 1972c; Bonaparte 1975; Arcucci et al. 2010). Marasuchus, silesaurids and dinosaurs com- 1987). Various studies positioned these taxa as successive prise together the Dinosauriformes (Novas 1996; Langer Downloaded by [Sistema Integrado de Bibliotecas USP], [Jonathas Souza Bittencourt] at 08:09 16 February 2015 outgroups to Dinosauria, including Lagerpetidae, Marasu- & Benton 2006; Nesbitt et al. 2010), into which the poorly chus and Silesauridae (see Nesbitt 2011, for review). known Saltopus from the Late Triassic of Scotland has Lagerpetids comprise three species (i.e. Lagerpeton cha- been recently included (Benton & Walker 2011). narensis, Dromomeron romeri and D. gregorii), which An enigmatic specimen collected by the La Plata-Har- are currently known from Ladinian and Norian deposits of vard expedition during 1964–1965 in the Chanares~ For- Argentina and USA (Arcucci 1986; Sereno & Arcucci mation (Romer 1966; Romer & Jensen 1966; Rogers et al. *Corresponding author. Email: [email protected] Ó The Trustees of the Natural History Museum, London 2014. All Rights Reserved. 190 J. S. Bittencourt et al. 2001), La Rioja, Argentina, became the holotype of Lewi- History and Science, Albuquerque, NM, USA; NMT: suchus admixtus Romer, 1972c. The specimen comprises National Museum of Tanzania, Dar es Salaam, Tanzania; a partial skull and post-cranial remains, including most of PULR: Universidad Nacional de La Rioja, La Rioja, the pre-sacral column, pectoral and hind limb elements. Argentina; PVL: Fundacion Miguel Lillo, San Miguel de As it was recovered from a concretion that also included Tucuman, Argentina; PVSJ: Universidad Nacional de remains of cynodonts and proterochampsids, the associa- San Juan, San Juan, Argentina; SAM: South African tion of the non-articulated parts to the preserved skeleton Museum, Cape Town, South Africa; SMNS: Staatliches is problematic (Arcucci 1998). Museum fur€ Naturkunde, Stuttgart, Germany; UCMP: Although the taxonomic validity of L. admixtus has University of California Museum of Paleontology, never been disputed, its phylogenetic position is contro- Berkeley, CA, USA; UFRGS: Universidade Federal do versial. Romer (1972c, p. 13) allied the taxon with the tra- Rio Grande do Sul, Porto Alegre, Brazil; ULBRA: ditional ‘pseudosuchians’ (Cruickshank 1979), supporting Universidade Luterana do Brasil, Canoas, Brazil; ZPAL: a possible bearing on the origin of ‘coelurosaurs’. Other Institute of Paleobiology of the Polish Academy of authors have suggested affinities with gracilisuchids Science, Warsaw, Poland. (Carroll 1988; Sues 1997), or basal crocodylomorphs (Sereno 1991a), more specifically with sphenosuchians Systematic palaeontology (Bonaparte 1981; Olshevsky 1991). Parrish (1993) per- formed a phylogenetic study in which L. admixtus resulted Archosauria
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