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The Early Evolution of Rhynchosaurs

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The Early Evolution of Rhynchosaurs ORIGINAL RESEARCH published: 11 January 2016 doi: 10.3389/fevo.2015.00142 The Early Evolution of Rhynchosaurs Martín D. Ezcurra 1, 2*, Felipe Montefeltro 2, 3 and Richard J. Butler 2 1 Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia,” Buenos Aires, Argentina, 2 School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK, 3 Departamento de Biologia e Zootecnia, FEIS, Universidade Estadual Paulista, Ilha Solteira, Brazil The rhynchosaurian archosauromorphs are an important and diverse group of fossil tetrapods that first appeared during the Early Triassic and probably became extinct during the early Late Triassic (early Norian). Here, the early evolution of rhynchosaurs during the Early and early Middle Triassic (Induan-Anisian: 252.2-242 Mya) is reviewed based on new anatomical observations and their implications for the taxonomy, phylogenetic relationships and macroevolutionary history of the group. A quantitative phylogenetic analysis recovered a paraphyletic genus Rhynchosaurus, with “Rhynchosaurus” brodiei more closely related to hyperodapedontines than to Rhynchosaurus articeps. Therefore, a new genus is erected, resulting in the new combination Langeronyx brodiei. A body size analysis found two independent increases in size in the evolutionary history of rhynchosaurs, one among stenaulorhynchines and the other in the hyperodapedontine lineage. Maximum likelihood fitting of phenotypic evolution models to body size data Edited by: Michel Laurin, found ambiguous results, with body size evolution potentially interpreted as fitting either Muséum National d’Histoire Naturelle, a non-directional Brownian motion model or a stasis model. A Dispersal-Extinction- France Cladogenesis analysis reconstructed the areas that are now South Africa and Europe Reviewed by: Sean P. Modesto, as the ancestral areas of Rhynchosauria and Rhynchosauridae, respectively. The Cape Breton University, Canada reconstruction of dispersal events between geographic areas that are broadly separated Fernando Abdala, paleolatitudinally implies that barriers to the dispersal of rhynchosaurs from either side of University of the Witwatersrand, Johannesburg, South Africa the paleo-Equator during the Middle Triassic were either absent or permeable. Juan Carlos Cisneros, Universidade Federal do Piauí, Brazil Keywords: Permo-Triassic, Diapsida, Archosauromorpha, body size, phylogeny, paleobiogeography *Correspondence: Martín D. Ezcurra [email protected] INTRODUCTION ∼ Specialty section: The Permo-Triassic mass extinction occurred 252 million years ago, and produced a dramatic This article was submitted to change in the composition of floral and faunal communities (Raup and Sepkoski, 1982; Erwin, Paleontology, 1994; Looy et al., 2001; Benton and Twitchett, 2003; Fröbisch, 2013; Benton and Newell, 2014; a section of the journal Smith and Botha-Brink, 2014). In the case of vertebrates, numerous new lineages first appeared or Frontiers in Ecology and Evolution Received: 20 August 2015 Institutional Abbreviations: AM, Albany Museum, Grahamstown, South Africa; BRSUG, University of Bristol, School of Accepted: 30 November 2015 Earth Sciences, Bristol, UK; EXEMS, Royal Albert Memorial Museum, Exeter, UK; FZB, Fundação Zoobotânica do Rio Published: 11 January 2016 Grande do Sul, Porto Alegre, Brazil; GPIT, Paläontologische Sammlung der Universität Tübingen, Tübingen, Germany; ISI, Indian Statistical Institute, Kolkata, India; MACN-Pv, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia,” Citation: Paleontología de Vertebrados, Buenos Aires, Argentina; NHMUK PV, Natural History Museum, Palaeontology Vertebrates, Ezcurra MD, Montefeltro F and London, UK; PIMUZ, Paläontologisches Institut und Museum der Universität Zürich, Zurich, Switzerland; PVSJ, Museo Butler RJ (2016) The Early Evolution of de Ciencias Naturales, Universidad de San Juan, San Juan, Argentina; SAM-PK, Iziko South African Museum, Cape Rhynchosaurs. Town, South Africa; SIDMM, Sidmouth Museum, Sidmouth, UK; SHYMS, Shropshire Museums, Ludlow, UK; UFRGS, Front. Ecol. Evol. 3:142. Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil; WARMS, Warwickshire Museum, doi: 10.3389/fevo.2015.00142 Warwick, UK. Frontiers in Ecology and Evolution | www.frontiersin.org 1 January 2016 | Volume 3 | Article 142 Ezcurra et al. Early Rhynchosaurs diversified in the aftermath of this extinction. Many of these Fodonyx spenceri based on new, first-hand observations of lineages replaced clades that flourished during the Paleozoic but specimens. We added three characters from previously published vanished or were decimated at the end-Permian mass extinction phylogenetic analyses relevant to the basal relationships of event (e.g., pareiasaurs, non-mammalian synapsids, such as Rhynchosauria (Dilkes, 1998; Ezcurra et al., 2014, 2015) and gorgonopsians and anomodonts). Among the new Triassic we modified the formulation of two characters from the clades are the first representatives of several modern vertebrate original character list of Butler et al. (2015: characters 63 groups, including teleosts, lissamphibians, eucynodonts, stem- and 84; see Supplementary Material). We also expanded the testudinatans, lepidosauromorphs, crocodylomorphs, and stem- taxonomic sampling of the analysis by adding the oldest known avialans, including the first non-avian dinosaurs (Bonaparte, rhynchosaur, Noteosuchus colletti (Watson, 1912; Carroll, 1976; 1982; Benton, 1983a; Colbert, 1984; Gaffney, 1986; Arratia, 2001; Dilkes, 1998; Ezcurra et al., 2014). Scoring of taxa was based Bonaparte et al., 2003; Evans, 2003; Marjanovic and Laurin, 2008; primarily on first-hand examination of specimens, with the Nesbitt, 2011; Jones et al., 2013; Ezcurra et al., 2014; Schoch and exception of Isalorhynchus genovefae, which was scored using Sues, 2015). Langer et al. (2000a) and Whatley (2005). The Triassic also witnessed the evolution of numerous The final matrix (15 taxa and 96 characters) was analyzed amniote groups that occur only within this time interval using TNT version 1.1 (Goloboff et al., 2008) using the implicit and which became extinct at or before the end-Triassic enumeration algorithm. Multistate characters 63, 70, 73, and mass extinction event (e.g., traversodontids, doswelliids, 75 were treated as additive because they represent nested tanystropheids, aetosaurs, phytosaurs; Abdala and Ribeiro, 2010; sets of homologies. Zero branch length nodes were collapsed Liu and Olsen, 2010; Desojo et al., 2013; Stocker and Butler, following the search (Coddington and Scharff, 1994). Absolute 2013; Sues et al., 2013; Pritchard et al., 2015). Although restricted and GC bootstrap frequencies were calculated after 10,000 to the Triassic, these groups achieved high morphological pseudoreplicates. GC bootstrap frequencies are the difference diversity and taxonomic richness, and some of them become key between the frequencies with which the original group and ecological components of their communities (Benton, 1983a; the most frequent contradictory group are recovered in the Sues and Fraser, 2013). The rhynchosaurian archosauromorphs pseudoreplicates (Goloboff et al., 2003). Templeton tests were were one of the most successful of these groups, and radiated conducted in PAUP∗ 4.0 (Swofford, 1998). widely in continental ecosystems (Romer, 1963; Chatterjee, 1980; Benton, 1990). Most rhynchosaurs were bulky, herbivorous Body Size Analysis and quadrupedal animals, often considered as superficially The phylogenetic reconstruction of early rhynchosaurs obtained pig-like in appearance, with a transversely broad skull and a here was merged with the phylogenetic tree of the best- highly specialized dentition (Chatterjee, 1980; Benton, 1984, known species of the genus Hyperodapedon recovered by 1990; Langer and Schultz, 2000; Hone and Benton, 2008; Langer and Schultz (2000) (i.e., Hyperodapedon mariensis, Figures 1B,C). The rhynchosaur genus Hyperodapedon is the Hyperodapedon sanjuanensis, Hyperodapedon gordoni, and most commonly found tetrapod within the oldest dinosaur- Hyperodapedon huxleyi) to form an informal supertree for bearing assemblages (e.g., the Ischigualasto, Santa María 2, lower Rhynchosauria. We merged the trees manually because their Maleri and Pebbly Arkose formations), and, as a result, has been topologies are consistent with each other where their taxonomic broadly used for global biostratigraphic correlations (Langer, content overlaps (R. articeps, S. stockleyi, F. spenceri, Teyumbaita 2005; Lucas, 2010; Martínez et al., 2011). sulcognathus). The early rhynchosaur N. colletti was excluded a Because of the importance of rhynchosaurs during the priori before merging both trees because it lacks cranial remains beginning of the Mesozoic, the early evolution of the group and it is not possible to estimate its skull length confidently. during the Early and early Middle Triassic (Induan-Anisian: Two analyses were conducted based upon this supertree to 252.2-242 Mya) is reviewed here. New anatomical observations explore the evolution of body size across Anisian-early Norian are presented, and their implications for the taxonomy, rhynchosaur history (∼20 million years). In one analysis, we phylogenetic relationships and macroevolutionary history of the optimized skull length (i.e., length from the anterior tip of the group are analyzed and discussed. premaxilla to posterior margin of the distal end of the quadrate) as a proxy of body size and
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