New insights onPrestosuchus chiniquensisHuene, 1942 (Pseudosuchia, Loricata) based on new specimens from the “Tree Sanga” Outcrop, Chiniquá Region, Rio Grande do Sul, Brazil

Abstract

The ‘rauisuchians’ are a group of Triassic pseudosuchian archosaurs that displayed a near global distribution. Their problematic taxonomic resolution comes from the fact that most taxa are represented only by a few and/or mostly incomplete specimens. In the last few decades, renewed interest in early archosaur evolution has helped to clarify some of these problems, but further studies on the taxonomic and paleobiological aspects are still needed. In the present work, we describe new material attributed to the ‘rauisuchian’ taxon Prestosuchus chiniquensis, of the Dinodontosaurus Assemblage Zone, Middle Triassic (Ladinian) of the Santa Maria Supersequence of southern Brazil, based on a comparative osteologic analysis. Additionally, we present well supported evidence that these represent juvenile forms, due to differences in osteological features (i.e., a subnarial fenestra) that when compared to previously described specimens can be attributed to ontogeny and indicate variation within a single taxon of a problematic but important osteological structure in the study of ‘rauisuchians.’

Anatomy, taxonomy and phylogenetic relationships of Prestosuchus chiniquensis (Archosauria: Pseudosuchia) from the original collection of von Huene, Middle-Late Triassic of southern Brazil

“…Although several groups of pseudosuchians constitute well-defined, monophyletic units, such as the phytosaurs, aetosaurs, gracilisuchids, ornithosuchids, erpetosuchids, and crocodylomorphs, "rauisuchians" are often regarded as a waste-basket taxon for a variety of pseudosuchian archosaurs that cannot be referred to any of these groups (see Gower, 2000;Nesbitt et al, 2013a;Ezcurra, 2016). One of the principal problems with "rauisuchians" is our still poor understanding of the alpha taxonomy of the taxa included in this group and their anatomy (Gower, 2000;Brusatte et al, 2010;Nesbitt, 2011), although great advances have been made in this regard in the last decade (see Weinbaum and Hungerbühler, 2007;Gower and Schoch, 2009;Brusatte et al, 2010;Nesbitt, 2011;Lautenschlager and Desojo, 2011;Butler et al, 2011;Lautenschlager and Rauhut, 2015;Lacerda et al, 2016;Lessner et al, 2016;Nesbitt and Desojo, 2017). Moreover, "rauisuchians" consist of large-bodied, short-necked predatory quadrupedal animals (e.g., Prestosuchus chiniquensis von Huene, 1938, Saurosuchus galilei Reig, 1959, Stagonosuchus nyassicus von Huene, 1939, Fasolasuchus tenax Bonaparte, 1981, Luperosuchus fractus Romer, 1971) and long-necked, partially edentulous, bipedal taxa (e.g., Arizonasaurus babbitti Welles, 1947, Sillosuchus longicervix Alcober and Parrish, 1997, Effigia okeeffeae Nesbitt and Norell, 2006, Shuvosaurus inexpectatus Chatterjee, 1993 included in several categories (e.g., Rauisuchidae, Poposauroidae, Ctenosauriscidae) by some authors (e.g., Bonaparte, 1981;Chatterjee, 1985;Parrish, 1993;Gower, 2000;Butler et al, 2009;…”

“…The original specimens of von Huene (1938Huene ( , 1942 are kept in the collections of the Bayerische Staatssammlung für Paläontologie und Geologie in Munich, Germany. Among these fossils were several taxa of pseudosuchians, including Prestosuchus chiniquensis von Huene, 1938, Prestosuchus loricatus von Huene, 1938, Procerosuchus celer von Huene, 1938, Hoplitosuchus raui (von Huene, 1938) (originally named as Hoplitosaurus raui by von Huene, 1938 and later as Hoplitosuchus raui by von Huene, 1942 and subsequent authors, e.g., Krebs, 1976;Kischlat, 2000, since Hoplitosaurus was preoccupied, see Lacerda et al, 2016), Rhadinosuchus gracilis von Huene, 1942, and the namebearing taxon of the "Rauisuchia", Rauisuchus tiradentes von Huene, 1938. Although these remains potentially represent one of the most diverse "rauisuchian" faunas known, some of these fossils have not been revised in detail since their original description.…”

“…Although these remains potentially represent one of the most diverse "rauisuchian" faunas known, some of these fossils have not been revised in detail since their original description. Moreover, Barberena (1978) referred a partial skeleton, including a complete huge skull from the same geological unit to Prestosuchus chiniquensis (see also Azevedo, 1991Azevedo, , 1995, and more specimens were referred to the same taxon more recently (Mastrantonio et al, 2013;Raugust, 2014;Lacerda et al, 2016;Roberto-da-Silva et al, 2018;Mastrantonio et al, 2019).…”

“…A more detailed revision of this fauna was presented by Kischlat (2000), who considered Prestosuchus chiniquensis, Procerosuchus celer, and Rauisuchus tiradentes as valid "rauisuchian" taxa. In that revision, some of the material included in Prestosuchus loricatus by von Huene (1942) was referred to a new genus, Abaporu loricatus Kischlat, 2000, whereas other material of this taxon was referred to other taxa or not mentioned at all (Lacerda et al, 2016). Furthermore, other material previously referred to Prestosuchus, including that originally referred to Prestosuchus chiniquensis (most probably the paralectotype SNSB-BSPG AS XXV 7, although the specimen number was given as "BSPGH 1933 L/7" by Kischlat, 2000, p. 291) and the calcaneum of the type of Prestosuchus loricatus (SNSB-BSPG AS XXV 24; erroneously given as "BSPGH 1933 L/24" by Kischlat) was furthermore described as "Karamuru vorax Kischlat and Barberena" (Kischlat, 2000, p. 290-291).…”

“…Furthermore, only a list of material included in this taxon (including materials from different collections and material provisionally referred to this taxon) is given, but no type material is explicitly designated, also violating ICZN article 16.4. Thus, we also consider Karamuru vorax to be a nomen nudum (see also Langer et al, 2007, p. 205;Lacerda et al, 2016).…”