First Sauropodomorpha (Dinosauria) for the Vila Botucaraí site (Hyperodapedon Assemblage Zone, Candelária Sequence), Rio Grande do Sul, Brazil

Abstract

The Vila Botucaraí site is located west of the municipality of Candelária, Rio Grande do Sul State, southern Brazil, and is particularly important because it represents the type locality of the species Exaeretodon riograndensis (Cynodontia, Traversodontidae), Charruodon tetracuspidatus (Cynodontia, Probainognathia) and Proterochampsa nodosa (Archosauriformes, Proterochampsidae). The site is correlated to the Hyperodapedon Assemblage Zone whose fossiliferous content allows to correlate it to the lower half of the Ischigualasto Formation (Ischigualasto-Villa Unión Basin), of late Carnian age, in Argentina. The aim of this study is to record the first remains of dinosaurs from this locality, found in 2001 during the Pró-Guaiba Project and stored in the Scientific Collection of the Paleontology Section of the Museu de Ciências Naturais, Secretaria Estadual do Meio Ambiente e Infraestrutura, Porto Alegre, RS. In addition to the taxa mentioned at the Vila Botucaraí site, the archosauromorph Hyperodapedon sp. was also preliminarily recorded. The Dinosauria specimen includes four dorsal vertebrae (MCN-PV 10347a, b, c, d). The general characteristics observed are: (i) absence of a ventral keel in the vertebral centra, shared with Guaibasaurus, Bagualosaurus, Pampadromaeus; (ii) amphicoelic centra with concave ventral surface, shared with Bagualosaurus, Guaibasaurus, and most non-sauropod sauropodomorphs (exceptions are, for example, Riojasaurus; also, this character does not appear in herrerasaurids); (iii) vertebral laminae connected to the diapophysis, and their arrangement results in different fossae, as in Bagualosaurus, Buriolestes, Guaibasaurus, and herrerasaurids; (iv) neural spine anteroposteriorly elongated and transversely narrow, as in Bagualosaurus, Pampadromaeus, Buriolestes, Macrocollum, differing from herrerasaurids and theropods. This set of characters is similar to that observed in basal sauropodomorphs, quite different from the neural spine with a spine table, such as the observed in herrerasaurids. Specimen MCN-PV 10347 is here considered a member of the Sauropodomorpha clade and tentatively identified as cf. Bagualosauria. The features of this specimen are shared among Carnian (e.g., Buriolestes schultzi, Bagualosaurus agudoensis) and Norian (e.g., Unaysaurus tolentinoi, Guaibasaurus candelariensis) sauropodomorphs. In addition to this, the new material expands the knowledge regarding the number of outcrops with the occurrence of sauropodomorphs for the Triassic in Brazil, as well as about the paleofauna of the Vila Botucaraí site, allowing us to infer its biostratigraphic correlation with one of the sub-divisions already proposed for the Hyperodapedon AZ, the Exaeretodon Subzone, interpreted as the top of this AZ. Despite the abundance of sauropodomorphs in Rio Grande do Sul, this record confirms the occurrence of this clade at the Hyperodapedon AZ in the Candelária region.