New record of a stahleckeriid dicynodont (Therapsida, Dicynodontia) from the Late Triassic of southern Brazil and biostratigraphic remarks on the Riograndia Assemblage Zone

ABSTRACT

Dicynodonts represent a speciose clade of non-mammalian synapsids that lived from the middle Permian to the Late Triassic, exhibiting a Pangaean distribution. The South American Norian fossil record is represented by two species: Jachaleria colorata from Argentina and J. candelariensis from Brazil. The Brazilian specimens come from a relatively small quarry located in the site known as Botucaraí or Botucaraí Hill (Candelária, Rio Grande do Sul). We describe here four dorsal vertebrae of a single individual referred to cf. Jachaleria candelariensis from a site named Alto Guarda Mor, located in the Faxinal do Soturno municipality, State of Rio Grande do Sul, Brazil. This taxonomic proposal and the lithological features of the site support that the outcrop belongs to the Riograndia Assemblage Zone (AZ; Candelária Sequence, Santa Maria Supersequence). Although the specimen cannot be referred unambiguously to Jachaleria candelariensis due to the lack of cranial material, it likely represents the second record of the genus in the Triassic of Brazil. We further discuss the faunal composition and relative age of some sites referred to the Riograndia AZ, which exhibit odd faunal context likely representing an AZ between the top of the Hyperodapedon AZ and the base of the Riograndia AZ.

KEYWORDS:

• Jachaleria
• Riograndia Assemblage Zone
• Rio Grande do Sul State
• South America

Acknowledgments

We especially thank Marina Bento Soares, Carlos Rodrigues, Ana Maria Ribeiro, Voltaire Paes Neto, Flávio Pretto, Marcel Lacerda and Paulo Romo de Vivar for constructive discussions on the Riograndia AZ fauna during the last years. The photographs of UFSM 11097 were skillfully taken by Luiz Flávio Lopes (UFRGS). We also thank the MACN-CONICET (Argentina) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 313494/2018-5 to AASD-R; 309414/2019-9 to LK). We thank the Editor in Chief G. J. Dyke and reviewers C. Kammerer and M. C. Langer for their comments that considerably improved this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico [309414/2019-9,313494/2018-5].