Old fossil findings in the Upper Triassic rocks of southern Brazil improve diversity of traversodontid cynodonts (Therapsida, Cynodontia)

In this contribution we describe a new genus and species of gomphodontosuchine cynodont from the Late Triassic Hyperodapedon Assemblage Zone (AZ) of the Santa Maria Supersequence of southern Brazil, based on material collected 20 years ago. The new taxon, Santagnathus mariensis gen. et sp. nov., is based on numerous cranial and postcranial remains, which altogether provide data on several parts of the skeleton. Santagnathus mariensis is closely related to Siriusgnathus niemeyerorum and Exaeretodon spp. and expands the knowledge about gomphodontosuchine cynodonts. Morphologically, the new species has a skull bauplan particularly similar to S. niemeyerorum and E. riograndensis, differing from them by a unique combination of traits such as three upper incisors, the absence of a descending process in the jugal, a more posterior position of the postorbital bar and a preorbital region larger than the temporal one. The new traversodontid was found associated with the rhynchosaur Hyperodapedon sp., corroborating the assignment of the cynodont fossils to the Hyperodapedon AZ. We also provide comments on the status of the Argentine traversodontid cynodont Proexaeretodon vincei, typically considered a junior synonym of Exaeretodon argentinus, and here accepted as a valid taxon.

New rhadinosuchine proterochampsids from the late Middle-early Late Triassic of southern Brazil enhance the diversity of archosauriforms

Proterochampsidae is a clade of non-archosaurian archosauriforms restricted to the Middle to the Late Triassic of the Ischigualasto-Villa Unión Basin of Argentina and the Santa Maria Supersequence of Brazil. A reappraisal of proterochampsid specimens from the Brazilian Dinodontosaurus Assemblage Zone (AZ) of the Pinheiros-Chiniquá Sequence (late Ladinian-early Carnian) is presented here. One of the specimens was preliminary assigned to Chanaresuchus sp., whose type species comes from the Massetognathus-Chanaresuchus AZ of the Chañares Formation of Argentina. However, our revision indicates that it differs from Chanaresuchus, being more closely related to the middle-late Carnian Rhadinosuchus gracilis. We therefore propose the new taxon, Pinheirochampsa rodriguesi, to reallocate this specimen. Additionally, we present a revision of other putative Chanaresuchus occurrences in Brazil, including the only known specimen described for the Santacruzodon AZ (Santa Cruz do Sul Sequence; early Carnian), also proposing it as a new taxon: Kuruxuchampsa dornellesi. Both new species are characterized, among other features, by transverse expansion of the anterior end of the rostrum, similar to the condition present in Rhadinosuchus, but absent in Chanaresuchus, Gualosuchus, Pseudochampsa, and non-rhadinosuchine proterochampsids. These two new species expand the growing knowledge of the non-archosaurian archosauriform diversity during the Middle-Late Triassic in South America and enhance faunal and chronological comparisons between approximately coeval geological units between Argentina and Brazil.

Reassessment of the enigmatic "Prestosuchus" loricatus (Archosauria: Pseudosuchia) from the Middle-Late Triassic of southern Brazil

Our knowledge of the diversity and evolution of South American Triassic pseudosuchians has greatly improved in the past 15 years, due to new discoveries, but also to the revision of several historically important specimens. One of the earliest descriptions of pseudosuchians from the Triassic of Brazil stems from the classic work of Huene from the first half of the 20th century, who described several species, including such influential taxa as Rauisuchus tiradentes or Prestosuchus chiniquensis, which have recently been reviewed. The more poorly known proposed second species of Prestosuchus, P. loricatus, is the focus of the present work. The original material included some elements of the axial skeleton (cervical and caudal vertebrae, ribs, osteoderms) and the hindlimb (ischia, calcaneum, metatarsus), collected from the Dinodontosaurus Assemblage Zone of the Chiniquá area, west of São Pedro do Sul. "Prestosuchus" loricatus shows numerous differences to P. chiniquensis, including the shape of cervical neural spines, presence of epipophyses on the cervical vertebrae, presence of a pit in the iliac articulation of the ischium, lack of longitudinal furrows in the dorsolateral surface of the ischial shafts, the more slender calcaneal tuber and a less pronounced ventral pit in the calcaneum, and is thus referred to a new genus, Schultzsuchus gen. nov. Phylogenetic analysis indicates an early branching position within Poposauroidea for Schultzsuchus, making it the oldest known member of this clade in South America.

Postcranial anatomy of Prestosuchus chiniquensis (Archosauria: Loricata) from the Triassic of Brazil

Prestosuchus chiniquensis is the best represented pseudosuchian archosaur from the Pinheiros-Chiniquá Sequence, Middle-Late Triassic (Ladinian/Carnian) of the Santa Maria Supersequence, Southern Brazil. Several incomplete specimens attributed to this species have been described, but the morphology of the postcranial skeleton of P. chiniquensis is poorly known. In this contribution we present the postcranial material of the UFRGS-PV-0629-T specimen, concluding its description, as its skull and endocast have already been described. Additionally, histological data provided new information on the poorly known ontogenetic series of P. chiniquensis, and on its growth patterns suggesting a longer period of slow growth when compared to other basal Loricata species. A phylogenetic analysis placed UFRGS-PV-0629-T in a group composed by the lectotype, paralectotype, and other described P. chiniquensis specimens, further corroborating our taxonomic hypothesis, that specimens of basal Loricata collected in Brazil are closely related to each other. Due to the association of characters found in the phylogenetic analysis, the specimen UFRGS-PV-0629-T is attributed as the most complete material ever found for P. chiniquensis. As such, it is clear that the material presented here provides important new information on P. chiniquensis. Based on the results presented here, we revised the diagnosis for P. chiniquensis. However, it also evidences the need for new discoveries and studies of other specimens seeking to understand this and other closely related species, which were important components of worldwide trophic webs of the Triassic biotas.

Reassessment of Faxinalipterus minimus, a purported Triassic pterosaur from southern Brazil with the description of a new taxon

Faxinalipterus minimus was originally described as a purported pterosaur from the Late Triassic (early Norian) Caturrita Formation of southern Brazil. Its holotype comprises fragmentary postcranial elements, whereas a partial maxilla was referred to the species. The assignment of Faxinalipterus minimus to Pterosauria has been questioned by some studies, but the specimen has never been accessed in detail after its original description. Here we provide a reassessment of Faxinalipterus minimus after additional mechanical preparation of the holotype. Our interpretations on the identity of several bones differ from those of the original description, and we found no support favoring pterosaur affinities for the taxon. The maxilla previously referred to Faxinalipterus minimus is disassociated from this taxon and referred to a new putative pterosauromorph described here from a partial skull and fragmentary postcranial elements. Maehary bonapartei gen. et sp. nov. comes from the same fossiliferous site that yielded Faxinalipterus minimus, but the lack of overlapping bones hampers comparisons between the two taxa. Our phylogenetic analysis places Faxinalipterus minimus within Lagerpetidae and Maehary bonapartei gen. et sp. nov. as the earliest-diverging member of Pterosauromorpha. Furthermore, the peculiar morphology of the new taxon reveals a new dental morphotype for archosaurs, characterized by conical, unserrated crowns, with a pair of apicobasally oriented grooves. These two enigmatic archosaurs expand our knowledge on the Caturrita Formation fauna and reinforce the importance of its beds on the understanding of Late Triassic ecosystems.

New insights on Prestosuchus chiniquensis Huene, 1942 (Pseudosuchia, Loricata) based on new specimens from the "Tree Sanga" Outcrop, Chiniquá Region, Rio Grande do Sul, Brazil

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.’