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

Abstract

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.

Skull anatomy and paleoneurology of a new traversodontid from the Middle‐Late Triassic of Brazil

“…The ventral contact between this process and the jugal is observed on the right side, but the dorsal contact is not observed (Figure 3a). Hence, the jugal extends posteriorly almost up to the end of the zygomatic arch, similar to other traversodontids (Abdala et al, 2002;Liu & Powel, 2009;Pavanatto et al, 2018;Schmitt et al, 2024). On the other hand, it is not possible to observe the anterior extension of the squamosal process.…”

“…ULBRA PVT-049 was scored in the data matrix of Cynognathia of Hendrickx et al (2020), modified by Schmitt et al (2024). The analyses were processed in the software TNT v.1.5 (Goloboff & Catalano, 2016).…”

“…In the narial region, the internarial bar is broken but preserves its premaxillary process (Figure 3a-c). This bar is present in most traversodontids, except for some gomphodontosuchines, such as Protuberum cabralensis, Exaeretodon argentinus, E. riograndensis, S. niemeyerorum, and Santagnathus mariensis (Abdala et al, 2002;Pavanatto et al, 2018;Reichel et al, 2009;Schmitt et al, 2024). On the left side, a portion of the facial process of the septomaxilla penetrates between the nasal and maxilla (Figure 3a).…”

“…The morphology of this structure departs from the pattern observed in T. stahleckeri, which shows a relatively well-developed process (Figure 9a) (It is scored in phylogenetic matrices as conspicuously projected in the character that describes this process; Liu & Abdala, 2014, #13;Gaetano & Abdala, 2015, #13;Melo et al, 2015, #13;Pavanatto et al, 2018, #13;Hendrickx et al, 2020, #133). There is considerable variation in this process among different species of cynodonts (Abdala & Damiani, 2004;Schmitt et al, 2019Schmitt et al, , 2024. The process may be absent (e.g., Me.…”

Evolution of postcanine complexity in Gomphodontia (Therapsida: Cynodontia)

“…Black bar in each branch indicates temporal extension of the taxa. The phylogenetic tree follows the results of the cladistic analyses obtained by Hendrickx et al (2020) and Schmitt et al (2024). Black silhouettes credit: Gabriel Ugueto (Cricodon), Sergey Meleshin (Scalenodon), José Eduardo Camargo Martínez (all others).…”