Siriusgnathus niemeyerorum (Eucynodontia: Gomphodontia): The youngest South American traversodontid?

Roese-Miron, Lívia; Pavanatto, Ane Elise Branco; Pretto, Flávio Augusto; Müller, Rodrigo Temp; Dias‐da‐Silva, Sérgio; Kerber, Leonardo

doi:10.1016/j.jsames.2019.102394

Cited by 15 publications

(11 citation statements)

References 35 publications

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“…The presence of four upper incisors represents the plesiomorphic condition in traversodontids (e.g., Massetognathus , Luangwa , Santacruzodon , Scalenodon ), and three upper incisors in more derived taxa (e.g., Exaeretodon , Protuberum , Scalenodontoides ), a condition convergently present in Pascualgnathus and Mandagomphodon attridgei . A conspicuous trait in S. niemeyerorum is the presence of only two upper incisors (Miron et al, 2020; Pavanatto et al, 2018), apparently exclusive to this species among traversodontids. Currently, all known specimens of S. niemeyerorum which preserve premaxillae have two upper incisors, but the lower incisors vary from two to three (Miron et al, 2020; Pavanatto et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

“…Some of these species are particularly abundant in the levels they are found, especially E. riograndensis and E. argentinus known from dozens of specimens, among which are several almost complete skeletons (Abdala et al, 2020;Bonaparte, 1963b;Desojo et al, 2020;Oliveira et al, 2007;Schultz et al, 2020). Additionally, the study of cranial endocasts by means of computed tomography (CT) scanning and histological analyses of bones and teeth have brought news insights on the paleobiology of traversodontids (e.g., Botha-Brink & Abdala, 2012;Chinsamy & Abdala, 2008;Franco et al, 2021;Hoffman et al, 2019;Melo et al, 2019;Miron et al, 2020;O'Meara et al, 2018;Pavanatto et al, 2018Pavanatto et al, , 2019Veiga et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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

Schmitt

Martinelli

Kaiuca

et al. 2023

The Anatomical Record

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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.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Schmitt

Martinelli

Kaiuca

et al. 2023

The Anatomical Record

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“…Siriusgnathus niemeyerorum is the most abundant fossil found at this site, which also contains remains of probainognathians, dinosaurs, and indeterminate archosauromorphs (Pavanatto et al, 2018; Müller, 2020; Stefanello et al, 2020). The strata exposed at this site are considered younger than those of the Janner site (for further details, see Martinelli et al, 2020; Miron et al, 2020).…”

Section: Methodsmentioning

confidence: 99%

“…Both taxa are the largest traversodontids found in Brazil, with adult skulls reported up to 25 cm long. The external osteology of E. riograndensis was studied by Abdala et al (2002), Oliveira et al (2007), and Liparini et al (2013), and that of S. niemeyerorum by Pavanatto et al (2018) and Miron et al (2020). Recently, the brain endocast morphology of both cynodonts was studied by Pavanatto et al (2019).…”

Section: Introductionmentioning

confidence: 99%

The nasal cavity of two traversodontid cynodonts (Eucynodontia, Gomphodontia) from the Upper Triassic of Brazil

et al. 2021

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Traversodontidae is a group of Triassic herbivorous/omnivorous cynodonts that represents the most diversified lineage within Cynognathia. In southern Brazil, a rich fossil record of late Middle/mid-Late Triassic cynodonts has been documented, with Exaeretodon riograndensis Abdala, Barberena, and Dornelles, 2002 and Siriusgnathus niemeyerorum Pavanatto et al., 2018 representing two abundant and well-documented traversodontids. The present study provides a comparative analysis of the morphology of the nasal cavity, nasal recesses, nasolacrimal duct, and maxillary canals of both species using computed tomography, highlighting the changes that occurred in parallel to the origin of mammaliaforms. Our results show that there were no ossified turbinals or a cribriform plate delimiting the posterior end of the nasal cavity, suggesting these structures were probably cartilaginous as in nonmammaliaform cynodonts. Both species show lateral ridges on the internal surface of the roof of the nasal cavity, but the median ridge for the attachment of a nasal septum is absent. Exaeretodon riograndensis and S. niemeyerorum show recesses on the dorsal region of the nasal cavity, which increase the volume of the nasal cavity, potentially enhancing the olfactory chamber and contributing to the sense of smell. On the lateral sides of the nasal cavity, the analyzed taxa show a well-developed maxillary recess. Although E. riograndensis and S. niemeyerorum have roughly similar nasal cavities, in the former taxon, the space between the left and right dorsal recesses of the nasal cavity is uniform along its entire extension, whereas this space narrows posteriorly in S. niemeyerorum. Finally, the nasolacrimal duct of S. niemeyerorum is more inclined anteroposteriorly than in E. riograndensis.

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“…Shouldering, the mesial projection of the mesiolabial border of the upper postcanine resulting in a 'shoulder'-like process on the preceding tooth (Figure 1m,o), is a major dental feature differentiating basal from derived traversodontids (Abdala & Ribeiro, 2003;Romer, 1967) and contributing in the dental complexity of derived traversodontids. Absent in basal traversodontids like traversodontines, Pascualgnathus, Andescynodon, Mandagomphodon, and Scalenodon ribeiroae, a shouldering is incipiently developed in massetognathines, some arctotraversodontines (Boreogomphodon, Plinthogomphodon, Habayia), and basal gomphodontosuchines (Menadon, Gomphodontosuchus), whereas an extensive shouldering characterizes the upper postcanines of derived gomphodontosuchines such as Scalenodontoides, Exaeretodon, Siriusgnathus, and Santagnathus (n.b., the basal gomphodontosuchine Protuberum and the arctotraversodontines Rosieria and Microscalenodon are devoid of a shouldering; Abdala & Ribeiro, 2003;Abdala et al, 2006;Abdala & Sa-Teixeira, 2004;Hopson, 1985;Liu & Sues, 2010;Martinelli, 2010;Melo et al, 2015Melo et al, , 2017Miron et al, 2020;Pavanatto et al, 2018;Ranivoharimanana et al, 2011;Reichel et al, 2009;Schmitt et al, 2024). Functionally, the presence of a shouldering resulted in the development of a more extended occlusal basin and obliquely orientated crests enabling a wider tooth surface for food gridding.…”

Section: Herbivory and Stasis Of Traversodontid Dental Complexitymentioning

confidence: 99%

Evolution of postcanine complexity in Gomphodontia (Therapsida: Cynodontia)

Hendrickx,

Abdala,

Filippini

et al. 2024

The Anatomical Record

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Gomphodonts form a Triassic radiation of small to medium‐bodied (<0.5–2.5 m in length) quadrupedal cynodonts characterized by labiolingually expanded gomphodont postcanines. They were the dominant cynodont group in Middle and Late Triassic ecosystems from the Southern Hemisphere and the first predominantly herbivorous cynodonts to evolve. Gomphodonts were also the first therapsids to develop hypsodonty and a dentition with complex occlusal patterns, and their highly diagnostic upper and lower postcanines show many different morphologies. Here, we explored dental complexity in gomphodont cynodonts through time using geographic information system analysis and orientation patch count applied on 3D crown surfaces of upper and lower gomphodont postcanines belonging to 32 gomphodont taxa. This study reveals that the peak in postcanine complexity was reached early in the evolution of gomphodonts with the emergence in the Early Triassic of omnivorous or insectivorous forms with postcanines made of well‐separated cusps and cingular cuspules. Traversodontids evolved simpler postcanines via coalescence of cusps into crests and the development of large occlusal basins, and the Middle Triassic radiation of traversodontids led to a sharp decrease in mean postcanine complexity. Simplification of the postcanines in traversodontids is interpreted as being related to a gradual increase in the consumption of plant material. Interestingly, the trend of insectivory/omnivory high postcanine complexity and herbivory low dental complexity in gomphodonts is opposite to the trend of dental complexity reported in some extant mammals, with omnivorous having low dental complexity and herbivorous higher. Postcanine complexity remained relatively stable throughout the evolution of traversodontids and only slightly diminished in the Late Triassic due to the presence of minute forms with particularly simple postcanines in the Rhaetian. The major phylogenetic diversity and taxonomic richness of Gomphodontia are represented in two periods of time: at the end of the Anisian, an age in which the postcanine complexity is simplifying, and at the early Carnian when the postcanine complexity in traversodontids, the only Gomphodontia represented, is stable.

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Siriusgnathus niemeyerorum (Eucynodontia: Gomphodontia): The youngest South American traversodontid?

Cited by 15 publications

References 35 publications

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

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

The nasal cavity of two traversodontid cynodonts (Eucynodontia, Gomphodontia) from the Upper Triassic of Brazil

Evolution of postcanine complexity in Gomphodontia (Therapsida: Cynodontia)

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