Upper Triassic of Brazil: Siriusgnathus (traversodontid cynodont) fossil + hyperodapedontine rhynchosaur skull
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Ben Creisler
Jul 18, 2024, 12:42:49 AMJul 18
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Ben Creisler
New Triassic tetrapod papers
Lívia Roese-Miron, Pedro Henrique Dotto, Thais Gotuzzo de Menezes Medina, Átila Augusto Stock Da-Rosa, Rodrigo Temp Müller & Leonardo Kerber (2024)
Stranger in the nest: On the biostratigraphic relevance of a new record of a traversodontid cynodont in southern Brazil (Candelária Sequence, Upper Triassic)
Palaeoworld (advance online publication)
doi: https://doi.org/10.1016/j.palwor.2024.05.008
https://www.sciencedirect.com/science/article/abs/pii/S1871174X2400088X
The Várzea do Agudo is an Upper Triassic site of the Candelária Sequence of Southern Brazil that boasts an extensive fossil record. It is assigned to the Exaeretodon subzone of the Hyperodapedon AZ (mid-late Carnian) mainly due to the prevalent presence of the traversodontid Exaeretodon riograndensis — up to now the sole traversodontid discovered at the site. In this study, we report the first record of the traversodontid Siriusgnathus niemeyerorum in the Várzea do Agudo site. The new specimen was excavated from the upper layers of the outcrop. Its identification as S. niemeyerorum is substantiated by diagnostic features such as a poorly developed interorbital depression, an inconspicuous suborbital process of the jugal, a not deeply concave base of the lambdoidal crest, the distal accessory labial cusp of the upper postcanines more labially oriented than E. riograndensis, and two upper incisors — so far, a trait autapomorphic to the species among traversodontids. The age of the type locality of S. niemeyerorum has been a subject of debate. Whereas the Siriusgnathus-bearing sites had been associated with younger levels than those of the Hyperodapedon AZ, the absence of index fossils hampered proper biostratigraphic approaches. The finding of a S. niemeyerorum specimen in the same site as E. riograndensis poses a challenging scenario for the biostratigraphy of the fossiliferous outcrops of the municipality of Agudo. It is noteworthy, however, that the new specimen was excavated above the layers yielding E. riograndensis. This raises the question of whether the fossiliferous stratum of the Várzea do Agudo site was deposited in a single event or in a short period, or if it reflects two different time horizons. In the case of the latter, the existence of early Norian sites with distinct faunal composition near the Siriusgnathus-bearing sites could imply the existence of an intermediate fauna between this AZ and the Exaeretodon subzone of the Hyperodapedon AZ, of which S. niemeyerorum would be a constituent. Considering this context, this study discusses the possible biostratigraphic implications of the new record for the biostratigraphy of the sites of the Candelária Sequence.
Jeung Hee Schiefelbein, Mauricio Silva Garcia, Sérgio Furtado Cabreira, Lúcio Roberto da Silva & Rodrigo Temp Müller (2024)
Craniomandibular osteology and the first record of the ocular skeleton in a South American rhynchosaur (Archosauromorpha, Hyperodapedontinae)
Palaeoworld (advance online publication)
doi: https://doi.org/10.1016/j.palwor.2024.07.002
https://www.sciencedirect.com/science/article/abs/pii/S1871174X24000751
A new rhynchosaur specimen from the Upper Triassic (Candelária Sequence) of Southern Brazil is presented in this contribution. While these reptiles constitute some of the most sampled fossils from these beds, their taxonomic, phylogenetic, and palaeobiological status remain understudied. Delving into the cranial elements of the new specimen we performed a taxonomic and phylogenetic assessment, assigning it to “Hyperodapedon” sanjuanensis, a form that occurs in Brazil and Argentina. This assignment was based on distinctive craniomandibular features such as the absence of lingual teeth in the dentary, a unique feature among hyperodapedontine rhynchosaurs. Furthermore, our phylogenetic analysis supports this scenario. Our approach emphasizes the broader need for comprehensive anatomical descriptions of South American rhynchosaurs, particularly in Brazil, where some crucial taxa remain undescribed and/or unfigured. This study also reinforces the need for a revision of the clade Hyperodapedontinae and the Hyperodapedon genus. The orbital region of the new specimen reveals delicate scleral ossicles, presenting a unique window into the visual adaptations and habits of these reptiles. This is the first record of the ocular skeleton for a rhynchosaur of South America. Beyond the taxonomic and phylogenetic implications, this study elucidates the role of the ocular skeleton in regards to sensory adaptations in hyperodapedontine rhynchosaurs.
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Lívia Roese-Miron, Pedro Henrique Dotto, Thais Gotuzzo de Menezes Medina, Átila Augusto Stock Da-Rosa, Rodrigo Temp Müller & Leonardo Kerber (2024)
Stranger in the nest: On the biostratigraphic relevance of a new record of a traversodontid cynodont in southern Brazil (Candelária Sequence, Upper Triassic)
Palaeoworld (advance online publication)
doi: https://doi.org/10.1016/j.palwor.2024.05.008
https://www.sciencedirect.com/science/article/abs/pii/S1871174X2400088X
The Várzea do Agudo is an Upper Triassic site of the Candelária Sequence of Southern Brazil that boasts an extensive fossil record. It is assigned to the Exaeretodon subzone of the Hyperodapedon AZ (mid-late Carnian) mainly due to the prevalent presence of the traversodontid Exaeretodon riograndensis — up to now the sole traversodontid discovered at the site. In this study, we report the first record of the traversodontid Siriusgnathus niemeyerorum in the Várzea do Agudo site. The new specimen was excavated from the upper layers of the outcrop. Its identification as S. niemeyerorum is substantiated by diagnostic features such as a poorly developed interorbital depression, an inconspicuous suborbital process of the jugal, a not deeply concave base of the lambdoidal crest, the distal accessory labial cusp of the upper postcanines more labially oriented than E. riograndensis, and two upper incisors — so far, a trait autapomorphic to the species among traversodontids. The age of the type locality of S. niemeyerorum has been a subject of debate. Whereas the Siriusgnathus-bearing sites had been associated with younger levels than those of the Hyperodapedon AZ, the absence of index fossils hampered proper biostratigraphic approaches. The finding of a S. niemeyerorum specimen in the same site as E. riograndensis poses a challenging scenario for the biostratigraphy of the fossiliferous outcrops of the municipality of Agudo. It is noteworthy, however, that the new specimen was excavated above the layers yielding E. riograndensis. This raises the question of whether the fossiliferous stratum of the Várzea do Agudo site was deposited in a single event or in a short period, or if it reflects two different time horizons. In the case of the latter, the existence of early Norian sites with distinct faunal composition near the Siriusgnathus-bearing sites could imply the existence of an intermediate fauna between this AZ and the Exaeretodon subzone of the Hyperodapedon AZ, of which S. niemeyerorum would be a constituent. Considering this context, this study discusses the possible biostratigraphic implications of the new record for the biostratigraphy of the sites of the Candelária Sequence.
=======
Jeung Hee Schiefelbein, Mauricio Silva Garcia, Sérgio Furtado Cabreira, Lúcio Roberto da Silva & Rodrigo Temp Müller (2024)
Craniomandibular osteology and the first record of the ocular skeleton in a South American rhynchosaur (Archosauromorpha, Hyperodapedontinae)
Palaeoworld (advance online publication)
doi: https://doi.org/10.1016/j.palwor.2024.07.002
https://www.sciencedirect.com/science/article/abs/pii/S1871174X24000751
A new rhynchosaur specimen from the Upper Triassic (Candelária Sequence) of Southern Brazil is presented in this contribution. While these reptiles constitute some of the most sampled fossils from these beds, their taxonomic, phylogenetic, and palaeobiological status remain understudied. Delving into the cranial elements of the new specimen we performed a taxonomic and phylogenetic assessment, assigning it to “Hyperodapedon” sanjuanensis, a form that occurs in Brazil and Argentina. This assignment was based on distinctive craniomandibular features such as the absence of lingual teeth in the dentary, a unique feature among hyperodapedontine rhynchosaurs. Furthermore, our phylogenetic analysis supports this scenario. Our approach emphasizes the broader need for comprehensive anatomical descriptions of South American rhynchosaurs, particularly in Brazil, where some crucial taxa remain undescribed and/or unfigured. This study also reinforces the need for a revision of the clade Hyperodapedontinae and the Hyperodapedon genus. The orbital region of the new specimen reveals delicate scleral ossicles, presenting a unique window into the visual adaptations and habits of these reptiles. This is the first record of the ocular skeleton for a rhynchosaur of South America. Beyond the taxonomic and phylogenetic implications, this study elucidates the role of the ocular skeleton in regards to sensory adaptations in hyperodapedontine rhynchosaurs.
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