Craniomandibular osteology and the first record of the ocular skeleton in a South American rhynchosaur (Archosauromorpha, Hyperodapedontinae)

Abstract

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.