A new morphotype of Traversodontidae (Cynodontia) from the Candelária Sequence (late Triassic), Brazil.

SCHMITT, MAURÍCIO RODRIGO; MARTINELLI, AGUSTÍN G.; SCHULTZ, CESAR; SOARES, MARINA B.

São Jao do Polesine

Simposio; PaleoRS; 2019

Traversodontids are gomphodont cynodonts from the Triassic, discovered in almost allcontinents, being most diverse and abundant in Gondwanan landmasses. They arecharacterized by their labio-lingually enlarged postcanines with a quite precise occlusionand enlarged cranial structures (e.g., zygomatic arches, sagittal crest) for powerfulmuscles related to mastication. Among traversodontids, Gomphodontosuchinae includesthe most derived taxa, composed by six genera: Gomphodontosuchus, Menadon,Protuberum, Exaeretodon, Scalenodontoides and Siriusgnathus. We present here thespecimen UFRGS-PV-1419-T that was collected in Santa Maria city (Rio Grande do Sulstate) in 2003, in an outcrop located on the margins of the Cancela stream. It wasassociated with dozens of postcranial bones of cynodonts, as well a skull and post-cranialbones of at least two rhynchosaur specimens, including a maxilla (UFRGS-PV-1458-T)assigned to Hyperodapedon sp. Due to this associated material, the taphocoenosis of thisoutcrop is referred to the Hyperodapedon Assemblage Zone (Candelária Sequence).UFRGS-PV-1419-T was identified as a Gomphodontosuchinae based on the presence ofthree large upper incisors, reduced lower canine and lack of a central cusp in transversecrest of postcanines. Comparisons were made with Exaeretodon riograndensis (CAPPAUFSM-0030, MCP-1522-PV), Exaeretodon argentinus (MACN-PV-18063) andSiriusgnathus niemeyerorum (CAPPA-UFSM-0032) as follow: UFRGS-PV-1419-Tshares with Exaeretodon three upper incisors, while only two are present inSiriusgnathus; the postorbital bar of UFRGS-PV-1419 is more posteriorly positioned thanin Siriusgnathus and anteriorly than in Exaeretodon; the orbital floor in UFRGS-PV-1419-T is smooth as in Exaeretodon, but with a crest in Siriusgnathus; the dorsoventralcrest in the zygomatic process of the squamosal is absent in UFRGS-PV-1419-T andSiriusgnathus but well pronounced in Exaeretodon species. Thus, comparisons indicatethat UFRGS-PV-1419-T cannot be referred to any known species and it can represent anew morphotype, closely related to Exaeretodon and Siriusgnathus. This newmorphotype, as Siriusgnathus, has a morphologic resemblance to the Argentinean taxon?Proexaeretodon?, which was considered synonymous of Exaeretodon. Additionalcomparisons and a revision of ?Proexaeretodon? specimens are needed to elucidate thevalidity of this genus and the possible affinity with the Brazilian taxa/specimens. Thisnew material increases the knowledge of traversodontids as well as its diversity in theHyperodapedon AZ. [CAPES, CNPq]