CRANIAL OSTEOLOGY AND PALEONEUROLOGY OF TARJADIA RUTHAE: AN ENIGMATIC PSEUDOSUCHIAN FROM THE TRIASSIC CHAÑARES FORMATION (LATE LADINIAN -?EARLY CARNIAN) OF ARGENTINA

DESOJO, J. B.; BACZKO, M. B.; EZCURRA, M. D.; FIORELLI, L. E.; BONA, P.; MARTINELLI, A.G.; TROTTEYN, M. J.; LACERDA, M.

Trelew

Jornada; Reunion de la Asociación Paleotntológica Argentina; 2022

MEF

Tarjadia ruthae is a quadrupedal terrestrial pseudosuchian from the Middle-early UpperTriassic of the Chañares Formation, La Rioja Province, Argentina. Originally, thisspecies was identified as an indeterminate archosaur and later as a doswelliidarchosauriform, based on very fragmentary specimens characterized by theornamentation of the skull roof and osteoderms. New referred specimens (includingskulls and postcrania) recovered in the last decade show that Tarjadia is anerpetosuchid. The Erpetosuchidae is an enigmatic pseudosuchian group composed of sixspecies registered in Middle-Upper Triassic continental units of Tanzania, Germany,Scotland, North America, Brazil, and Argentina. Tarjadia from Argentina andParringtonia gracilis from Tanzania are the best documented and more abundantspecies. Their monophyly is well supported, but alternative high-level positions withinArchosauria, such as sister taxon to Crocodylomorpha, Aetosauria or Ornithosuchidae,have been recovered. In order to improve the knowledge about the erpetosuchids, wepresent a detailed description and paleoneurological reconstruction of the skull ofTarjadia based on two articulated partial skulls (Centro Regional de InvestigacionesCientíficas y Transferencia Tecnológica en Anillaco, CRILAR-Pv 478 and CRILAR-Pv495) and other fragmentary specimens. We analyse the stratigraphic and geographicoccurrence of historical and new specimens of Tarjadia and provide a new emendeddiagnosis along with a comparative description of the cranial endocast. The skull ofTarjadia is robustly built, with a thick and strongly ornamented skull roof, andtriangular in dorsal view as a result of an abruptly widened posterior region. Theantorbital fossa is deeply excavated and has a small heart-shaped fenestra with bothlobes pointing anteriorly. The supratemporal fenestrae are as large and rounded as theorbits, and the infratemporal fenestrae are L-shaped with an extensive excavation along the jugal, quadratojugal and quadrate. The hemimandibles are low, slightly concave onthe dentigerous region and strongly convex on the posterior region, conferring them a Sshapedprofile in dorsal view. The external mandibular fenestra is small and elliptic,being twice longer than high. The maxillary dentition is restricted anteriorly to the midlengthof the rostrum. The dorsal surface of the brain could not be entirely reconstructedbecause of damage on available braincases. As a result, the endocast is anteroposteriorlyelongated and seemingly flat, and the cephalic flexure lower than expected for asuchian. The inner ear is twice wider than high, the semicircular canals are remarkablystraight, and the anterior canal is longer than the posterior one.