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

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

Salta

Congreso; Reunión de Comunicaciones de la Asociación Paleontologica Argentina 2022; 2022

Asociación Paleontologica Argentina

Tarjadia ruthae is a quadrupedal terrestrial pseudosuchian from the late Middle-early Upper Triassic of the Chañares Formation, La Rioja Province, Argentina. Originally, this species was identified as an indeterminate archosaur and later as a doswelliid archosauriform based on very fragmentary specimens characterized by the ornamentation of the skull roof and osteoderms. Additional specimens (including skulls and postcrania) recovered in last decade show that Tarjadia is an erpetosuchid pseudosuchian. This enigmatic pseudosuchian group is composed by six species registered in Middle-Upper Triassic continental outcrops of Tanzania, Germany, Scotland, North America, Brazil, and Argentina. Tarjadia ruthae from Argentina and Parringtonia gracilis from Tanzania are the best preserved and more abundant species. Although the monophyly of Erpetosuchidae is well supported, alternative high-level positions within Archosauria have been suggested, such as sister taxon to Crocodylomorpha, Aetosauria, or Ornithosuchidae. In order to improve the knowledge about the erpetosuchids, we present a detailed description and paleoneurological reconstruction of the skull of Tarjadia ruthae, based on two articulated partial skulls (CRILAR-Pv 478 and CRILAR-Pv 495) and other fragmentary specimens. We analysed the stratigraphic and geographic occurrence of historical and new specimens of Tarjadia, we provided a new emended diagnosis, and we made a comparative description of the cranial endocast. The skull of Tarjadia ruthae is robust, with a thick and strongly ornamented skull roof, triangular in dorsal view, with concave lateral margins at mid-length that form an abrupt widened posterior region. The external nares are the smallest openings of the skull. The antorbital fossa is deeply excavated and has a small heart-shaped fenestra with both lobes pointing anteriorly. The supratemporal fenestrae are as large and rounded as the orbits, and the infratemporal fenestrae are L-shaped with an extensive excavation along the jugal, quadratojugal and quadrate. The hemimandibles are low, slightly concave on the dentigerous region and strongly convex on the posterior region, conferring them a S-shaped profile in dorsal view. The external mandibular fenestra is small and elliptic, being twice longer than high. The maxillary dentition is restricted to the anterior region of the rostrum. The cranial endocast is anteroposteriorly elongated and seemingly flat because the dorsal surface of the brain could not be entirely reconstructed and therefore the cephalic flexure seems to be lower than expected for a suchian. The labyrinth is twice wider than high, the semicircular canals are remarkably straight, and the anterior canal is longer than the posterior one.