Cranial osteology and paleoneurology of Tarjadia ruthae: An erpetosuchid pseudosuchian from the Triassic Chañares Formation (late Ladinian-?early Carnian) of Argentina

DESOJO, JULIA B.; VON BACZKO, BELÉN; EZCURRA, MARTÍN D.; FIORELLI, LUCAS; MARTINELLI, AGUSTÍN G.; BONA, PAULA; TROTTEYN, M. JIMENA; LACERDA, MARCEL B.

Anatomical Record

John Wiley and Sons Inc

Año: 2024

Tarjadia ruthae is a quadrupedal terrestrial pseudosuchian from the MiddleearlyUpper Triassic of the Chañares Formation, La Rioja Province, Argentina.Originally, this species was identified as an indeterminate archosaur and lateras a doswelliid archosauriform based on very fragmentary specimens characterizedby the ornamentation of the skull roof and osteoderms. Additionalspecimens (including skulls and postcrania) recovered in the last decade showthat Tarjadia is an erpetosuchid, an enigmatic pseudosuchian group composedof six species registered in Middle-Upper Triassic continental units of Tanza-nia, Germany, Scotland, North America, Brazil, and Argentina. Tarjadiaruthae from Argentina and Parringtonia gracilis from Tanzania are the bestpreserved and more abundant species. Although the monophyly of Erpetosuchidae is well supported, alternative high-level positions within Archosauriahave been suggested, such as sister taxon to Crocodylomorpha, Aetosauria,or Ornithosuchidae. In order to improve the knowledge about theerpetosuchids, we performed a detailed description and paleoneurologicalreconstruction of the skull of Tarjadia ruthae, based on two articulated partialskulls (CRILAR-Pv 478 and CRILAR-Pv 495) and other fragmentary specimens.We analyzed the stratigraphic and geographic occurrence of historicaland new specimens of Tarjadia and provided a new emended diagnosis (thesame for the genus as for the species, due to monotypy) along with a comparativedescription of the cranial endocast. The skull of Tarjadia is robust, with athick and strongly ornamented skull roof, triangular in dorsal view, with concavelateral margins at mid-length that form an abrupt widened posteriorregion. The external nares are the smallest openings of the skull. The antorbitalfossa is deeply excavated and has a small heart-shaped fenestra with both lobespointing anteriorly. The supratemporal fenestrae are as large and rounded asthe orbits, and the infratemporal fenestrae are L-shaped with an extensiveexcavation along the jugal, quadratojugal and quadrate. The hemimandiblesare low, slightly concave on the dentigerous region and strongly convex on theposterior region, conferring them a S-shaped profile in dorsal view. The externalmandibular fenestra is small and elliptic, being twice longer than high. Themaxillary dentition is restricted to the anterior to mid region of the rostrum.Since the braincase of both specimens is partially damaged, the dorsal surfaceof the brain could not be entirely reconstructed. As a result, the endocast isanteroposteriorly elongated and seemingly flat, and the cephalic flexure seemsto be lower than expected for a suchian. The labyrinth is twice wider thanhigh, the semicircular canals are remarkably straight, and the anterior canal islonger than the posterior one.