New specimen bolsters the presence of stahleckeriid dicynodonts in the Ladinian??earliest Carnian levels of the Chañares Formation, La Rioja Province, Argentina

MARTINELLI, AGUSTÍN G.; DESOJO, JULIA B.; EZCURRA, MARTÍN D.; ESCOBAR, JUAN A.; FIORELLI, LUCAS E.

Congreso; 1° Reunión Virtual de Comunicaciones de la Asociación Paleontológica Argentina.; 2020

The taxonomy of the dicynodonts of the latest Ladinian-early Carnian Chañares Formation has been a contentious issue since their original referral to the genera ?Chanaria? and Dinodontosaurus. Subsequent revisions generally restricted their diversity to Dinodontosaurus, but a comprehensive reappraisal is lacking. Indeed, the postcranium of the Chañares dicynodonts remains mostly ignored, excepting a shoulder girdle (MCZ 3459) originally related to some stahleckeriid taxa, and an ulna recently referred to Stahleckeria. Here, we report on a new, large dicynodont specimen (CRILAR-Pv 82) from the Tarjadia Assemblage Zone (AZ) of the lowermost levels of the Chañares Formation (Ischigualasto-Villa Unión Basin). This specimen includes a right scapula, left ilium, sternum, and a few other bone fragments. The gradual dorsal expansion and posterodorsally-to-anteroventrally oriented distal edge of the scapular blade resemble the stahleckeriids Stahleckeria, Ischigualastia and Jachaleria. The strongly raised, vertical spine on the anterolateral border of the blade also occurs in MCZ 3459 and Stahleckeria, but it is absent in Brazilian specimens of Dinodontosaurus. The long iliac preacetabular process of CRILAR-Pv 82 is strongly curved anteroventrally, like Stahleckeria and Eubrachiosaurus, differing from the slight curvature of Brazilian specimens of Dinodontosaurus. Absence of postcranial data of ?Chanaria?/Dinodontosaurus from Chañares precludes any comparison with CRILAR-Pv 82, although it is expected to be similar to its Brazilian cogeneric forms. Thus, CRILAR-Pv 82 and MCZ 3459 are interpreted as stahleckeriids, bolstering the evidence for the presence of this clade in the Tarjadia AZ and supporting the presence of two dicynodont lineag