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

26. ESCOBAR J.A., MARTINELLI A.G., EZCURRA M.D., FIORELLI L.E., DESOJO J.B.

Congreso; Reunión 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 issuesince their original referral to the genera ?Chanaria? and Dinodontosaurus. Subsequent revisions generally restricted theirdiversity to Dinodontosaurus, but a comprehensive reappraisal is lacking. indeed, the postcranium of the Chañaresdicynodonts remains mostly ignored, except for 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 theTarjadia Assemblage zone (Az) of the lowermost levels of the Chañares Formation (ischigualasto-Villa unión Basin). Thisspecimen includes a right scapula, left ilium, sternum, and a few other bone fragments. The gradual dorsal expansion andposterodorsally-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 MCz3459 and Stahleckeria, but it is absent in the Brazilian specimens of Dinodontosaurus. The long iliac preacetabular processof CRiLAR-Pv 82 is strongly curved anteroventrally, like Stahleckeria and Eubrachiosaurus, differing from the slight curvatureof the Brazilian specimens of Dinodontosaurus. Absence of postcranial data of ?Chanaria?/Dinodontosaurus from Chañaresprecludes comparisons 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 theTarjadia Az and supporting the presence of two dicynodont lineages in the Chañares Formation.