A reassessment of the mandibular anatomy of Dinodontosaurus brevirostris (Synapsida, Dicynodontia) from the Ladinian–early Carnian Chañares Formation (northwestern Argentina), and its taxonomic and phylogenetic significance

ESCOBAR, JUAN A.; AGUSTIN GUILLERMO MARTINELLI; 4.EZCURRA, M.D.; FIORELLI, L.E.; M. BELÉN VON BACZKO; NOVAS, F.; DESOJO, JULIA B.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2023 vol. 60

0002-7014

Two lineages of Kannemeyeriiformes (Synapsida, Dicynodontia) are currently known in the Ladinian–Carnian Chañares Formation(Ischigualasto-Villa Unión Basin, Argentina): stahleckeriine stahleckeriids, based upon postcrania, and a single non-stahleckeriine species,Dinodontosaurus brevirostris, known mostly by cranial material. Available data on the mandible of Dinodontosaurus brevirostris is mainly basedon specimen PULR-V 03, holotype of D. “platygnathus.” Here we present a comprehensive and comparative osteological study of the lower jawof D. brevirostris, based on PULR-V 03 and the new specimens CRILAR-Pv 94 and PULR-V 144, and revise its phylogenetic relationships withthe inclusion of the mandibular data. Our results resemble previous analyses, with a monophyletic Dinodontosaurus as the sister group of theAngonisaurus + Stahleckeriidae clade. Dinodontosaurus brevirostris is reinterpreted has having an angular contribution to the mandibularsymphysis, rounded and hypertrophied reflected lamina of the angular, wide angular gap, and well-developed and anteriorly curvingretroarticular process. Previous hypotheses of stahleckeriine affinities are rejected based on the markedly convex symphysial chin, wide angulargap, median symphysial ridge, and moderately sloping articular surface, but the shape and size of the reflected lamina is consistent with theposition of Dinodontosaurus as a close relative of Stahleckeriidae. Traits potentially relevant for the distinction from D. tener and otherkannemeyeriiforms (tall medial ridge on the dentary table, anterolateral trough in the angular, angular contribution to symphysis, extremenarrowness of the symphysial ridge, wide and deep median dentary groove) need further research in other dicynodont groups in order torobustly interpret their evolutionary history.