A reassesment of the mandibular anatomy of the non-stahleckeriine kannemeyeriiforms (Synapsida, Dicynodontia) from the Ladinian-Early Carniana Chañares Formation (Northwestern Argentina), and its taxonomic and phylogenetic significance

ESCOBAR, JUAN A.; MARTINELLI, AGUSTÍN G.; EZCURRA, MARTÍN D.; FIORELLI, LUCAS E.; VON BACZKO, M. BELÉN; NOVAS, FERNANDO. E.; DESOJO, JULIA B.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2023

0002-7014

Two lineages of Kannemeyeriiformes dicynodonts (Synapsida, Dicynodontia) are currently known in the Ladinian-Carnian Chañares Formation (Ischigualasto-Villa Unión Basin, Argentina): stahleckeriine stahleckeriids, based upon postcranium, and a single non-stahleckeriine species, Dinodontosaurus brevirostris, known mostly by cranial material. Available data about the mandible of Dinodontosaurus brevirostris is mainly based on specimen PULR-V 03, type material of D. “platygnathus”. We present for the first time a comprehensive and comparative osteological study of the mandibular anatomy of D. brevirostris based on PULR-V 03 and the new material CRILAR-Pv 94 and PULR-V 144, and revise its phylogenetic relationships with the new data included. Our results are similar to previous analysis, with a monophyletic Dinodontosaurus as the sister group of the Angonisaurus + Stahleckeriidae clade. D. brevirostris is reinterpreted has having an angular contribution to the mandibular symphysis, rounded and hypertrophied reflected lamina of the angular, a wide angular gap, and well-developed and anteriorly curving retroarticular process. Previous hypothesis of stahleckeriine affinities are rejected considering the markedly convex symphysial chin, wide angular gap, median symphysial ridge and moderately sloping articular surface, but shape and size of the reflected lamina is consistent with the position of Dinodontosaurus as an outgroup of Stahleckeriidae. Traits potentially relevant for the distinction from D. tener and other kannemeyeriiforms (tall medial ridge on the dentary, anterolateral trough in the angular, angular contribution to symphysis, extreme narrowness of the symphysial ridge, wide and deep median dentary groove) need further research in other groups in order to be corroborated.