Osteology of the first skull of Aetosauroides scagliai Casamiquela 1960 (Archosauria: Aetosauria) from the Upper Triassic of southern Brazil (Hyperodapedon Assemblage Zone) and its phylogenetic importance

BIACCHI BRUST, ANA CAROLINA; DESOJO, JULIA BRENDA; SCHULTZ, CESAR LEANDRO; PAES-NETO, VOLTAIRE DUTRA; DA-ROSA, ÁTILA AUGUSTO STOCK

PLOS ONE

PUBLIC LIBRARY SCIENCE

Año: 2018 vol. 13

1932-6203

Aetosauria, which includes 30 species, is a diverse group of armored pseudosuchian archosaursrestricted to Upper Triassic beds. Three species occur in Brazil, and one of these,Aetosauroides scagliai Casamiquela, 1960, also occurs in Argentina. The specimen UFSM11505, found at Faixa Nova±Cerrito I Outcrop, Santa Maria Formation (HyperodapedonAssemblage Zone), Santa Maria, Rio Grande do Sul State, Brazil, is here referred to asAetosauroides scagliai. This specimen preserves most of the skull with both hemimandiblesin association with most of the postcranium, thus representing one of the most completeaetosaur skeletons found in Brazil. The premaxilla, one of the key elements of the cranialmorphology of aetosaurs, along with the posterior portion of the mandible, was not describeduntil now for A. scagliai. In contrast to the typothoracinae aetosaurs, the premaxilla ofUFSM 11505 presents a shovel-shaped tip, but it is not as prominent as the lateral expansionof desmatosuchian aetosaurs, including both species of Stagonolepis, S. robertsoniAgassiz, 1844 and S. olenkae Sulej, 2010. The retroarticular process of the mandible iselongate and not tall, as in Stenomity huangae Small & Martz, 2013 and other typothoracinaeaetosaurs. Unlike previous descriptions of A. scagliai, the maxillary teeth are recurvedziphodont-like with serrations on the entire length of both margins. Premaxillary teeth arealso present, being less recurved than the maxillary teeth and cylindrical. We recoveredAetosauroides scagliai as the most basal taxon within Aetosauria, like previous phylogeneticanalyses. Furthermore, our analyses reinforce that recurved and unconstricted maxillaryteeth, the shovel-shaped premaxilla and the presence of a tuber on the surangular are plesiomorphicfeatures of Aetosauria.