A new herbivorous sphenodontian from the Late Triassic Los Colorados Formation at La Esquina, La Rioja Province, Argentina

SEBASTIAN APESTEGUIA; RICARDO MARTÍNEZ; GUILLERMO WALTER ROUGIER; FERNANDO FABIO GARBEROGLIO

Salta

Congreso; Reunión de comunicaciones de la Asociación Paleontológica; 2022

Asociación Paleontologica Argentina

Triassic herbivorous sphenodontians are known mainly from United Kingdom and South America. British taxa are represented by small forms but in South America, despite the discussed alimentary habits of the clevosaurids, the only unquestionable herbivorous sphenodontian is the large Sphenotitan leyesi Martínez, Apaldetti, Colombi, Praderio, Fernández, Santi Malnis, Correa, Abelin and Alcober 2013, from the Norian/Rhaetian Quebrada del Barro Formation. We present here an almost complete skull (Museo de Ciencias Antropológicas y Naturales, Universidad Nacional de la Rioja PULR-V 138) belonging to an herbivorous sphenodontian from the upper layers of the Norian Los Colorados Formation at Quebrada del Viento site close to La Esquina locality, La Rioja Province. The specimen was collected together with a basal sauropodomorph and a cynodont. The skull is triangular and about half the size than the Sphenotitan holotype. The shape of the premaxilla and the remarkable height of the posterior additional maxillary teeth of PULR-V 138 agree with the morphology present in Sphenotitan. However, other features suggest this specimen represents a different taxon. Despite the difference in size, supratemporal fenestrae are not long and narrow as in Sphenotitan but wide and squared as in Sphenodon and angled anterolaterally as in Clevosaurus hudsoni Swinton 1939. Additionally, the pineal foramen is not positioned between parietals and frontals and before the supratemporal fenestrae as in Sphenotitan but more posteriorly, between parietals, as in clevosaurids. The new material preliminarily suggests that more than one large herbivorous sphenodontian was present in the Upper Triassic terrestrial ecosystems of South America, further research is necessary to consider this initial conclusion.