New observations on the morphology of the frontal bones in Secernosaurus koerneri (Ornithischia, Hadrosauroidea).

SALINAS, G.C.; JUÁREZ-VALIERI, R.D.; FABIANELLI, M.N.; BECERRA, M.G.

Bogotá

Congreso; I Congreso Latinoamericano de Evolución; 2021

Sociedad chilena de Evolución / Sociedad Argentina de Biología Evolutiva / Asociación Colombiana de Biología Evolutiva

The first revision of Kritosaurus australis and Secernosaurus koerneri (Campanian-Maastrichtian ofPatagonia) led to consider the former as a junior synonym of S. koerneri, depicted as a sister taxon of Willinakaqe salitralensis (all from Patagonia) within Gryposaurini. However, new findings and phylogenies in Hadrosauroidea overthe pastdecade could compromise the clustering of this patagonian lineage, so a new review of Secernosaurus is needed. One of the proposed autapomorphies of Secernosaurus is the V-shaped nasofrontal suture, where the anterior margin of each frontal forms a triangular process anteriorly with its apex displaced laterally and bears an excavated articulation region with its ventral edge more prominent anteriorly. Such morphology is more common than previously thought in basal hadrosauroids as Gobihadros, Lesnesovia, Eotrachodon, Lophorhothon, Bactrosaurus, Jintasaurus and Tanius, but differs with the interdigitated or W-shaped nasofrontal suture in species of Saurolophinae, a more derived clade.The exclusion of the frontals from the margin of the orbit due to a slight prefrontal-postorbital contact in Secernosaurus is an intermediate state between that present in basal Hadrosauroidea and nonsaurolophinians Saurolophines (frontal included in the orbit), and that displayed in saurolophinies, Naashobitosaurus and the lambeosaurines more derived than Aralosaurus (wide prefrontal-postorbital contact). These features previously considered as unique of Secernosaurus might now correspond to retained plesiomorphies in a derived taxon or represent evidence of a more basal placement. Pending a deep revision and redefinition on the diagnosis of Secernosaurus koerneri, it is expected that these observations contribute to understanding the phylogenetic placement of Secernosaurus and other patagonian forms.