A rhynchocephalian remain from the Late Cretaceous La Colonia Formation (Chubut Province, Argentina)

APESTEGUÍA, SEBASTIÁN; GUILLERMO W. ROUGIER; ROCIO VERA

san luis

Encuentro; Reunión de comunicaciones de la Asociación Paleontológica Argentina; 2017

universidad de san luis

Rhynchocephalians or sphenodontians form a clade that, although gone extinct in the northem hemisphere by Albian times, survives to the present in southem continents. K/Pg extinction reduced systematic and morphological diversity, particularly size. Sphenodontians are known from the Campanian-Maastrichtian Los Alamitos and Allen formations in Patagonia Argentina, being represented by the opisthodontian Kawasphenodon Apesteguía 2005 from Los Alamitos, and Lamarquesaurus Apesteguía and Rougier 2005 plus a Sphenodon-like form from the Allen Formation. Screenwashing of a fossiliferous lens (Anfiteatro 1) in the likely younger Late Cretaceous La Colonia Formation, Chubut Province, Argentina, provided the first rhynchocephalian remain from this unit. The material MPEF 2371 consists on an isolated but complete right palatine, which preserves eight acrodont teeth devoid of flanges, but showing, perhaps due to wear, low transverse crests, as those of eilenodontine sphenodontians. As in eupropalinal forms, the palatine shows a single tooth line but, as in non-eupropalinal species, the tooth line is not straight but gently curved. The pterygoid process is well preserved and, differing from opisthodontians, exceeds the posterior limit of the bone. The maxillary process is prominent but broken. The palatine can be referred to a 10-12 mm skull, most probably a hatchling specimen. Considering that it bears several opisthodontian traits but also sorne plesiomorphic features more typical of non-eupropalinal forms, the specimen likely represents a new taxon.