A new possible thyreophoran record from the Lower Cretaceous (of South America): remains from the Paja Formation of Colombia

CORTES, DIRLEY; RIGUETTI, FACUNDO; PEREDA-SUBERBIOLA, XABIER

Villa de Leyva

Congreso; VI Congreso Latinoamericano de Paleontología de Vertebrados; 2018

Centro de Investigaciones Paleontológicas de Villa de Leyva - CIP Grupo de Investigación Biología para la Conservación - Universidad Pedagógica y Tecnológica de Colombia

Thyreophora is a group of Early Jurassic to Late Cretaceous ornithischian dinosaurs that include ankylosaurs and stegosaurs. These armor-bearing dinosaurs are well known from Laurasia, but their record is comparably poorly known from Gondwana. Only three thyreophoran occurrences have been reported in South America: the stegosaurian species Isaberrysaura mollensis from the Middle Jurassic Los Molles Formation of Argentina, a set of bones from the Lower Cretaceous La Amarga Formation of Argentina assigned to Stegosauria and trackways from the Jurassic?Cretaceous boundary of Bolivia.Here, we report a new possible thyreophoran record from shallow marine deposits of the Paja Formation of Colombia, which is considered to be Early Cretaceous (Barremian-Aptian) in age. The specimen, which is still under preparation, consists of a single individual represented by vertebrae and osteoderms. Computed Tomography (CT) imaging and visual inspection of prepared portions of the block indicate that the osteoderms are large and plate-like (laterally compressed), lacking an expanded, hollow base. In this regard they resemble stegosaur armor more than an ankylosaur armor. Vertebral centra are amphiplatyan with subcircular articular faces. The centra slightly longer than tall or broad.This could be the first record of a thyreophoran in Northern South America and thus be the first Early Cretaceous stegosaur found at low latitude. Further preparation of the material, CT imaging, and histological thin sections will increase our knowledge about the anatomy and life history of this individual and will have implications for the phylogenetic relationships and paleobiogeographic history of thyreophorans in Gondwana.