Returning the dragon to its cave: the spinosaurid nature of the purported ornithopod materials from the ‘Middle’ Cretaceous Alcântara Formation, northeastern Brazil

Le résumé fourni par la source

We have conducted a reassessment of dinosaur caudal vertebrae from the Cenomanian Alcântara Formation in the Maranhão State, northeastern Brazil. These elements were originally described as belonging to the coeval African theropod Sigilmassasaurus. Subsequently, they were reassigned to a large ornithopod similar to the slightly older Ouranosaurus, representing the first occurrence of a basal hadrosauriform in South America. Here we review the anatomy of the caudal vertebrae from the Alcântara Formation, emphasizing comparisons with both spinosaurid theropods and hadrosauriform ornithopods to re-evaluate their taxonomic assignment between these two distantly related groups. Characters such as centra with subrectangular lateral walls, ventral surface bearing a longitudinal depression, low base of the neural arches, rod-shaped neural spines and transverse processes not reaching the anterior and posterior borders of the centra, among others, allow referral of these vertebrae to Spinosaurinae.The only nominal spinosaurid described for the Alcântara Formation is Oxalaia quilombensis. However, the absence of overlapping material precluded the referral of the Maranhão caudal vertebrae to this species. Furthermore, the existence of multiple dental morphotypes in the Alcântara Formation that suggests a greater diversity of spinosaurids opens the possibility of those vertebrae belonging to a different species. Nevertheless, the reassignment of the Maranhão caudal vertebrae to Spinosauridae nullifies the evidence of ornithopod remains in the Alcântara Formation and limits its record in northeastern South America to footprints from Cenomanian strata.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.