Investigação dos padrões de coossificação intervertebral dos elementos do sacro de dinosauria

Abstract

The main objective of this dissertation is to present a descriptive and comparative study of sacral anatomy and the occurrence of sacral coossification in Saurischia (Theropoda and Sauropomorpha) and Ornithischia, in addition to documenting the earliest record of coossified sacral vertebrae in dinosaurs. The specimen CAPPA / UFSM 0228 is composed of two fused primordial sacrals, collected from the Buriol outcrop, located in São João do Polêsine, assigned to the Candelária Sequence, Santa Maria Supersequence. It is possible to identify that the articular facets of the lateral process of the first sacral are C-shaped in lateral view, one of the typical features of sauropod dinosaurs. Computed microtomography data reveal that the specimen presents restricted fusion between the centra of its vertebrae. The comparative analysis regarding sacral structure in dinosaurs revealed that it occurs independently in the major dinosaur lineages, being common in virtually all Ornithischia and Theropoda. In Sauropodomorpha, it common in taxa starting in the Norian. In addition, the degree of fusion observed in taxa of the three analyzed lineages suggests that there may be a sequential fusion pattern between the elements of the sacrum, at least in Sauropodomorpha. According to the review presented in this study, it is suggested that the primordial sacral vertebrae coossify earlier in the lineage and intervertebral fusion progressively encompasses the adjacent vertebrae (dorsosacrals and caudosacrals) as the lineage progresses. Finally, intervertebral fusion spreads to the neural arches and spines, starting at the primordial sacrals. The new specimen provides data that contribute to the understanding of sacral co-ossification, indicating that it already occurred at the beginning of the evolution of dinosaurs.