Origem e irradiação dos sauropodomorfos: novos espécimes e suas implicações

Abstract

The origin and early irradiation of sauropodomorph dinosaurs received much attention in response of new discoveries from fossiliferous strata from South America. However, there are still doubts regarding the transitionary period from carnivorous to herbivorous feeding behaviour and the ecological shift in which sauropodomorphs became the most abundant large vertebrates from their faunas. Moreover, there are several disputes regarding the phylogenetic affinities of triassic sauropodomorphs. Thus, in the present thesis, some sauropodomorphs yielded from Triassic strata of Rio Grande do Sul are studied in order to produce new information on these issues. Among the main results, it was noted that the morphological disparity resulting from ontogenetic variation is high in basal forms, affecting the recovered topologies. Similarly, the sedimentary compression impacts character codification, resulting in artificial scores. The excellent preservation degree of one of the studied specimens (CAPPA/UFSM 0035) provides a better understanding of the anatomy of the earliest sauropodomorphs. In addition, the specimen reinforces the hypothesis that sauropodomorphs evolved from a carnivorous ancestor and accumulated traits related to an herbivorous diet during a second evolutionary moment. The morphological transition of the clade could also be tracked through findings from Rio Grande do Sul strata, including the skeletons that compose CAPPA/UFSM 0001 (another specimen studied in the present thesis). Indeed, these specimens allow to track the modifications on the body plan of sauropodomorphs during a time interval of eight million years, revealing a plausible scenario where the clade changes from small and rare to large and abundant animals. CAPPA/UFSM 0001, a new taxon, also brings new data regarding the biology of sauropodomorphs, suggesting the oldest evidence of gregarious behaviour for the clade. Finally, a new phylogenetic analysis employing a new data matrix revealed a rich diversity of non-plateosaurian sauropodomorphs, still poorly studied. This new hypothesis helps to understand how were the first moments of diversification of the group and how was their dispersion during their first phase of irradiation.