Descrição e posicionamento filogenético de um novo espécime de sauropodomorfa da Formação Caturrita

Abstract

The present dissertation aims to present the osteological anatomy of an early sauropodomorph found in Triassic rocks from the municipality of Agudo, Rio Grande do Sul (RS), Brazil. In addition, it aims to tests the biostratigraphic utility of this specimen. CAPPA/UFSM 0002 is composed of postcranial elements from the locality called Sítio Wachholz, ascribed to the Caturrita Formation. Some typical features present in prosauropods are verified in the specimen. For instance, the concave caudal margin of the neural spines of the medial trunk vertebrae, the convex proximal surface of the metacarpal V, and the distal end of the ischium higher than two times the width. On the other hand, typical features of more derived groups than Plateosauridae are absent and the slender shape of the first phalanx of the digit I of the foot corresponds to a common state of basalmost sauropodomorphs. A comparative and phylogenetic analysis among several early sauropodomorphs suggests affinities with Unaysaurus tolentinoi, the only unequivocal sauropodomorph from Caturrita Formation. Based upon such results, a biostratigraphic framework is proposed, which includes the Wachholz, Botucaraí Hill (Candelária, RS), and the Água Negra sites (São Martinho da Serra, RS), this last one so far producing the only record of U. tolentinoi. This corresponds to the first biostratigraphic framework proposed based on fossil vertebrates for the type locality of U. tolentinoi. Considering the presence of the genus Jachaleira in the Los Colorados Formation (Argentina) and in the Botucaraí Hill Site, an early Norian age is suggested to the correlated sites, as recent studies point this age to the portion that yielded Jachaleria in the Los Colorados Formation. Such age places U. tolentinoi and the other sauropodomorphs evaluated here in a unique position regarding the evolutionary history of the sauropodomorphs, suggesting that they lived in a transitional moment, between a period of low representativeness to an of extreme abundance of the group on Earth.