Descrição e posicionamento filogenético de um dinossauriforme do triássico superior do sul do Brasil

Abstract

This study aims the description of a new dinosauriform specimen from Santa Maria Formation, which gathers the oldest unequivocal registers of this clade to Brazil, all ascribed to Dinosauria. The specimen was recovered in the Site Janner outcrop, which late Carnian age, situated in the Agudo municipality, Rio Grande do Sul. This specimen was cataloged in the Paleobiology Laboratory of Universidade Federal do Pampa under the acronym UNIPAMPA 0632. This consist fossil in a partial left femur with about 11 cm length, where much of the proximal portion not are preserved. Features as a ‗fourth trochanter‘ with crest-like form and the presence of a ‗lesser trochanter‘ allow ascribed the specimen to Dinosauriformes. The absence of a cleft separating the proximal portion of the ‗lesser trochanter‘ from the femoral axis and the absence of a ‗trochanteric shelf‘ might indicate that specimens is not a dinosaur, once the dinosaurs of the same age of UNIPAMPA 0632 generally have the cleft between the ‗lesser trochanter‘ and the femoral axis and a ‗trochanteric shelf‘ associated to ‗lesser trochanter‘. Still the quite longitudinally extended popliteal fossa may indicate some Silesauridae affinity. Thus, the specimen was scored in a matriz along with other dinosauriforms and related groups in order to testing their phylogenetic affinities. This matriz was processed with TNT 1.1 software, where UNIPAMPA 0632 was positioned in a less inclusive clade within of Silesauridae, which is more derived than Asilisaurus postiting UNIPAMPA 0632 as sister-taxon of a clade uniting Eucoelophysis, Diodorus, Sacisaurus and Silesaurus. The position of UNIPAMPA 0632 seems parsimonious and persuasive in evolutionary and chronological terms, considering that UNIPAMPA 0632 was recovered from younger rocks than Asilisaurus and older than Eucoelophysis, Sacisaurus and Silesaurus. In evolutionary terms may indicate that the loss of the ‗trochanteric shelf‘ in silesaurids ocurred before the development of a protunding ‗lesser trochanter‘ separated from the femoral shaft by a cleft. Additionally, if UNIPAMPA 0632 position is correct, this fóssil become to represent the older silesaurid register in Brazil.