Estudo tafonômico de vertebrados terrestres da Formação Açu (Albiano -Cenomaniano da Bacia Potiguar), Nordeste do Brasil

Abstract

The Potiguar Basin has been paleontologically known since the 19th century for its outcrops of the Jandaíra Formation, but very little was known about other formations. Through recent research in the Açu Formation (operational unit 4), researchers have collected fossils of large vertebrates, identified as dinosaurs, associated with fish and crocodyliforms. Therefore, this work aims to describe and interpret, for the first time, macro and microscopic taphonomic signatures of some specific points in the outcrop area. The analyzed material consists of 142 specimens, most of which are composed of vertebrae and long bones. The fossils are listed in the Paleontology Collection of the Department of Geology (DEGEO), Institute of Geosciences (IGEO), of the Federal University of Rio de Janeiro (UFRJ). Three collection points called Point 1.1, Point 1.2 and Point 2.3 were used. The following macroscopic features were evaluated: (A) articulation and fragmentation; (B) bone representativeness; (C) hydraulic equivalence; (D) breakage patterns; (E) weathering marks; (F) abrasion; (G) trampling marks; (H) bioerosion caused by invertebrates; (I) root marks and (J) staining patterns. For microscopic analysis, the following were analyzed: (A) histological index; (B) fill rate; (C) replacement rate; (D) fracturing. All specimens were disarticulated. The transportability analysis by FTI indicates a peripheral assembly due to the predominance of Group I (53.45%), being 50% of vertebrae. In relation to abrasion, 34% present abrasion and 32% moderate abrasion, suggesting moderate transport. There is a prevalence of grade 2 weathering (40%), suggesting moderate subaerial exposure. The presence of bioerosion by insects and teeth marks reinforce that there was subaerial exposure. There are fossils with root marks, showing that there was vegetation at the burial site. The analysis of the petrographic slides showed high rates of replacement by calcium carbonate and iron oxide, as well as the filling of osteons, in addition to high rates of fracturing by physical weathering related to dryness. In addition, the biostratinomic and fossildiagenetic data indicate a humid environment with moments of low rainfall, showing that there are differences between the points but they correspond to the same taphonomic environment.