Estudo tafonômico de icnofósseis atribuíveis à diplópodos (Myriapoda) no Parque Municipal do Varvito, município de Itu (São Paulo, Brasil)

Abstract

The arthropods represent the most extensive fossil register and the most abundant and diverse group of all terrestrial animals. Their track and trails provide important data for the study of this group evolution besides helping understanding their diversity and modern distribution. By analyzing the oscillation of the density of ichnofossils along the horizons of Varvito´s Park (Itu – SP), were made inferences about the geological history of the area, the population of arthropods that probably lived there and on the environmental conditions that surrounded them. For the analysis of the density and direction of the tracks, the methodology used was the esquadrinhamento. Also, an experiment was conducted in order to replicate the tracks in similar conditions to those found in the Park during the Carboniferous. It was made a taxonomic classification of the tracks and they were assigned to terrestrial diplopods (Myriapoda). The contextualization of the taphonomic analysis and the depositional history of Varvito´s Park led to the conclusion that myriapods, which have terrestrial habits, inhabited an area of cyclic flooding and therefore experienced environmental stress conditions in the summer, when the area received an influx of meltwater from a glacier located at a relatively long distance of the Park during the Carboniferous. The condition of environmental stress for this fauna, which may or may not cause episodes of mortality, was taking place due to the a thin sheet of water that came from the glacier. Because the tracks were in a preferred direction, one can infer that these animals got away from floods during the summer (stressful condition), which flow of water would probably have a reverse orientation. Considering the evidences of periglacial influence and the outflow of meltwater, the cold might have led to the freezing of soils in the terrestrial environment, creating shallow underwater environments, as well as the formation of ice sheets, thereby impeding gas exchange and the obtainment of nutrients. The tracks also present circular and semi-circular forms and have been interpreted as marks of animals’ agony under stressed conditions, corroborating the paleoecological reconstruction inferred.