Neoicnologia como ferramenta para interpretação de traços fósseis da Icnofauna de aracnídeos da formação Botucatu (cretáceo inferior, bacia do Paraná)

Abstract

Ichnofossils are abundant in the sandstones of the Botucatu Formation, Paraná Basin, of Neocomian age. This formation covers much of the Midwest, Southeast and South of Brazil, and other countries in South America. Several sandstone samples containing trace fossils were collected and deposited in the paleontological collection of the Departmento de Ecologia e Biologia Evolutiva (DEBE) of the Universidade Federal de São Carlos (UFSCar). In this work, trace fossils attributed to arachnids, i.e. ichnogenera Paleohelcura Gilmore, 1926 and Octopodichnus Gilmore, 1927, were studied and their presence is recorded for the first time in Brazil. The aim of this study was to infer how different environmental conditions such as moisture, texture, substrate inclination and even behavioral aspects of the organisms can affect the structure of the traces left by different arthropods. To do this, several neoichnological experiments were made, with six arachnids (two Tityus serrulatus, one Lycosa sp., one Loxosceles sp., and two individuals of the family Gonyleptidae) and five individuals of other invertebrate classes (three insects, one isopod and one diplopod). The experiments consisted on making the animals walk on a tray with sand of different grain sizes, different inclinations and different moisture levels. The results of these experiments, which showed different trace morphologies, according to each imposed condition, proved the influence of these conditions on the morphology of the footprints and on the behavior of the studied animals. In addition, these results showed how, in some situations, for example, in an uphill movement in a slope of 30° of inclination, it’s possible that animals with highly different track’s shapes leave very similar tracks, thus making much more difficult the identification of the track’s producer animal through the analysis of the ichnofossils. It was also possible to prove how the moisture level and the substrate inclination are important for the tracks’ preservation.