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.