Occurrence of urolites related to dinosaurs in the Lower Cretaceous of the Botucatu Formation, Paraná Basin, São Paulo State, Brazil

Abstract

The geological units that correspond to the Mesozoic in the Paraná basin, São Paulo State, are included in São Bento Group, by correlation with the Pirambóia, Botucatu and Serra Geral formations. The Botucatu Formation’s age is bracketed between the Upper Jurassic and the Lower Cretaceous (Neocomian). The Botucatu Formation is composed of aeolian sandstones showing cross-stratification from medium to large scale, a typical trait of migrating dunes. Ichnofossils were collected in the São Bento Quarry, located in the city of Araraquara, São Paulo State. Samples MPA-002 e MPA-003, respectively, are the negative epirelief and positive hyporelief of the same trace fossil. MPA-001 is a negative epirelief. These features show a removal of sedimentary material, in contrast to the morphology of ornithopod and theropod dinosaur tracks, where compression and deformation of unconsolidated sedimentary layers occurs. These trace fossils show a pattern corresponding to erosion caused by evacuation of liquid wastes and are classificated as urolites, because this term has already been applied to the occurrence of ichnofossils of this type in France and Germany. The morphostructure of these urolites is very similar to the erosional geometry produced in the substrate by expelled liquid waste of modern ratite birds, such as Struthio camelus (ostrich). These urolites are the first records in Brazil of this type of ichnofossil, and is also one of the first examples of trace fossils attributed to liquid waste expulsion by dinosaurs.