Distinct preservational pathways of insects from the Crato Formation, Lower Cretaceous of the Araripe Basin, Brazil

Abstract

This study compares two different preservation pathways of fossil insects in the lacustrine deposits of the Crato Formation, Lower Cretaceous (Aptian) of the Araripe Basin, northeastern Brazil. Three hundred seventy-seven specimens were examined and separated into ten taxonomic groups. Of this total, one hundred twenty-three are kerogenized insects, and two hundred fifty-four are pyritized insects. We carried out quantitative analyses of their taphonomic characters, such as body articulation, and morphological preservational quality (e.g. discernible eyes). Of all morphological categories, the thorax presented the highest degree of preservation quality, while the antennae had the lowest. Our statistical results show significant differences in the preservation quality of individual morphological categories among the insect taxa. We expected that mineralized insects would have lower preservational quality than the kerogenized ones, but instead found the opposite pattern to be true. Counter to the findings of other studies, we found that pyritized insects had higher preservation quality than kerogenized insects. The expected lower preservation fidelity of pyritized fossils occurs due to longer time exposed to microbial decay before final burial. Few studies have presented a quantitative comparison of preservational/ biostratinomic patterns in different insect taxa, especially within the same geological setting. In this context, the Crato Formation presents an intriguing and unique opportunity to understand the taphonomic bias that results from two different preservation pathways of insects.