Mayfly larvae preservation from the Early Cretaceous of Brazilian Gondwana: Analogies with modern mats and other Lagerstätten

The Crato Formation paleoentomofauna is noticeable for its high abundance, diversity and morphological fidelity, so the preservational approach of the Ephemeroptera larvae fossils becomes relevant, since they are aquatic insects living in a lacustrine environment of one of the major terrestrial ecosystems of the Early Cretaceous in the Gondwana supercontinent. The mayfly larvae fossils were analyzed under a stereomicroscope and a scanning electron microscope with coupled x-ray spectroscopy (SEM/EDX) for morphological, textural and geochemical purposes. The microfabric analysis confirms the most recent hypothesis that the main factor responsible for the preservation of the Crato Formation fossils was the influence of the microbial mats on the fossilization process. The microscopic signatures left by the mats occur in the insect’s cuticle and internal parts, represented by micro cracks and wrinkles, micro spheres, filaments and mineralized EPS. These features have been compared in light with deposits containing Quaternary microbial mats in the Vermelha Lagoon and its associated salt pans, in Brazil. Also, we discussed our results with taphonomic data of other mayfly larvae fossils from the Lagerstätten La Huérguina (Spain) and Yixian (China) Formations, specifically in relation to the taphonomic settings regarding these Early Cretaceous ephemeropterans. This study corroborates to the idea of the fundamental role of the microbial mats in the exquisite preservation of the Crato Formation invertebrate fossils, with an approach that permits some fundamental paleoenvironmental and paleoclimatic inferences for the Aptian of the Araripe Basin, in Brazil.