Unraveling the Crato Formation's preservation and paleoenvironment through the lens of insect taphonomy

• Ano de defesa: 2024
• Autor(a) principal: Storari, Arianny Pimentel
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal do Espírito Santo; BR; Doutorado em Biologia Animal; Centro de Ciências Humanas e Naturais; UFES; Programa de Pós-Graduação em Ciências Biológicas
• Palavras-chave em Português: Paleontologia; Entomologia; Tafonomia; Tafonomia de insetos; Preservação; Ephemeroptera; Orthoptera; Odonata; Solnhofen; Insect taphonomy; Preservation; Zoologia
• Link de acesso: http://repositorio.ufes.br/handle/10/17658

The Crato Formation (Santana Group, Araripe Basin, Brazil) is a well-known Konservat Lagerstätte that preserves a great number of various insect taxa that are exceptionally well preserved both in micro and macro scales. This unit represents a lacustrine paleoenvironment, and therefore, is also important for the study of aquatic insects and their interaction with this past environment. To date, only a few investigations have analyzed the general insect taphonomy of the Crato Formation so far, yet none used actualistic data, which we apply in the third chapter of the thesis. The first part of this thesis consists of a published paper containing the first detailed description of fossilized proventriculi from nine Grylloidea (Orthoptera: Ensifera) specimens of the Crato Formation. Based on the morphological and preservational signatures of the specimens, we bring new morphological data to explore the differences among extinct and extant taxa, that gives insight into the evolution and physiological development of Orthoptera, but mostly, about their exceptional preservation in this unit. The second part of this thesis presents a manuscript with the results on preservational modes of mayflies (Ephemeroptera) and crickets (Orthoptera) of the Crato Formation. We also present the modes of preservation of mayflies from the Solnhofen limestones (Upper Jurassic, Germany) for comparison. The majority of Crato specimens have several conserved external and internal microfeatures, and are preserved by replacement of the cuticle and of internal organs by iron oxides after pyritization, while the Solnhofen fossils are 11 preserved as impressions. In most Solnhofen fossils, their micron-scale morphology is obliterated by coarse mineral growth of calcite crystals. In general, Solnhofen fossils are complete, fully articulated, but with no submicron-scale replication of both external and internal morphology, and are extremely poorly preserved if compared to the insects of the Crato Formation. Lastly, the third manuscript presented in this thesis brings the results of experiments performed to determine the nature of the taphonomic processes and patterns which caused the state of preservation seen in the larvae of mayflies and dragonflies and adult mayflies preserved in the Crato Formation. Our results with experimentation show indications that carcasses of larval Hexagenitidae suffered little disturbance, typical of an autochthonous assemblage. We also noticed that adult fossil specimens with signs of longer decay time were extremely rare. The fossil dragonflies analyzed are preserved in a characteristic position that indicates minimal transport after death, which we find out after experiments with modern larvae. Data on disarticulation also suggest that the dragonfly gomphid larvae were not transported for long distances. Finally, our experiments have shown that when small insects, such as mayflies, die in sub-aerial conditions, there are few possibilities of overcoming the surface tension and sink. Thus, we believe microbial biofilms on the surface of the water were acting during carcass sinking in the Crato Formation