Reconstructing paleo-trophic relationships on the Brazilian Romualdo Formation (Early Cretaceous) through mercury analysis in fossils

Lucas Silveira Antonietto^1*Igor Hamid²Borja Holgado¹Antonio Leite Rocha¹Maria Andréia Ferreira²Antônio Álamo Feitosa Saraiva¹Luiz Drude de Lacerda²

• ¹Regional University of Cariri, Crato, Brazil
• ²Federal University of Ceara, Fortaleza, Ceará, Brazil

Mercury (Hg) biomagnification values tend to reflect relationships between species in the trophic web the larger the value, the higher their position in the web. Here we present the first attempt to reconstruct paleo-trophic linkages during the onset of the Romualdo Formation in the Araripe Basin (Northeastern Brazil), based on analyses of Hg concentration ([Hg]) of fossil specimens recorded in this lithological unit. The aim is to understand possible relationships between vertebrate and invertebrate species inhabiting its paleoenvironments during the early "lagoon" phase of its deposition. Observed ratios (log[Hg]Sample) between [Hg] in fossils ([Hg]Fossil) and their surrounding concretions ([Hg]Rock) indicate greater biomagnification with change in feeding habits and size of evaluated vertebrate taxa, being lowest in the small actinopterygian fish genera Rhacolepis and Tharrhias and reaching its peak in the large predators Cladocyclus and Calamopleurus (the apex species of the trophic pyramid). Feeding habits of Vinctifer were also reviewed, and the genus was reinterpreted from filter feeder to mesopredator; Neoproscinetes and an unidentified batoid (Chondrichthyes), two durophagous bottom-feeding taxa, recorded values compatible with their predicted feeding habits. Low log[Hg]Sample ratios were observed in ornithocheiraean pterosaurs (Reptilia), suggesting it a mesopredators specialized in the smaller fish species, while Thalassodrominae presented intermediate to high log[Hg]Sample, pointing out to a unique trophic role as a terrestrial opportunistic generalist, ranging from predator to scavenger.