Taxonomic paleodiversity of the Marizal Formation (Aptian), Tucano Basin (NE Brazil)

The Amargosa Bed is a fossiliferous stratigraphic marker within the Marizal Formation, cropping out throughout the Tucano Basin in Northeastern Brazil. The fossil record of this unit was first reported during the 1650s and 1960s and currently comprises the remains of dinocysts (Subtilisphaera sp.), pollen (Schizaeaceae and Matoniaceae), plants (e.g., Bennettitales), invertebrates (e.g., caridean shrimps), vertebrates (Ophiopsidae, Amiidae, Aspidorynchidae, Cladocyclidae, Chanidae, and Clupavidae), as well as ichnofossils. These taxa are mostly indicative of a freshwater ecosystem. In light of continued excavation work, several new remains (35 scale impressions and approximately 200 articulated fish remains) have been retrieved and are currently being studied in order to assess their taxonomic identity and significance. So far, morphological approaches have shown the existence of three scale morphotypes, unlike those present in the previously described fish taxa—which were reevaluated and redescribed in detail. In the same sense, the articulated remains, still under study, can be assigned to at least four morphotypes with distinct proportions and morphological characteristics that hint at possible new taxa for the Amargosa Bed. These new findings, although still preliminary, highlight the biological paleodiversity of the unit—which likely comprises a higher number of taxa and ecological actors than previously thought.