Using computed tomography scanning in exceptionally preserved Lower Cretaceous ostracods from Brazil to reassess the evolutionary history of Paracyprididae (Podocopida: Cypridocopina)

Abstract

Calcareous concretions typical of the Lower Cretaceous Romualdo Formation (late Aptian–Albian of the Santana Group), in the northeastern Brazilian Araripe Basin, occasionally yield exceptionally preserved ostracods with pristine soft parts. These rare specimens allow in-depth studies of ostracod taxonomy and systematics. This is particularly important when dealing with the classification of groups where carapace ornamentation is less common, such as the cypridocopines that have been abundant in continental and transitional environments since Late Jurassic times. Damonella grandiensis is a commonly occurring species in the Romualdo Formation that has long caused taxonomic and systematic arguments due to its mostly featureless carapace—the reason it has been known previously as ‘Ostracode n.º 207’. New detailed CT scans of Damonella grandiensis specimens, coupled with scanning electron microscopy and improved stereoscopic micrographs of additional specimens, allow a review of the species, including first descriptions of their caudal rami and paired sperm pumps (Zenker organs). These indicate not only that Damonella grandiensis must be placed within the genus Reconcavona (as Reconcavona grandiensis comb. nov.), but also that this genus is not representative of the Candonidae, but instead of the Paracyprididae—which impacts on the early evolutionary history of paracypridids.