Freshwater ostracod Theriosynoecum pricei (Pinto and Sanguinetti, 1958): ecophysiological variations, taxonomic review and palaeoenvironmental implications

摘要

The origin of the nodes on ostracod carapaces has been widely discussed in recent decades, and studies have shown that these characters can be produced as an individual response to changes in the environment which the specimens inhabit. Previous experiments with living ostracod species have shown that the variation in water salinity during the ecdysis phase, added to a deficiency in the regulation of internal osmotic pressure, may result in the formation of nodes on the new carapace. Based on this knowledge, a reassessment of fossil species may be necessary, especially in those in which the nodes were considered a diagnostic feature. The present work addresses a taxonomic review of the species Theriosynoecum pricei (Pinto and Sanguinetti, 1958), which is a marker for the Tithonian in the sedimentary basins of Northeast Brazil, adding an emendation to its description and bringing new information about the development of its nodes as ecophysiological and ecophenotypic response. Geochemical and lithological aspects are discussed, corroborating the palaeoenvironmental inferences presented here.