Miocene ostracod (Crustacea) biostratigraphy of the upper Amazon Basin and evolution of the genus Cyprideis

The Ostracoda in this study come from an area in the Western Amazon river region shared by Peru, Colombia, and Brazil. Fauna was recovered from 125 samples collected at 26 outcrop localities of the Pebas Formation. Five ostracod zones are proposed and referred mainly to the Middle Miocene. The zonation is based on the stratigraphical distribution of 21 endemic species of the euryhaline genus Cyprideis, probably the largest brackish-water ostracod evolutionary radiation of the American Neogene. This study illustrates that Ostracoda can constitute a useful biostratigraphical tool in such environments as those obtained in the Neogene of the upper Amazon Basin.