Ostracods from the Upper Ordovician Phu Ngu Formation, Northern Vietnam: systematics, paleoecology and paleobiogeographical significance

The first detailed systematic documentation of Late Ordovician (Katian) ostracods from the Phu Ngu Formation, northern Vietnam, yields nine species, two described in open nomenclature, from seven genera, two identified tentatively, with six new species, including two new palaeocopine species, five binodicopine species (three new species, including one new genus, one species described in open nomenclature, and the previously described Kinnekullea gaia Wong Hearing et al.), one new leiocopine species and a possible metacopine species. The ostracods co-occur with brachiopods, trilobites and graptolites, in lithofacies interpreted as deposited in a deep marine paleoarc setting on the South China paleoplate. Several ostracod genera from the Phu Ngu Formation are known from paleocontinents that were remote from South China during the Ordovician, including Baltica, Laurentia and the Argentine Precordillera. Assessing the taxonomic composition of the Phu Ngu ostracod assemblage, alongside other Ordovician ostracod faunas from the South China paleoplate reveals that there are very few endemic genera and high proportions of cosmopolitan genera, questioning the utility of ostracod genera for paleogeographical determination, and raising the possibility they were able to migrate via deep, cooler ocean waters.