Calpionellids are an extinct group of eukaryotic single celled organisms of uncertain affinities. Their fossils are found in rocks of Upper Jurassic to Lower Cretaceous age. They were planktic organisms with urn-shaped, calcitic tests that had a widespread distribution across the Tethys Ocean from the late Tithonian to the early Valanginian and were characterised by rapid evolution, and their abundant remains in deep sea sediments from this interval are important as they allow long distance biostratigraphic correlation and precise dating. Calpionellids were not confined to the Tethys, have been found as far south as the Vaca Muerta of northern Patagonia. Calpionellids are divided into two families, the Chitinoidellidae, which are the earliest members of the group, appearing in the mid Tith