Abyssosaurus nataliae

Abyssosaurus is an extinct genus of cryptoclidid plesiosaur known from the Early Cretaceous of Chuvash Republic, western Russia. The type specimen, consisting of a fairly complete postcranial skeleton and parts of a skull, was discovered around the left tributary of the Sura River by Vasily V. Mita; it was found alongside the remains of a possible fetus, though this has not been described. Subsequently, the specimen entered the collection of the Museum of Chuvash Natural Historical Society. It was described in 2011 by Alexander Yu Berezin, who named its type species, A. nataliae, after his wife and colleague, Nataliya Berezina. While Berezin initially believed that Abyssosaurus was a basal aristonectid, part of a lineage whose later members evolved into giant filter-feeders, later studies have concluded that it was instead related to Colymbosaurus.