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Rudists are an extinct group of various heterodont bivalves. They formed a bizarre shell; one valve is usually cone-shaped (attached valve), and the second one is strongly reduced, and it forms a flat operculum-like structure in some representatives. Both valves are connected with teeth and holes. The marked growth lines and prominent ornamentation are apparent at the valve surface. The oldest rudists are known from the Late Jurassic (155 Ma) and they probably became extinct in the latest Cretaceous (68 Ma). The largest valves exceeded almost 2 meters in length. They lived in warm tropical seas and built prominent reefs in the Cretaceous period. ## Keywords Mesozoic, Jurassic-Cretaceous, Bivalvia, Heterodonta
