Uncommon Fossil Bivalve, 100 milion years old, Caprina distefanoi, on matrix. This specimen is very beautiful with a funny question mark shape, looks like marble sculpture. 18 x 12 cm. Rudists are a group of extinct box-, tube- or ring-shaped marine heterodont bivalves belonging to the order Hippuritida that arose during the Late Jurassic and became so diverse during the Cretaceous that they were major reef-building organisms in the Tethys Ocean, until their complete extinction at the close of the Cretaceous. Although they have been very abundant organisms, it is very difficult to find whole and well preserved ones, due to many reasons, such as the hardness of the rock that contains them, very compact and hard, almost like marble. Can be displayed in two ways. Rare, unseen, complete specimen. From an old collection. The specimen has been glued, the stone in which it was included is a very hard solid limestone, impossible to extract without breaking. Plastic standing included. Rare