"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." - (en.wikipedia.org 09.03.2020)
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