Olcostephanus is an extinct ammonoid cephalopod genus belonging to the family Olcostephanidae.

These fast-moving nektonic carnivores[1] lived during the Cretaceous, from the upper Valanginian to the lower Hauterivian age.

[2][1][3] Fossils of species within this genus have been found in the Cretaceous sediments of Antarctica, Argentina, Austria, Bulgaria, Chile, Colombia (Macanal Formation, Eastern Ranges),[4] Czech Republic, France, Hungary, Italy, Mexico, Morocco, Poland, Portugal, Romania, Slovakia, South Africa, Spain, Russia, United States, as well as in the Jurassic of Argentina.

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