Cardioceras buckowski Jurassic ammonite fossil collected from the Oxfordonian Lower Calcareous Grit near Scarborough, UK. Cardioceras are a genus of ammonite which existed during the Oxfordinian stage of the Jurassic approximately 154 to 146 Mya. They were nektonic carnivores and upon death their shells fell to the sea floor. This specimen exhibits very fine sinuous ribs with a feint keel. The shell measures 2 cm in diameter and it is supplied in a small plastic bag with an information label.