East Riding Museums

Box of fossils including a plant leaf and a belemnite. Belemnites were small tentacled sea creatures (a member of the cephalopod group), which lived during the Mesozoic period (about 248-66 million years ago). In antiquity these fossils were popularly known as "thunderbolts", since it was thought they had been flung out of the sky during thunderstorms. The long, bullet-shaped shell of the creatures was made of calcite (calcium carbonate).