Belemnites lived during the periods of Earth history known as the Jurassic and Cretaceous.

Reconstruction of a 'living' belemnite

Cross-section through a belemnite rostrum

Belemnites were marine animals belonging to the phylum Mollusca and the class Cephalopoda. Their closest living relatives are squid and cuttlefish. They had a squid-like body but, unlike modern squid, they had a hard internal skeleton. In the animal's tail, this formed a bullet-shaped feature sometimes referred to as a guard, but more correctly termed a rostrum (plural: rostra). These are the parts which are normally found as fossils.

Belemnites take their name from the Greek word belemnon meaning dart or javelin. The fossilised rostra were widely believed to have been flung down as darts from heaven during thunderstorms (thunderbolts). Some have a finger-like shape and, in folklore, they have been called Devil's Fingers and St Peter's Fingers.

One of the smallest belemnites, Neohibolites minimus