Belemnites – a bullet-shaped cephalopod

Belemnites were a group of cephalopods resembling squid, and are related to the modern-day cuttlefish. They first appeared about 360 million years ago, but were most abundant in the Jurassic and the Cretcaeous, becoming extinct at the same time as the dinosaurs. This species, Belemnites semihastatus, had an ink sac and ten arms like other members of the belemnites.

Although fossils of their chambered internal shell called the phragmacone and small hooks that lined their grasping limbs have been found, the most commonly found remains of belemnites are the bullet-shaped structures called guards. These were also internal structures, and they formed the tip of the phragmacone at the ‘tail end’ of the animals.