Of Ammonites and Belemnites

Ignoring jokes from Partner-who-loves-tea about me being a living fossil there are two fossils on display in our house. One is small ammonite. These are probably the most commonly found and best known fossil.


The second is a larger and, in my view more interesting, Belemnite - probably the most well known extinct cephalopod after the ammonites. Belemnites were squid-like carnivores with a soft body around an internal, pencil-shaped shell. Early forms evolved in the Carboniferous period and are thought to have evolved from the same ancestors as the ammonites. Belemnites were common from the Lower Jurassic period to the end of the Cretaceous period and became extinct at the same time as the dinosaurs - approximately 65 million years ago. They are quite common fossils and have a worldwide distribution. They are a very characteristic and easily recognisable fossil usually resembling a bullet in shape, although this only represents the extreme 'tail' of the animal.


The name 'Belemnite' is derived from the Greek word belemnon which means javelin or dart due to the obvious resemblance in the shape of the fossil. It was a common folklore tale for many centuries that belemnites were formed from the point of strike of lightning bolts into the ground; hence they are frequently referred to as 'thunderbolts'. Zeus is often depicted throwing a thunderbolt which looks very much like a Belemnite fossil.


The idea of the belemnite shape obviously gave rise to the name of this aircraft – the Thunderbolt.


The cuttlefish is the modern-day relative of the belemnite. Belemnites were efficient carnivores that caught small fish and marine animals with their tentacles, and ate them with their beak-like jaws. Their tentacles were different to the modern squid, as they had hooks instead of suckers to grab prey. They were built for speed and probably lived in shoals and fossil evidence shows they formed a major part of the diet of ichthyosaurs.