The ancient mystery of St Hilda's 'snake stones': what do ammonites really look like?

Despite being among the most recognisable, common fossils, not one has been found that gives us an accurate idea of how the animals looked in life

Think of a generic fossil and - alongside dinosaur skeletons or trilobites - it's likely that the coiled shells of ammonites spring to mind. Ammonites are an extinct group of cephalopods, the mollusc group that contains octopuses, vampire squid, 'squids' (there are many different kinds of squid, so squids will be used to generically refer to them all throughout), cuttlefish, nautiluses, the extinct belemnites and other forms.

You can see ammonites everywhere; they're widely used as an icon for company logos from publishers to construction companies, museums and fossil shops. Visit the Jurassic Coast World Heritage Site in the UK, and ammonite road signs greet you at every town and city and even the lampposts on the seafront feature a familiar coiled shell.