As a young boy Sy Donne found what he thought was a fairly ordinary rock on a beach south of Whitby. But it wasn’t until he was tidying up his house 35 years later that he decided to crack it open.
To his amazement, the salesman found beautiful ammonite fossils from the Jurassic period.
The ancient sea creatures sported a ribbed spiral-form shell, and lived between 240-65 million years ago, when they were wiped out along with the dinosaurs.
This fossils are believed to be around 180 million years old and could be worth around $3000 (£2,200), although Mr Donne says it’s not for sale.