150-million-year-old oyster which is ten times normal size probably contains the world's biggest pearl - but no-one wants to open it to find out



A 145million-year-old oyster fossil trawled up off the south coast by fishermen could contain the mother of all pearls.

Experts used medical MRI scanning technology to analyse the fossil to discover if there was a rare gem inside.

And their results showed up a mysterious smooth object about the size of a golf ball.

Bigger on the inside: Aquarist Jenna MacFarlane from the Blue Reef Aquarium holds the gigantic oyster could it contain the world's biggest pearl. Something round in the middle: An MRI scan revealed what is likely to be a large pearl within the oyster FORMED AS A DEFENCE MECHANISM

Natural pearls are formed inside the shells of bivalve molluscs as a defence mechanism against a potentially threatening irritant, such as a parasite.

The mollusc creates a pearl sac of external mantle tissue cells and secretes the calcium carbonate and conchiolin to seal off the irritation.

Typical stimuli include organic material, parasites, or even the mollusc's own mantle tissue that has been damaged.

The commonly held belief that a grain of sand is the trigger is in fact rarely the case.

This secretion process is repeated many times, producing a pearl.

Natural pearls come in many shapes, with perfectly round ones being comparatively rare. If it were removed and identified as a pearl, it could be worth many thousands of pounds.

But experts will not explore the contents any further because it would mean the fossil would have to be destroyed.

The oyster – which measures about 7in across – remains at the Blue Reef Aquarium in Portsmouth, where it is kept securely and brought out only for lectures. Lindsay Holloway, from the aquarium, said: ‘It was discovered in the nets of a fishing boat which was dredging here in the Solent.

When the fishermen came back to port they thought it was real, but when they picked it up, cleaned it, and had a closer look they could tell it was a fossil. It had completely turned to stone.’ Jewellery expert Geoffrey Munn said: ‘To have a pearl the size of a golf ball would be exceptional. The biggest that have been recorded are about half that size.’ Following news of the discovery a company in Cheltenham called Cobalt, which provides state of the art scanning services to the NHS and private patients, volunteered to scan the oyster to see what was inside.



Overgrown: The Jurassic monster is displayed next to a normal oyster. The prehistoric mollusc is more than 100million years old Lindsay Holloway added: 'A member of the public called and informed us it was on display at a local fishmongers so we called them and they gave it to us to have in the aquarium.

'Oysters can be aged by annual growth rings on their shells and we have counted more than 200 rings on this oyster making it an extremely long-lived individual.

'It's obviously a million-to-one chance that it would contain anything but, if you were to go purely on the dimensions of the shell then you'd be looking at a golf ball-sized pearl.'