Experts at London's Natural History Museum have been asked to help identify a mystery fossil of a sea creature discovered in County Durham.
The fossil of the snake-like marine animal was found by a father and son on a nature walk organised by Natural England at a quarry near Thrislington.
Natural England said the find was like nothing ever found in the area before.
About 250 million years ago the surrounding area was covered by a body of water known as the Zechstein Sea.
Joe Davies, Natural England's local outreach advisor, said the fossil was discovered in "marl slate" deposits close to where remains of ancient fish have been unearthed previously.
But he said he was "amazed" by the latest find.
He said: "This fossil is an unusual discovery as the animal looks nothing like any of the fish that have come from the fossil-bearing marl slate seam before.
"What has been discovered is the remains of a creature that appears to have had a long, narrow body. My first impression is that it looks like a species of snake or an eel-like creature."
Photographs of the fossil have been sent to the Natural History Museum in London in the hope that experts there can identify the mystery creature.
Mr Davies added: "Geological sites of the quality and importance of those to be found in north-east Durham are few and far between and discoveries of fossils like this one give a unique window on our past."