Christine Clark, 64, was hunting for fossils during a Boxing Day walk on Holy Island, Northumberland when something caught her eye.
A tiny pebble seemed to be "smiling at me", she said. "It looked like someone's fake teeth."
She took it home and posted it to a Facebook fossil identification page.
Thousands of likes and comments later, others seemed to confirm her suspicion that it was, in fact, an ancient marine animal.
Christine holidays every year to Northumberland with her husband Gerard where, she said, they regularly go hunting for Cuddy's beads on the Holy Island.
