A four-year-old girl stunned paleontologists after she found a perfectly-preserved dinosaur footprint that dates back 220 million years.

Lily Wilder made the discovery on January 23 while walking along a beach in South Wales with her father and dog. The family was on their way to the supermarket when Wilder saw the footprint imprinted on a rock.

“It was on a low rock, shoulder height for Lily, and she just spotted it and said, ‘look, Daddy,’ her mother, Sally Wilder, told NBC News. “She is really excited but doesn’t quite grasp how amazing it is.”

At first, the family thought the print, which is just over 10 cm (4 inches) long, was scratched out on the rock by an artist.

But mother Sally was aware that similar footprints had been found along that piece of the coast before, so she posted about their discovery on social media.

“I found this fossil identification page on Facebook and I posted it on there and people went a bit crazy,” she told Wales Online.

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Shortly after, The National Museum of Wales was in touch with the Wilder family, and officials have since retrieved the print and put it in the museum.

Experts believe the footprint was most likely left by a dinosaur that stood about 75 centimeters (29.5 inches) tall and 2.5 meters (about 8 feet) long and walked on its two hind feet.

It is impossible to identify exactly what type of dinosaur left it, although experts typically classify the print as a Grallator.

Read more: Science Alert