A passer-by on Christmas Day found a meter-long shell on a riverbank in Argentina which may be from a glyptodont, a prehistoric kind of giant armadillo, experts said Tuesday.

A local man thought the black scaly shell was a dinosaur egg when he saw it lying in the mud, his wife Reina Coronel told AFP.

Her husband Jose Antonio Nievas found the shell beside a stream at their farm in Carlos Spegazzini, about 40 kilometers (25 miles) south of the capital Buenos Aires.

"My husband went out to the car and when he came back he said, 'Hey, I just found an egg that looks like it came from a dinosaur," she said.

"We all laughed because we thought it was a joke."

Nievas told television channel Todo Noticias he found the shell partly covered in mud and started to dig around it.

Various experts who saw television pictures of the object said it was likely to be a glyptodont shell.

"There is no doubt that it looks like a glyptodont," said paleontologist Alejandro Kramarz of the Bernadino Rivadavia Natural Sciences Museum.

"The animal became extinct thousands of years ago and it is very common to find their fossils in this region," he told AFP.

Glyptodonts are the ancestors of modern armadillos. They had big round armored shells and weighed up to a ton.

They lived in South America for tens of millions of years.

Kramarz estimated the specimen found by Nievas was relatively young at 10,000 years.