Live bacteria believed to be 11,000 years old were found in the intestines of a mastodon, researchers said. It was the first documented discovery of live bacteria in an extinct species, they said.

However, some experts were skeptical.The single-cell organisms were found in a mastodon unearthed in pieces in a peat bog at a Newark, Ohio, golf course, researchers said.

"To my knowledge, bacteria that old haven't been recovered from any higher organism," said Daniel Fisher, a University of Michigan geological paleontologist who analyzed the intestinal contents.

Fisher said Thursday that older bacteria might have been found in soil or fluids but none in connection with a mammal. It was unclear if the bacteria had been dormant.

The find could provide clues to bacterial evolution as well as mastodon diets, he said.