The skin, which is at least 286 million years old, was found at a quarry and cave system called Richards Spur. Researchers think animals fell into the cave system and were preserved by oil that seeped in, encasing them.

Researchers have discovered a fossilized skin they say is the oldest on record.

The crocodile-like skin, which is at least 286 million years old, was preserved in an ancient, infilled cave in present-day Oklahoma. The find could help unlock evolutionary mysteries and is an important clue from a time when some animals were transitioning to life on land.

“Finding such an old skin fossil is an exceptional opportunity to peer into the past and see what the skin of some of these earliest animals may have looked like,” Ethan Mooney, a graduate student at the University of Toronto and a lead author of the paper, said in a news release.