Tucked deep inside the winding, limestone labyrinth of Mammoth Cave, scientists just uncovered something unexpected: a shark. Not a living one, thankfully—unless you’re into waking nightmares—but the fossilized remains of a long-extinct species that swam here over 340 million years ago.The shark, Macadens olsoni, turned up in Kentucky’s Mammoth Cave, inside rock that used to sit at the bottom of a tropical sea. Back then, the whole region was submerged. Now it’s home to over 426 miles of explored passageways and one of the richest fossil collections in the U.S., especially for ancient fish.“This discovery is a remarkable addition to our understanding of ancient marine life,” said Barclay Trimble, superintendent of Mammoth Cave National Park. He called it a reminder of how valuable these underground records are for science and education.What We Know About the Shark FossilThe shark may have been small, but it was fully armed. Its curved tooth whorl helped it crush mollusks, worms, and any soft-bodied and unfortunate prey. Researchers believe it inhabited reef-like habitats teeming with coral, crinoids, and creatures that resembled a mix of alien and pincushion-like forms.The name Macadens honors Mammoth Cave. Olsoni is named after Rickard Olson, a retired park scientist who spent years helping to catalog these fossils. The team behind the discovery includes researchers from the National Park Service, the Smithsonian Institution, and Mammoth Cave’s own paleontology program.They also reclassified another shark, now known as Rotuladens, with a similar mouth setup and the same ancient address. It’s more proof that the Mississippian Sea was teeming with sharp-toothed weirdos.More than 70 extinct fish species have been identified inside Mammoth Cave so far. Some are still being studied. Others haven’t even been named. It’s not just bats and darkness down there. It’s an entire lost world, fossilized into the walls.And while Macadens olsoni won’t be starring in a reboot of Jaws, it’s proof that deep inside the Earth, the past isn’t gone. It’s just buried. Deep, deep inside a vast cave system right here in the U.S. of A. The post An Ancient Shark Fossil Was Found Inside the World’s Longest Cave System appeared first on VICE.