Scientists have found ancient nail tooth shark fossils deep inside Mammoth Cave in Kentucky, revealing new information about a mysterious group of extinct predators.

The surface of Mammoth Cave National Park encompasses about 80 square miles. No one knows how big the underside is. More than 365 miles of the five-level cave system have been mapped, and new ...

We’ve now got a slightly clearer picture thanks to the discovery of a small but mighty ancient shark species found fossilized in the depths of the world’s longest cave system, Mammoth Cave.