Mammoth Cave has fossils of between 30–70 extinct species of shark, depending on where you get your numbers. The remains of ancient sharks are usually just teeth, since sharks have cartilage skeletons, but the ancient sea floor where Mammoth Cave, Kentucky now lies had the perfect conditions to fossilize soft tissue. There is even a fossil of a shark’s brain down there. So even though Mammoth Cave National Park doesn’t celebrate Shark Week, I made this poster to celebrate Mammoth Cave, the longest cave system in the world.