They both have unique skin that is covered in tiny modified teeth. These teeth reduce drag and make the shark swim faster. All sharks and rays have teeth – even the ones that eat plankton!

In the depths of the world's longest cave, researchers have uncovered the fossilized remains of a 340-million-year-old shark.

The shark’s distinctive teeth were identified as a new-to-science species during a Paleontological Resource Inventory at Mammoth Cave National Park in southern Kentucky this year. The inventory ...