Fossil tooth spiral

Fossil tooth whorl of ancient shark.
© Chip Clark/Smithsonian Institution

This fossil tooth whorl of the ancient shark Helicoprion, dates back 290 million years. For a long time, people didn't know what the shark looked like—but, thanks to a CT scan of a fossil, researchers finally put the pieces together in 2013. Read more about this story in our great white shark overview, and learn more about top predators like Helicoprion in the Ocean Over Time section.