It’s Fossil Friday, and we’re celebrating amazing ammonites!

The extinct mollusks known as ammonites inhabited the planet for more than 300 million years—almost twice as long as dinosaurs—before disappearing in the mass extinction event more than 65 million years ago. As many as 10,000 species may have existed, ranging from tiny organisms that measured only a fraction of an inch across to formidable animals more than 2 feet (0.6 meters) in diameter.

Learn more about these extinct cephalopods