Ammonites are extinct marine animals related to modern squid, octopus and nautilus. They lived in ancient seas for an incredible span of time, first appearing around 400 million years ago and becoming especially abundant during the Jurassic and Cretaceous periods before disappearing around 66 million years ago. Their distinctive coiled shells often preserve beautiful ribbing, chambers and natural patterns, while their rapid evolution makes them important fossils for helping geologists date ancient marine rocks.
