Ammonites existed over a massive span of time, appearing first around 450 million years ago and surviving up until around 66 million years ago. Most ammonites disappeared around the same time as the extinction event that killed most of the non-avian dinosaurs, though some survived a bit longer.
The name “ammonite” refers to the Egyptian god Ammon, who was often shown wearing the horns of a ram. The shells of ammonites resemble a spiraling ram’s horn, so the name “ammonite” was used to refer to them.
Before it was known that ammonites were molluscs, their fossils were thought to be snakes that had turned to stone, and they were sometimes referred to as “snakestones”.