I recently discovered a fairly large fossil in a place I have walked many times through the years. How I could have not seen it before is a mystery, but finding it is a gift. I believe it to be an ammonite fossil, because of its spiral shape. I read that ammonites are perhaps the most commonly known fossils, in part due to their longevity as a species. They lived in shallow waters from 240-65 million years ago. The last died at the same time as the dinosaurs became extinct. Some ammonite fossils are tiny, while others may be larger than platters.