These beautiful fossils are millions of years old; they are thought to have gone extinct around the time of the end of the Cretaceous period, roughly 66 million years ago. Ammonites were shelled cephalopods. All of them had a chambered shell that they used for buoyancy. These are 6-7.5" in diameter. These are one of a kind gifts of nature. Each is unique so the pictures are representative only. A small plastic stand is included.