These unusual fossil shells are all found in the same ares in conjunction with several other types of ammonites. The Kosmoceras can be smooth or bumpy on the exterior shell and sometimes the shell comes off, leaving an iron pyrite layer underneath.
Ammonites were free-swimming mollusks of the ancient oceans, living around the same time that the dinosaurs walked the Earth and disappearing during the same extinction event. They came in a range of sizes, from tiny species only a couple of centimeters across, to large ones reaching over two meters in diameter. The animal would have lived in the last and largest of a chain of spiraled chambers. Filling these chambers with fluid or gas allowed the ammonite to sink like a stone to avoid predators, though ammonite shells with tooth marks on them have been found, evidence that it didn't always work. Fossilized shells are usually, but not always, beautiful spirals.
All of these fossils are very rare and must be handled with care.
This fossil requires special care - exposure to water and other chemicals, such as cleaning products or aerosols, will damage it over time. If you polish the stone, use a dry cloth only, or an air duster that does not contain any disinfectant or other chemicals.