10% survived an extinction event during the Permian, flourished during the Triassic period then died, leaving only one species. They began to thrive again from the Jurassic period until the end of the Cretaceous period when all species died.
They lived in shallow waters, moving by jet propulsion and proper little predators they were. Mollusks, fish and other cephalopods would be stalked and chomped after the tentacles grabbed the prey drawing it to the jaws located at the base of the tentacles between the eyes. But there's always something bigger and hungrier, mosasaurs and other marine reptiles sank teeth into the shells and extracted the squid like bodies. The empty shells then sank to the sea floor to be buried in mineral rich sediment.
While ammonites are found every where, only in one place can the beautiful iridescent form of the fossil be found. Southern Alberta, Canada in the Bearpaw Formation which is a large marine formation of mostly shale approximately 70 to 75 million years old. The photo above gives some idea of the size of the ammolite fossils.
Ammolite is grouped into two general categories. Fractured ammolite as in the photo above is named for its stained glass appearance from the fossil being crushed in the sediment.
Sheet ammolite, on the other hand has little or no crushing so the colour is a solid mass of intense iridescence and is made into beautiful jewellery that constantly changes as the angle of light changes. The best stones can rotate 360 degrees giving a full display of colour. As with opals, the thicker the layer (3 to 10 mm) and the size of the piece reflects the price.