Ammonites lived during the periods of Earth history from the early Devonian period(about 440 million years ago) to the Cretaceos period (about 65 million years ago). Ammonites are invertebrates, meaning they have no backbone and are distant relatives to the living sea creature known as the nautilus, squid, cuttlefish and octopus.  They became extinct at the end of the Cretaceous Period at roughly the same time as the dinosaurs disappeared.