The earliest ammonites appear during the Devonian, and the last species vanished in the Cretaceos-Paleogene extinction event. Only the last and largest chamber, the body chamber, was occupied by the living animal at any given moment. As it grew, it added newer and larger chambers to the open end of the coil. The creatures that these fossils come from belong to the family of cephalopods, which are creatures like octopus that live in our oceans today.