Ammonite shells Computerenhanced engraving of an assortment of ammonite species Side and front views of the spiral shells are seen each with many chambers Ammonites are a type of extinct cephalopod mollusc that resembled a squidlike animal within a coiled shell The many chambered shell protected the delicate organs of the mollusc and was also used for buoyancy when some of the chambers were pumped full of air Ammonites lived from the Devonian period approximately million years ago to the end of the Cretaceous period million years ago Engraving taken from Ernst Haeckels famous treatise Art Forms of Nature