Ammonites were shelled cephalopods that died out about 66 million years ago. Fossils of them are found all around the world, sometimes in very large concentrations.
The cool thing about the Cleoniceras Ammonite is the morphology of the tissue wall they build between the chambers is not just a smooth curved wall. Instead it has a bizarrely complex fractal 3-dimensional shape. These patterns are called “suture patterns” and they mark the intersection of the septum walls with the shell.
