Mature Modifications and Dimorphism in Ammonoid Cephalopods

The shell of an ammonoid is a kind of autobiography of the animal that once occupied it. Different parts of the shell tell different parts of the life history. The growth lines and the tiny intervals in between, along with the shape of the shell itself, record what was happening at the anterior end of the body. The septa and their sutures relate the tale of the other extremity.