What is an Ammonite ?

                                                        A Ammonite Fossil (Cardioceras sp).                                What Ammonites might have looked like millions of years ago.

Ammonites are one of the most well known and most common fossil found and collected all over the world. The well recognisable spiral and ribbed shape shell as pictured above. These animals lived in the prehistoric seas around the world between 240 - 65 million years ago. These creatures also became extinct along with the dinosaurs 65 million years ago. The name "Ammonite" comes from the Ram-horned Greek god: Ammon. Ammonites belong in the predators group called cephalopods, this makes them related to the living cephalopods like nautilus, cuttlefish, squid and octopus (pictured below).

                                                                            Nautilus                       Cuttlefish                           Squid                             Octopus

Ammonites evolved rapidly during the time it was alive. The Ammonites first evolved from small coiled squids called Ammonoids. The animal lived in the body chamber the last-formed part of the shell. The earlier chambers were filled with gas and liquid which could be added or extracted through the siphuncle. The liquid that was taken in the chambers increased the density of the animal causing it to sink. When the liquid is removed then the animal will rise. The ammonite shell opening is called aperture. The shells that were tightly coiled are called involute, the loosely or open coiled shells are called evolute. The area in which the animal was living is called the body chamber. The Ammonite shells were divided into chambers separated by partitions or septa. The septas strengthen the shell and prevented it from crushing from the surrounding sea pressures. The septas formed intricate lines called sutures (pictured below). The Ammonite shell had a thin strand of soft tissue, the siphuncle,passed through the septa and linked each chamber.

                                                                                                  Ammonite with sutures visible.               Close up of sutures.

The ribs of an Ammonite helps to determine the species. There are many different species of Ammonites all over the world and many new species are being found all the time.

                                                      Polished Ammonite                   Sliced and polished Ammonite.                   Crushed Ammonite on a shale slab.

The Nautilus is the closest we can get to seeing what ammonites once looked like. The shell has the same structures as Ammonites (pictured below).

Here is a picture of a death bed of Ammonites: