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Ammonites inhabited our oceans for 440 million years, from the Devonian to the end of the Cretaceous period (66 million years ago). They are very varied and abundant cephalopod molluscs. Cephalopod animals are characterized by having tentacles on their heads –hence their scientific name, which literally means "head with feet"–, like the current octopuses or squids.

Ammonites had a soft part and a hard part, their shell. This was made of aragonite and was divided into 2 parts: the Phragmocone, where the empty chambers of the ammonite are located, and the Body Chamber, where the soft part of the ammonite was housed, that is, the organs and the animal itself. However, the Body Chamber was not as mineralized as the Phragmocone. This is the reason why it rarely fossilized. Although we currently find only the shells of ammonites, their approximate appearance was as follows:


Ammonites regulated their flotage thanks to an organ called siphon, the only one located inside the Phragmocone, which injected or extracted water and gas from its shell to ascend or descend. This was very useful, because the ammonites lived in the depths during the day and rose to the surface at night.

Currently, we know that they lived both near the coast and in open oceans, at a depth of up to 500m. Regarding his diet, it is not yet known exactly. However, a finding in 2011 revealed that it could be composed of plankton. We leave you at the end of this entry a file with this study, carried out by researchers from France and the United States.

It is also known that their main predators were mosasaurs, which could have caused evolutionary pressure on some species of ammonites, which evolved into larger forms. This is what happened with the giant fossil ammonites of the species P. seppenradensis, whose impressive shells could measure 1.8 meters in diameter (three times the average size) and which evolved from a smaller species: Parapuzosia leptophylla.

"In a hostile environment surrounded by marine reptiles that reached tens of meters in length, the smallest ammonites were easy prey for mosasaurs that could easily gobble them up. For this reason, after tens of generations and thousands of years, the specimens of smaller ammonites became scarcer and they died eaten, while the larger ones were more difficult to swallow and therefore more often survived encounters with their predators".


As a curiosity: there are ammonites that have fossilized thanks to the pyritization process or have fossilized in opal due to the sediment in the area. The result is these fossils with fascinating colors:

On the left: Pyritized Pleuroceras spinatum ammonite (Toptrilos Catalogue)

On the right: Opalized Cleoniceras besairei ammonite (Toptrilos Catalogue)

After more than 400 million years inhabiting our oceans, ammonites disappeared at the end of the Cretaceous. The effects of the intense volcanic activity of this period, together with the impact of the asteroid in Yucatan, caused an acidification of the waters of the oceans. Ammonite hatchlings failed to survive, as the acidic water destroyed their fragile calcium carbonate protoshells, and those of the adults were also severely damaged.

We hope that this information has been as fascinating to you as it was to us. If you want to continue learning and see specimens of ammonites, you can visit our catalogue. With respect and enthusiasm, we share with you our great passion, always offering the best quality, 100% natural, without restorations.

Study about plankton in ammonites
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