Fossilized ammonite

Ammonites

Ammonites were free-swimming molluscs of the ancient oceans, living around the same time that the dinosaurs walked the Earth and disappearing during the same extinction event. They came in a range of sizes, from tiny species only a couple of centimetres across, to large ones reaching over two metres in diameter. The animal would have lived in the last and largest of a chain of spiralled chambers. Filling these chambers with fluid or gas allowed the ammonite to sink like a stone to avoid predators, though ammonite shells with toothmarks on them have been found, evidence that it didn't always work. Fossilised shells are usually, but not always, beautiful spirals.

Scientific name: Ammonitida

Rank: Order

Common names:

Snake stones

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Behaviours

Discover what these behaviours are and how different plants and animals use them.

Additional data source: Animal Diversity Web

When they lived

Discover the other animals and plants that lived during the following geological time periods.

What killed them

Cretaceous-Tertiary mass extinction Cretaceous-Tertiary mass extinction
The Cretaceous-Tertiary mass extinction - also known as the K/T extinction - is famed for the death of the dinosaurs. However, many other organisms perished at the end of the Cretaceous including the ammonites, many flowering plants and the last of the pterosaurs.

Fossil types

Learn more about the other animals and plants that also form these fossils.

Trace fossils Trace fossils
It's not only the actual bodily remains of dead animals and plants that can become fossils. Things created or left behind by animals can also fossilise, such as their footprints, burrows and dung.

Fossil Folklore

Ammonites have featured it our folklore - learn more our ancestors beliefs before we understood fossilisation and evolution.

BBC News about Ammonites