Ammonites with uneven coils like these are called heteromorph ammonites. The shells of this ammonite were coiled tightly when it was young and wider as it got older. Why? No-one is really sure but this must have had a profound impact on how the animal lived. It is thought that Scaphites probably floated in the water filtering it with adapted tentacles in order to capture microscopic food. But as no soft parts have been found so far, we may never know.
Find out more about ammonites on the molluscs pages.