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Recognising ammonites
Ammonites are some of the easiest fossils to recognise because most of them have a spiral shell.
The spiral is always in a flat plane. This is usually enough to make
it easy to separate an ammonite from a gastropod (snail) shell. The number of overlapping spirals is usually much larger than those of gastropods. Goniatites have fewer coils and tend to be more bulbous.
(Left and below) This goniatite (Goniatites globostriatus) shows the typical V-shaped suture patterns.
Septal sutures
(Above and right) Harpoceras is a smooth, tightly coiled ammonite from the Lower Jurassic. It has a narrow shell.
Septal sutures on ammonites can form very complex patterns. Each species has a different suture pattern, making this a good form of identification.
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