Ammonoids lived as nektonic predators in marine environments. Their diversity, and the widespread nature of fossils, has led to them being used as biostratigraphic markers, especially during the Jurassic and Cretaceous.


  • Phylum: Mollusca
  • Class: Cephalopoda
  • Subclass: Ammonoidea

Diagnostic features

These are the features that will help you to identify fossils as ammonoids, and that you should be attempting to label on a sketch.

  • Aragonite shell
  • Planispiral
  • Septa
  • Suture
  • Chambers
  • Siphuncle

Stratigraphic range

Devonian to Cretaceous