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This knobbly ammonite, Mantelliceras, is the most common and most distinctive fossil found in the Lower Chalk in East Devon. This rock layer is known as the Cenomanian Limestone and spans about six million years. Yet it is only about one metre thick in most places, and as a result, there is a lot crammed into it! This is known as a ‘condensed sequence’ where either sediment was deposited slowly, or erosion has taken place, removing some of the sediment after it was laid down. Both apply to the Cenomanian Limestone but as a result, it is very rich in all kinds of fossils.
Find out more about ammonites on the molluscs pages.