Ammonite

Telling time

Many ammonites evolved rapidly through time and therefore certain species can be used to identify very specific periods of time which are known as zones. This specimen, Echioceras raricostatum, is the highest zonal ammonite in the Black Ven Marls. It marks the Raricostatum Zone which is also the youngest zone in the Sinemurian Stage.

So if someone talks about rocks, anywhere in the world, being within the Raricostatum Zone, they know that they are the same age as those at Charmouth.

Find out more about ammonites on the molluscs pages.

Common name

Ammonite

Scientific name

Echioceras raricostatum

Type

Molluscs > Cephalopods


Strata

Belemnite Marls

Time period

Lower Jurassic

Age

c. 201-174 million years

Where found

Charmouth

Found by

Unknown

Museum

Bridport Museum

Accession number

BRPMG 1170