Bivalve xenomorph of ammonite

An ammonite on an oyster?

In very muddy seas, oysters need a hard surface to attach to when they start life, otherwise they are simply smothered by the mud. In the Oxford Clay sea, dead ammonites lying on the sea bed provided a good starting point. As the oyster grew, it made an exact copy of the original ammonite in its own shell – known as xenomorphism.

Find out more about bivalves on the molluscs pages.

Common name

Bivalve xenomorph of ammonite

Scientific name

Gryphaea

Type

Molluscs > Bivalves


Strata

Oxford Clay

Time period

Upper Jurassic

Age

160

Where found

Furzy Cliff

Found by

Found by E F Coetzee in 1979

Museum

Dorset County Museum, Dorchester

Accession number

DCM.G.03382