Fossilised Oyster deltoideum delta (liostrea delta) (Dorset) 14cm across
This fossilised Giant Oyster shell (deltoideum delta) measures 14cm across, and is from Dorset. This is an excellent example, and is in fact two shells, ‘back to back’ from the same colony. These fossilised bivalve shells are from the ‘Kimmeridge Clay Beds’ in Ringstead Bay. This is part of Dorset’s Jurassic Coast, a World Heritage Site. These fossils date back to the Late Jurassic period, so are approximately 155-160 million years old.
Bivalves have been in existence for around 500 million years. During the course of 500 million years tens of thousands of different species have evolved. Basically though they have changed very little. Examples that exist today are the cockles, mussels, and various types of oysters. Some bivalves form colonies attached to rocks or the sea bed. Others are buried under the sand or sediment. The oysters found today have changed very little from these fossils from the Dorset Coast. Some species adapted to fresh water while others required saline conditions. Their soft and delicate body is protected by the two sections of hinged shell. They fed by opening the shell and exposing a foot and siphon. This filters water borne particles some species extract nutrients directly from the sediment.