Fossilised Oyster deltoideum delta (liostrea delta) (Dorset) 12.8cm across
This fossilised Giant Oyster deltoideum delta measures 12.8cm 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, part of Dorset’s Jurassic Coast. 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 this time tens of thousands of different species have evolved. Basically though they have changed very little. Examples that exist today are the cockles, mussels scollops and various types of oysters. Some bivalves form colonies attached to rocks or the sea bed. Others are buried under the sand or sediment. Todays oysters have changed very little from these fossils from Dorsets Jurassic 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 feed by opening the shell and exposing a foot and siphon. This filters water borne particles some species extract nutrient directly from the sediment.