This Post features one of many fossil oysters that I have picked up on the beach over the years because they were in some way unusual and because of my interest in the variation in oyster shells from both present day populations and from samples of oyster shell from archaeological excavations.
I am particularly interested in the range of sizes, shapes, and the evidence for both encrusting or infesting epibiont organisms. These features reflect the variability in a species which can be a response to the immediate natural environment of the oyster during life and the effect of taphonomic processes (things that happen to the shell after the death of the animal) on the appearance of the shell, whether it be fossil, archaeological or recent in origin.
The paired shells of the oyster in this specimen from Ringstead Bay in Dorset, UK, were still together in situ. There was very little internal space between the right and left valve – as is typical for the species which is Deltoideum (Liostrea) delta. It is a common find in the Kimmeridge Clay of the Jurassic Period that outcrops on the beach. The left valve had another broken oyster shell attached to it externally. This would have been the substrate on which the spat oyster had originally settled.
On opening and separating the two valves, it was possible to examine the hinge or ligament area. The ‘scar’ where the flexible ligament had conected the two shells showed many growth lines indicating some age had been achieved prior to death. Petrified material attached to the ligament scar, fragments on both valves but more noticeable on the left valve, could be the fossilised remains of the ligament itself.
COPYRIGHT JESSICA WINDER 2013
All Rights Reserved