Fossil Oysters 3

This is the third in the series featuring fossil oyster shells. The photographs are of Deltoideum delta (also known as Liostrea delta) from the Upper Jurassic Period Kimmeridge Clay at Ringstead Bay, Dorset, UK. The most noticeable feature of this pair of matched valves is the way in which the outline shape differs from the examples already shown in Fossil Oysters 1 and Fossil Oysters 2. Here the shell has a basically regular almost tear-shaped outline in contrast to the others shown in the previous Postings. However, it has in common with them a number of smaller attached oyster shells. Again, two on the left valve (part of the settlement substrate); and one on the right valve which had settled upon it in turn.

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Fossil Oysters 2

This is the second in a series of Postings about fossil oysters. In this Post there are detailed photographs, taken from all angles, of a fossil oyster found with the two halves still in position, on the beach at Ringstead Bay, Dorset, UK. It’s a specimen of Deltoideum delta, and in common with many species of present day oysters such as Ostrea edulis, the shells of this extinct species can exhibit a wide variety of variations – in shape, size, and many other characteristics.  The most noticeable feature of this particular specimen is the attachment of six other oyster shells – four to the outer surface of the left valve and two to the exterior of the right valve.

The left or lower valve would have been the original surface of attachment for the spat oyster as it settled after a brief larval life. Old oyster shells are a preferred settlement substrate. It is not possible to say whether the oyster shells on which it settled were empty or still occupied by the living animals. Eventually the oyster would have overgrown and incorporated the other oyster shells as it developed.

On the other hand, the oyster shells attached to the outer surface of the right or uppermost valve would have settled on it only when the oyster had itself reached maturity.

Additionally, the ligament – which is the horny proteinaceous (conchyiolin) structure that connects the two halves of the oyster at the dorsal margins of the shells in life – seems to have been fossilised along with the calcareous shell valves. The shells have a brittle texture and an almost porcelain-like appearance. There are multiple cracks and fractures, as is common with the oyster fossils from this locality, and a certain flattening of the valves seems to have occurred so that there is now very little space indeed between the the two halves of the oyster.

[At the bottom of this posting is a slide show of the oyster shells photographed with a reference scale to indicate size. These pictures have a minimum of labelling. If anyone should want more information about these fossil oysters, please do not hesitate to get in touch.]

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COPYRIGHT JESSICA WINDER 2013

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Wild Oysters on the Queensland Coast Part 2

Reblogged from Jessica's Nature Blog:

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The oysters that I found on the rocks at the northern end of Three Mile Beach in Port Douglas were so different from the ones I had seen at Cape Tribulation that I wondered if they were oysters at all.

The identification of Rock Oysters of the Saccostrea Group in the Indo-West Pacific is a fairly hot topic and some very interesting work was completed a few years ago to try and sort out what is what.

Read more… 254 more words

Wild Oysters on the Queensland Coast Part 1

Reblogged from Jessica's Nature Blog:

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I have written a lot about the natural variations in oyster shells belonging to the British Native, Flat, or European Oyster, Ostrea edulis Linnaeus. However variable these shells may be, it is always possible to identify the shells as belonging to that species, and to distinguish them from other species.

In Australia and the Far East, the oysters that grow wild and naturally on the tropical shores include several species of…

Read more… 270 more words

Black Oyster Shells on the Beach 3

A most unusual form of very thick-shelled burial-blackened oyster shell right valve. It looks almost like a set of nesting bowls. It is clearly an old shell – it lived a long time – but it failed to grow much in diameter. All the energies were diverted into increasing the thickness of the shell rather than widening it. This kind of oyster is termed a ‘stunter’. When found in catches from commercially-fished natural or wild oyster beds, this undersized but mature oyster would typically, be returned to the sea bed to grow on. However, they never do achieve the minimum legal size to catch and market. This means that they can breed and potentially produce more specimens of ‘stunters’ should this growth anomaly be inheritable.

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Black Oyster Shells on the Beach 2

These Black Oyster Postings are about the multiplicity of variations in shells of the British Native Oyster, also known as the Flat or European Oyster, Ostrea edulis Linnaeus. Sometimes, as in this Posting, the shells are photographed just as found, in situ, on the beach. In other posts, the shells have been collected for more detailed examination and have been photographed indoors. By understanding the range and variety in macroscopic differences, and the causes of the variations, it is possible to interpret more accurately the meaning of variations in archaeological and palaeontological specimens of oyster shell. These posts can therefore be considered as a database for oyster variation – and a starting point for discussions and understanding.

COPYRIGHT JESSICA WINDER 2013

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Black Oyster Shells on the Beach 1

An example of a black-stained oyster shell, Native or Flat European Oyster (Ostrea edulis Linnaeus), washed ashore at Rhossili Bay on the Gower Peninsula. The colour is due to prolonged burial in anoxic sediments.

For more information about this phenomenon see:

Colour variation in oyster shells 1

and Black Oysters at Rhossili Bay.

COPYRIGHT JESSICA WINDER 2013

All Rights Reserved