GuidesMagazineShopBuy FossilsJoin Hunts
Buffer
Hi 
I would really appreciate it if somebody could give me some advice on what this might be.  I have spent quite a while looking myself but can't find anything similar.  It was found in a field where I normally find lots of Gryphaea and bits of Ammonite and Belemnite.
Many Thanks
Rich
IMG_6199.jpg  IMG_6200.jpg  IMG_6201.jpg 
Quote 0 0
Barrow Museum
It is the umbo of a rather large fossil Gryphaea (which I note you already have found here).  It looks from the photos like the smaller valve of a large example, typical of the Upper Jurassic clays which underlie a lot of Bedfordshire (Oxford or Ampthill Clay).  The strange convoluted shape  is where the major ligament holding the two valves together was attached.  The thin laminae are the successive layers of shell laid down as the animal grew.  These can reach 20cm or more across in some examples.  Being made of tough calcite, they weather up easily into the soil from the bedrock.  Your belemnite finds at this locality have survived for the same reason.  It would be interesting to see what ammonites have been found, as this would probably identify the age.
Quote 1 0
Buffer
Thanks so much for identifying that.  I have looked at more images of Gryphaea and it seems most just show the curved shells and very few if any really show this bit.  So I could never have worked that out.
Here is a piece of Ammonite I found in the same field.  Its small but I hope it helps.  Also I have included another photo of a large piece of shell I found at the same time.  I am now expecting this to also be a piece of a large Gryphaea but it does look a lot bigger and flatter than most of the ones we find.   Many Thanks Rich
IMG_6206.jpg  IMG_6207.jpg 
IMG_6208.jpg  IMG_6209.jpg  IMG_6211.jpg     


Quote 0 0
Barrow Museum
First, your big flatish shell is as you suspect, a piece of Gryphaea. They occur frequently in the higher parts of the Oxford Clay, and during the time of its deposition,  grew to immense sizes so I suspect that is the origin of your two specimens.  The species is probably Gryphaea dilatata

What I find particularly interesting about them, and other oysters in the Jurassic clay formations, is how they developed.  The larval stage was free-swimming, but to become adult, they needed to settle on the sea floor.  The soft muddy bottom was unsuitable and they would have perished in the soupy muddy substrate.  Instead, they needed to find something hard to which they could attach, keeping themselves above the mudline until such time as they were big enough for the larger, convex valve to tip over and effectively float on top of the mud.  At umbo (the point at which growth started) by the join between the two valves, there is often a small impression of what they first attached to - another Gryphaea shell or bivalve, or even a dead ammonite shell being typical.  This attached lifestyle sometimes suited them so much that they remained there for a long time and a large area of attachment is evident.  We call these curiosities "Xenomorphs".

The ammonite is more difficult, as it is a piece of one of the Perisphinctid family, which are rather similar thoughout the mid-late Jurassic.  If you label it "Perisphinctes sp", that would suffice.  Again, it could well have come from the same horizon as the Gryphaea, but as Bedfordshire has extensive deposits of Pleistocene "Glacial Till", it might have been dragged there in an ice sheet from farther afield, north or east.  The preservation appears to be phosphatic (from the photo alone) which would not be unusual in the Jurassic clays. Keep looking as I am sure more interesting material will turn up.
Quote 1 0
Buffer
Thanks for your reply thats really great of you.
I will put up one more item I found in Dorset and its definitely not a Gryphaea or an Ammonite!
Regards
Rich
Quote 0 0
Write a reply...


Discussions on fossils, fossil hunting, rocks, locations, and identifying your finds.
(C)opyright 2019 - UKGE Ltd and UK Fossils - Contact us