I discovered this fossil when walking my dog on common land in Surrey. - It was just laying on the surface of the path. - Approximately 70mm in diameter.
Alex & Singha,
It is an internal mould of a bivalve (a bit like a cockle).
As internal moulds go, your specimen is moderately distinctive, but I still can't put a name to it.
If you told us whereabouts in Surrey, that would help .
...A fine place.
For the unitiated:
'Chobham Common is the largest National Nature Reserve in the south-east of England and one of the finest remaining examples of lowland heath in the world."
The rocks were laid down in the Palaeogene period 34-55m years ago as mud, clay, silt, sand and gravel, in shallow seas. The stratigraphy comprises the Windlesham, Camberley Sand, and Bagshot Formations.
I'll have a think about which genus of bivalve you have,
though anybody else please feel free to jump in...
Thank you very much Mike. I have lived in Chobham all my life (62 years now !!!) - I spent my childhood roaming all over the common but never ever found anything like this before.
You have nudged me to find out a bit more about the area. .... Thanks again.
I have just found another one of these internal casts while walking my dog. - Only about 200 feet from where I found the last one. It is not quite as big and not as good condition but definitely a second specimen.
Interesting: not a one-off, then.
"Oystershell Hill on the north Chobham Common is said to be so named due to the fossilised oyster shells found there. But no examples are known to exist."
(oysters are bivalves)
Methinks you might want to get in touch with the webmaster David Stokes (see http://www.chobham.info/)
PS. There's also 'evidence of Mesolithic flint making' at Oystershell Hill (http://www.chobham.info/early_s_a_.htm).
As to which bivalve you have...
Here's an interesting antique print,
entitled 'BRITISH FOSSILS: Upper Eocene, Barton, Bracklesham & Bagshot Beds. STANFORD;1880'
We don't know the location(s) it may pertain to (these strata occur far outside Chobham Common), but it shows some bivalves which could be candidates for your specimen, especially:
- Cardita planicosta
- Cardium purulosum
- Cytherea trigonula
- Pectunculus pulvinatus
(I don't think Pecten corneus or Chama squamosa)
However, as I wrote before, it is difficult to make a close ID from an internal mould.
Today I found a third internal cast of a bivalve. All were found within a few hundred feet of each other. The first cast was in very good condition but the two found since have been smaller and in poorer condition.
Probably walked over them many times without realising what they were. After seeing the first one I now recognise them straight way.
I sent David Stokes photos and explained that I found them on Choham Common. He said he was no expert on fossils and would defer to you. I sent a second email to say maybe this could support his statement that fossilised oyster shells had been found on Oystershell Hill. He just referred me back to his Chobham.info website.
We have a very small museum in Chobham. They can use them if they ever do a display about the geology of the area. - Until then they can just sit on my window sill as a talking point.
Thanks for all your help and advice.
I know you said I was "getting my eye in" Mike but today I found another 5 casts .... they seem to leap out at me !!!
I now have a total of 8.
Hi Alex and Singha,
Fossil moulds of bivavles bivavle puzzled early naturalists. This preservational style is common in species of bivalves that had aragonitic shells. Unlike the more stable calcite shell found in oysters, araonite is routinely dissovled by pore waters passing through the rock, leaving spaces where the shell was formerly located surrounding hardened sediment core. The core is an internal mould, oftern known by the German name 'steinkern'. Steinkerns are solid objects that may fall out of the rock cleanly when it is broken open.
I hope this is interesting to you,
Thank you for your post,
Although I found these casts at Oystershell Hill it sounds as if they are unlikely to be from oysters. - If they are from aragonitic shells and these shells dissolve, it seems unlikely that I will be able to establish exactly which species I have found.
If I find actual shell fossils I will update the post. - I don't think it would be appreciated if I started digging on the Common, but I will keep my eyes open for anything laying on the surface. (All the fossils so far were laying on the surface, or showing through the surface.)
I find all the info I've received very interesting. - Thank you very much for your help.
Latest info ....
Since finding that first fossil in July I have found many more since, more than 20. I don't pick them up any more, I just leave them for someone else to find.
They have all been casts in varying condition. - Today I found the first one which still has part of the shell. Does this help any further identification?
It could possibly be a fossilised cockle shell. I used to have a few of these as a kid and I seem to remember that's what it was. I'm not an expert so just a guess at the moment from me.
Alex & Singha,
Persistence pays off!
I think this is looking like one of the possibilities I mentioned earlier - Cardita planicosta, now called Venericor planicosta.
Here's a super example from the Bracklesham Beds, Bracklesham, Hampshire.
If you look here, you'll see both the whole fossil and an internal mould
(search for 'Venericor planicosta', it'll be near the middle of the (long) page)
I think you'll agree the internal mould matches yours quite well.
So I think that is a reasonable ID, at least for now.
Both of those sites focus on the Bracklesham Beds, which is in the middle of the Bagshot Formation (mentioned earlier), stratigraphically speaking.
You will also find another pre-mentioned possibility on the brackbiv.htm page - Glycymeris pulvinata
(called Pectunculus pulvinatus in the old print I was referring to at the time). If you compare the two, you'll see how different they are in terms of their hinge dentition. That's an important factor in discriminating between candidates when trying to ID bivalves.
So "your mission Jim – should you choose to accept it…”, is to find an specimen that shows not just the shell but the hinge dentition!
I know I am asking a lot!
Maybe that will point to Venericor planicosta, or to Glycymeris pulvinata, or to something else (see that brackbiv.htm page again).
We then have to be careful. Just because we ID one specimen as a particular species, that doesn't mean the other specimens are the same species; you could be collecting multiple species. It is common for fossils to occur in assemblages. We'll cross such bridges if and when we come to them.
Keep up the good work; keep looking!
Thanks for all the info. I looked at the sites you recommended. The cast on the brackbiv.htm page is identical to the first cast I found. This would indicate Venericor planicosta as the front runner when it comes to identification.
A while ago you set me the task of finding an actual shell. I found part of a shell but you resolve one question and immediately set another task ... now I have to find a shell with 'hinge dentition'' !
I think I'll be taking my dog Singha for quite a few walks yet on my quest for the holy grail ... not that he's complaining. - I think it might be a while (if ever) before I am back to update this post !!!
Thanks again .... Alex.
Well, since you're the expert on these now, you have to do the hard stuff - so your groupies will be really impressed!
It may be off-topic, but I'd really quite like to see a photo of Singha, and preferably while she's sniffing out a bivalve, or holding such a find proudy in her mouth. (I don't suppose there's such a breed of dog as an oyster hound?!)
Hello Alex and Singha
A few images of the fossils similar to what created your negatives.
Good finds well done and keep them coming.
-- this is intended as a temporary posting --
Stupid me, I originally used the term 'internal cast' in this thread, where I should have been using 'internal mould'. I have edited my posts correcting those mistakes.
Please could other folks who have posted in this thread edit their posts to change 'cast' to 'mould'.
...This being in the best interests of people reading the thread in future - so as not to lead them into making the same error as me!
I apologise for the mix-up.