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Anon88
Evening all,

I’m still returning to the stream in Cambridgeshire and looking hard for that perfect ammonite.

Two finds I need your help with:

1. Rock which I suspect is vertebrae of ichthyosaur. Could you have a look and tell me whether I have maybe just found... a rock? 😃

2. I’ve found a second ammonite segment where there appears to still be the shell on the surface. I’m in the the river bed, and scratching the surface. Is there a chance of finding a full ammonite segment with the shell in this formation in the U.K? Should I bring a spade and start digging? Just getting some general advice for getting that perfect ammonite.

Both found in the Kimmeridge Clay formation.

Thanks for your help! Click image for larger version - Name: 8DA429F0-09A9-48C0-A97F-2C184662DD98.jpeg, Views: 42, Size: 259.78 KB Click image for larger version - Name: A8A5F6AE-3D3D-41DB-B66B-E88FD55C26C3.jpeg, Views: 43, Size: 194.75 KB Click image for larger version - Name: 1B67D4CD-B4C3-4353-B431-6E76F9F7CBD1.jpeg, Views: 42, Size: 296.70 KB Click image for larger version - Name: 47BE09F3-C404-43F4-A038-A92440DD235C.jpeg, Views: 44, Size: 271.64 KB Click image for larger version - Name: 7A002556-8E83-42FE-9B74-0823C00B66D0.jpeg, Views: 43, Size: 201.44 KB Click image for larger version - Name: 77316D94-8134-4AEC-9686-A0BFE8CC4CB1.jpeg, Views: 43, Size: 198.07 KB Click image for larger version - Name: 1A796B78-04C3-4740-9AE4-D0E78746C633.jpeg, Views: 41, Size: 226.53 KB
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Barrow Museum
Hi again!
You most definitely have an Ichthyosaur centrum.  It is a little eroded, but not a bad specimen at all.  Once upon a time I could have told you from which part of the Ichthyosaur's spine it came.  Maybe another correspondent can help out on this.
As for your ammonite...I suspect that a lot of your Cambridgeshire fossil finds in this Ice Age "Boulder Clay" or "Till" that you have been searching in, will have been scraped from fairly local to where you found them - I am thinking of some previous entries in this website.  Alternatively, it is not impossible that what you have found actually came from the Upper Jurassic bedrock (check out the Geological Survey map of the area).  So, they will be Jurassic (and often Upper Jurassic) clay species.  Your latest find, of an incomplete ammonite whorl, does remind me of genera that are common around the Oxfordian-Kimmeridgian boundary (that would be the top of the Ampthill Clay and the base of the Kimmeridge Clay).  But sadly, it is just too incomplete to be a positive identification.  Look up images of Ringsteadia, Pictonia, Rasenia.  The bigger they get, the smoother the shell, and all the adults look pretty much the same.  The iridescent shell is original aragonite ammonite mother of pearl.  This is only preserved when the ammonite was buried and hermetically sealed, as in a fine grained clay, which is one way I suggest that yours originated from the formations mentioned.
I'm not sure that digging with a spade would pay dividends.  You could give it a try, with permission of course.  But do investigate any temporary exposure in building developments, ditching operations and the like.  There you will find fresh and probably more complete material.  That elusive perfect ammonite can't be far away.
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Anon88

Thanks for the answers above, I will read around them and do some learning. Great detail as always!

In this small stream, there are clear pockets of shingle (not very wide or long) dotted along it. I was picking stones for my kids to throw into the stream when I noticed all the bivalves amongst the shingle and I’ve been going there once a month or so. (The initial sandstone Ammonite and Clay/mud nodule was from another location 20mins away). It runs along a forest on one side but the sides of the stream bank are near vertical and 2m deep, it looks like it gets cleared by machines but I would say not recently. I don’t know how the shingle pockets came to collect like this. The fossil explorer app gives this location as Kimmeridge Clay as the bedrock but being in a stream, I’m unsure what the geology is doing. It is definitely a natural stream as opposed to farm drainage ditch.

Yes I will keep going until I find that elusive ammonite, so far just segments. Also going to try Grafham water in the summer.

If I find another Ichthyosaur centrum I can make a set of earrings for my wife, she will be delighted. 

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