strange fossil from Bailly, France

At Bailly, near Auxerre, southeast of Paris, the river Yonne runs at the foot of a steep limestone escarpment. Most of the limestone used in the building of Paris came from this escarpment, leaving large caverns, which are now used as cellars for maturing wine. Last year we visited these, and when we had finished the tour we walked up the road to the top of the escarpment. The road is cut into the escarpment, with a fairly high bank on the uphill side. Near the top I found a pile of loose pieces of limestone in the gutter, and examined them out of curiosity. One had a very strange fossil, which is unlike anything I have seen before, either animal or vegetable. It is shaped roughly like a gherkin, and the inside appears to have been empty, apart from a row of very strange structures which appear to have formed a spiral. It has broken roughly along the centre line, and the cross-section of these internal structures looks like a line of some Asian writing along each side.

Several photos of the fossil are shown at the reference below, and I would be very grateful if anybody can tell me what it is. I have already posted this message to sci.geo.geology.

I apologise for my very primitive website

I'm no expert on Cephalopods, but those sure look like an ammonite sutures to me. Might be a cross section of a straight cepholopod such as _Baculites_ rather than a cut across the curve of a coiled animal. Hard to tell from the pictures which don't give a lot of feel for depth.

If anyone else tells you something different, they're probably right.

Roger

Nice specimen, excellent photos.

I agree with Don. Looks very like an ammonite to me. From your description I had thought that it was probably a spiriferid brachiopod from the late Palaeozoic but it's obviously not, Much more likely a Mesozoic ammonite.

I am sorry that I cannot be more specific but I am not too familiar with Mesozoic fossils.