Again I can only reiterate Clem. Thankyou very much for posting this picture, some of us had been searching for this image for months, I admit that I had practically given up!
Now we can see it, I must admit to being somewhat puzzled by the image. Could the black spur at the rear of the main black 'mass' be a trace of the point of attachment of the siphuncle? I can see no trace of the aptychus in this specimen, though I do not know if they are known from Sigaloceras. I'm not convinced those black threads are 'tentacles' as the caption states, though I suppose they could be muscles of some kind.
To me the "threads" at the back could be retractor muscles or pieces of the membrane between the mantle and the shell. But I'm not convinced that some other organism or process isn't responsible. It's an interesting fossil but it does seem to have "re-written the history books", presumably because it is so ambiguous. The collectors hoped to use ultraviolet light to see things differently, but to my knowledge the results were never published.
Ok, would someone mind attaching a few labels to that picture .... 'twould help in interpretation. Has anyone contacted either Neville Hollingworth or Jason Hilton to find out what is up? Maybe they'd post something online ... an update ... another couple of pics (higher res). Maybe they wouldn't ... but if they don't then we'll talk and gossip about them online until they do (the power of media).
Someone help me with that picture! If the phragmocone is full of gas chambers and you can see a little light thru it, then the light parts are empty space, so the back part of the living chamber is empty, and the front part is filled with the remains of the mantle and tentacles. Or are the light parts the animal? or am I just not seeing it right? I'll blame it on the 60's.
I sent pleading letters to Messrs. Hollingworth and Chilton (and the third co-author, Leslie Cherns) many months ago, to no avail. The ambiguity of the images they obtained might account for their quiet since the 1999 PALASS conference in Edinburgh, when they announced the thing.
I'd like to see some (provisional) labels stuck on that thing, myself. I'd also like to know what process was used to obtain the image we're looking at.
Hope this helps. Oh, in my previous posting I meant to say I don't think it has rewritten the history books. As far as I can tell the fossil "sunk without trace" in the literature. Very sad, because it is indeed very curious.
It seems a crying shame that nothing has been subsequently published; Clem, perhaps we should compose a nice wee letter online, then send it to them and see if we can get them to respond with more information (like it is pretty whiz-bang exciting stuff), directing them to this site.
Neale, ta muchly for those labels. Wouldn't it be exciting if they took cores from the sample to see if there's anything really odd therein, or subject the ammonite to some more whiz-bang less-invasive image-taking something-or-other (3D CT, computer animation or what have you; anything but a hammer).
The thing that I've marked with a great big, dirty line ... this is rather interesting. At the rear of the chamber/body, a position that I'd expect one of gonad, stomach caecum, ???gizzard (and maybe even 'gizzard plates' .... we're back on this subject again), or something to do with the siphuncle/gas/fluid/haemolymph storage/production, or vacuum generation (pressurised or vacuum in these things??) .... maybe even some sort of posterior sucker to hold the animal within the shell (is this where suckers first evolved ... to enable an otherwise non-octopus/squid-like animal to clamber/suck its way inside the shell? ... were the first 'arms' and suckers the functional equivalent of 'retractor muscles' ... hence the general lack of muscle scars?). Can anyone hazard a guess whether this ammonite is male or female, mature or not (big/small for the species) .... as an index of reproductive maturity (to eliminate gonad from the equation)?
So is this the only pic of the brute out there (public domain)? Is the fossil well-localised ... and have others been to the site and dug, detonated or otherwise surveyed? If it happens once then it might happen again ....