Soft-part preservation in ammonoids

[Architeuthoceras]

And to TONMO Ruby

 

[OB]

indeed!

 

[Ruby Tuesday]

Thanks for the reply, Kevin. (And for the welcome) but I have to admit that you lost me a bit with the answer. I don't have any idea what "spar filling the phragmocone" means, for example.

All I can say is this: the fossil is very worn down. It came from the beach at Lyme Regis (notice how round the matrix is?) So yes, a lot of the details are gone. I'm sure a lot more was originally preserved but has worn away. But that part on the end...there are tentacle-y looking things (like my scientific words?) coming out of it. It looks like that could have been the animal itself. That's the part that my professor thought could be the soft parts.

And though I'm light years away from being an expert I can google pics of what an ammonite looked like. In my eyes, it looks curiously similar to the pics I've seen. And if it's not the body that's sticking out, what is it?

 

[OB]

As I interpret the photographs, you are looking at parts of the (proximal) shell towards the living chamber. The "arms" are partly eroded "ribs" (On the outside of the shell), illustrated by the fact that they are perpendicular to the inner coilings as well as in the eroded away curved bit of the matrix. Spar is a mineral that replaced the actual shell and other animal material, creating the fossil as it now presents itself. A carbon copy ofthe original beasty, so to say

 

[Architeuthoceras]

All I can say is this: the fossil is very worn down. ... And if it's not the body that's sticking out, what is it?

The "arms" are partly eroded "ribs"...Spar is a mineral that replaced the actual shell and other animal material

The fossil is very worn down, in fact the only thing left of the outer whorl is, as OB says, the ribs, the body chamber is gone, worn away.

Spar is closely packed crystals of calcite, in carbonate rocks it usually grows in voids such as the empty chambers of cephalopods. Sometimes it will replace the original aragonite of the shell and septa and grow inward, others it will grow and displace everything inside the void.

Hope this helps.

 

[Terri]

Ruby! Even without "soft parts", nice little fossil. If you go back into the Soft Part Preservation forum there are some really excellent links, discussions and photographs that explain what must occur to cause soft part fossilization, very interesting stuff.

 

[Architeuthoceras]

A quick little sketch to show how I see your fossil and what is missing. Consider (most) of the pink lines as ribs on the outside of the shell. The two tentacle-y (very nice scientific word ) are the last preserved ribs, there may have been more and the ammonite may have been much larger, but it has wore away while the sea was making a round rock out of it.