Soft-part preservation in ammonoids

Hajar;142770 said:
Here's Figure 1 from the Seilacher paper. Well worth a read I think.

I just took a closer look at Figure I in this drawing :shock:. To quote Seilacher...
Admittedly, the arms shown in the cartoons(I) are unrealistic, but little more so than the arms in standard ammonite reconstructions.
 

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Yes, nice to see Seilacher having a bit of fun!

The Dzik picture also greatly reduces the tentacles and the Klug and Korn pictures make the tentacles extremely flimsy - everybody is worrying about why they don't show up in the exceptionally preserved faunas whereas the tentacles of the coleoids do. X-Rays of La Voulte ammonites would be one approach to take (though I've never seen ammonites from there myself).
 
If you'd like to catch up on the powerpoint presentation looking at whether the aptychii and radula of (at least SOME) ammonites were within the last body chamber or not, go to this thread.

Ta
 
Excellent stuff Steve! How did you break the SEM?

That's an amazing structure inside the body chamber of the Rhaeboceras.
Kennedy et al. (http://www.geologie.ac.at/filestore/download/AB0057_113_A.pdf) note a number (4) of differences between these structures and radulae known from other ammonoids, but say that similar large hollow teeth are associated with Hoploscaphites and Jeletzkyites. They say "The radula mass in Rhaeboceras ... appears to be two or three times larger in relation to shell diameter than in other ammonites in which this figure can be determined, and four times larger in relative terms than in Nautilus.

How could you pursue your suggestion that these might be gizzard teeth? e.g. anything distinctive in the structure of gizzard teeth? finding a distinct and more normal-sized radula in one of these specimens would help!

These forms with the giant teeth seem to stand out as different from other ammonoids with preserved radulae, so the "big head" argument could hold good for them and yet not for the ammonites found in Jurassic and Cretaceous exceptionally-preserved biotas. We're still left with the question of why ammonite tentacles don't show up whereas we have such a large number of fossil coleoid examples in which they do.

Thanks!
 
Steve, doesn't the specimen with the teeth preserved between upper and lower jaws (BHMNH 2156) pose a problem for the gizzard teeth idea?
 

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It's very hard to see the teeth in there Hajar, but I can see some structures that look kind-of (far too) large for them to be true radula teeth relative to the 'jaw plates'.

Have you absolute dimensions for those structures?

The easy way around this problem is to consider those jaws gizzard plates, rather than mandibles.
 
So the Buccal Mass would be forward of these "Gizzard Plates and teeth"? And there would be a Beak and Radula?

What would be the function of the gizzard plates and teeth? Would they take the place of "gizzard stones"?

Correct me if I'm wrong, but most animals (at least vertebrates) with a gizzard, are herbivores using the gizzard to condition plant material before sending it to the stomach. Were (some) ammonoids herbivorous?
 
Kevin, most octopus have a crop (but not some of the deep water ones I recently read) that I understand is sort of a holding facility for their one track, two-way digestive system (assuming I am understanding what I read correctly). Is that the same as a gizzard?
 
Architeuthoceras;143609 said:
So the Buccal Mass would be forward of these "Gizzard Plates and teeth"? And there would be a Beak and Radula?

What would be the function of the gizzard plates and teeth? Would they take the place of "gizzard stones"?

Yes, the mass would be forward of the gizzard; there would be an oesophagus connecting it to the buccal mass, possibly via a separate crop (maybe not), but definitely a separate buccal mass, beaks and radula. Hence a lot of the animal being outside the last body chamber.

Architeuthoceras;143609 said:
Correct me if I'm wrong, but most animals (at least vertebrates) with a gizzard, are herbivores using the gizzard to condition plant material before sending it to the stomach. Were (some) ammonoids herbivorous?

Or deposit feeders (not what you really want to think an ammonite as doing); a number of opisthobranchs (like Philine) have these structures.

We're just throwing ideas around Kevin; until Phil develops his time machine we'll never know; perhaps some ammonite taxa were like slugs in behavour.
 
dwhatley;143610 said:
Kevin, most octopus have a crop (but not some of the deep water ones I recently read) that I understand is sort of a holding facility for their one track, two-way digestive system (assuming I am understanding what I read correctly). Is that the same as a gizzard?

Not the same, but almost D. The gizzard plates would serve as a grinding surface upon which some style might operate, releasing digestive enzymes (you see this in some bivalves) into the lumen. The teeth within the gizzard might serve to assist in mastication of prey items, but I'd want to read up on this before I swear this to be the case. The crop is just a storage space within which surplus food is stored prior to being passed through for digestion (possibly via a gizzard).

You are quite correct. Many of the deeper-water octopodid taxa lack an anterior diverticulum to the dilatation of the oesophagus that we usually refer to as a crop, though most (ok, all octopus) that I have looked do have some dilatation of the oesophagus, so all have what we usually refer to as a crop. (So, some octopuses have and some do not have an anterior diverticulum to the 'crop,' but all have, as far as I am aware, what we would refer to as a crop.)
 

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