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Soft-part preservation in ammonoids

Hajar

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#1
What are the best examples of soft-part preservation in ammonoids?

The attached 11 cm Late Jurassic ammonite from Solnhofen has some suggestive structures in its body chamber.

I found the attached image of a 49 mm Allocrioceras with probable stomach contents (thought to be remains of pelagic comatulid crinoids) preserved, from Wippich & Lehman (2004).

Are there examples of soft-part preservation in ammonites from La Voulte or Christian Malford? - and if not why not?

Thanks.
 

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Steve O'Shea

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#2
A wonderful post! We've been working away on something very similar for several months; very shortly (hopefully tomorrow) I'll post series of slides that will be of interest to you (re radulae, aptychii, and soft-part anatomy of ammonites (reconstructed)).

Please, if you find any more information like this (stomach contents), post away!

(ps, I don't see much in the first image; what am I meant to see?)
 

Hajar

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#3
Excellent Steve, looking forward to your slides and information.

Here attached is a detail of the Solnhofen ammonite with some features highlighted. I feel fairly confident in ruling out compaction-related crushing of shell, preparation-related artefact or trace fossils, so could these elongate structures record soft parts? This one doesn't have a clear aptychus like so many other individuals from here, including the little 3 cm specimen shown to the right.
 

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Hajar

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#4
A couple of stumbled-upon reconstructions, one from Jerzy Dzik (1981) and the other from Klug & Korn (2004). I like the delicate arms in the Klug & Korn Devonian ammonoids.
 

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Steve O'Shea

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#5
Hajar;142690 said:
.... doesn't have a clear aptychus like so many other individuals from here, including the little 3 cm specimen shown to the right.
:shock:

That image to the right is SENSATIONAL!

I have to ask you; what do you think the aptychus is, and what function did it have for that specimen?

Is that specimen yours? Do you have others like it if so? Would you sell one .....?

I don't understand Fig C (oral view) in the first image; can you explain a little about that structure that serves as an operculum when it appears the nautiloid has completely retracted into its shell. I see in the cross-sectional image/reconstruction (Fig A) the aptychus within the head musculature, but cannot see how the aptychus as depicted in this Figure could be homologous with the operculum-like structure in Fig C.

Depressions in the last body chamber could be partly attributed to post-mortem bioturbation when the chamber was filled with mud; hard to say (or it would be difficult to eliminate this possibility).
 

hallucigenia

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#6
Wow! These are AMAZING! :bugout:

Do you have a higher-resolution photo of the one with the stomach contents? I am very very interested in that one, and I think my advisor might be too...
 

Hajar

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#7
Steve, I'll let Jerzy speak for himself in the attached paper http://www.paleo.pan.pl/people/Dzik/Publications/Cephalopoda.pdf, though it dates from 28 years ago.

Here's another old one: http://earth.geology.yale.edu/~ajs/1993/11.1993.02Seilacher.pdf

I don't think these Solnhofen aptychus specimens are very rare, but I only have that one example.

I see that there has already been plenty of discussion about aptychi on this forum, e.g. http://www.tonmo.com/community/index.php?threads/6864/
and Sordes provided a translation of the text in a German webpage dedicated to the subject.

Neale Monks' guidance for this model http://www.tonmo.com/community/index.php?threads/11182/ was for it to act as a trap-door resting on top of the head.

Hallucigenia, I don't have a high resolution image of the Allocrioceras, but here attached is the interpretation from Wippich & Lehman (2004).

I'll be very interested in some expert views on the "state-of-the-art" (my own curiosity about fossil cephalopods only dates from earlier this year after coming across those Paleogene belemnoids).
 

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CaptFish

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#13

Steve O'Shea

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#14
:smile:

I love it; we have concluded the exact opposite!

I must I must I must get our pp presentation up!

Quite a contentious field, isn't it.
 

Hajar

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#15
I've also only seen the abstract, but I doubt that models of aptychi functioning as opercula (e.g. Lehmann, Seilacher) rest on a few specimens with aptychi preserved in a shell-closing position. I'd expect that to be a fabulously rare occurrence in any case - I've never seen a fossil gastropod with operculum in place.

Seilacher compares several features of aptychi with opercula of the modern gastropod Turbo. These have calcite layers added to the outer side when the operculum is stowed away whereas the organic layer coating the inner side is secreted from within. I spent the last several days camping by a spectacular beach on a desert Island (Masirah) and by happy coincidence there were plenty of these opercula to be found, both on the beach and a little higher on an older raised beach. Here attached is a photo of some of them (resting on a whale vertebra). These are Lunella coronata of the Family TURBINIDAE. The smooth faces showing a spiral are the inner sides and the domed textured sides face outwards.
 

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cuttlegirl

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#17
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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Hajar

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#19
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).
 

cuttlegirl

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#20
Did ammonites have to have tentacles? I know that it is a standard trait of cephalopods but isn't it possible that they had some other feeding mechanism? Would love to see the La Voulte ammonites.
 

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