Soft-part preservation in ammonoids

So a crop is not really a little sack off to the side like I envisioned but just an enlargement where food can be smushed along the sides to allow two-way traffic?
 
It's a 'through gut' D, so it's one-way traffic. Stuff goes into it, and keeps going into it until the octopus cannot eat anything else. From there it will be drip-fed into the stomach, then spiral caecum, and eventually (with some storage of something in the digestive gland via 2 ducts .... not quite sure what goes on) enters the intestine and is expelled via the (cough). The crop is, as you say, definitely just an enlargement; some species have a diverticulum of it - probably just serving to increase storage area for these gluttons - but some do not. They used to believe that the presence or absence of this crop diverticulum had some phylogenetic value, and it was used to differentiate the genus Bathypolypus from Benthoctopus, but we now realise this to be an oversimplification, and its phylogenetic value to be far more limited (this was a large part of my MSc back in the early 90s). That's not to say that it has no systematic value - a species may lack a crop diverticulum but another may have it, but not all species that lack a diverticulum of the crop are more closely related to each other than they are to species that have one. The same applies to species with and without an ink sac - you cannot lump them together into subfamilies, as the ink sac has been lost many times over in the evolution of benthic octopodids.
 
Steve O'Shea;143712 said:
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.

Richard (The benthic critter expert on our last expedition) told me there were no trace fossils that could be attributed [yet?] to any kind of ammonoid slug. Maybe these things just had a lot of drapery hanging from their floating shells.
 
hmm just wondering though, did the shells of ammonoids floated and got carried around by the currents before it finally sinks (like present nautiluses do) and thus, the scavengers had the chance to finish their bodies? Have we ever found a nautiloid fossil with the soft body impression(s) intact? And just like what I pointed in my first introduction, does nautiloid, ammonoid and coleoid flesh possess different tissue composition, and hence their different tendencies to fossilize?

If there's anything extinct in this world that I would like to be resurrected, it would be ammonoids.
 
What an interesting suggestion, but, given the close evolutionary relationship, likely the tissues of all three would be rather similar. Another downside is, that almost all kinds of organic matter are up for scavenging by one organism or the next. Even the awful ammoniacal meat of our friend Architeuthis is considered a delicacy by many a marine predator or scavenger, lest we forget bacteria... Fossilization is a rare event, especially for pelagic species, bottom dwellers can get caught in underwater mudslides, and oceanic species are hardly ever collected, as we only have ready access to sediments of former shallow seas, now turned terra firma, once more.
 
Good point! The buoyancy of their gas-filled chambers must usually have delayed arrival on the sea floor after death.

Some at least must have taken a pretty direct route to the seabed though, e.g. Bear Gulch ?Stroboceras: http://gsa.confex.com/gsa/2001AM/finalprogram/abstract_19314.htm “Ten specimens show preserved carbon and phosphate? films that can be interpreted as the remains of the intestinal tract, specifically the mandibles, crop, stomach and intestine.” Scavengers didn’t finish off these bodies, but “no evidence of gills, tentacles, hood, hyponome, or mantle cavity tissue is preserved in these fossil specimens.” This is a similar observation to all those ammonite examples with aptychi, radulae and crop etc. preserved in situ (discussed in various posts above).

Wippich & Lehman in the Allocrioceras paper discussed above cite Nixon (1988) who “pointed out a correlation in modern cephalopods between size of buccal mass and structure of arms: extant taxa with relatively small buccal mass, such as squid, have few muscular arms, which serve for holding and manipulating prey while pieces are bitten out of it; the large buccal mass of Nautilus by contrast correlates with numerous weak tentacles and food is largely ingested whole …………….. ammonite arms or tentacles should not generally be regarded as muscular as in most recent cephalopods.”

So that’s a very tempting explanation for the cases of only partial preservation of soft parts.
 
Rereading Wippich & Lehman, they write: "The phragmocone must have become waterlogged immediately after death and the ammonite must have rapidly sunk to the bottom in view of the in situ preservation of internal structures."
 
I just took a few moments to look at the body chamber of one of these Lebanese Allocrioceras specimens. There are some interesting features in there.
 

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but if the 7 mm "sack-shaped" area containing calcite spines/rods (fragments of comatulid crinoids?) at the left of the picture is the stomach (it closely matches the inferred stomach in the specimen described by Wippich & Lehman and is in about the same position as in their specimen) then it doesn't make sense to have the gills further back. I think the orange structure must be something else.
 
I just took a few moments to look at a couple of Lebanese ammonites (one a juvenile), each with aptychus in place and difficult-to-interpret remains of soft parts. Sketches attached.
 

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Ammonite soft parts?

Hi gang,

First let me say that I'm new here and I'm an amateur fossil hunter so please go easy on me. :biggrin2:

I found this ammonite in Lyme Regis, England and my old geology professor (who is a paleontologist) said that it looks like the soft parts were preserved. I thought I'd ask you guys what you think since this group specializes in that area.

Note: The fossil is worn and these are not the best pics. I have it mounted and this is the best I could do without dismantling it.

Thanks in advance for any help.

 

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It may just be the photos, but I can't even see that the septa were preserved. If the hard septa are not preserved I don't see how the soft parts could be preserved. Without holding the fossil and having a lot closer look I would have to say it is just spar filling the phragmocone. :-/
 

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