Devonian Spiny Nautiloid

Brilliant Link Kevin - the same discussion but for ammonites. Solenochilus is another beast I had never heard of before. It's quite dramatic. Have you read any discussion of the possible purpose/use of this single pair of long hollow spines?
 
Here's a photo to show a horn (length about 8 mm) on the shell of the nautiloid and the smooth internal mould on the opposite side.

I also just took a photo of two of the horns of a weathered Omani Cunningtoniceras showing that these horns had no internal plugs. Field of view about 7 cm wide.
 

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Hajar;164788 said:
Brilliant Link Kevin - the same discussion but for ammonites. Solenochilus is another beast I had never heard of before. It's quite dramatic. Have you read any discussion of the possible purpose/use of this single pair of long hollow spines?
No, I have not read a discussion on these. Just as conjecture though, extant Nautilus has a pair of arms(?) just behind the eye that would assume the same position as these spines, could the spines be an extension and/or support for whatever purpose these "occular arms" have? And could similar spines on other shelled cephalopods have the same purpose, only form iteratively?


Hajar;164789 said:
Here's a photo to show a horn (length about 8 mm) on the shell of the nautiloid and the smooth internal mould on the opposite side.

I also just took a photo of two of the horns of a weathered Omani Cunningtoniceras showing that these horns had no internal plugs. Field of view about 7 cm wide.
That smooth opposite side could be the sign of a torticonic shell, or that the spines were solid and independent of the body chamber, or possibly even some kind of pathology. Is there any sign of spines at all on the opposite side?

It looks like the horns on Cunningtoniceras were just enlarged nodes, with just the shell covering them, no elongated spines to speak of. :smile:
 
Here's another picture of the nautiloid Kevin showing the broken edge of the shell, which is about 1 mm thick, and the smooth internal mould on the other side from all the horns. No bumps on that side as far as I can see so I'd guess that the spines/horns were solid.

I like the arm support idea. I just read that the "name "Nautilus" originally referred to the Argonauta, otherwise known as paper nautiluses, because the ancients believed these animals used their two expanded arms as sails."

In your ammonite spine/plug link above Kevin the photo shows multiple laminae (at least 4 including the "plug") in the shell. ?successive episodes of secretion from within, each addition filling more of the spine?
 

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I may be basing all this on a single genera, and they are the only ones that formed plugs. And it may be that only certain spines were plugged, say those that were broken or malformed in the first place. :oops:
But a hollow spine would just be extra space that the animal would have to constantly fill as it moved forward in the living chamber, or fill with gas once a septum was deposited in front of it. Plugging the spine would make less space for cameral fluid and gas, the move through the living chamber easier, and home a little tidier. :smile:
 
In the portrayal of Solenochilus as provided by Kevin, the two spines appear almost as hydrodynamic adaptations, aiding stability, not very likely for such (presumably) slow swimmers.
 
Hajar;164826 said:
Here's another picture of the nautiloid Kevin showing the broken edge of the shell, which is about 1 mm thick, and the smooth internal mould on the other side from all the horns. No bumps on that side as far as I can see so I'd guess that the spines/horns were solid.
That is very strange, you'd think it would have at least left a remnant of some kind, if all that were found were internal molds, you would never know it had spines at all. It seems to be a lot of wasted energy secreting so much solid shell material. I'm inclined to think that side never had spines.

Hajar;164826 said:
I like the arm support idea. I just read that the "name "Nautilus" originally referred to the Argonauta, otherwise known as paper nautiluses, because the ancients believed these animals used their two expanded arms as sails."
That explains the sails on ammonites on this old painting :sly:

Hajar;164826 said:
In your ammonite spine/plug link above Kevin the photo shows multiple laminae (at least 4 including the "plug") in the shell. ?successive episodes of secretion from within, each addition filling more of the spine?
But they still left a node on the internal mold.
 
Very well spotted Kevin! I know that painting well, but had never registered the argonauts.

Don't know about the nautiloid spines. Barrande shows Hercoceras internal moulds with bumps preserved, whereas the one in your Treatise picture is very nearly smooth. One with spines on only one side would be a radical novelty!

Turek writes, "the general appearance of specimens preserved only as corroded internal moulds can differ by being almost smooth or by showing only inconspicuous nodes."
 
Do you do mostly desalination for drinking water then? I spent a little time trying to learn about the terrain after reading your newsletter and I saw mention of desalination plants and that much is desert but only a few days of rain a year?
 
Did it work D? Works here.

Now, I'm wondering about how this fossil fits into the family tree.

The Paleobiology database places it in the family Rutoceratidae in the order Nautilida, but Manda & Turek (2009) place it in family Hercoceratidae in superfamily Rutoceratoidea in order Oncocerida (so not an early nautilid).

They also write something about the spines: "Signor & Brett (1984) suggested that highly elaborated shell sculptures in nautiloids (e.g., spines, wings, collars, distinct growth walls) functioned as protection against predators and they also pointed out that increasing diversity of well-sculptured nautiloids during the Devonian represents an adaptive reaction to the radiation of durophagous predators. Appearance and diversification of rutoceratoids in the Early–Middle Devonian seems to be in agreement with these suggestions."
BUT, "It may be pointed out that rutoceratoids represent a single new Early Devonian cephalopod clade with highly sculptured shells and shell outgrowths. Remaining new Early Devonian clades exhibit clearly similar sculpture as analogous Ordovician and Devonian cephalopod morphotypes ................. Consequently, the radiation of rutoceratoids (i.e., highly sculptured cephalopods) in the Early Devonian probably represents an effect (fabricational noise) of cephalopod faunal recovery after the Silurian-Devonian boundary Event rather than a radiation of durophagous predators."

This is the first time I meet the term "fabricational noise", so browsing further I find that "it has been applied to features of morphology that contain information about the mechanism by which a structure is manufactured (Seilacher 1970, 1973, 1974)" - something about patterns "occurring in accidental or functionally neutral situations" (and I'll read this tomorrow). I'd like to understand this better. Can anyone enlighten?
 

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