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Devonian Spiny Nautiloid

Hajar

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#1
Here's an interesting thing; a 7 cm Early Devonian nautiloid from Eifel, Germany with a number of partially preserved large tubercles. It looks quite similar to Hercoceras though the height/width ratio of the whorls seems higher than in that genus. I like the painting by Jan Sovák.

Does anyone have similar spiny nautiloids or have more of an idea about the identification?
 

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DWhatley

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#2
Looking at the "bumps" gave immediate thought about how similar they look to the papilliae that many octopuses and cuttlefish can produce on their skin.
 

Hajar

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#3
Reading the paper a bit more carefully I see that Turek describes Hercoceras mirum as a "highly variable species" and he writes that "the shape of the cross-section varies greatly".
 

Hajar

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#4
I see what you mean D (having just looked at a photo of an Enteroctopus dofleini). Most of the bumps on the fossil are just the bases of initially longer spines (as shown in the painting).

On mode of life, Turek writes "the poor hydrodynamic properties of the shell of H. mirum is interpreted here to indicate a benthic habit with a limited ability for active swimming."
 

Hajar

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#7
I was completely amazed when first I saw cuttlefish doing that: one second smooth and pale blue-grey; the next patterned browns with long tubercles. I wonder what use these nautiloids had from their spines (and "wings" in the case of Ptenoceras). Enhanced stability?
 

Hajar

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#9
I just noticed that Cooperoceras is from the Glass Mountains so there are probably some spectacular etched out silicifed specimens. have you ever seen one?
 

Hajar

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#13
Excellent Cooperoceras image Kevin. Thanks. That Hercoceras seems to have lost its spines, probably an internal mould.

My specimen could be gently torticonic, but it's a bit difficult to see. The shell has gone from the other side (so there's a smooth internal mould without tubercles) and the centre is not yet exposed. The observation that the tubercles don't show on the internal mould suggests that the spines were not hollow. On a quick search though it seems that Cooperoceras spines were hollow; Flower (1949) talks about solid nodes; Turek writes "Parabolic ventrolateral outgrowths, which appeared earlier in the ontogeny, show a tendency to transform into hollow adaperturally opened spines." Don't know, but with the single specimen I have in hand I'd say "not hollow".
 

DWhatley

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#14
Thanks Hajar,
I would never have thought about the possibility except for one looks hollow in Kevin's pirated picture and it was even more interesting to think that cephs could for internal papillae while they had shells. Obviously this would not have been for camouflage but could be another case where, like poison, a biologic feature evolved a new use. Kind of exciting to my little brain :grin:
 

Architeuthoceras

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#15
I think that while the spines were forming they were crescent shaped half spines, the mantle (or arm? or papillae?) extended to the end of the spine. As the shell grew it eventually closed off forming a hollow spine. Most were probably sealed off with a plug (see post 66 in this thread), the position of the plug in the spine determined the size of the node on the internal mold. In the attached photo, this critter formed a single pair of spines, probably after reaching maturity, the internal mold here would be as long as the spine. Parabolic nodes such as in Hercoceras were probably kept in the crescent form until the next spine was ready to form, whereas in Cooperoceras, the shell grew continuously (not seeing the internal mold in the pic, I can't see if it had a plug or not). Of course there are probably as many ways to form a spine as there are different forms of shells so the growth lines on different forms would have to be followed to see how each was made. :talker:
 

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Hajar

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#16
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?
 

Hajar

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#17
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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Architeuthoceras

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#18
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:
 

DWhatley

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#19
Now I am wondering why they would grow a hollow spine and then a plug. All these animals were permenantly attached to their shells, right?
 

Hajar

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#20
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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