Devonian Spiny Nautiloid

Joined
Mar 7, 2009
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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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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.
 
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".
 
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."
 
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?
 
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".
 
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 :biggrin2:
 
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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