Scars On Cephalopod Fossils

[ondrej.zicha]

Hello, I wonder if anyone have seen something like this. Never mind the cephalopod ID, I'm interested in the scar-like structures on them.

Here is cephalopod from early devonian of Czech Republic:

and second one from different locality, but similar age:

Here's one from the shales of late ordovician (Bohdalec formation, I think this corresponds with lower Katian)

Not sure if the devonian and ordovician "scars" are the same thing, but they do look similar. At first I thought it was a bryozoan colony, but the shape is too regular. My best guess is it might be traces of some brachiopod similar to Philhedra, but I'm not very convinced.

Thanks for any ideas.

Ondrej

[Ludwigia]

I'm not quite certain, but the first four may be the remnants of crinoidal holdfasts(roots). The last two appear to be impressions of an individual crinoid columnal section.

[ondrej.zicha]

Thank you, interesting idea, I'll try to ask some local crinoid specialist.

However on the last two photos I'm not sure if you mean the same thing as do I. I'm asking about the two asterisk-like impressions above the crinoid column section. I'll try to take a better photo of the negative when the light is better. The positive piece I've brought to some experts and they weren't sure either, but they're keeping it. I've inspected large number of cephalopods on the location and this was the only one bearing such marks. But to be sure, it was also a very crinoid rich locality.

[Nandomas]

No ideas, just a thought: some kind of Clonograptus? :wacko:

Edited May 24, 2014 by Nandomas

[4circle]

Seconded to the crinoid holdfasts in first four photos.

As for the last two photos, above the crinoid ossicle impression, these are synformational lithification structures. This cephalopod is preserved as an internal mould, i.e. the sediment cast of the internal surface of the shell which formed as sediment entered the shell and then remained once the (aragonite) shell was redissolved. We're looking at the upper surface of that internal cast, and this is where the sediment was more weakly indurated as it struggled to displace all the air in the top of the chamber. Imagine forcing wet cake mixture into an inverted glass mixing bowl (from the bottom margins) - the cake mixture will displace the air as it's pushed up, but near the top there will be a small area of trapped air where the mixture stuck to the bowl and sealed the air in. If you then baked this cake, it would retain the shape of the inside of the bowl except this small portion which would have a wrinkled appearance. The same happens with wet sediment. Sorry to disappoint with such a lengthy but non-fossil explanation!

We can tell it's not an encruster because this is an internal mould - any encrusters would be on the external surface, and so would be preserved in negative relief in the counterpart.

[ondrej.zicha]

Thanks for all your answers, the non-fossil explanation, though of course a bit disappointing, is very interesting and probably a correct one :-) I haven't seen anything like this on any other fossils yet. I'm attaching a detail of the counterpart, since I've managed to catch a moment of good light a while ago.

[4circle]

Thanks for all your answers, the non-fossil explanation, though of course a bit disappointing, is very interesting and probably a correct one :-) I haven't seen anything like this on any other fossils yet. I'm attaching a detail of the counterpart, since I've managed to catch a moment of good light a while ago.

IMG_0040.JPG IMG_0041.JPG

So, yes, this counterpart preserves the structure in hyporelief of the part (that is, they would nest inside one another perfectly) showing us that this structure formed on the under side of the interior of the shell.

They should maintain sedimentological homogeneity with the rest of the matrix, but the only way to show this is to cut a thin section. This would obviously be criminally destructive to a pristine fossil!

[miraspis]

I have found something similar. According the specialist from Charles university it could be bryozoa colony Hederella sp.

http://paleoweb.cz/paleo/kameny_miraspis/ukaz_kamen.php?jmeno=miraspis&kod=&cislo_polozky=353

Best regards,

A.