Strange infestation on orthocone shell, Mississipian, NE England

[TqB]

Found this piece of large (for the location) orthocone yesterday in a Brigantian (Mississippian) mudstone.

 

The thin bits of surviving shell are apparently pierced through with many small round objects, mostly circular, 0.3 - 0.5 mm in diameter.

Each one is now a very low cylinder (like a watch battery) with apparently vertical sides and depressed centre. Many are filled with pyrite.

They have left impressions on the mudstone internal mould - the whole shell fossil is covered with them, both the living chamber and chambered phragmocone.

 

Ostracods came to mind but these seem to go right through the shell and the spacing is quite regular so was whatever they were growing there?

 

Orthocones and many other types of shell are common from this location but I've never seen this before.

 

And one more:

[ynot]

My first thought is beekite. 

[Carl]

I don't see beekite here. This looks pretty biological to me. I doubt they are ostracods because they are so circular but beyond that, I've got nothing...

[FossilDAWG]

Beekite only occurs on silicified fossils, and nothing about the fossil suggests it is silicified.  

 

Don

[Bullsnake]

Wild guess...sponge borings?

[Miocene_Mason]

Strange. At first I thought it had been pressed on top of other fossils, maybe crinoid bits, but the shapes are irregular. 

[ynot]

So much for first impressions.

[Arizona Chris]

Possibly serpulids.  (?)

[doushantuo]

They bear a slight resemblance to fossil bioimmured (gastropod) eggs,as detailed by Zaton

 

from his APPolonica article:

 

[TqB]

Thanks for all the suggestions! 

 

 

 

@Arizona Chris It may well be something wormy though serpulids themselves apparently didn't appear until the Permian.

 

@doushantuo Eggs would be amazing but these seem to be structures penetrating the shell material, and also not confined to the living chamber.

 

 @Bullsnake Sponge borings could be a very good wild guess , I think something like Entobia might be it - I've just had a hard look at a scrap of shell that's slightly worn through and there seem to be connecting galleries - look particularly at the bottom of the white patch of shell.

(The recent Porifera Treatise has possible Entobia as far back as the Silurian.)

 

This is as close in as I can get:

 

EDIT A clearer photo taken later:

[supertramp]

 

3 hours ago, Bullsnake said:

Wild guess...sponge borings?

+1

...my first thought was boring sponges

 

ciao

[Missourian]

They remind me of ooids. Is there any trace of anything like them in the matrix?

[TqB]

3 minutes ago, Missourian said:

They remind me of ooids. Is there any trace of anything like them in the matrix?

 

Me too but no, there aren't any at that location and I've only ever seen these structures on this shell.

 

Boring sponges are very persuasive at the moment (though I've never seen a Carboniferous specimen).

[Archie]

Very interesting piece Tarquin! They remind me of macrospores is there much in the way of plant remains in this formation?

[TqB]

1 hour ago, Archie said:

Very interesting piece Tarquin! They remind me of macrospores is there much in the way of plant remains in this formation?

 

No plant material at all in these beds, Sam, but I see what you mean. These definitely go through the shell wall though rather than being scattered against it.

[Rockwood]

Genetic 

Had it been advantageous enough 'cones would still be around. 

[TqB]

11 hours ago, Rockwood said:

Genetic 

Had it been advantageous enough 'cones would still be around. 

 

A new shell ornament would be nice.  Pesky sponge seems the best explanation so far - I'll see if I can track down a specialist...

[RiseOfTheExtinct]

I think it could be a coral that could have indented this specimen. Or, it could be very old barnacle spots, where the barnacles, over time, broke off and left those dents. Then again, the little imprints seem to be placed in a pattern. A trace fossil...maybe? Those are all possibilities. Very interesting....

[Shamalama]

On 9/22/2017 at 1:16 PM, Missourian said:

They remind me of ooids. Is there any trace of anything like them in the matrix?

I'm with @Missourian, I think they are ooids of some sort.

[TqB]

2 minutes ago, Shamalama said:

I'm with @Missourian, I think they are ooids of some sort.

 

Thanks - I agree the resemblance but these are confined to the shell layer on just this one specimen (I've collected a lot of material from this site). Within the shell structure itself they are interlinked (and filled with pyrite) so something like Entobia fits well.

 

 

[TqB]

1 hour ago, RiseOfTheExtinct said:

I think it could be a coral that could have indented this specimen. Or, it could be very old barnacle spots, where the barnacles, over time, broke off and left those dents. Then again, the little imprints seem to be placed in a pattern. A trace fossil...maybe? Those are all possibilities. Very interesting....

 

Thanks for the suggestions - I'm sure that coral isn't involved but I agree that an organism of some sort has left the holes. Barnacles might be a contender for something Mesozoic onwards (Rogerella is a well known burrow from then) but they are hyper-rare as fossils in the Palaeozoic.  

[Missourian]

I cropped one image to zoom into a couple features.

 

 

1. Some of these overlap. This may preclude them being borings.

 

2. Could you get a little better view here. There may be cross sections present.

 

3. These look as if they were removed, leaving residual rims behind.

[Bullsnake]

32 minutes ago, Missourian said:

I cropped one image to zoom into a couple features.

 

 

1. Some of these overlap. This may preclude them being borings.

 

2. Could you get a little better view here. There may be cross sections present.

 

3. These look as if they were removed, leaving residual rims behind.

Great points and well spotted. If possible, microscopic details may be helpful, too.

[TqB]

28 minutes ago, Missourian said:

 

 

 

1. Some of these overlap. This may preclude them being borings.

 

2. Could you get a little better view here. There may be cross sections present.

 

3. These look as if they were removed, leaving residual rims behind.

 

Thanks for your interest! Good points there and I'll look harder and try for some more images tomorrow.

Briefly:

1) I think the overlapping is OK for Entobia - type borings.

2) Had a look with a microscope and can't see deeper cross sections, the pits in the internal mould are very shallow.

3) Those are near the bottoms of the pyrite filled holes, at the very inside of the shell, before all the pyrite (which looks granular) has dropped out (I can see this happening in a few places).

[westcoast]

This is a fascinating piece. Quite a head scratcher! Check out parasitic foraminifera for something similar..