Fossil id- crinoid stem segment?

[carolinej]

Hi all,

This is my first post

I found this fossil which i think is a crinoid segment from Carboniferous shale, in NW Ireland.

It doesn't have radiating crenulate (if that is the correct term) but has parallel sutures? Best seen in right portion of fossil, which go down in the fossil at an angle.

Fossil is approx 2cm in length.

 

Any help would be great!

 

Thanks

[Fossildude19]

Welcome to the Forum.

I cropped and contrasted your item a bit.

 

 

Can we see some other views of the item? For example, top, bottom, back, and side views?

My first impression was of a pith cast of Calamites, but not sure on this at all. 

[carolinej]

Thank you for cropping the pic.

This is the only view I can give, as it is embedded in the shale, and is not visible on the opposite side, it does not go deep into the rock, maybe 5mm, as the rock starts to become narrower. I can show a side view, but not sure if that would help.

I would like to remove it from the shale but i don't want to damage it. Also I don't know how to do it!

The surface is smooth to touch, where undamaged, and shines in the light.

 

Sorry this is the only info I can give

[Ludwigia]

I have my doubts that this is from a crinoid, but I'm not sure what it could otherwise be until we can view it from other angles.

[Fossildude19]

Even different angles of the encasing matrix are helpful.  

[Rockwood]

My money is on crinoid. Lumen of a large cerrus is my thought.

[carolinej]

 Here are some more pics. Oblique side view, side view, opposite side/ underneath.

 

Thanks for the input!

[ynot]

I am with the crinoid sections, cut at an oblique angle and showing 5 segments (2 partial).

Tony

[BobWill]

Yep, Tony is seeing what I see, just faster on the reply, and Rockwood spotted the cirrus.

[carolinej]

Thanks for the replies.

Is it unusual for a crinoid stem section to display those features, and not have a radial pattern? Or is it as they are cut at an oblique angle suggested by ynot?

[ynot]

I think the radial pattern is an external characteristic and does not appear in the internal view.

Tony

[carolinej]

Ah I see, thanks to all for the input. 

[westcoast]

I agree with Tony. There Is a smaller one on the opposite side. You will only see the radial pattern in some crinoids and only then if the flat  surface of the ossicle is exposed, not in oblique sections like you have there. Is this from Sligo or Donegal? 

[Rockwood]

24 minutes ago, carolinej said:

Thanks for the replies.

Is it unusual for a crinoid stem section to display those features, and not have a radial pattern? Or is it as they are cut at an oblique angle suggested by ynot?

The structure that is seen as a radial pattern is seen in cross section as the lines running from top to bottom in the first photo.

[carolinej]

Hi all, again,

Westcoast, the rock is from the shale above the limestone at Streedagh, Co. Sligo. Thanks for the continued input. Good to know what the fossil is!

[westcoast]

Lots of other carboniferous coral and brachiopod fossils there if you looking for more..

[abyssunder]

I'm not convinced that the "hole" is a sectioned cirrus scar or attachment point of a cirrus to the crinoid pluricolumnal. It could be something else, like a boring (syn-vivo bioerosion trace) similar to Tremichnus, but is just a hypothesis.

 

Figure 3: A-C. A crinoid pluricolumnal with multiple Tremichnus from the Sheinwoodian (Jaagarahu Formation) of Saaremaa Island (Sepise) (GIT 405-165).

 

link to source

 

[Rockwood]

The nature of the fragment would argue in favor of the possibility that tends to enhance it's own prospect for existence.

Bioerosion -

Cirrus scar +

[abyssunder]

There are no evidences supporting any of the theories in the actual condition.

Everything beyond the visual evidence will be merely a guess.

 

If, we suppose that the circular - to semicircular hole is the axial canal (lumen) of a cirrus, then the cirrus diameter (cirrus transverse section) should be very large , something around the dimension of 3 columnal heights, or more than the half (2/3-3/4) of a columnal diameter. This looks a little too big for a cirrus.

[Rockwood]

54 minutes ago, abyssunder said:

There are no evidences supporting any of the theories in the actual condition.

Everything beyond the visual evidence will be merely a guess.

 

 

Okay, then I shall make another attempt to explain since I believe the actual condition is one of the most primary forms of evidence that there is.

Ossicles tend to disarticulate once the ligaments holding them together degrade. The presence of a cirrus, to me, would if anything tend to prolong that period enhancing the odds of it being fossilized in this form.

Bioerosion on the other hand would seem more likely to diminish those odds due to the structure being already compromised.

There also seems, to me, to be evidence of a structure tangential to the articulated section which provided an enhancement to the odds of this exposure being produced by the alignment of it's minerals to act as a cleavage plain.       

[westcoast]

Compare with this. Second from left: http://woostergeologists.scotblogs.wooster.edu/?attachment_id=12375 

[BobWill]

Can we tell for sure that what we see of the stem is the whole width. If some of the margins of the stem are missing the diameter of the portion in question could be more proportionally correct for a cirrus.

[Rockwood]

16 minutes ago, westcoast said:

Compare with this. Second from left: http://woostergeologists.scotblogs.wooster.edu/?attachment_id=12375 

Sorry. I don't think it does.

[abyssunder]

Take a look at the pictures below and try to compare the dimensions of cirri or cirri scars with their tiny central canals to the dimensions of the crinoid columns (stems). Crinoid cirri have very small central canals which bifurcate from the axial canal of the stem like a branch.

 

first picture from here