Devonian Cedar Valley Formation Unknown

[minnbuckeye]

Last week, when on an excursion to the Devonian, Cedar Valley Formation, of Iowa, I encountered this fossil. Thinking crinoid, I threw it in my bucket, so that I could examine it closer at home. Now, haven taken a closer look at it, I am unsure..... Crinoid? Cephalopod? Or something else. Your thoughts are very welcome!!

 

Mike

 

 

 

 

[Tidgy's Dad]

Looks like a crinoid stem to me. 

Interesting. 

Edited May 25, 2022 by Tidgy's Dad

[minnbuckeye]

@Tidgy's Dad, the ends do not exhibit typical crinoid appearance and the coloration is completely different than crinoidal material found in this location. Unfortunately the ends are not clean breaks. Tomorrow, I may cut one end and re-photo in attempts to rule crinoid in or out.

[Rockwood]

The outside does look funny for a crinoid, but the inside doesn't look nautiloid. Suppose it is a reworked fossil crinoid stem ?

[connorp]

Interesting specimen Mike. Hard to say without clearer pictures though, these are a bit blurry.

[minnbuckeye]

A cut was made to one end and sanded a bit in hopes it may be informative. This should have been done before I posted the 'unknown'. I now am solidly in the crinoid corner but something just sits wrong with me. Can't explain it!!

 

 

And a few better focused pictures after a  quick dip in vinegar.

 

 

 

 

Thanks @Tidgy's Dad, @Rockwood, and @connorp for your thoughts!

Edited May 25, 2022 by minnbuckeye

[Rockwood]

1 hour ago, minnbuckeye said:

something just sits wrong with me. Can't explain it!!

It's an odd one alright.

[Lone Hunter]

Probably a longshot... Pseudorthorceras

Edited May 25, 2022 by Lone Hunter

[minnbuckeye]

Now @Lone Hunter made me reconsider cephalopod. Because I see no tapering in the fossil, it would lessen its  chance of being  a cephalopod. But after re-examining the recent cross section, I noticed the central "hole" is NOT situated in the center like the lumen of a crinoid stem should be. So is this a siphuncle instead?? My confusion with this fossil continues! Maybe it is time to place it in the children's give away pile! 

[Tidgy's Dad]

I think that the lumen was central, but the specimen has been slightly deformed and that optical trickery may be partly responsible. 

[connorp]

It is an interesting specimen. The preservation definitely looks more cephalopod than crinoid to me.

[abyssunder]

I think it's a crinoid partial column (stem) with the lumen visible in the transverse section you make. Some crinoids may have eccentric lumen without geological stress.

[Rockwood]

Crenulae aren't always present, but shouldn't there be some interlocking ?

[Rockwood]

Found the answer to that. No. It's called synostosis. 

[minnbuckeye]

38 minutes ago, Rockwood said:

Found the answer to that. No. It's called synostosis. 

 

Found this in Charles Messing's Crinoid Pages: 

Articulations

• Articulations
• Synostosis
• Symplexy
• Syzygy
• Synarthry
• Symmorphy
• Stereom

Successive ossicles articulate via ligaments or combinations of muscles and ligaments that anchor in depressions (fossae) on the articular faces (or facets). Living crinoids appear to have four basic articulations: synostosis, symplexy, syzygy, and synarthry. The latter is often highly modified during development or with growth into several secondary articular forms that may converge on the first three.

 

Now I feel educated and can  answer any "Jeopardy" questions asked regarding crinoid articulations. Actually this made me feel so uneducated regarding something seemingly so simple as crinoid articulation.

Edited May 25, 2022 by minnbuckeye

[Tidgy's Dad]

1 hour ago, minnbuckeye said:

 

Now I feel educated and can now answer Jeopardy questions regarding crinoid articulations.

Splendid! 

So what's the sort of spotty rim around the outside of the columnal you show called? 

[fifbrindacier]

I'm in the crinoid camp.

[minnbuckeye]

53 minutes ago, Tidgy's Dad said:

So what's the sort of spotty rim around the outside of the columnal you show called

do you mean crenulae??

[Tidgy's Dad]

1 hour ago, minnbuckeye said:

do you mean crenulae??

 

1 hour ago, minnbuckeye said:

do you mean crenulae??

Most splendid; the crenularium! 

Ten points. 

What about the spotty bit just around the lumen? 

Edited May 25, 2022 by Tidgy's Dad

[Rockwood]

24 minutes ago, minnbuckeye said:

do you mean crenulae??

Yes. The pleural of crenula. A notch.

[Rockwood]

You don't suppose this is actually a siphuncle ?

[minnbuckeye]

11 hours ago, Tidgy's Dad said:

spotty bit just around the lumen? 

 

My answers to your questions have come from a forum post made by @abyssunder . It provided this well constructed diagram.

 

[Tidgy's Dad]

2 minutes ago, minnbuckeye said:

 

My answers to your questions have come from a forum post made by @abyssunder . It provided this well constructed diagram.

 

Very useful.

The ring around the lumen is called the perilumen. 

[westcoast]

A longitudinal or oblique cut section would reveal the shape of any septae (if present, if cephalopod), however it would also damage your specimen...

[minnbuckeye]

@Tidgy's Dad, I forgot to put my answer into my response. The picture shows the area just outside the lumen as the areolus. So my answer to question 2 was "Areolus". Unfortunately the picture did not transfer well. At least I cannot enlarge it without it becoming blurry. Maybe @abyssunder can provide a clearer version of it.