Fossil find in Yellow Jasper

[Ren_Iain]

Found this in the ‘Golden Gravel’ in our garden. Source unknown as it was here when we moved in and rock ID’d (using an app) as Yellow Jasper. The closest thing I’ve been able to find for the fossil is Hamulina or Toxoceras (last image), but not been able to find any mention of this being found in Jasper. Any ideas?

[Rockwood]

Looks like a bivalve hinge to me.

[Ren_Iain]

Got any example images? The spiral form is too long and looks nothing like any hinge I’ve been able to find. 

[jpc]

cool looking thing, whatever it may be.

 

[Rockwood]

16 minutes ago, Ren_Iain said:

Got any example images? The spiral form is too long and looks nothing like any hinge I’ve been able to find. 

Large bivalves can be measured in meters. It would be an odd section. You are not likely to find an exact match.

[caterpillar]

Not an ammonite for me.

[JohnJ]

Just now, Rockwood said:

Large bivalves can be measured in meters. It would be an odd section. You are not likely to find an exact match.

 

True; but the spiral form does not match bivalve hinge morphology.

 

It is more like a gastropod than cephalopod, but the whorls do not show much consecutive size reduction.

[Rockwood]

4 minutes ago, JohnJ said:

 

True; but the spiral form does not match bivalve hinge morphology.

 

It is more like a gastropod than cephalopod, but the whorls do not show much consecutive size reduction.

Where do you see a spiral ? I only see half of one.

[JohnJ]

8 minutes ago, Rockwood said:

I only see half of one.

Precisely.  Half a spiral is visible.  This is more apparent in the circled red area.

 

Seeing the blue area in better focus might provide more clues.

 

[Rockwood]

16 minutes ago, JohnJ said:

This is more apparent in the circled red area.

Or is that the crystals of a degraded shell with slanted tooth socket articulation ?

[JohnJ]

1 minute ago, Rockwood said:

Or is that the crystals of a degraded shell with slanted tooth socket articulation ?

Doubtful, in my opinion.  A hinge with this quality of preservation would likely preserve more of a bivalve's features...not just the 'hinge teeth.

[Tidgy's Dad]

Internal mold of a crinoid stem perhaps?

Because it has been preserved in some form of microcrstalline or cryptocrystalline quartz a lot of the structure has not been preserved and distortion has occurred, but I think I can see 'holes' which may be lumen in the third photo in some of the loops on the right of the photo. 

I am not very convinced by my own explanation, but just throwing another idea into the mix. 

[Ren_Iain]

On 3/29/2022 at 11:15 AM, JohnJ said:

Precisely.  Half a spiral is visible.  This is more apparent in the circled red area.

 

Seeing the blue area in better focus might provide more clues.

 

 

 

 

Here’s more snaps. Just using my iPhone but will try and get the wife to get some better shots with her fancy camera.

[JohnJ]

Thanks for the extra photos.  I was hoping there might be a remnant mold of the missing exterior surface.

[piranha]

It compares well with the siphuncle of a cephalopod similar to Armenoceras.

figures from:

 

Foerste, A.F. 1924

Silurian Cephalopods of Northern Michigan.

Contributions from the Museum of Geology, University of Michigan, 2(3):19-120  PDF LINK

[Ren_Iain]

22 hours ago, piranha said:

It compares well with the siphuncle of a cephalopod similar to Armenoceras.

figures from:

 

Foerste, A.F. 1924

Silurian Cephalopods of Northern Michigan.

Contributions from the Museum of Geology, University of Michigan, 2(3):19-120  PDF LINK

This does indeed look very similar. Assuming the image is not reversed, there’s a difference in that the spiral is in the opposite direction. Would this be of any relevance?

[piranha]

6 minutes ago, Ren_Iain said:

This does indeed look very similar. Assuming the image is not reversed, there’s a difference in that the spiral is in the opposite direction. Would this be of any relevance?

 

That characteristic is variable. Here is another example from Foerste 1924: Armenoceras rotulatum

 

[Ren_Iain]

This may well be what it is. Excuse the questions as I’m new to this, but the one I have is in Yellow Jasper- would that have any bearing?

 

Quote

That characteristic is variable. Here is another example from Foerste 1924: Armenoceras rotulatum