Unknown ordovician fossil, foram or rugose coral?

[PaleoOrdo]

Can please someone help me? I found this fossil from an middle ordovician place. Could it be a horncoral or a foram with a spiralform?

The specimen is about 2 cm in diameter, some parts hidden in the stone. 

Any help very appreciated.

[Bev]

Very unique find, I believe, for the Ordovician! I have not seen anything presented like this in the Ordo of Minnesota, USA. I'm interested in knowing what it is also. Good luck!  :-D

[FossilDAWG]

It may be an impression of the calyx of a solitary rugose coral.

 

Don

[Bev]

9 minutes ago, FossilDAWG said:

It may be an impression of the calyx of a solitary rugose coral.

 

Don

In that spiral form, Don?

[FossilDAWG]

There are several rugose coral genera where the septa twist as they approach the center. An impression of the calyx would seem to slightly spiral.

 

Don

[TqB]

I agree it's a coral calyx impression, or a reverse weathered section of one. There are impressions of short, secondary septa at the outer edges too.

[PaleoOrdo]

Thank you all for your viewpoints on my fossil. They are partly also my own thoughts on the possibilities. First, I think the fossil is unique or seldom to find in the ordovician period.  Second, the chance that it is a rugose coral seems high according to the knowlegde Don refers to. On the other hand, it is puzzeling that each "arm" of the "coral" have 4 parts or joints, and that the 4th is bifuracted; the end of the arm is divided into two. Corals do not seems to have this property, or what do you think? But forarms do. Is there any sceintific articles about this subject?

Best wishes Martin

[Bev]

Could this possibly be a crinoid calyx looking from the top down, or from the bottom up, with it fossilized in a spiral form before it starts with the characteristic links on the arms or "stalk"? Sometimes there is real distortion in the fossilization process...  Just a thought...  :-)  Oops, I just read the above comment. Agree. Coral calyx.  :-)

Edited July 28, 2020 by Bev

[TqB]

9 hours ago, PaleoOrdo said:

Thank you all for your viewpoints on my fossil. They are partly also my own thoughts on the possibilities. First, I think the fossil is unique or seldom to find in the ordovician period.  Second, the chance that it is a rugose coral seems high according to the knowlegde Don refers to. On the other hand, it is puzzeling that each "arm" of the "coral" have 4 parts or joints, and that the 4th is bifuracted; the end of the arm is divided into two. Corals do not seems to have this property, or what do you think? But forarms do. Is there any sceintific articles about this subject?

Best wishes Martin

The "arms" are the sediment infill between the thin septa, which here are either weathered away or preserved as an impression. The bifurcations at the end are caused by short, secondary septa. The septa themselves do fuse towards the centre, making an axial structure.

 

It may be a streptelasmatid which are generally common in the Ordovician, though maybe not where you are. Search "Streptelasma" for similar examples.

 

From the rugose coral Treatise:

 

Another related genus (actually Silurian) that shows more obvious secondary septa.

 

[PaleoOrdo]

Thank you for the information Tarquin. I agree with your views. In the beginning I thought, for a moment  there, it was similar to the Ediacaran Euandromeda, but even if nature make so wonderful shapes it could not belong to Ordovicium! Moreover, the forarms are organised (mostly, but not all) in a structure of chambers so it is a passage from one chamber to the next. That is not a property in my fossil, althougg it is a spiralform. Hence, it is very probable (not absolute certain though) that it is a rugose coral.

Martin