Uncommon Gastropod from the Ordovician/ Galena (Asgardaspira)

[minnbuckeye]

I had brought home a piece of Galena/ Ordovician matrix that had some unidentifiable critters hidden in the rock. Time was taken to extract what I am sure is a cephalopod from the matrix. Haven hunted this formation for years, I can honestly say this is the first cephalopod found exhibiting its curved features discovered by me. Attempts to ID the fossil have been fruitless, so I am asking for help! 

 

The fossil fractured during its prep revealing what I see as a siphuncle.

 

 

 Here is the repaired specimen:

 

 

 

 

[FossilDAWG]

There are a number of oncocerid nautiloids with this sort of very open coil.  You might check into Richardsonoceras, Loganoceras, or Manitoulinoceras, for example.  Nice find!

Don

[connorp]

Could be Centrocyrtoceras.

From Figure 11-11 of "Fossils of the Upper Ordovician Platteville Formation in the Upper Midwest USA: An Overview" (Kolata, 2021).

[Tidgy's Dad]

Tremendous find, Mike. 

I like the suggestion of Centrocyrtoceras, as it twists slowly off the flat plane. 

[RCFossils]

Nice find!

Those loosely coiled ones are hard to find that complete.

[minnbuckeye]

I had to re-post. Something goofy happened above. @connorp, I like the suggestion!! But I can not find it mentioned in the Galena, only the Platteville locally. Was it present through many formations?? 

 

Mike

[connorp]

@minnbuckeye According to John Catalani, there is at least one species present in the Galena. You might email him photos to get his thoughts.

"Biostratigraphy of the Middle and Late Ordovician Cephalopods of the Upper Mississippi Valley Area" (Catalani, 1987)

Edited September 21, 2022 by connorp

[minnbuckeye]

@connorp, Funny you should suggest John. I had already forwarded the pictures to him and if it is a unique specimen, offered it up for his collection. apparently he is out on a hunting excursion currently. Will post his response when recieved!

  

Mike

[minnbuckeye]

@connorp, John had a chance to look at the pictures. Here is his response.

I believe that specimen is a gastropod.

They have been variously named Ecculiomphalus and, more recently, Asgardaspira. The most interesting thing about these guys is that they were septate. 

 

 

 

Asgardaspira evolvens (Koken, 1897), CNIGRM 5756 (80/10903), internal mould; A, detail of umbilical wall showing muscle attachment scar (m1); B, oblique basal view showing spiral trace on outer whorl surface and muscle attachment scar m2; C, detail of muscle attachment scar m2; D, upper surface showing broad dorsal ridge; E, detail of circumbilical ridge and groove complex; F, standard orientation of dextral hyperstrophic shell, showing location of muscle attachment scar m1 and the dorsal angulation (da); G, basal surface; H, oblique umbilical view showing circumbilical ridge and groove complex and muscle attachment scar m1 (arrow). Scale bars: 2 mm (A, C); 4 mm (B); 10 mm (D-H).

[FossilDAWG]

I was actually not aware of these septate gastropods.

 

Don