Platteville Cephalopod

[Reklaw]

So this is a fossil from Beloit Wisconsin found in the Platteville formation. I am pretty sure it is a cephalopod but I have no idea what genus or species. The siphuncle is hollow except for two septa that run right through it. 3" post-it note for scale.

[FossilNerd]

I agree that it is a cephalopod, but I think it will be hard to say what genus or species this is. There are a few different straight cephalopods found in the Platteville Formation (Ordovician). It might be a section of Actinoceras, as I believe it is fairly common in that formation, but not sure.

[Manticocerasman]

I would keep it at "Cephalopod orthocone" It will be hard to make out more of it.

[FossilDAWG]

The straight siphuncle without deposits,and the lack of deposits in the camerae, is suggestive of a michelinocerid.  Actinocerids have large siphucles, which expand into the camerae (so they look like a string of flattened disks strung together), filled with deposits.  In addition the camerae are filled with deposits on the ventral side.  Basically, michelinocerids were active swimmers with lightly built shells and actinocerids lived on the sea floor and had heavy deposits in their shell to weight them down.

 

Don

[Reklaw]

Thank you! Looks about right to me!

[Reklaw]

An update to this post, I found a very similar looking fossil in "The Geology of Minnesota" (1872) and it is labeled as a Tripteroceras planodorsatum. And I found another one that was out of the matrix with the characteristic flattened triangle shape of the Tripterocerids, so I am pretty sure it is in fact a T. planodorsatum not a michelinocerid.