ID of large intact fossil from Wyoming USA

[Alpineguy]

I have visited this fossil for many years and still am not sure what it is. It is located in the northern Bighorn Mountains, Bighorn County, Wyoming, USA. It's elevation is 2900m (9600 feet) and is embedded in Bighorn Dolomite limestone from the Ordovician Period.  The fossil is 60 cm (23 inches) long and approximately 18 cm (7 inches) wide. One photo shows the fossil with a trekking pole that is 1m long for scale. I am attaching 4 photos.

 

I am new to the site and would appreciate any help that you can give.   Thanks, John Campbell

[FranzBernhard]

Welcome to TFF from Austria?

 

Trace fossil?

Franz Bernhard

Edited 14 hours ago by FranzBernhard

[mighty micraster]

Cephalopod impint?

[Rockwood]

Or maybe combine the two and call it a nautiloid feeding trace?

[Fossildude19]

Looks like an orthocone nautiloid imprint to me.

[anonaddict]

I'd be interested in seeing images of any large orthocones people have found for comparison. perhaps its my lacking knowledge of anatomy but the camerae seem very close, could anyone explain how this works? compared to ammonoids where the camerae are increasing in size or other orthocones where they are _cone_ shaped, this one seems pretty much entirely square which would presumably mean it would have been gigantic?

 

do not take this as definitive in any way it's based entirely on feelings. I also dont know what else it would possibly be. Any info people can provide on this would be much appreciated

 

 

[Rockwood]

4 hours ago, anonaddict said:

I'd be interested in seeing images of any large orthocones people have found for comparison. perhaps its my lacking knowledge of anatomy but the camerae seem very close, could anyone explain how this works?

It's likely an external mold (imprint). That would make the features ribs on the outside of the shell rather than camerae. My initial thought was that they appeared too irregularly shaped. It is likely the condition of the mold that caused me to think that, however.