Gonioceras fossil anatomy

[Mochaccino]

Hello,

 

I just purchased this interesting-looking partial Gonioceras "internal cast" fossil originating from Rock County, Wisconsin. I had some questions regarding the anatomy of this specimen:

(EDIT: I forgot to mention dimensions; the rock is about 9cm x 8.5cm)

 

 

 

 

1. From a quick internet search (https://equatorialminnesota.blogspot.com/2016/02/gonioceras-when-nautiloid-is-also.html) it seems the lateral edges of the shell chambers curve away from the body as the shell tapers towards the tip.

 

 

From this information, in this photo of my specimen would the tip/apex be towards top-right and body towards bottom-left?

 

2. Toward the top-right of my specimen, there appear to be exposed cross-sections of portions of the apical chambers. Here I see holes aligned at the center of the chambers looking as if a narrow cylinder passed through them. I'm thinking these are the holes that the siphuncle went through in the animal. Is this a reasonable assessment?

 

3. I read that Gonioceras siphuncles are described as being "sub-central". Judging by the position of the putative "siphuncle holes", would that mean this photo of my specimen is looking at the ventral surface of the animal's shell? Or is this too much to infer from this specimen?

 

Thanks! 

 

 

 

Edited January 28, 2022 by Mochaccino

[Lone Hunter]

I can't answer your questions but that's a neat fossil!  Thought if this was refreshed maybe someone will see it that can help.