Nautiloids or Gastropod? And Bryozoan Branch?

[Pippa]

I went fossilling last Sunday (in the 50sF, in Chicago, in the middle of Winter!)  and found some cool fossil rocks.

I assume this one is either a orthocone nautiloid or a gastropod. Either one will be a first for me, so that's pretty exciting. 

 

No matter what it turns out to be, am I looking at a Steinkern here?

 

 

 

 

Second photo:

I think that #1 might be a nautiloid?  The apparent crushed "spine" is  confusing though. Could it be that the siphuncle does run in a siphuncle "deposit channel"?  And here it was crushed and flattened?

I even researched silurian trilobites, but their spines are much wider in relation to the rest of their bodies than is the case here.

I'm stumped.

 

I believe #2 is a stem of a branched bryozoan which has been worn  so that the inner structures have become visible.  Possible?

Oops,  I forgot to indicate the height of the rock. It's 2cm high.  

The width of the bryozon is about 7mm.

 

 

Thanks in advance to everyone who'll chime in, I appreciate it!

[Tidgy's Dad]

Yes, the first one is a gastropod with the shell eroded away to reveal an internal mold. 

I'm not sure about the others, but number one could be an orthocerid and number two, I think is a solitary rugose coral rather than a bryozoan. 

[Rockwood]

The first one is a nearly complete (internal + external) mold of a tall spired gastropod.

I'm fairly certain that both of the second set are rugose corals. The features are from the center of this form, so look more like dissepiment than the usual septa.

[Ludwigia]

I agree with Rockwood.

[Pippa]

14 hours ago, Tidgy's Dad said:

Yes, the first one is a gastropod with the shell eroded away to reveal an internal mold. 

I'm not sure about the others, but number one could be an orthocerid and number two, I think is a solitary rugose coral rather than a bryozoan. 

 

Yeah, I was hoping for an Orthocerid... but according to Rockwood and Ludwigia, both number 1 and 2 on the second photo are rugose corals. 

Now that I look at them, yes, that makes total sense, that's the rugose's tabulae or columnal that's visible. And other than the long thin shape, it doesn't resemble a bryozoan. 

Oh well. I still like this rock a lot. The horn corals are so differently preserved, they ARE cool, letting us see right inside. 

Thanks much, Tdgy's Dad. 

 

[Pippa]

 

14 hours ago, Rockwood said: The first one is a nearly complete (internal + external) mold of a tall spired gastropod. I'm fairly certain that both of the second set are rugose corals. The features are from the center of this form, so look more like dissepiment than the usual septa.   13 hours ago, Ludwigia said: agree with Rockwood. Hmm, so both the internal and external are visible?  I guess I don't understand. The shell is gone. How or where do you see the external?  Thanks for explaining the horn corals.  Duh!  Now I'm thinking, how did I not see that? Oh well, live and learn...   Thank you both!

 

[Rockwood]

1 hour ago, Pippa said:

The shell is gone. How or where do you see the external? 

Everything that would have been outside the shell is the external mold. Its presence defines the outside of the shell the way the steinkern (internal mold) defines the living space inside.

 

[fifbrindacier]

I agree with the others. I like very much the color of your second piece.

[Rockwood]

10 hours ago, Pippa said:

The shell is gone.

My calling it a mold does imply this. There must be some of the shell body fossil present though. Otherwise the steinkern would just rattle out.

[Pippa]

14 hours ago, Rockwood said:

Everything that would have been outside the shell is the external mold. Its presence defines the outside of the shell the way the steinkern (internal mold) defines the living space inside.

 

6 hours ago, Rockwood said:

My calling it a mold does imply this. There must be some of the shell body fossil present though. Otherwise the steinkern would just rattle out.

Yes, yes, of course! You're so right.

It's funny, I like this piece better than many larger fossils that show lots of detail and are freed from any matrix. What I like here is that I can see how the "animal" through the surrounding matrix, is still at least somewhat connected to the place it became fossilized. Stand-alone fossils found at the beach don't allow me to see this. I guess that's why I keep collecting hash plate rocks, even though I ask myself sometimes, why I need more of them...

 

[Rockwood]

Understood

[Pippa]

 

3 minutes ago, Rockwood said:

Understood

 

Nice, a cousin!

Both these gastropods seem to crawl out of their matrices so they could be found! ;-)

 

[Pippa]

19 hours ago, fifbrindacier said:

I like very much the color of your second piece.

I do too, thank you.