Great but unidentified fossils from Kankakee River

[jmay]

Found all three of these at different times in Kankakee River State Park in Illinois. In the river. 

 

Two of them were just laying out. I got the other one hammering rocks. The rock it was embedded in was kind of a medium sandstone.

 

(EDIT - I'm just attaching two because of the MB limit. You can see one of them from two different angles, including the interesting stuff in the middle, and the other from a single angle. I can post more if needed).

 

I'm fascinated by the three-dimensional quality of these. The one - you can see pretty well - even seems to have some internal structure visible, looks like a notochord, but who knows.

 

Anyway, at first I thought that I had Tully Monsters, until I learned those are never found in this form or location. Then I thought maybe I had ammonites, but apparently those are very rare in the Midwest, so I'm not so sure. 

 

What do we think?

[Kane]

Welcome to the Forum.  

 

The first piece looks like an orthoconic nautiloid. Not sure about the second piece, which could be a concretion.

[Fossildude19]

Welcome to the Forum.  

 

The second piece could be the siphuncle of a large orthocone cephalopod. 

You might check out Rob Russell's cephalopod gallery.

I believe he is from that area. 

Regards,

 

I took the liberty of cropping, turning, and brightening your photo.

 

[Innocentx]

Some forum info regarding your find:  

 

[deutscheben]

I agree with the others that these two pieces are both cephalopods, most likely Silurian in age. These are not particularly rare in Illinois, and can be found at a few different sites, but they are still neat! You should post your other find in here as well.

[Rob Russell]

Your First photo is a piece of Dawsonaceras cephalopod.  The second appears to be a  siphuncle of a larger cephalopod, as Tim mentioned.  And Your third pice may be a cross section of a burrow or another cephalopd.  

All Silurian in age, and from the Sugar Run formation.