Crustacean body part or fish? Concretion fossil from Missouri

[Samurai]

Location is in Missouri

The area is dated to the Pennsylvanian 

Formation:  Muncie Creek Shale 

 

I assume this could be some part of a fish, as I have found other parts of them inside a few of the concretions from the Muncie Creek formation such as cartilage, or it could be some sort of crustacean part but I do not know what this one could be.

 

[Missourian]

It looks similar to shark fins I've found in the Muncie Creek:

 

 

 

Chondrichthyan cartilage would be indicated by cellular structure shown in the second specimen.

[Samurai]

5 hours ago, Missourian said:

 

Chondrichthyan cartilage would be indicated by cellular structure shown in the second specimen.

While It is most likely fin in nature, I would like to mention how bizarre these "fish fins" are,

It is very difficult for me to visualize/know if these are merely quirks of fossilization, or what they would actually look like 

[jdp]

So technically that is not cellular structure; it is tesselated calcified cartilage. The tesserae are far bigger than individual chondrocytes. 

 

In terms of overall anatomy, there are good specimens of animals like Fadenia and Campodus preserved in various black shales in Illinois, Nebraska, etc. Something like this might be a good example:

 

 

 

You're only seeing a couple of those little cartilage rods, called pterygiophores, which support an otherwise sharklike fin.