Pennsylvanian mystery of Arizona!

[gieserguy]

Hey all, last week I was visiting my grandma in Arizona, and of course I had to stop at a local fossil spot!

I’m just now cleaning up everything we collected (I’ll hopefully post a trip report tonight !!!) and I revealed this little thing from the mud. 

I believe the brachiopods on the flip side are Derbyia crassa. If you could help me with my little mystery, I’d really appreciate it!  

From the Pennsylvanian Naco Formation of Arizona. 

 

 

 

 

[gieserguy]

As I was going through the rest of the fossils, I found another piece that appears to be from the same spot, with the same “white mystery fossil” and the same species of brachiopod on the flip side. 
 

 

 

[DPS Ammonite]

I agree that the ribbed brachiopods are Derbyia crassa.

 

The mystery fossil is poorly preserved. It might be a bivalve such as Myalina. 

See fossils from the Naco:

 

http://www.savalli.us/BIO113/113downloads/FossilIDGuide.pdf