Pelecypod from North Dakota ID

[Nimravis]

I am looking for help on some pelecypods that I recently acquired. 
 

The Id states that they are Paleocene in age and from the Tongue River Formation of Riverdale, North Dakota.

 

 

 

 

 

[ClearLake]

Interesting,  Here is a link to a thesis that lists many of the bivalves from the Tongue River Fm.   It looks like Unios might be a possible genus for yours, but at least something in the family Unionidae

 

https://commons.und.edu/cgi/viewcontent.cgi?article=1062&context=theses

[ClearLake]

@Thomas.Dodson is pretty familiar with North Dakota stuff, he may be able to give a more definitive answer. 

[Thomas.Dodson]

Nice finds. I concur with unionids.

 

I wish I could keep the answer that simple. First let me say that Paleocene deposits (with the exception of the Cannonball) have a history of poor differentiation in North Dakota which makes keeping track of some organisms in the literature difficult. That said, there isn't a lot of good info on the molluscan fauna of the Fort Union Group/Formation (which includes the Tongue River). This is a primarily terrestrial group. I'm familiar with a thesis 2 years after the one ClearLake posted that only lists Plesielliptio priscus (Meek and Hayden) and Rhabdotophorus senectus (White) as the unionids that occur in the formation of the area both thesis were written. https://commons.und.edu/theses/72/ By the way, "Unio stantoni" that ClearLake's thesis mentions is now also placed is Plesielliptio. These sites aren't actually close to Riverdale. There are Fort Union group and Tongue River outcrops is the area but all the ones I've seen there are terrestrial so the only records of these unionids come from Golden Valley and Billings county to my knowledge.

 

 

 

 

[Nimravis]

@ClearLake and @Thomas.Dodson thank you both for the info, I really appreciate it very much.