Snyder TX - Bi-valve

[MSirmon]

I found this gorgeous bi-valve In the side of a road cut near Snyder TX peaking out from under the roots of a prickly pear. Any ideas on identification?

[caldigger]

@Max-fossils

[Spoons]

Do you have any info on Stratigraphy? What age are the rocks where this specimen comes from. 
 

My initial thoughts are something in the genus Macoma?

[MSirmon]

2 minutes ago, Spoons said:

Do you have any info on Stratigraphy? What age are the rocks where this specimen comes from. 
 

My initial thoughts are something in the genus Macoma?

Thank you. I believe the area is Cretaceous 

[JohnJ]

Michael, your find appears to be a relatively recent mussel shell.  Lots of easy scenarios could put it in the roadcut.  Research freshwater mussels to find a match.

[ClearLake]

I think @JohnJ may be on to something here. I have looked through the HGMS volume on Texas Cretaceous Bivalves and do not see anything that matches your shell. But I do see the Pimpleback (Quadrula pustulosa) in my book on modern Texas freshwater mussels that seems to look pretty similar to yours including the namesake pustules on the surface.  We’ll see what others have to say.  

[JohnJ]

10 minutes ago, ClearLake said:

I think @JohnJ may be on to something here. I have looked through the HGMS volume on Texas Cretaceous Bivalves and do not see anything that matches your shell. But I do see the Pimpleback (Quadrula pustulosa) in my book on modern Texas freshwater mussels that seems to look pretty similar to yours including the namesake pustules on the surface.  We’ll see what others have to say.  

 

It is a highly eroded find.  I suspect it is a Quadrula sp., too.  

[Pemphix]

And, what is unusual for cretaceous mussels from this area is that nacre can be seen.

So I'm with JohnJ, too.

[Max-fossils]

After looking at Quadrula specimens after @ClearLake and @JohnJ mentioned that genus, that definitely does seem to fit pretty well. I'm also afraid that the shell is probably recent (geologically speaking). I had never heard of this genus before though, and that hinge is nuts! Very cool, thanks for indirectly teaching me something new guys  

 

However, to answer @Spoons's suggestion of Macoma, I can see why you said that as the overall shape is quite similar, but the hinge is clearly inconsistent. For reference, here are some Macoma balthica specimens (that I collected on the Zandmotor, Netherlands; these are from the Eem Formation, Eemian, late Pleistocene ~120'000 years old) where their hinge is clearly visible:

The top-right one has a very well-preserved hinge, and if you compare it to the hinge of the OP specimen, you can see that they're very different. This one has a very thin hinge with two small teeth, while the specimen in OP has a really 'fat' hinge, that includes a 'spoon' with 4 teeth, a tooth on either side of the spoon, and a long lateral tooth running down its right side. The hinge area is always a really important factor when identifying different bivalves from each other, as it is usually quite distinctive. 

Hinge set aside, there are 2 other differences between the two genera: the little bumps on the Quadrula never appear on Macoma (except maybe if it has some kind of pathology, but I've never seen it), and the nacre of the shell: Macoma are never nacreous. 

While this may seem tedious, all of these differences are actually more important than you think, because as a consequence, the two species are more distantly related than we humans are to dolphins (different Orders) according to the Linnean classification. Anyways, I hope that this explanation will help you in future bivalve identifications  

[MSirmon]

Thank you everyone. This was a great opportunity for me to learn and I appreciate your patience.