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Clams in coal shale ?


Rockwood

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Found on a coal shale dump near Jolliette, PA. Fresh water bivalves ? Marine bivalves washed in during a transgression ?

Or could they be Branchiopods ?

Other ?

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IMG_4514a.jpg

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Certainly bivalve. My first guess about carboniferous bivalves is always Carbonicola but it is just a guess. Bivalves can be very tricky. Somebody with experience of your area will be able to help.

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These actually look like conchostracans to me. (Clam shrimp)

Something similar to Cyzicus or Estheria.

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I'm not honestly sure how you can tell from first principles that they aren't bivalves but I agree with Tim. They look like ones I've seen that other people have told me are Estheria. :)

 

Tarquin

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16 minutes ago, TqB said:

first principles

Refers to the form of preservation, or would a few more examples help ? 

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Very difficult to tell just by looking if they're chitinous or not. But they look like conchostracans. 

I'm just wondering, as in your original post, if there are juvenile/dwarf bivalve molluscs that are effectively indistinguishable.  

Tarquin

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13 minutes ago, TqB said:

Very difficult to tell just by looking if they're chitinous or not. But they look like conchostracans. 

I'm just wondering if there are juvenile/dwarf bivalve molluscs that are effectively indistinguishable.  

I see. Pesky convergence, sort of has me. 

Thanks 

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As others have suggested, these are conchostracans. They're pretty common in the freshwater Carboniferous and Permian shales of Pennsylvania, which is exactly where you are finding them. They indicate that the environment where the rocks were deposited had lots of temporary water pools that would flood part of the season but be dry during other parts of the season. That sort of severe seasonal climate (a "megamonsoon") is characteristic of the late Carboniferous.

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3 minutes ago, jdp said:

As others have suggested, these are conchostracans. They're pretty common in the freshwater Carboniferous and Permian shales of Pennsylvania, which is exactly where you are finding them. They indicate that the environment where the rocks were deposited had lots of temporary water pools that would flood part of the season but be dry during other parts of the season. That sort of severe seasonal climate (a "megamonsoon") is characteristic of the late Carboniferous.

Can you point out the salient ID features in the pics above to help with future possible ID's as I'm sure I may have overlooked conchostracans in the past. Thanks.

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For one, not all of them are complete, and when they broke down (prior to deposition), they seem to have broken along the ridges rather than cracking like a clam shell would. Additionally, the concentric ridges do not always extend uninterrupted across the entire animal. Finally, there is no interdigitating tooth structure in the valve where the two sides would have met.

 

If these were clams, you'd also expect to see a separate calcitic shell in there as well, instead of simply glossy impressions.

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Thanks to this thread I have re-examined some of my samples that were destined to be ignored and I think I can now say deserve more study and some may actually be conchostracans. I'm hoping for a glimpse of an appendage....

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Having found conchostracans before..they sure look the same as mine.

"Faith is to believe what you do not see; the reward of this faith is to see what you believe" - Saint Augustine

"Those who can not see past their own nose deserve our pity more than anything else."

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I will join the chorus in agreement about the clam shrimp ID- the genus Leaia is commonly associated with Pennsylvanian plant fossils in central Illinois, and look very similar to these.

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