Is This A Crab Claw?

[BLT]

Hello,

 

I’m hoping someone can tell me whether or not this is a crab pincer? If not, what could it be? I found it in Alabama on the Tennessee River. (Mississippian)
 

Thanks!

Edited December 29, 2021 by BLT

[ClearLake]

I think Mississippian age is a bit to old for this to be a crab claw.  It is probably some type of mineral inclusion.  But someone might have a more definitive idea.

[BLT]

Gotcha. Thanks!

[Plax]

talk about a ringer though! If you said it was cretaceous the first guess would be crab claw

[Crusty_Crab]

Short answer: in my opinion no, this is not a crab claw, just a suggestively shaped nodule.

 

Since I'm just a rando on the internet giving my unqualified opinion, I will try to lay out my rationale.

 

Line of evidence 1: From appearances, the texture is too uneven and rough to suggest a crab's exoskeleton and the outline doesn't actually conform to a claw.

 

Line of evidence 2: If it were in fact Mississippian in age, it would be extremely unlikely to be a crab. The thinking so far is that true crabs (Brachyurans) diverged from their lobster ancestors sometime during the early Jurassic and radiated rapidly during the Cretaceous. As an aside, there are other Crustaceans that look like crabs but are not true crabs (Anomurans) but they emerged later. However, crabs are not the only Crustaceans with claws and the molecular evidence for lobsters extends potentially past the Mississippian, but it is highly unlikely you found one due to the next line of evidence. 

 

Line of evidence 3: Crabs are actually unusual in the fossil record, and the thinking is that they require some very special conditions to fossilize. The matrix is not consistent with what is normally found with crabs. Most commonly, they are found in concretions, fine grained shales, or impressions in limestone. If I had to guess, this looks more like a limestone but is not an impression.   

Edited December 29, 2021 by Crusty_Crab

[BLT]

5 minutes ago, Crusty_Crab said:

I will try to lay out my rationale.

Thank you! I appreciate your taking the time to explain things.

[minnbuckeye]

I think you just posted something that was IDed as primitive shark teeth. Could this be a boney piece from similar fish?

[BLT]

1 hour ago, minnbuckeye said:

I think you just posted something that was IDed as primitive shark teeth. Could this be a boney piece from similar fish?

That’s right. Here are three more pictures of different areas of this rock. I cannot find my micro lens, but I tried to zoom in on a couple of tiny bits that *might* be pieces of bone. One is more of an outline just under the surface. Any thoughts on those areas? Are they just crushed shell fragments? 

[Coco]

On the first and third photo of the last post, it looks like a crinoid stem element.

 

Coco

[kgbudge]

8 hours ago, Coco said:

On the first and third photo of the last post, it looks like a crinoid stem element.

 

Coco

Agreed. The five-pointed hollow center is a dead giveaway.

[BLT]

Gotcha. Thanks!

[abyssunder]

The five-folded internal structure is the place of the lumen. I agree with the crinoid columnal fragment ID.

[abyssunder]

Maybe the fist photos may have syneresis cracks?

 

[Plax]

On 12/29/2021 at 12:55 PM, Crusty_Crab said:

 

 

Line of evidence 3: Crabs are actually unusual in the fossil record, and the thinking is that they require some very special conditions to fossilize. The matrix is not consistent with what is normally found with crabs. Most commonly, they are found in concretions, fine grained shales, or impressions in limestone. If I had to guess, this looks more like a limestone but is not an impression.   

In the east decapod claws are quite common. Whole ones are even common in some strata. I agree with the balance of your evaluation.