Tentative guess, giant scute? Limestone cave find.

[Fishkeeper]

This is in a limestone cave out in West Texas. I don't know anything further, I'm not there in person- the pics are from my brother. It looks a little like a turtle shell to me, but not segmented like they are.  What really comes to mind is a crocodile scute, but I don't think there were any giant crocodiles in Texas, and I don't think any of them got quite THIS big anyway. 

The size of it really has my attention. If it was tiny, I'd think it was some form of invertebrate sea life or another, something I'm just not familiar with. That size, though? I have no idea. 

(Best picture they could get, it was by flashlight. Second pic shows texture.)

 

[grandpa]

So, W. Tx. is a pretty big area, bigger than some states, and I'm not sure what part of W. Tx. your brother is in, but you might find this interesting:

 

https://www.nps.gov/bibe/learn/nature/deinosuchus.htm

 

I'm not saying it's a croc, I'm just saying.

[Rockwood]

It would really need to be cleaned up a bit. I wouldn't rule out a dislocated piece of cone in cone structure though.

[FossilNerd]

1 hour ago, Rockwood said:

It would really need to be cleaned up a bit. I wouldn't rule out a dislocated piece of cone in cone structure though.

I agree that it could be some sort of dislocated cave/geological structure and more cleanup would be necessary. Limestone can have some strangely weathered and water eroded shapes. Doubly so in a leaky cave.