SE Texas - What is this from?

[johnnyvaldez7.jv]

I found this Saturday on a river gravel bank. It's completely mineralized... thin...has an unusual shape and I cannot figure it out. It seems thin like perhaps from a turtle?? But it has such a weird shape plus I don't know if that's an articulated surface on one end... and at the other end... the filler in the center (dark brown) reminds me so much of dentin or cementum which can't be because it's not a tooth. But it looks like that stuff based on what I find here. If it's just a fragment of bone then the interior and exterior are worn to basically match each other in appearance because i can't tell the outside from the inside. Thanks.

[Mahnmut]

Hi,

I tend to call it the proximal part of a mandible, but could not exclude a proximal ulna completely.

Best Regards,

J

[johnnyvaldez7.jv]

@Mahnmut

Wow! That's cool. Never would have guessed it could be a proximal mandible.  I was close saying dentin or cementum was involved but I couldn't see a mandible at all. Mine is pretty thin and I only used this photo to compare what section it came from. Now to see if I can figure out what it might have came from based on size and shape remaining.  Thanks!