Turtle Nuchal Bone

[GPayton]

Found on the Brazos River just southwest of Houston. I'm fairly confident that this is a nuchal bone, but I my real interest lies in identifying what species of turtle it is from. I seem to remember reading a post on here mentioning that nucal bones are diagnostic to taxon, so that should make it easy. Unfortunately, I can't find anything anywhere about different Texas Pleistocene turtle species. Hopefully someone here is more knowledgable than me! I would appreciate any suggestions.  

 

[Harry Pristis]

Probably not too different from Florida turtles in the Pleistocene, but that's a guess. I don't recognize your specimen -- it's incomplete and quite stream-polished.  Here are some Florida specimens:

 

 

[GPayton]

What I can't figure out is why there seems to be a groove running down the middle of my piece. In all of the pictures you provided this feature is either entirely absent or replaced by a crest with a groove on each side. I wish Texas had books specifically about Pleistocene fauna the same way Florida does, but unfortunately it seems like we're out of luck on that front. 

[Harry Pristis]

I did notice the apparent lack of symmetry in your find.  I assumed that it was caused by stream-wear.

 

OTOH, I provided an image showing the variation possible in these bones -- it's quite pronounced.  (These are museum IDs, BTW.)

 

 

[turtlesteve]

The front of the nuchal is missing which may hamper identification.  It seems generally consistent with pseudemys or trachemys though.  
 

The extra line is likely a scute boundary that should not be there (e.g birth defect).  Look up turtle “split scutes” on google.