Dermal scute? Epiphysis?

[hemipristis]

Picked this one up at a rock shop when I was back in Philadelphia over Christmas. The lady working that day said this piece was bought by the owner with a bunch of dino bones (mostly vertebra) that the finder said was from Montana.  No other info.  The vertebra that were in the box with this were definitely dino, but in rough shape, so I didn't grab any.

 

This is 13cm x 11cm x 8 mm thick.  It is solidly lithified, and resembles agate.  Based upon shape, my first thought was epiphysis, but do reptiles have those?  Then I wondered if it were a whale epiphysis mixed in with the dino material inadvertently.  But it is agate and very solid, which is unlike any cetacean epiphysis that I've seen.  The patterning on the front and back also don't remind me of the cetacean epiphysises (epipysisi?) that I've seen.  The texture does indeed remind me of dino bone.  So then I wondered if it were a dermal scute.

 

Thoughts?

[Lone Hunter]

Reminds me of a glyptodon scute.