Unknown vertebrate from upper kootenai formation (gastropod beds) in the block mountain area outside of Dillon Montana.

[Necropedia]

Hello all. I was hoping for additional insights on what this may be as well. I know this is a vertebrate bone of Cretaceous age found near block mountain outside of Dillon Montana during a classical  mapping trip. 

 

On one side of the specimen there is a prominent yet thin plate of bone with a robust ridge along one margin. On the opposite side of the specimen is a rectangular structure which may be a scute or possibly another type of mineralized structure. Any insights are appreciated. 

 

 

[jpc]

chunkosaurs?

Hard to tell from the photos.

How small are they?