Where Does the Rock End and the Fossil Begin? + Other Identification

[Salamander0421]

Hello. This is my first real post to these forums, so let me know if I do something incorrectly. I found these last year in Montana, USA. For the first one, I’m not quite sure where the fossil ends and the rock begins. I am worried about accidentally chipping away the fossil.  It's 10x5.5cm. Here is the piece in question:

 

 

 

 

 

I also found two other large pieces. The first I will call “trident” (because it has three prongs). It's 8 x 7.5cm. I am wondering where the rock begins and fossil ends on this one as well:

 

 

 

And the last one, which is 5 x 4cm:

 

 

Thank you and good luck!