Just a rock?

[that_one_girl]

Found this while hunting for fossils in South-Central Minnesota. Most of the fossils we found were easily identified brachiopods.The shape of this rock was very different from those around it. The curve was so uniform, maybe it's just a rock. I am less than a novice at this so I really don't know. It also appears to have some plant fossils on it and between some layers. Maybe Bryozoan?? I would really appreciate some help in identifying any feature in the picture. Thank you so much!

 

The first photo is the back, second picture is close up of the front, third picture is broken side showing layers. The other sides are smooth with no lines or visible patterns. 

[Kane]

I think your guess of bryozoan is on the mark. I believe I can make out the small zooecia in your piece.