This is a fossil from the devonian era, measurements in pictures. This piece is fairly heavy, I assume, due to the stone the fossil is lodged in. I can see what looks to be shell and non-silt/sandtone material in the rock. It's possible there are more fossils embedded in the rock that could be carefully extracted, but I wouldn't wager anything more interesting is there. I have an email from a paleontology professor at the University of Michigan that verified it is an actual Devonian Cephalopod, email in pictures.
Discovered this myself in Petoskey MI
Thank you for contacting Mearto with your appraisal inquiry. So that I may best assist you, can you please state the measurements? Thank you.
With kind regards,