Horn coral or calamite?

[Sam S]

I found these two fossils at my camp in munising, Michigan thinking that they were horn coral fossils. But now I am having doubts and am thinking they might be calamite fossils (or some sort of plant fossil). 

[caldigger]

Looks to be horn coral impressions.

[Rockwood]

Agreed. The nodes wouldn't be that close even if such a three dimensional  external mold of a calamites were formed.

[Carl]

+1 for horn coral

[Sam S]

Ok thanks for all of your help! Most of the fossils found at this site are corals and bryozoan so it doesn’t make much sense that these two specimens would be calamite. These are definitely horn corals but I think the way that these fossils formed threw me off as this formation of horn coral is uncommon for the site at which I found them.

[Rockwood]

2 hours ago, Sam S said:

I think the way that these fossils formed threw me off as this formation of horn coral is uncommon for the site at which I found them.

Horns are basically growing in a way that keeps them up where they can feed. That means that the shape of their theca varies with the conditions that that individual encounters.