A Mushroom??

[JK1990QWERTY]

I found this in a river in central Indiana. Looks like a mushroom to me but I'm interested in what you guys think.

[JK1990QWERTY]

[Tidgy's Dad]

Tis an eroded solitary rugose 'horn' coral. 

[TqB]

9 minutes ago, Tidgy's Dad said:

Tis an eroded solitary rugose 'horn' coral. 

I agree.

[Ludwigia]

I agree with my predecessors. Fossilized mushrooms are extremely rare, although I can understand why you took this for one.

[Mark Kmiecik]

A very nice solitary rugose coral. Great find. You should be able to find more and possibly bigger and better. Corals lived in large groups just as they do today, so if one got fossilized you can bet that at least a few thousand of its closest neighbors did as well.