...fossils aren't made of bone.

They're rock.

You should inform your friend of this and then laugh in their face at how ignorant they are.

Seriously, how conceited do you have to be to think you're capable of overthrowing hundreds of years of scientific work, when you know precisely shit-all about the subject at hand and have made no attempt to research it?

Sometimes the only way to deal people like this is by shaming them.