Wouldn't you need calcium for bones? Or both? Anyway there are plenty of animals that don't have bones - and there's no reason to assume our chemical kind of b

Wouldn't you need calcium for bones? Or both? Anyway there are plenty of animals that don't have bones - and there's no reason to assume our chemical kind of bones are the only kind possible. You could maybe have iron bones evolve on some worlds - I don't know of anything that would prohibit that.