The iguanodon's fingernail

Once, this was thought to be a horn. Through some studies, this was corrected as a fingernail of a thumb. We don't know what the iguanodon used this big fingernail for. Because the iguanodon was a plant-eating animal, it may have used the fingernail for fighting with predators.
Even now, we don't know whether this is a fingernail actually, because we had never seen iguanodons. Ten years later, scientists may say that this is a horn again.