Hi doma,
or alternatively, erosion (perhaps from the action of water on rock, for instance), may cause a shape that looks like a foot.
Not trying to annoy you. It's just if you are doing paleontology, you have to leap the evidential threshold. 200m year old giant footprints in molten rock? Not likely for at least three reasons: the timeline, the biology and the medium.
I think there's often at least one reason that certain theories are excluded from received wisdom.