>>48188120Maybe. Legendary pokemon is kinda vague concept but boils down to mysterious folk tales and their existence is questioned. While fossils are known to exists and there is concrete proof. What about unown? Is it common knowledge in pokemon world?
Rock type consists of prehistoric animals like fossils, dino, rhino, golem, turtle etc. Then there are weirder ones like onix, sudowoodo, shuckle, lycanroc but did not look if there is explanation for them. Few ground types that could have been rock type but were not, claydoll, golurk, runerigus. Gen 1 beta also had that ghost kabutops, it is possible rock might have been pure fossil mon type but they slapped it to few others.