Why are mamoswine and relicanth not fossils? Also, Relicanth should evolve into a Dunkleosteuss pokemon. Cool idea, no?
Well, the whole point of Relicanth is being based on something that’s actually not extinct but just looks like it should be. Making Relicanth a fossil would sort of defeat the purpose, in a way. I mean, you could have Relicanth available as both a fossil and a wild Pokémon, which I think would be a cool way of emphasising its unusual status, but from Game Freak’s perspective, why would you do that? And would most players actually like that, or would they feel cheated by getting a ‘fossil’ Pokémon that they could just catch normally? Dunkleosteus… eh. Sure? It is again kind of defeating the purpose of Relicanth, but it’s not like evolutionary history in the Pokémon world makes any damn sense anyway.
As for Mamoswine… well, one of the ideas I have about fossil Pokémon is that they’re all Rock-types because Rock-type skeletons are unusually robust, and so representation in the fossil record is overwhelmingly skewed towards Rock Pokémon. Fossils of prehistoric Pokémon of other types – including Mamoswine – are rare enough that we just never come across them in the games.