Speaking of which, I was just reminded of Relicanth, the Poké-version of the coelcanth. It somehow managed to survive the vast extinction approximately 65 million years ago, though no one knows why. And especially since it barely changed over the millenia. I wouldn't call that immortal, since Pokémon do reproduce. These are the descendents of those long ago, yet have adapted to the environmental changes. Makes you wonder why it is other prehistoric sea creatures didn't survive. It's called natural selection.
WAIT. *thinks* No... there was that episode from the first generation at Grand Father Canyon (I believe that's the name) where Ash and Team Rocket fell through a hole due to explosives and woke up hibernating prehistorics. Which doesn't make sense how they survived that whole time. That's like saying a frozen mammoth is only taking a nap and that melting the ice would wake it up
.
And people have mentioned the fossil Pokémon ressurected are clones. I guess this meant that Mewtwo ISN'T the only successful, living clone in existance. I find that funny, actually. Supposedly, because cloning is so imperfect, no specimens survive. And yet, scientists have been cloning successfully prehistoric Pokémon before Giovanni went power-hungry.