Devonian Pokemon

Petrobyte, the 3-lobe pokemon
Petrobyte is an ancient rock and bug-type pokemon from before the age of dinosaurs. Their fossils are some of the most common all over the world, illustrating how successful they were in their time. The seas they lived in were rich and vibrant, full of pokemon ancestors like anorith and kabuto. It is believed that they died out when the climate turned hostile and they were unable to adapt, possibly because they could not evolve. It is unknown why ancestral petrobytes did not evolve, though several theories exist: some scientists believe that their diet or the chemical composition of the ocean stopped them from gaining the necessary energy for evolution, while others believe the ability for revived petrobyes to evolve is a form of mutation. Petrobyte evolves into Xenobyte at level 40.

Xenobyte, the 3-claw pokemon
Xenobyte is a medium-sized rock and steel-type pokemon who does not appear in the fossil record, despite evolving from a fossil pokemon. Its appearance is vastly different from its previous form, leading some scientists to wonder if this evolution is a mutation brought about from the fossil revival process. If the evolution is natural and merely unattainable while the petrobytes were alive millions of years ago, it raises questions about what our own futures could have looked like. Xenobyte would have been the top predator of its time, its slashing tail and sharp claws the match of any land or sea-based pokemon, while its armoured head and back would have protected it from the teeth and claws of its would-be predators. This utter supremacy would have let it dominate the landscape, and if petrobyte had ever managed to evolve into xenobyte in the past, modern pokemon and humans may not have had a chance to exist.