Temnoclast - the paradoxical amphibian pokemon
Temnoclast is an ancient pokemon that can be revived from a gill fossil.
The reason for temnoclast’s exctinction is clear just from looking at it. The pokemon became adapted to living inside volcanoes during a mass extinction, but since they were amphibian pokemon they couldn’t live for very long without water. Once the volcanoes became dormant, temnoclast were overtaken by their close relatives, wooper, who were much better at being amphibians.
Water is necessary for the survival of a temnoclast, as they will dry out without it, but it has to be boiling hot for it to be bearable to the pokemon. Ideally the water should be even hotter, but this is not possible without high pressure, which is expensive and dangerous, and also harms the pokemon due to its nature as a rock type. It is thought that the pokemon only lasted so long because they found hot springs near their volcano homes.
Temnoclast are slow both on land and whilst swimming in lava, as there is no need for speed when you can just avoid predators in lava by going on land, or avoid predators on land by going in lava. Temnoclast may have been one of the first tetrapod pokemon.
[I wish I was better at drawing temnospondyls because they’re really cool.]