Prehistoric is one odd ability. I think it should mean it dies to natural moves because they where extinct when we made all of this technology.
That would mean these are only hit by natural types (Normal, Bug, Flying, Rock, Water, Grass, Fire, Ground, Ice, Fighting, Dragon, and Poison) and not man-made ( Ghost, Dark, Steel, Electric, Psychic)
But, because some of these have gone extinct due to a volcano or a meteor, or whatever you believe, each one with the ability has no resistance or weakness to Poison and Ice. This means Outrados is not weak to Ice and Impenedon is vulnerable to Poison attacks.
Does this seem over-powered?