Pulmonoscorpius

This is by far the smallest creature of the list, but it would still cause hysteria, and perhaps even some heart attacks, if it showed up today. It was very similar to todays scorpions but could grow up to one meter long, perhaps more, and was armed with sharp chelae (claws) and a venomous stinger. Of course, we dont know how toxic its venom was, but considering the considerable amount it injected with each attack, it was most likely a very deadly critter indeed. A predator, Pulmonoscorpius roamed the swampy forests of the Carboniferous in what is today Scotland. Just so you know, during the Carboniferous there were also giant roaches the size of house cats, dragonflies the size of hawks, and centipederelatives up to three meters long. No kidding.