Pulmonoscorpius kirktonensis is a giant, extinct species of scorpion that lived during the Visean epoch of the Carboniferous. Its fossils were found at East Kirkton, West Lothian in Scotland. In life, this monstrous species would have grown to be up to 1 meter in length, and bore a superficial similarity to smaller, modern scorpions. Pulmonoscorpius was thought to have reached such a large size because of the higher atmospheric oxygen content in the Carboniferous. This was 35%, whereas today's is only 20%. It is believed to be a diurnal hunter because of the presence of relatively large lateral compound eyes, which have atrophied in the primarily nocturnal modern scorpions. As with all other known scorpions, P. kirktonensis is assumed to have been a predator. However, because the stinger w