The Pulmonoscorpius were giant terrestrial scorpions that lived in the Carboniferous Period and reached as much as 50-70 centimetres long; a truly gnarly and frightful creature for many no doubt. Fossils of this creature have been found in Scotland, UK. The reason of why they were so large, when we compare them to scorpions today, is that the higher oxygen level prevalent at the time (over 60% higher than today), allowed the arthropods to grow to very large sizes. This is because it was easier for the oxygen to be taken in by their invertebrate, ''book lung'' respiratory systems, due to it being much more readily available in the atmospheric composition.
In turn, it was easier for them to process, and quicker. It also meant that all animals, vertebrate or invertebrate, were able to move with less energy expenditure than under conditions we are familiar with. This would make them potentially scarily quicker than we might otherwise have thought they were, grimly enough. The downside of the super oxygenated atmosphere, fuelled by the lush, near global terrestrial forests, was that it was potentially volatile. In other words, prone to being ignited and causing massive forest fires instantly. These would feed off both the massive amount of bio-matter in the palaeoecosystem, but the immense oxygen. Plenty of carbonated matter rotting in the swamps, becoming a fuel source all of its own over geological history (as in, coal, oil and gas fossil fuels) was probably also liable to ignite.
Pulmonoscorpius would have had no defence against such a catastrophe, being able only to flee in fear like all other animals that could, from them. However, Pulmonoscorpius eventually became extinct when the changing climate destroyed its old swamp forest habitats, a fate suffered by many Carboniferous Period fauna and flora.
They fed on smaller arthropods and tetrapods and they were probably preyed upon by the giant labyrinthodont amphibian Crassigyrinus.
Several Pulmonoscorpius were shown in the fifth episode of Prehistoric Park (The Bug House). Nigel Marven was stung by one of them but the venom had not evolved enough and wasn't capable of killing him.