Researchers reclassified Praearcturus gigas from 410-million-year-old British fossils as a giant scorpion, identifying it as one of the earliest known large arachnid apex predators.
CT scans, digital reconstructions and reanalysis of all known remains found hallmark scorpion traits, including grasping pedipalps, an elongated triangular sternum and a possible sound-producing organ.
The study also folds Brontoscorpio anglicus and Bennettarthra annwnensis into Praearcturus gigas, expanding the fossil record and supporting a fuller body reconstruction with claws about 16 cm long.
Lateral abdominal expansions and river-deposited sediments suggest the animal was aquatic or amphibious, likely feeding in freshwater as well as on land during the Early Devonian.
That habitat would imply scorpions moved from water to land more gradually than thought and that giant arthropods evolved before later high-oxygen periods.