Fossil Reclassified as Largest Known Scorpion After Century-Long Debate

A study published June 2 in Palaeontology reclassifies Praearcturus gigas, a set of fossils housed at the Natural History Museum in London since 1870, as the largest known scorpion to have ever lived. Originally described as a giant isopod, the species was debated for over a century, with proposals ranging from a millipede relative to a sea scorpion. Paleobiologist Richard Howard and colleagues re-photographed, traced, and CT-scanned the specimens, comparing them to other ancient arthropods. Key clues included the pincers' movable finger pointing away from the fixed claw—a scorpion trait—and a long sternum with a groove shared with Eramoscorpius brucensis, a fossil scorpion discovered in Canada in 2015. The ancient scorpion, estimated at four to five times the length of the largest modern scorpion Gigantometrus swammerdami, lived about 415 million years ago in what is now England and Wales. Researchers suggest it grew large due to a lack of other large predators and may have hunted in fresh water. Some scientists, like Jason Dunlop of the Museum of Natural History in Berlin, remain skeptical due to the fragmentary nature of the fossils.