Largest scorpion ever, size of a baseball bat, roamed Earth 415 million years ago

Imagine a scorpion the size of a baseball bat scuttling over mossy rocks and ancient, tree-like structures before slipping into a nearby stream. This is how scientists describe the Praearcturus gigas, the largest scorpion known to have existed, which roamed what is now Great Britain around 415 million years ago.

Researchers arrived at this fascinating new understanding by re-examining fossils that had been housed in London's Natural History Museum for over a century. By combining these specimens with newly discovered fossils, they were able to create a more complete picture of the organism, which was once thought to be a type of crustacean. Scientists estimate the Praearcturus gigas measured about one meter in length, a finding detailed in a study published on June 2 in the journal Palaeontology.

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It's a truly hefty creature. You wouldn't want to run into it in a dark alley. It would be a real beast.

"It's a truly hefty creature," said Russell Bicknell, a paleobiologist at the University of Adelaide in Australia, who was not involved in the research. "You wouldn't want to run into it in a dark alley. It would be a real beast." Earlier research on the scorpion, first identified in the 1870s, suggested it might belong to a group of crustaceans known as isopods. It wasn't until the 1980s that scientists began to consider it a different type of arthropod, specifically, a scorpion.

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The key evidence that the fossilized remains belonged to another species was a 2015 study that described a scorpion found in Canada.

The research team utilized CT scans and other methods to study the specimens. Key evidence confirming the fossilized remains belonged to a scorpion came from a 2015 study describing a scorpion found in Canada. This animal, Eramoscorpius brucensis, shared a crucial characteristic with P. gigas: its sternum, the plate on the underside of the body between the leg bases, was long, triangular, and grooved down the middle, identical in both species. This similarity indicates they are closely related animals.

P. gigas lived during the early Devonian period, a time when life on Earth was still largely confined to water. The presence of such a large scorpion so early in evolutionary history is surprising. "It's much earlier than we would expect giant arthropods to appear," said study lead author Richard Howard, curator of fossil arthropods at the Natural History Museum.

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It's much earlier than we would expect giant arthropods to appear.