The largest scorpion to walk the Earth was more than 3 feet long - CNN

- Scientists revisited fossils at London's Natural History Museum that sat misidentified for over a century before recognizing them as scorpion remains.

- The creature measured roughly 3 feet long and lived 415 million years ago in what is now Great Britain.

- Researchers believe the baseball bat-size scorpion lived an amphibious lifestyle and fed on primitive fish in ancient streams.

Imagine a huge scorpion the size of a baseball bat, scrambling over mossy rocks and around large, treelike structures before slipping into a nearby stream.

That’s how a team of scientists describes what the largest ever known scorpion would have looked like as it prowled its environment roughly 415 million years ago in what’s now Great Britain.

To arrive at this fascinating new understanding, experts revisited fossils that had been in London’s Natural History Museum for more than 100 years. Piecing together those specimens along with more newly discovered fossils allowed the group to form a more complete picture of an organism that was once thought to be a crustacean, much like lobsters and other shellfish.

Praearcturus gigas was roughly 1 meter — a little more than 3 feet — in length, the scientists estimated in a study published June 2 in the journal Palaeontology.

“That is a chonky-looking organism,” said Russell Bicknell, a paleobiologist and research fellow at Flinders University in Adelaide, Australia, who wasn’t involved with the new report. “You would not want to run into this thing in a dark alley. It would be an absolute beast.”

Previous work on the scorpion, first identified in the 1870s, had suggested that it might have been part of a group of crustaceans known as isopods. It wasn’t until the 1980s, as scientists learned more about P. gigas and related animals, however, that the field also began considering it may have been another type of arthropod, or an invertebrate with an exoskeleton and jointed appendages — specifically a scorpion.

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The study underscores the importance of revisionary science, said Elizabeth Dowding, chair of paleoenvironmental analysis at Friedrich-Alexander University of Erlangen-Nuremberg in Germany. She was not involved in the new research.

“How we think about extinction and evolutionary biology comes from the ability of scientists to work over the same ground, by repetition,” Dowding said. “It’s just amazing that this story itself is one of revision and consistent curiosity over the same set of rocks. … It’s demonstrative of the way science works.”

Identifying an early giant scorpion

Working with eight fossils excavated over the years from three sites, the study team used CT scans and other tools to take a closer look at the specimen in the Natural History Museum’s collection. The researchers also worked with an artist to create renderings of what the animal might have looked like in the environment of that time.

The “smoking gun” that the fossilized remains belonged to another species, said lead study author Richard Howard, curator of fossil arthropods at the Natural History Museum, was a study from 2015 that described a scorpion in Canada.

That creature, Eramoscorpius brucensis, had a key feature that, to Howard and his colleagues, was the teller. Its sternum, which is the plate on the underside of the scorpion between the bases of its legs, was long and triangular and had a groove down its middle just like P. gigas’ sternum, Howard said.

“It’s exactly the same in the two scorpions. So, we can infer from that that these are two closely related animals,” he said.

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P. gigas lived in what’s known as the early Devonian Period, when life on Earth was still primarily aquatic. The presence of such a scorpion during that time, therefore, is somewhat of a surprise, according to Howard.

“That’s much older than we would expect to find giant arthropods,” he said. Scorpions and other giant arthropods, including early versions of dragonflies and millipedes, lived some 50 million years later, Howard explained. Jungles and trees during that time created an influx of oxygen that made giant terrestrial life possible, he said.

But during the early Devonian, when there wasn’t much oxygen, “The lines between what is a land-living animal and what is an aquatic animal are much more blurred,” Howard said.