Fossil fragments found in the U.K. have been identified as remains of the largest scorpions ever. Measuring more than a meter in length, Praearcturus gigas was among the first large predators to ever stalk the land. Hundreds of millions of years ago, England and Wales were home to the biggest scorpion in the world. While fossils of Praearcturus gigas have been known about for more than a century, its identity has been the subject of controversy.
New research examining a range of fossils has now confirmed its status as one of the largest prehistoric scorpions. With 16-centimeter-long pincers and an estimated body length of more than a meter, Praearcturus gigas would have towered over the floodplains 415 million years ago. Life on land was still fairly new during the Early Devonian Period, meaning few other animals would have reached such enormous sizes.
As a result, this giant scorpion would have had its pick of prey as it hunted small arthropods on land. But Praearcturus would likely have been a fearsome aquatic predator as well, feeding on fish and other large animals. Dr. Richie Howard, the lead author of the study and our Curator of Fossil Arthropods, says that the presence of the biggest scorpion ever found so early in the history of life on land changes what we know about the evolution of these animals.
“When we think of giant arthropods, people tend to think of enormous millipedes like Arthropleura or the dragonfly-like griffinflies,” Howard says. “But these species lived in the Carboniferous Period, at least 55 million years after Praearcturus, once land-based ecosystems had time to develop. “Instead, Praearcturus lived when life on land was just starting out and the ancestors of reptiles, mammals and birds were yet to leave the water. It suggests that this species might have grown so big because there weren’t any other large predators, allowing it to dominate its environment.”
Almighty arthropods
Arthropods, the phylum containing insects, scorpions, spiders and crustaceans, are the most diverse group of animals on Earth. Not only are they incredibly species rich, but they also have a wide range of sizes. The smallest species, such as Stygotantulus stocki, are less than a millimeter long, while the largest arthropods are thousands of times bigger. The Japanese spider crab, for instance, measures almost 4 meters long when its limbs are fully stretched out.
Crustaceans and other aquatic species tend to be able to reach large sizes as water provides support for their bodies. In contrast, land-based arthropods such as the Indian forest scorpion are much smaller. Even though it is the living world’s biggest scorpion, it only reaches a maximum length of about 23 centimeters. When Praearcturus was first named by Henry Woodward in 1871, it was thought to be a giant woodlouse-like crustacean rather than another arthropod. This interpretation is still reflected in its name, as Arcturus is a group of living woodlice.
In the 1980s, scientists first started to suspect that Praearcturus might actually be a scorpion. However, this was difficult to prove. Only a few fragments of the animal’s body survived as fossils, and didn’t include the characteristic scorpion tail. This changed when an ancient scorpion called Eramoscorpius was described from Canada in 2015. “Eramoscorpius was named from a well-preserved fossil, and is clearly a scorpion,” Howard says.
“One key feature of its anatomy is the sternum, which is a long triangular structure with a groove running down the middle that’s on the bottom of the carapace. “Praearcturus is a similar age to Eramoscorpius and also has one of these structures. So, this shows beyond doubt that Praearcturus must be a scorpion.”
