UK Researchers Confirm 1-Meter Praearcturus as Largest Known Scorpion

Q: This giant scorpion conquered land, so why did it return to the water to hunt its prey?

It likely returned to the water because Early Devonian land could not yet provide enough large prey for an animal of its size. Researchers say *Praearcturus gigas* lived about 415 million years ago, when terrestrial ecosystems were still primitive. Land plants and fungi were spreading, but there were no complex forests or rich food webs, and most land animals were small arthropods. For a scorpion more than a meter long, that would have made hunting on land less rewarding than hunting in water, where larger prey such as fish and other aquatic animals were available. Its anatomy supports that idea. The study found flap-like structures called epimera, comparable to features seen in modern lobsters and crabs, suggesting it was adapted to spend time in water. That fits the view that it was not fully tied to land, even if it belonged to an early scorpion lineage that had already made the move onto land. Water may also have helped support such a massive body. Buoyancy would have made movement and ambush hunting easier for a giant arthropod than on open floodplains. Paleontologists say this reflects how fluid the boundary between land and water still was at the time. As Greg Edgecombe noted, if scorpions descended from air-breathing ancestors, *Praearcturus gigas* may represent a lineage that moved onto land and then partly returned to the water because that was still the richer hunting ground.

3 articles · Updated · ScienceAlert · Jun 9

415-million-year-old fossils from the UK have been identified as Praearcturus gigas, settling a debate that began after the specimen was first found in 1870.
CT scans, camera lucida tracings and comparisons with Early Devonian fossils — including Canada's Eramoscorpius — showed the animal was a true scorpion more than 1 meter long.
16-centimeter pincers and ridged limbs linked to sound-making suggest it was a dominant predator, while flap-like structures indicate it likely hunted partly in water as well as on land.
The finding sharpens scientists' picture of early life on land, when ecosystems were still sparse, and may point to a scorpion lineage that survived another 40 million years before disappearing.