World's Largest Known Scorpion Roamed Earth Before Forests Existed

A newly analyzed fossil predator from what is now England and Wales has been identified as the largest scorpion known to science. Researchers from the University of Manchester and the Natural History Museum reached the conclusion after revisiting fossils that had sat in museum collections for more than 150 years. The animal, Praearcturus gigas, reached roughly one meter in length with pincers more than 16 centimeters long, and was an imposing predator in Early Devonian floodplains around 415 million years ago. The findings are published in the journal Palaeontology.

"When we think of giant arthropods, people often picture Carboniferous rainforests with giant millipedes or dragonfly-like insects," said Dr. Richard J. Howard, curator of fossil arthropods at the Natural History Museum and lead author of the study. "But Praearcturus lived at least 50 million years earlier, well before the evolution of trees, when life on land was only just getting started. Confirming that this animal is a scorpion fundamentally changes our understanding of how and when these creatures evolved to such extraordinary sizes."

High atmospheric oxygen levels have often been linked to the enormous size of some later arthropods, but Praearcturus lived before those oxygen-rich conditions existed. The researchers suggest ecological opportunity may explain its size instead: with few other large predators competing for resources, Praearcturus may have been able to dominate its environment. "What makes Praearcturus so interesting is that it became enormous at a time when life on land was otherwise very small," said Dr. Russell Garwood, a paleontologist at the University of Manchester.

The fossils also hint that Praearcturus may have spent part of its life in water: some specimens preserve flap-like abdominal structures resembling features seen in modern crustaceans such as lobsters. An analysis of the broader arachnid fossil record, led by Garwood, found scorpions unusually common in rocks from this period compared with other arachnids, a pattern consistent with some early scorpions living in freshwater environments.

Scientists first described Praearcturus gigas in 1871, but interpreted it as a giant crustacean resembling a woodlouse, since the fossils were incomplete and lacked a tail. The new identification became possible only after researchers compared the historic specimens with better-preserved fossils discovered more recently, which revealed anatomical traits found specifically in scorpions.