Measuring roughly a metre in length and armed with pincers larger than table knives, Praearcturus gigas has been confirmed as the largest scorpion to ever exist.
The fossils used to identify this giant species were discovered in the UK’s Welsh Borders more than 150 years ago and have been held in the Natural History Museum ever since. However, it wasn’t until they were recently re-examined that they were correctly identified as belonging to an ancient scorpion.
The study, published in the journal Palaeontology as part of a joint project between researchers from The University of Manchester and the Natural History Museum, used modern analytical techniques and comparisons with newly described fossil species to identify Praearcturus as a scorpion.
They were also able to identify a distinct species – P.gigas – and use their new, updated description to synonymise several other, similar-looking species identified from fossils found in the same rocks.
“Praearcturus has puzzled us palaeontologists for more than a century,” said Russell Garwood, a palaeontologist at the University of Manchester and co-author of the study. “By bringing together material from several collections and using cutting edge imaging techniques, we’ve been able to build a clearer picture of the animal that was previously possible, which is really exciting.”
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P.gigas was, like its name suggests, a giant, but it didn’t live at the same time as other iconic giant arthropods, such as Arthropleura and Meganeura. This enormous arachnid lived during the Early Devonian (415 million years ago), at least 50 million years before these other giants appeared in the Carboniferous.
The immense size of P.gigas would have made it a formidable predator. According to the researchers involved in this latest study, it may have even hunted in water, feeding on fish and other large, aquatic animals.
This aquatic lifestyle is evidenced by flap-like structures on its abdomen, which are similar to those found in modern crustaceans like lobsters and suggest P.gigas may have been capable of moving between water and land.
“The boundary between land and sea was much less defined at this time. Praearcturus gives us a fascinating glimpse into how early animals adapted to these changing environments. It may even represent a lineage that returned to the water after earlier ancestors had already begun living on land,” said Greg Edgecombe, palaeontologist at the Natural History Museum and co-author of the study.
P.gigas lived before the emergence of trees and during a time when small plants and fungi had only just begun to spread across the landscape. This means it didn’t benefit from the high atmospheric oxygen levels associated with the rise of forests, unlike later giant arthropods did.
Instead, P.gigas’ enormous size may reflect the fact it faced little competition from other large predators. This finding suggests that ecological factors, such as lack of competition, may have also played a crucial role in the evolution of giant arthropods, as opposed to just an increase in oxygen levels.
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The fossils used to identify P.gigas as a scorpion were first described in 1871 and originally thought to belong to a giant crustacean, similar to a woodlouse. These fossils lacked the key features needed for a more confident classification and it wasn’t until the recent discovery of better preserved fossils, complete with key anatomical features unique to scorpions, that they were able to be properly understood.
This discovery highlights the continuing scientific importance of museum collections, said the Curator of Fossil Arthropods at the Natural History Museum and lead author of the latest study, Richard Howard: “Specimens collected over a century ago can still hold entirely new insights. By revisiting them with modern techniques, we can uncover discoveries that reshape our understanding of life on Earth.”
Top image: Praearcturus gigas stalked floodplains across the UK more than 400 million years ago. Credit: Franz Anthony
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