Fossil Reclassified as Largest Scorpion on Record, Dated to Early Devonian Period

A fossil specimen held in a museum collection for over 150 years has been reclassified as the largest scorpion known to have existed.

The species, Praearcturus gigas, lived approximately 415 million years ago during the Early Devonian Period.

Identification and Reclassification

Fossil fragments of Praearcturus gigas were first discovered in Herefordshire, England, and Wales in the 1870s. The remains were originally described by Henry Woodward in 1871 as belonging to a giant crustacean. For decades, the classification of the fossils was debated. In the 1980s, some researchers proposed the remains were from a scorpion, but this hypothesis lacked supporting fossil evidence.

A recent study, published in the journal Palaeontology, confirmed the scorpion identity by using modern imaging techniques, including camera lucida tracings, computed tomography (CT) scans, and 3D modeling. Researchers compared the fossils with better-preserved specimens, including a sternum matching fossils from Canada described in 2015. A shared triangular structure on the cephalothorax with the species Eramoscorpius was also a key factor in the reclassification.

The fossils are held at the Natural History Museum in London. The study was led by Dr. Richard J. Howard of the Natural History Museum and involved researchers from the University of Manchester.

"Confirming the animal as a scorpion changes the understanding of how and when these creatures evolved to such sizes."
— Dr. Richard J. Howard, lead author

Physical Description and Size

Ridged surfaces on the scorpion's limbs were identified, which researchers interpreted as structures likely used for stridulation (sound production), a feature observed in other extinct scorpion species.

Ecological Context

Praearcturus gigas lived during the Early Devonian Period, a time before the evolution of trees and complex terrestrial ecosystems. Atmospheric oxygen levels were lower during this period than in later periods associated with large arthropods.

The animal's large size is not attributed to high oxygen levels. Researchers propose the size may have resulted from a lack of competition from other large predators. The scorpion may have had a partly aquatic or semiaquatic lifestyle. Several sources report that some fossils show flap-like structures (epimera) on the abdomen, which are analogous to similar structures found in modern lobsters and crabs.

Dr. Greg Edgecombe, a co-author, noted that scorpions are descended from an air-breathing ancestor, and Praearcturus may represent an animal that returned to water after its ancestors had moved onto land. Scorpion fossils from this time period are reported to be more abundant than fossils of other arachnids, possibly due to preservation in freshwater sediments.

Fragmentary fossils from Somerset, England, may indicate the species persisted for tens of millions of years, though this remains unconfirmed.

"The boundary between land and sea was less defined at that time, and Praearcturus provides insight into how early animals adapted to changing environments."
— Dr. Greg Edgecombe, co-author

Research and Statements

The research was conducted by scientists from the Natural History Museum in London and the University of Manchester.

• Dr. Richard J. Howard, lead author and Curator of Fossil Arthropods at the Natural History Museum, stated that the species lived at least 50 million years before the evolution of trees, when life on land was just beginning, and that the absence of other large predators may have allowed the species to grow so large.
• Dr. Russell Garwood, of the University of Manchester, stated that the fossils have puzzled paleontologists for over a century and that modern techniques provided a clearer picture of the animal.
• Dr. Greg Edgecombe, Merit Researcher at the Natural History Museum, described how the boundary between land and sea was less defined at that time, and Praearcturus provides insight into how early animals adapted to changing environments.