Life reconstruction of Praearcturus gigas
© Franz Anthony
Anyone attempting to reconcile Earth’s history with the creation myths in Genesis has another awkward fossil to explain: the remains of a scorpion that lived in Britain approximately 415 million years ago—more than 400 million years before the supposed biblical Creation Week.
The animal,Praearcturus gigas, inhabited the river channels and floodplains of what are now England and Wales during the Early Devonian Period. Although known only from fragmentary remains, its enormous pincers and body plates suggest that it may have approached a metre in length, making it the largest scorpion yet identified. One of its fossil claws is more than 15.9 centimetres long, while the preserved carapace is about 9.4 centimetres wide.
The fossils themselves are not a new discovery. Some were collected in the nineteenth century and have been held in the Natural History Museum’s collections for more than 150 years. First described in 1871,Praearcturus was originally classified as a giant isopod-like crustacean and was subsequently compared with several other arthropod groups. Its identity remained controversial because none of the known specimens preserves an entire animal, including the characteristic segmented tail and sting.
Now, as reported in Plaeontology, researchers from the Natural History Museum, the University of Manchester and Technological University Dublin have re-examined the specimens using detailed photography, anatomical comparisons and computed tomography. Features including its large claw-bearing pedipalps, the structure of its sternum and a stridulatory surface on one of its leg bases provide strong evidence that it was a true scorpion. The researchers also concluded that fossils previously namedBrontoscorpio anglicus andBennettarthra annwnensis probably belonged to the same species and should be treated as junior synonyms ofPraearcturus gigas.
Its age is established by its geological context. The specimens come from the St Maughans Formation of the Anglo-Welsh Basin, a sequence of river and floodplain deposits belonging to the Lochkovian Stage of the Early Devonian. Fossil spores place the relevant rocks within a recognised biological zone dated to approximately 415.8–412 million years ago. This was not the familiar green world of later geological periods: forests had not yet evolved, land plants were still small, and terrestrial ecosystems were only beginning to develop.
Yet this relatively sparse environment supported an arthropod predator vastly larger than the other land-dwelling arachnids then known. The lateral flaps on its abdominal plates, together with its occurrence in river sediments, suggest thatP. gigas may have been aquatic or amphibious. Buoyancy might partly explain its great size, while the scarcity of competing large predators may have allowed it to occupy an ecological niche that disappeared as terrestrial ecosystems became more complex.
This also places its gigantism long before the oxygen-rich Carboniferous forests usually associated with enormous arthropods such asArthropleura and the giant griffinflies.Praearcturus had already become a formidable predator at least 50 million years before those better-known giants appeared—and roughly 180 million years before the earliest dinosaurs.
Nothing in this discovery resembles the biblical narrative in which plants and animals were created in their modern categories during a few days on a recently created Earth. Instead,Praearcturus gigas belongs to a clearly ordered geological and evolutionary history in which ecosystems changed over hundreds of millions of years: small plants colonised the land, arthropods exploited newly available habitats, forests developed later, and vertebrates subsequently diversified on land.
The Early Devonian^ How Could a Giant Scorpion Live in a World Before Forests? When Praearcturus gigas lived, approximately 415 million years ago, the land bore little resemblance to the world we know today. This was the Early Devonian Period, when plants and fungi had only comparatively recently begun to spread across the continents.As the following University of Manchester news release explains, this ancient giant does more than add another remarkable animal to the fossil record. It provides another glimpse of an evolving world unimaginably older—and altogether more interesting—than the parochial creation story invented by the Bronze Age authors of Genesis.
There were no forests, grasses or flowering plants. Most vegetation was small and structurally simple, and the first large trees would not appear until tens of millions of years later. Vertebrate life remained overwhelmingly aquatic; the earliest tetrapods had yet to evolve, while terrestrial animal communities consisted principally of arthropods and other small invertebrates.
The rocks containing Praearcturus formed in the channels and floodplains of ancient river systems. They now belong to the St Maughans Formation, which crops out in parts of England and Wales. Fossil spores place these rocks within a biological zone dated to approximately 415.8–412 million years ago.
A giant among tiny contemporaries Although no complete specimen of Praearcturus has been found, the preserved fragments demonstrate that it was enormous by scorpion standards. One incomplete claw is more than 15.9 centimetres long and part of its carapace is approximately 9.4 centimetres wide. Comparisons with more complete scorpions suggest that the whole animal could have approached one metre in length, although this remains an estimate. Other known arachnids from this period were generally tiny. Early Devonian harvestmen, mites and trigonotarbids were usually measured in millimetres rather than tens of centimetres. If Praearcturus lived at least partly on land, it would therefore have towered over almost every other terrestrial arthropod around it. Giant arthropods without oxygen-rich forests
The enormous arthropods of the later Carboniferous Period are often associated with unusually high concentrations of oxygen in the atmosphere. Arthropods breathe through systems that become less efficient as bodies become larger, so a greater availability of oxygen may have helped some Carboniferous insects and other arthropods attain exceptional sizes.
That explanation cannot readily account for Praearcturus. It lived at least 50 million years before the great Carboniferous forests and their associated atmospheric oxygen peak. Its size must therefore have resulted from different, or additional, evolutionary and ecological circumstances.
Several possibilities have been proposed:The researchers interpret Praearcturus as an apex predator that was probably at least partly aquatic. However, its precise way of life remains uncertain. Its aquatic features could represent an ancestral condition retained from the early evolution of scorpions, or they could indicate that its lineage returned to the water after its ancestors had become terrestrial.
- Buoyancy: Structures along the sides of its abdominal plates suggest that Praearcturus may have been aquatic or amphibious. Support from water would have reduced the mechanical problems associated with carrying a heavy exoskeleton.
- Ecological opportunity: Large terrestrial or freshwater predators were scarce. With few competitors occupying that role, early scorpions may have been free to evolve into ecological niches unavailable to them later.
- Predator–prey relationships: A large body and powerful pincers could have allowed Praearcturus to overpower prey unavailable to smaller arthropods and to dominate the food web of its environment.
- Preservation bias: Aquatic animals are more likely to be rapidly buried in sediment and fossilised than animals living on dry land. The apparent abundance and size of early scorpions may therefore partly reflect where they lived and how readily their remains entered the fossil record.
Glossary
- Devonian Period:
- A geological period lasting from approximately 419 to 359 million years ago. It witnessed the diversification of fishes, the development of increasingly complex land plants and the eventual appearance of the earliest tetrapods.
- Arthropod:
- An animal with a segmented body, jointed limbs and an external skeleton. Arthropods include insects, arachnids, crustaceans and myriapods.
- Arachnid:
- A member of the arthropod group that includes scorpions, spiders, mites, ticks and harvestmen.
- Chelicerae:
- Small appendages near the mouth used to grasp, pierce or process food. In spiders they bear the fangs.
- Pedipalps:
- The second pair of appendages in arachnids. In scorpions they are enlarged to form the familiar pincers.
- Amphibious:
- Capable of living or moving in both aquatic and terrestrial environments.
- Apex predator:
- A predator occupying the highest level of a food web and facing little or no predation from other animals.
- Ecological opportunity:
- The availability of resources or unoccupied ecological roles that can allow a population to diversify or evolve new adaptations.
World’s largest scorpion revealed from 415-million-year-old fossils
- Fossil fragments suggest Praearcturus gigas represents the largest scorpion ever discovered, perhaps one metre in length
- Specimens held in the Natural History Museum collection since the 1870s have been reinterpreted using modern techniques
- Giant scorpion lived tens of millions of years before other famous “giant” arthropods, reshaping ideas about how and why early arthropods grew so large
A giant scorpion that once roamed what is now England and Wales has been confirmed as the largest of its kind ever to exist, thanks to new research by scientists at The University of Manchester and the Natural History Museum. Measuring around a metre in length and armed with pincers over 16 centimetres long, Praearcturus gigas would have been a formidable predator stalking floodplains around 415 million years ago. Remarkably, the fossils used to identify Praearcturus have been held in the Museum’s collection for more than 150 years. The study, published in the journal Palaeontology, used modern analytical techniques and comparisons with newly described fossil species to suggest that Praearcturus is a scorpion, and a distinct species.When we think of giant arthropods, people often picture Carboniferous rainforests with giant millipedes or dragonfly-like insects from later in Earth’s history. 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.
Dr Richard J. Howard, lead author
Division of Invertebrate & Plant Palaeobiology
The Natural History Museum
London, UK
Pincer of scorpion (about the size of today's largest scorpion)
NHM scorpion fossilPraearcturus gigas lived during the Early Devonian. Small plants and fungi had only recently begun to spread across the landscape, and complex terrestrial ecosystems like forests had yet to evolve. This means that, unlike later giant arthropods, Praearcturus did not benefit from the high atmospheric oxygen levels associated with the rise of forests. Instead, its enormous size may reflect a world with relatively little competition from other large predators. This suggests that Praearcturus might have grown so big simply because there weren’t many other large animals around meaning it could dominate its environment in a way that wouldn’t be possible later on.Praearcturus has puzzled us palaeontologists for more than a century. 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 than was previously possible, which is really exciting. What makes Praearcturus so interesting is that it became enormous at a time when life on land was otherwise very small. But it was a world that could somehow support a giant predator. To try and better understand this ancient world we compared the size of fossil scorpions with other animals alive at the time. To reach such extraordinary sizes, and conclude that perhaps it lived in water, where life was bigger.
Dr Russell J. Garwood, co-author.
Division of Invertebrate & Plant Palaeobiology
The Natural History Museum
London, UK
The fossils also hint that this giant scorpion may have led a partly aquatic lifestyle. Some specimens show flap-like structures on the abdomen similar to those found in modern crustaceans such as lobsters, suggesting it may have been capable of moving between water and land. Quantification of the wider arachnid fossil record, led by Dr Garwood and the team, shows that scorpions are unusually abundant in rocks of this age compared with other arachnids, supporting the idea that some early forms may have lived in freshwater environments where they are more likely to survive as fossils. This places Praearcturus at a pivotal moment in Earth’s history when animals were first experimenting with life outside the oceans.
This places Praearcturus at a pivotal moment in Earth’s history when animals were first experimenting with life outside the oceans.
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.
Dr Greg Edgecombe, co-author.
Division of Invertebrate & Plant Palaeobiology
The Natural History Museum
London, UK
First described in 1871, Praearcturus gigas was originally thought to be a giant crustacean, similar to a woodlouse. The known fossils fragmentary nature lacked key features such as a tail making it difficult to classify with confidence for more than a century.
The breakthrough came through comparison with better preserved fossils discovered in recent years, which revealed key anatomical features unique to scorpions. The discovery highlights the continuing scientific importance of museum collections.
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.
Dr Richard J. Howard.
The discovery of such a large scorpion so early in the history of life on land challenges assumptions about why prehistoric arthropods reached gigantic sizes. Rather than being driven solely by environmental factors such as oxygen levels, the findings suggest that ecological opportunity such as a lack of competition may have played a crucial role.
Publication:
What emerges from this research is not simply the discovery of a spectacularly large scorpion, but another glimpse of an Earth undergoing profound biological and ecological change hundreds of millions of years before humans appeared. Praearcturus gigas lived when terrestrial ecosystems were still in their infancy, forests had yet to evolve and vertebrate life remained overwhelmingly confined to water. Even so, evolution had already produced a giant arthropod predator capable of dominating its environment.
Its unusual size was not necessarily an adaptation to the oxygen-rich atmosphere invoked to explain the arthropod giants of the much later Carboniferous. It may instead have resulted from a combination of buoyancy, an aquatic or amphibious existence and the ecological opportunity created by an absence of competing large predators. There was no foresight involved and no plan to produce the later ecosystems with which we are familiar—only organisms responding to the conditions, opportunities and selection pressures of their own time.
The study also illustrates how science progresses. Specimens collected more than 150 years ago were not treated as sacred objects whose first interpretation could never be questioned. They were re-examined with improved imaging techniques, compared with newly discovered fossils and reclassified when the accumulated evidence supported a better explanation. Scientific knowledge advances precisely because its conclusions remain open to correction.
By contrast, the Genesis narrative offers a fixed tale in which the major components of the natural world appeared almost simultaneously during a few acts of creation. The fossil-bearing rocks of the St Maughans Formation record something entirely different: a riverine ecosystem more than 400 million years old, than the biblical chronology permits, belonging to a stage in life’s history long before forests, tetrapods, reptiles, dinosaurs, mammals or humans existed.
Creationists can preserve their mythology only by rejecting the geological succession, the fossil record, biostratigraphy and the mutually consistent evidence on which the geological timescale rests. Praearcturus gigas is therefore another of those inconvenient fossils that should not exist if Genesis were an accurate history of life—but sits exactly where evolutionary biology and geology predict that an Early Devonian animal should be.
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