Sea scorpions (eurypterids), now-extinct giant aquatic arthropods, were apex predators. New research suggests that early species of scorpion-like, spiny-limbed carcinosomatoid eurypterids fed on trilobites, and later species preferred armored fish. Carcinosomatoids evolved into scorpions, but 400-million-year-old giant scorpions like Prearcture And Brontoscorpionas presented in Walking with the monsters (TV series), were probably crustaceans.
Reconstruction of Pentecopterus (170 cm long), the oldest marine scorpion (eurypterid) from the Ordovician period (467 Ma) of Iowa, USA. Photo credit: John Alexander.
Sea scorpions (eurypterids) were ancient aquatic crawling insects (arthropods, with a segmented body, exoskeleton, and jointed limbs) that lived from 467 million years ago (Ma) to about 253 Ma.
Some pterygotid eurypterids reached nearly 2.6 m (8 ft) in length, making them the largest insects ever to have existed. Eurypterids also include the predatory carcinosomatoids, i.e. megalograptids, carcinosomatids, and mixopterids, which had long, spiny limbs and could reach 2 m (6 ft) in length.
Carcinosomatoids used their long, spiny limbs to capture and hold prey and to dig through mud. Computer modeling indicates that they were slow swimmers, preferring to live near the sea floor as ambush predators.
A new study of fossils discovered alongside megalograptids suggests that they are primarily associated with trilobites (various extinct marine arthropods).
Carcinosomatids tend to associate with lightly armoured phyllocarid crustaceans and lingulid brachiopods (lamp shells).
Mixopterids tend to associate with more heavily armored fishes, such as thelodonts, osteostracans, and pteraspids.
Fossilized feces (coprolites) confirm that they ate trilobites, armored fish and even their own kind (as cannibals).
The hypothesis that eurypterids influenced the evolution of armoured fish in a predator-prey arms race is often rejected.
This research suggests that mixopterids and pterygotids had some influence on their evolution (and on our own very ancient ancestors).
Megalograptus is interpreted as more basal than previously thought, meaning that the diversity of early (Ordovician) eurypterids has been overestimated.
Scorpions probably evolved from a mixopterid ancestor by developing claws (pedipalps), a stinger, and comb-like sensory pectins on their undersides.
Giant scorpions may be the stuff of nightmares, but they were real during the Carboniferous period in Scotland: Pulmonoscorpius And Gigantoscorpion.
Reconstruction of Pulmonoscorpius, a giant scorpion (70 cm long) from the Carboniferous period (330 Ma) of Scotland. Image credit: Junnn11 / CC BY-SA 4.0.
Reconstruction of PulmonoscorpiusA giant scorpion (70 cm long) from the Carboniferous period (330 Ma) of Scotland. Image credit: Junnn11 / CC BY-SA 4.0.
An even longer scorpion (1 m) called Prearctureoriginally from Herefordshire in England, also believed to have lived 412 million years ago.
However, the grooves on its carapace, its pustular ornament, and its curved first body segment suggest that it is in fact a crustacean.
Bennettarthrafrom the same layer and region, may be related to (or is slightly smaller than) Prearcture.
Brontoscorpio, a 86 cm long (400 Ma) scorpion featured in the BBC television series Walking with Monsters, is known only from a tiny piece of its claw and is probably a crustacean. Photo credit: Impossible Pictures.
Brontoscorpionsuggested as a 86 cm long scorpion (400 Ma), as featured in the BBC TV series Walking with the monstersis known only from a tiny piece of its claw and is probably a crustacean. Photo credit: Impossible Pictures.
Brontoscorpion (86 cm long), from Worcestershire in England (400 Ma), as featured in the award-winning BBC television series Walking with the monsters is also probably a crustacean.
Giant scorpions therefore did not exist until the Carboniferous period, 70 million years later, alongside monstrous 2 m long millipedes and giant dragonfly relatives with a wingspan of 75 cm.
Today’s scorpions gradually acquired their current characteristics. Early scorpions had more primitive legs and eyes and lacked a preoral cavity for feeding on land. They were therefore probably aquatic or amphibious.
The oldest scorpion was Parioscorpion from the Lower Silurian period (437 Ma) of Wisconsin, but it has been reinterpreted as a trilobite-like arthropod.
The oldest known scorpion is now Dolichophonus (433-438 Ma) from Scotland.
This research is published in New books for Geology and Palaeontology.
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Braddy, SJ 2024. Paleoecology and phylogeny of carcinosomatoid eurypterids: ichnology and paleocommunities. New books for Geology and Palaeontology; do I: 10.1127/njgpa/2024/1206
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