Sea scorpions (eurypterids), extinct giant aquatic arthropods, were apex predators. New research suggests that early species of the scorpion-like carcinosomatoid eurypterids, with spiny limbs, fed on trilobites and later species preferred armoured fishes. Carcinosomatoids evolved into scorpions but giant 400 million year old scorpions like Praearcturus and Brontoscorpio, as featured in Walking with Monsters (TV series), were probably crustaceans.
Reconstruction of Pentecopterus (170 cm long), the earliest sea scorpion (eurypterid) from the Ordovician period (467 Ma) of Iowa, USA. Image credit: John Alexander.
Sea scorpions (eurypterids) were ancient aquatic creepy-crawlies (arthropods, with a segmented body, exoskeleton and jointed limbs) that lived from 467 Million years ago (Ma) to ca. 253 Ma.
Some pterygotid eurypterids grew to nearly 2.6 m long, the biggest bugs that ever lived. Eurypterids also include the predatory carcinosomatoids, i.e. megalograptids, carcinosomatids and mixopterids, with long spiny limbs, that grew up to 2 m long.
Carcinosomatoids used their long spiny limbs to capture and hold prey and for mud-grubbing. Computer modelling indicates they were slow swimmers, preferring life near the seafloor as ambush predators.
A new review of the fossils found alongside megalograptids suggests that they mainly associate with trilobites (diverse extinct marine arthropods).
Carcinosomatids tend to associate with lightly armoured phyllocarid crustaceans and lingulid brachiopods (lamp shells).
Mixopterids tend to associate with more heavily armoured fishes, like thelodonts, osteostracans, and pteraspids.
Fossil faeces (coprolites) confirm that they ate trilobites, armoured fishes and even their own kind (as cannibals).
The suggestion that eurypterids influenced the evolution of armoured fishes in a predator: prey arms-race, is often dismissed.
This research suggests that mixopterids and pterygotids did have some influence on their evolution (and our own very ancient ancestors).
Megalograptus is interpreted as more basal than previously thought, which means that the diversity of early (Ordovician) eurypterids has been overestimated.
Scorpions probably evolved from a mixopterid-like ancestor by evolving claws (pedipalps), a sting and comb-like sensory pectines on their underside.
Giant scorpions may be the stuff of nightmares but they actually existed during the Carboniferous period of Scotland: Pulmonoscorpius and Gigantoscorpio.
Reconstruction of Pulmonoscorpius, a giant (70 cm long) scorpion from the Carboniferous period (330 Ma) of Scotland. Image credit: Junnn11 / CC BY-SA 4.0.
An even longer (1 m) scorpion called Praearcturus, from Herefordshire in England, has also been claimed to live 412 Ma.
However, the grooves on its carapace, pustular ornament and recurved first body segment all suggest that it is actually a crustacean.
Bennettarthra, from the same layer and region, may be related to (or is a slightly smaller) Praearcturus.
Brontoscorpio, suggested as an 86 cm long (400 Ma) scorpion, as featured in the BBC TV series Walking with Monsters, is only known from a tiny piece of its claw and is probably a crustacean. Image credit: Impossible Pictures.
Brontoscorpio (86 cm long), from Worcestershire in England (400 Ma), as featured in the award-winning BBC TV series Walking with Monsters is also probably a crustacean.
Therefore giant scorpions did not exist until the Carboniferous period, 70 Ma later, alongside 2 m long monster millipedes and giant dragonfly relatives with a 75 cm wingspan.
Living scorpions gradually acquired their modern features. Early scorpions had more primitive legs and eyes and lacked a pre-oral cavity for feeding on land, so were probably aquatic or amphibious.
The oldest scorpion was Parioscorpio from the Early Silurian period (437 Ma) of Wisconsin, but it was reinterpreted as a trilobite-like arthropod.
The oldest known scorpion is now Dolichophonus (433-438 Ma) from Scotland.
This research is published in Neues Jahrbuch für Geologie und Paläontologie.
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Braddy, S.J. 2024. Carcinosomatoid eurypterid palaeoecology and phylogeny: ichnology and palaeocommunities. Neues Jahrbuch für Geologie und Paläontologie; doi: 10.1127/njgpa/2024/1206
