#  Sea Scorpions Just Got a Lot Older — and a Lot Scarier 

 





From the Department of Organismic and Evolutionary Biology:



 

November 21, 2025

 

 

     ![a figure showing six views of a fossil sea scorpion](/sites/g/files/omnuum6431/files/styles/hwp_16_9__480x270/public/2025-11/rspb.2025.2061.f001%20%281%29.jpg?itok=tz_bJ282) 

A cropped version of Figure 1. Isolated appendages of ?*Carcinosoma aurorae* n. sp. from the Early Ordovician (upper Tremadocian) Fezouata Biota of Morocco. (A–D) Holotype NM S 5974 consisting of a walking limb, gnathobase and four fragmentary tergites, part. (C) Details of the limb and gnathobase, dry. (D) Details of the limb and gnathobase, under a mixture of ethanol and propanol. All scale bars represent 10 mm.



 



 

A set of spiny fossil limbs pulled from ancient rock in Morocco has pushed the origin story of “sea scorpions” back in time, revealing that these fearsome predators were already highly specialized hunters nearly half a billion years ago.

A new study published in [*Proceedings of the Royal Society B*](https://royalsocietypublishing.org/doi/full/10.1098/rspb.2025.2061#d2513296e1) describes the definitive remains of eurypterids, an extinct group of giant aquatic arthropods, from the Fezouata Biota in Morocco.

“These aren’t vague, questionable traces,” said co-author Javier Ortega-Hernández. “These are unmistakable eurypterid hunting limbs. Once you see the spines and joint structure, there’s no doubt what you’re looking at.”

The fossils include heavily armored, jointed appendages bristling with alternating long and short spines, along with a vicious, downward-curving terminal claw. The team, including PhD candidate Jared Richards and lead author Peter Van Roy (Ghent University), named the new species *?Carcinosoma aurorae*, a member of an advanced group called carcinosomatids — sea scorpions known for flat, scorpion-like bodies and raptorial, grasping limbs.

*?Carcinosoma aurorae* limbs were built for grabbing and shredding. The teeth-like structures at the base of the leg form a serrated feeding surface showing it was not a gentle filter feeder but a predator. Its anatomy also shows that by this early point in Earth’s history, sea scorpions had already split into major ecological types: some built for active swimming, others adapted to crawling along the sea floor. The Moroccan fossils in this study belong to the swimming type, meaning eurypterids must have diversified much earlier than their fossil record had suggested.

“What shocked us was how derived these animals already were,” said Ortega-Hernández. “You don’t get this level of specialization overnight. These lineages must have started evolving in the Cambrian, long before we had direct fossil proof.”

Fragments of scaly cuticle found alongside the limbs hint that at least a second sea-scorpion species lived in the same ecosystem, possibly a relative of the massive pterygotids, some of the largest arthropods to have ever lived. Despite their heavy armor, complete sea scorpion fossils are rare in the Fezouata deposits. The researchers believe that may be because these animals were powerful swimmers that may have escaped mud avalanches that buried other animals.

The Moroccan specimens suggest the animals are around 20 to 30 centimeters long, though it remains unclear whether the fossils represent juveniles or adults. Even at that size, their spined limbs and saw-like mouthparts leave little doubt about their lifestyle.

“These were the sharks of their day — before vertebrate sharks even existed,” Ortega-Hernández said. “They were grabbing, slicing and dominating their corner of the ancient seas.”

The discovery has implications far beyond sea scorpions. Eurypterids are close evolutionary relatives of modern spiders and scorpions, meaning the roots of today’s land-dwelling arachnids may reach back earlier than previously thought. Pushing eurypterids back in time also pushes back the origins of spiders and scorpions back, changing how we think about the early rise of complex predator ecosystems after the Cambrian Explosion.

The Fezouata Biota, already famous for preserving early animal life in exceptional detail, now appears to have hosted a surprisingly rich array of early euchelicerates. Ortega-Hernández says the findings underscore how much of arthropod history remains hidden.

“These fragments expand the early fossil record of sea scorpions and illuminate a crucial chapter in the origins of chelicerates,” he notes. “The Early Palaeozoic biosphere was more diverse—and more complex—than we previously realized.”



 

 

 



 

 See also:- [ Invertebrate Paleontology ](/news/invertebrate-paleontology)