This 500-Million-Year-Old Fossil of a Claw-Bearing Predator Uncovers the Origins of Spiders, Scorpions and Other Arthropods

A new analysis of a specimen found more than 40 years ago reveals the oldest known chelicerate, defined by its pair of pincer-like appendages

Margherita Bassi | Daily Correspondent

April 2, 2026

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A fresh look at a fossil found more than 40 years ago points to the origins of a widespread group of arthropods called chelicerates.

While that name might not sound familiar, its modern-day members include scorpions, spiders, ticks and horseshoe crabs. They’re defined by their pair of pincer-like appendages—chelicerae—that have evolved to carry out diverse functions today, such as venom-injecting fangs in spiders and food-ripping mouthparts in scorpions.

Now, scientists say a 500-million-year-old fossil with obvious claws provides the earliest known evidence of one of these creatures. The findings, described April 1 in the journal Nature, reveal an unexpectedly modern body layout and push back the evolutionary history of chelicerates by millions of years.

“It’s a very nice fossil,” study co-author Rudy Lerosey-Aubril, an invertebrate paleontologist at Harvard University, tells Science News’ Tom Metcalfe. “What’s amazing is that it’s been in our collection for decades.”

Amateur fossil collector Lloyd Gunther found the ancient specimen in the roughly 500-million-year-old Wheeler Formation in Utah. In 1981, he donated it to the University of Kansas Biodiversity Institute and Natural History Museum.

Fast forward to 2019, Lerosey-Aubril got his hands on the fossil to clean it when he noticed something strange: a claw sticking out of its head. “It took me a few minutes to realize the obvious—I had just exposed the oldest chelicera ever found,” he says in a statement.

Before this discovery, the oldest clear chelicerate was dated to about 480 million years ago. Researchers suspected that even more ancient ones were around during the Cambrian Period, roughly 541 million to 485.4 million years ago, and had proposed some contenders.

But “pinning down any of these candidates as an unequivocal chelicerate ancestor has proved impossible,” since the fossils lacked obvious pincers, writes James Lamsdell, a paleobiologist at West Virginia University who did not participate in the study, in an accompanying commentary in Nature.

The newly described creature, dubbed Megachelicerax cousteaui, is about 3.3 inches long and 2 inches wide at the broadest part of its body. Looking at the fossil under a microscope revealed the animal had a head shield and nine body segments, with six pairs of limbs for feeding and sensing its environment, and respiratory structures beneath the body, which resembled plate-like gills in modern horseshoe crabs. The pincers are located on two appendages beside the ancient predator’s mouth.

“This tells us that by the mid-Cambrian, when evolutionary rates were remarkably high, the oceans were already inhabited by arthropods with anatomical complexity rivaling modern forms,” study co-author Javier Ortega-Hernández, an invertebrate paleontologist at Harvard University, says in the statement. However, chelicerates didn’t take a leading ecological role for millions of years until they found their footing on land.

Not all researchers agree with M. cousteaui’s description as the earliest discovered chelicerate. Jean-Bernard Caron, a paleontologist at the Royal Ontario Museum in Canada, and a colleague reported in 2019 a slightly older arthropod with “robust but short chelicerae” between its eyes and plate-like gills.

Still, “Megachelicerax may have been the first with big chelicerae, and it may attest that this group was more diverse early on” than previously believed, says Caron, who wasn’t involved in the new study, to the New York Times’ Jack Tamisiea.

Lerosey-Aubril tells the outlet that M. cousteaui features stronger evidence—large, obvious pincers—that chelicerates existed during the Cambrian Period. “There is no debate anymore,” he says.

Margherita Bassi | Read More

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.