A 500-million-year-old fossil with 3-segmented claws has been identified as the oldest ancestor of spiders and scorpions, pushing back the origin of the group by 20 million years and surprising Harvard.

Written by Douglas Avila

Published on 15/04/2026 at 23:17

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A 500-million-year-old predator with giant claws has just been identified as the oldest ancestor of spiders and scorpions, pushing the group’s origin back by 20 million years

Harvard paleontologists have just identified the oldest chelicerate ever found: a 500-million-year-old marine predator that lived during the Cambrian Explosion.

The fossil, named Megachelicerax cousteaui in honor of explorer Jacques Cousteau, was published in the journal Nature on April 1, 2026. The discovery pushes the origin of spiders and scorpions back by 20 million years.

The animal measures 8.1 centimeters long and has exceptionally large chelicerae with three pincer-like segments. These frontal claws are the signature of the chelicerate group.

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Collected 40 years ago and overlooked: how a Utah fossil rewrote the history of spiders

The fossil was collected in the 1980s in the Wheeler Formation, in the Utah desert, but remained unidentified as a chelicerate for over 40 years.

Cambrian chelicerate fossil preserved in rock

Dr. Rudy Lerosey-Aubril, Harvard paleontologist and lead author, described the moment of discovery: “It took me a few minutes to realize the obvious: I had just exposed the oldest chelicerate ever found.”

The animal had six pairs of head appendages for feeding and sensing. Lamellar respiratory structures under the body resembled the gills of modern horseshoe crabs.

Dr. Javier Ortega-Hernández, associate professor of evolutionary biology at Harvard, explained: “Megachelicerax shows that chelicerae and the division of the body into two regions evolved before the appendages became like the legs of spiders today.”

What the spider ancestor reveals about the Cambrian Explosion

Research room at Harvard University with fossils

Ortega-Hernández added: “This tells us that, in the middle Cambrian, when evolutionary rates were remarkably high, the oceans were already inhabited by arthropods with anatomical complexity rivaling modern forms.”

As reported by G1, the fossil documents the Cambrian origin of chelicerates and shows that the spider body plan was already emerging 500 million years ago.

According to ScienceDaily, chelicerates took millions of years to ecologically dominate. Trilobites initially overshadowed them, and only later did they colonize land.

From marine claws to terrestrial webs: the long evolutionary journey of chelicerates

Modern spider in web with dew drops showing chelicerae

Megachelicerax reconciles several competing hypotheses about chelicerate evolution. “In a way, everyone was partially right,” said Ortega-Hernández.

The transitional species links Cambrian arthropods to Ordovician synziphosurines. It shows that chelicerae, body division, and gills emerged shortly after the Cambrian Explosion.

However, there are caveats. Only one specimen is known, limiting generalizations. Soft parts were inferred via reconstruction, and future fossils may refine interpretations.

According to Sci.News, the study is recent and subject to revisions. Still, Megachelicerax cousteaui has already become the key piece to understanding how spiders and scorpions emerged in the primitive oceans — 500 million years before building webs and hiding under rocks.

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A 500-million-year-old fossil with 3-segmented claws has been identified as the oldest ancestor of spiders and scorpions, pushing back the origin of the group by 20 million years and surprising Harvard.

A 500-million-year-old predator with giant claws has just been identified as the oldest ancestor of spiders and scorpions, pushing the group’s origin back by 20 million years

Collected 40 years ago and overlooked: how a Utah fossil rewrote the history of spiders

What the spider ancestor reveals about the Cambrian Explosion

From marine claws to terrestrial webs: the long evolutionary journey of chelicerates

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A 500-million-year-old fossil with 3-segmented claws has been identified as the oldest ancestor of spiders and scorpions, pushing back the origin of the group by 20 million years and surprising Harvard.

A 500-million-year-old predator with giant claws has just been identified as the oldest ancestor of spiders and scorpions, pushing the group’s origin back by 20 million years

Collected 40 years ago and overlooked: how a Utah fossil rewrote the history of spiders

What the spider ancestor reveals about the Cambrian Explosion

From marine claws to terrestrial webs: the long evolutionary journey of chelicerates

Seen from space, an image taken by an astronaut shows an unlikely oasis in the Saudi Arabian desert, protected by a terrain that slows the advance of sand, surrounded by green circles, remnants of an extinct lake and nearly 10,000 years of preserved history.

While the U.S. still faces limitations in deep space, China is developing unprecedented technology with strategic satellites that maintain communication with the far side of the Moon and aims for dominance by 2030.

In Botswana, a salt flat of up to 16,000 km² that was once an African megalake spends months as an absolute white desert, but during the rainy season it transforms into a shallow sea that reappears from nowhere and can be seen from space in the middle of southern Africa.

The Blood Falls of Antarctica hide a living ecosystem trapped under the ice for over 2 million years, where microbes survive without light, without oxygen, and without ever having seen the Sun.

Bavarian archaeologists unearthed a medieval skeleton that had an articulated iron hand in place of its left arm, and the discovery reveals that doctors were already creating sophisticated prosthetics over 500 years ago.

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