A 500-million-year-old spider has claws where they shouldn’t

The fossils were completely unremarkable. That’s what Harvard University paleontologist Rudy Lerosey-Aubril thought at first when he was examining arthropod fossils from the Cambrian period (538.8 to 485.4 million years ago).

Lerosey-Aubril says: Normal Science.

Early arthropod specimens do not have claws like this. Instead, Cambrian arthropods often have antennae in that region. In other words, the nails that Lerosey-Aubril saw were like that not which must exist.

These proud relics belong to me Megachelicerax cousteauithe sea predator is 500 million years old. Fossils were first excavated 40 years ago in the desert of western Utah and are the oldest known chelicerate – an arthropod group that includes modern times. spidersscorpions, horse crabs, and sea spiders. This one amazing specimen pushes the evolutionary history of chelicerates back 20 million years and helps explain the evolution of claws. The findings are detailed in a study published today in the journal Nature.

Here comes the nails

Co-author of the new study, Lerosey-Aubril spent more than 50 hours cleaning M. cousteaui fossils with a needle under the microscope to study its strange shape. Its body is over three inches long and has an exoskeleton made up of a single head shield on top and nine separate body parts.

Lerosey-Aubril explains: “The appendages below the head are adapted for feeding and sensory functions, while those near the trunk are used for breathing and swimming.” “This level of biology is remarkably advanced for a modern arthropod.”

Chelicerate arthropods have a body divided into a cephalothorax above and an abdomen below, four pairs of walking legs, and two front chelicerae and pedipalps for grasping objects. Before this discovery, the oldest known chelicerate arthropods date back to 480 million years ago. M. cousteaui It lived 20 million years earlier, making it the first known branch of the chelicerate family tree. Today, there are more than 120,000 living chelicerate species, including spiders and horseshoe crabs.

Keep digging

Despite the fossil’s age, Lerosey-Aubril was surprised by how modern it is. M. cousteaui it looks compared to animals that lived at the same time, including the trident-wielding trilobites.

“Without a few traces of its past, this half-billion-year-old chelicerate would seem at home in today’s oceans,” he says.

M. cousteaui It is also an important transitional species that combines Cambrian arthropods with no front claws and much smaller clawed crab-like chelicerates.

In the past, scientists were unsure of the order in which its claws and bifunctional body began to evolve. M. cousteaui shows that they evolved before these head parts disappeared and resembled the legs of modern spiders.

“It fits a lot of competing theories; in a way, everyone was right,” explains co-author Javier Ortega-Hernández, Curator of Invertebrate Paleontology at Harvard’s Museum of Comparative Zoology.

Megachelicerax cousteaui named in honor of the famous French explorer Jacques-Yves Cousteau whose documentation and environmental advocacy inspired generations to continue exploring. Lerosey-Aubril says the fossil itself is a reminder to keep digging.

“This fossil was discovered by a dedicated paleontologist [Lloyd Gunther] and later it was handed over to the museum, where it was carefully looked after for decades before we were lucky enough to uncover its scientific value.” “Fossils are found across much of the United States,” he says, “so get out there, explore, and see what stories might be hidden in the rocks around you.”