JUANA SUMMERS, HOST:
Rudy Lerosey-Aubril is a paleontologist who likes to relax by cleaning - cleaning fossils.
RUDY LEROSEY-AUBRIL: I listen to radio. I listen to podcast and this sort of thing. And it's just a moment, you know, when you relax a bit.
SUMMERS: That's what he was doing with a collection of tiny fossilized arthropods that were found in western Utah. The fossils were related to a paper he was working on. They dated to about 500 million years ago.
LEROSEY-AUBRIL: It's half a billion years ago, so it's very, very old.
AILSA CHANG, HOST:
But besides their age, these fossils had been pretty unremarkable.
LEROSEY-AUBRIL: That particular day, I remember it very well because it took me some time to realize what I had in front of me.
CHANG: He realized one fossil didn't look the way he expected it to look. A common arthropod of the period might have antenna on the front of its body, but this one looked kind of weird.
LEROSEY-AUBRIL: And then it's only when I fully prepared it that I realized that what was missing was actually a gap between two structures, and the two structures are basically the two part of a claw. And that's the moment I realized that it was not an antennae but a kind of pincer, you know?
SUMMERS: This fossil had a set of pincers, and pincers meant this species of ancient arthropod had been totally misidentified. It was actually a chelicera. That's a distant relative of spiders and horseshoe crabs and other creepy-crawlies. Lerosey-Aubril's findings show that the ancestors of spiders actually existed 20 million years earlier than previously thought.
JAVIER ORTEGA-HERNANDEZ: Using this fossil, we can understand how, you know, the great granddaddies of spiders came to be in the first place.
CHANG: That is Javier Ortega-Hernandez, a paleobiologist and co-author of a new study about the discovery.
ORTEGA-HERNANDEZ: Hey, spiders came from half a billion years old. They were basically fully marine back in the day. And they have changed a lot in terms of how they behave and also some of their body parts.
CHANG: Ortega-Hernandez admits that not everyone is exactly a fan of spiders or of scorpions or of anything else that could use their pincers on human flesh.
ORTEGA-HERNANDEZ: They're not conventionally attractive little creatures.
CHANG: But...
ORTEGA-HERNANDEZ: They have still capture our imagination over time.
SUMMERS: And to capture the imagination, Lerosey-Aubril wanted to give his fossilized chelicera a name that would nod to the creature's new watery origins.
LEROSEY-AUBRIL: Megachelicerax. It means basically big chelicerae, so big pincers. And then the name of the species is cousteau.
CHANG: After Jacques Cousteau, the famed underwater explorer, who, if he had been alive 500 million years ago, might have discovered this creature while diving in an ancient ocean.
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