Think Man-Sized Swimming Centipede — And Be Glad It's A Fossil This sea monster swam Earth's seas about 480 million years ago and was the biggest creature of its day, scientists say.

Think Man-Sized Swimming Centipede — And Be Glad It's A Fossil

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If living long and prospering is a measure of success, then arthropods are evolution's winners. They're the most common form of life - insects, spiders, crustaceans and centipedes, to name a few. And now scientists have the remains of one of the first arthropods ever. It lived 480 million years ago. And as NPR's Christopher Joyce reports, it was big and strange.

CHRISTOPHER JOYCE, BYLINE: The fossil was discovered in Morocco. Scientists spent 500 hours scraping away its rocky casing. The thing that emerged is, well, a man sized swimming centipede? A 7-foot lobster without claws?

PETER VAN ROY: It is one of the very biggest arthropods to have ever existed.

JOYCE: In fact, says Peter Van Roy, it was the biggest animal on the planet at the time. Van Roy is the paleontologist at Yale University who spent the 500 hours preparing it. It's called - and you better grab a pencil here, because I don't think I can say it twice - an anomalocaridid. It evolved at a special time during the Ordovician geological period. Scientists call it the Great Ordovician Biological Diversification, when the forms of life in the ocean exploded.

VAN ROY: The biggest diversification in marine animal life that we've ever known.

JOYCE: That was a bonanza for this creature. A lot of this new life was plankton, and the animal evolved a way to eat it. It developed a comb-like appendage to scoop up plankton the way whales do now. It also developed flaps on its body that later evolved into arthropod limbs.

Becoming a filter feeder did pose some risks.

VAN ROY: If you're filter-feeding, of course, you probably are not going to be able to defend yourself. You're not going to have, like, big fangs or anything. So one way of escaping from predation is just by growing so big - so massive - that there's just simply nothing else that can tackle you.

JOYCE: Van Roy describes the creature in the journal Nature as one of the first mother arthropods. He says it changed our world. Arthropods are everywhere now, from the dust mite you'll never see to the butterfly in the rainforest. Christopher Joyce, NPR News.

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