We have made so many advances over the past several decades when it comes to how we understand the past of this planet, both in terms of environment and animals.

But even they were stunned at how intact this 520-million-year-old worm was when they found it.

The worm larva are from the very beginning of the existence of arthropods, which means having so much of it to study could mean answers when it comes to how they evolved.

The fossil, named Youti yuanshi, lived during the Cambrian Explosion. A ton of key animal groups emerged during this time, alone with arthropods.

These are invertebrates characterized by hard exoskeletons and versatile body plans – arachnids, crustaceans, and insects, mostly.

They’re extremely adaptable in reality but often easily break down before they can become fossils.

This specimen was discovered in the Yu’anshan Formation in Yunnan Province, China. A team of scientists used synchrotron X-ray tomography to create 3D images that revealed brain regions, digestive glands, a primitive circulatory system, and some nerves.

The team, lead by Dr. Martin Smith of Durham University, issued a statement.

“When I used to daydream about the one fossil I’d most like to discover, I’d always be thinking of an arthropod larva, because developmental data are just so central to understanding their evolution.”

There’s a good reason he considered it a dream.

“But larvae are so tiny and fragile, the chances of finding one fossilized are practically zero – or so I thought. I already knew that this simple worm-like fossil was something special, but when I saw the amazing structures preserved under its skin, my jaw just dropped – how could these intricate features have avoided decay and still be here to see half a billion years later?”

They’re thrilled to have the opportunity to study the find more and to find insights into the steps evolution took between then and now.

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