Scientists make unbelievable discovery inside rare 520-million-year-old fossil that made their ‘jaws drop’

Scientists have been left gobsmacked after discovering a fossil which dates from hundreds of millions of years before the dinosaurs.

Dinosaurs first started appearing around 243 million years ago during the Triassic period, going on to become the dominant species around the world until a mass extinction event 66 million years ago.

I say this for context, because this fossil dates from an astonishing 520 million years ago.

This is around 130 million years before trees evolved and 70 million years before sharks evolved.

Or to put it another way - there is more time between this fossil and the appearance of the first dinosaurs, and the appearance of the first dinosaurs and today.

Science were awed (Yang Jie/Zhang Xiguang)

So in the absence of dinosaurs, trees and sharks, what on earth (see what I did there) was roaming around 520 million years ago?

This era is called the Cambrian Period, and is also known for an event called the 'Cambrian Explosion' - a huge increase in the number of complex life forms in the fossil record.

Most of these were arthropods, the ancestors of animals like crabs, insects and arachnids.

And this discovery was indeed an arthropod, and the fossil has been called Youti yuanshi.

But why is it so special?

Well, not only is the tiny fossil that of a larvae, giving a clue about how and when the life cycles of arthropods began, in something which is mind-blowing for this period, it has its internal organs intact.

It's already rare to find a much younger dinosaur fossil with intact internal organs, skin, or feathers, but one many times older is truly extraordinary.

Dr. Martin Smith of Durham University is a lead author on the study. He told Live Science that the creature's soft tissue had been replaced by phosphate and preserved in the rock, potentially because there were high levels of phosphorous in the water.

A scan of the fossil (Yang Jie/Zhang Xiguang)

Scholars working on the site said that they can make out 'the miniature brain regions, digestive glands, a primitive circulatory system and even traces of the nerves supplying the larva’s simple legs and eyes'.

Dr Smith said: “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."

He added: “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?”