A new study has uncovered an incredibly rare and detailed fossil, named Youti yuanshi, that gives a glimpse inside one of the earliest ancestors of modern insects, spiders, crabs and centipedes.

This fossil dates back over 520 million years to the Cambrian period, when the major animal groups we know today were first evolving. It belongs to a group called the euarthropods, which includes modern insects, spiders and crabs. What makes it so special is that the tiny larva, no bigger than a poppy seed, has its internal organs preserved in exceptional quality.

Scanning techniques

Using advanced scanning techniques of synchrotron X-ray tomography at Diamond Light Source, the UK’s national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire, researchers generated 3D images of miniature brain regions, digestive glands, a primitive circulatory system and even traces of the nerves supplying the larva’s simple legs and eyes.

This fossil allows researchers to look under the skin of one of the first arthropod ancestors. The level of complexity anatomy shows these early arthropod-relatives were much more advanced than the researchers thought.

The new study, published on July 31 in the Nature Journal, and which involves the University of Strathclyde, is led by researchers at Durham University.

Perfect preservation

Study co-author, Dr Katherine Dobson of Strathclyde’s Civil & Environmental Engineering and Chemical & Process Engineering Departments, said:

It’s always interesting to see what’s inside a sample using 3D imaging, but in this incredible tiny larva, natural fossilisation has achieved almost perfect preservation. 

Lead researcher, Dr Martin Smith of Durham University 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. 

“But larvae are so tiny and fragile, the chances of finding one fossilised 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?”