Scientists recently dug up an ancient fossil, dating to about 520 million years old. This fossil, of a strange-looking balloon-shaped creature, reveals more about what life was like in our ancient oceans.

The fossil, discovered in China by researchers from the Yunnan Key Laboratory for Palaeobiology at Yunnan University in China, as well as the universities of Leicester and Oxford, shows a creature covered with spines resembling a "squashed bird's nest." The creature, dubbed nidelruc pugio, belongs to a strange group of animals called chancelloriids.

The fossil is the only chancelloriid ever found in the Chengjiang fossil beds in China. It received its name, Nidelruc pugio, in honor of Professor Richard Aldridge from the University of Leicester, who died earlier this year. Aldridge was a major researcher at the Chengjiang fossil beds.

All chancelloriids were balloon-shaped, as far as we know, according to previous fossils found around the world, including in Russia, Canada, Mongolia and the United States. They went extinct around 500 million years ago. There are no known animals today related to them.

"There is only one fossil of this enigmatic animal after 30 years of collecting by our Chinese colleagues at Chengjiang," says Dr. Tom Harvey from the University of Leicester. "It is exceptionally rare, but it shows us just how strange and varied the shapes of early animals could be."

This makes chancelloriids extremely interesting because they tell a story of what life was like in our ancient oceans, where they lived. This one, in particular, is of particular importance, because of how intact it is.

"We usually only get the broken-up remains of ancient animal skeletons," says Tom Hearing, a PhD student from the University of Leicester. "With this specimen we can see how all the different parts of the skeleton stuck together. It tells us much about how early animals functioned, how they might have interacted with other animals, and how they might have protected themselves from predators."

Although the fossil is flat, the animal was originally shaped more like a balloon. The fossilization process itself squashed it to its current shape.

Other fossils gathered at the site include distant relatives of crabs and lobsters, as well as other fossils that don't fit with animals living today, including the chancelloriid.

The fossil's name, honoring Aldridge, nidelruc pugio, comes from the Latin word for bird's nest, nidus, and adelric, which is the Old English origin of the name Aldridge.