Bizarre, Balloon-Shaped Animal Fossil Discovered

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Justine Alford

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232 Bizarre, Balloon-Shaped Animal Fossil Discovered
Prof Derek J Siveter, Oxford University

An extremely rare, and extremely weird-looking, fossil dating to approximately half a billion years ago has been unearthed in China by an international team of researchers. The specimen belongs to a strange, balloon-like animal that dwelled in Cambrian seas some 520 million years ago, and is helping us understand more about the diversity of life in Earth’s ancient oceans.

As described in Scientific Reports, the fossil was collected a few years back from the Heilinpu Formation in the Yunnan Province of southern China. Thousands of diverse fossils have been gathered from ancient rocks in this area over the past 30 years, including more than 30 different species with exceptional preservation. Remnants of their soft anatomy could also be seen in some specimens, such as their eyes, guts and brains. Nonetheless, the new specimen had never been documented before, highlighting its rarity.


The animal lived during the Cambrian Period, a time when an incredible array of life began to emerge on Earth, including the majority of the major groups of animals. Because these diverse life forms appeared over a relatively short time period, the event is often referred to as the “Cambrian Explosion,” but the scale was probably exaggerated. This is because hard-bodied animals began to proliferate during this time, which are more likely to leave behind fossilized remains for us to find than their soft-bodied precursors.

To examine the morphology of the specimen, the researchers created 3D images using X-ray Computed Tomography. Although the animal now somewhat resembles a squished birds nest, originally it was balloon-shaped and adorned with an outer skeleton of triangular spines. These animals were sessile, or immobile, so the spines would have served as a defense mechanism to prevent them from being eaten by predators.

Prof. Derek J Siveter, Oxford University

The fossil’s striking nest-like appearance served as inspiration for its name, Nidelric pugio, after the Latin word Nidus, meaning bird’s nest. The latter part of the word is derived from an Old English name, Aedelic, which is a source for the name Aldridge, in honor of the late Professor Richard Aldridge who was an expert in Cambrian fossils from the area where the new species was discovered.


The animal was probably a chancelloriid, a bizarre group of spiny, bag-shaped animals that does not appear to be the ancestor of any living species today. The fossilization process flattens these bloated animals, which is why they tend to resemble a spiky bird’s nest. Researchers are often forced to work with very fragmented fossils due to erosion over time, but this new specimen was exceptionally well-preserved.

“With this specimen we can see how all the different parts of the skeleton stuck together,” Ph.D. student Tom Hearing explains in a news release. “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.” 

[Via Scientific Reports, University of Leicester and Live Science]


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