The Chinese ‘mud dragon’ that helped change the world? Spiky, armoured worm that lived half a billion years ago may unriddle Cambrian explosion
Scientists discover ancient species of worm in China’s Sichuan that may have just preceded evolutionary event when life exploded on planet earth.
A recently discovered worm whose ancestors have been dubbed “mud dragons” may have been deaf and blind, but it shows how even tiny prehistoric invertebrates could be intimidating when Mother Nature wanted them to be.
A team of Chinese researchers found the fossilised remains of Eokinorhynchus rarus, which is believed to have lived on the seabed around 535 million years ago, in southwestern China’s Sichuan province, an area famous more for its pandas than creepy crawlies or crustaceans.
More spiky, bizarre-looking creatures from the same or similar period have been unearthed in other parts of China in recent months and years, including one in Yunnan province, which borders Vietnam, in June.
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But E. rarus ranks as one of the earliest heavy-armoured worms in the planet’s history.
It lurched in the cold and dark mud half a billion years ago with a body full of armour and spikes, and a mouth full of fangs to swallow anything that got in its way. It thrived in the deepest oceans and also on sandy beaches.
It measured just 2 millimetres, making it shorter than a grain of rice and meaning it was only able to prey on tiny organisms like algae.
Yet daunting as they may have looked to similarly sized creatures, its spikes were not designed to maim or kill but rather help it move faster, according to its discoverers in a paper published in the journal Scientific Reports.
In fact, E. rarus would most likely have been very timid, they said.
By analysing evolutionary patterns, molecular biologists believe it may have first appeared on earth 600 million years ago.
“Remarkably, no [other] fossils have been discovered,” said the authors in their paper. The team was led by Dr Zhang Huaqiao at the Nanjing Institute of Geology and Paleontology.
Researchers are still not quite sure why the marine invertebrate proved so hard to find because its living environment meant the creature would have been easily preserved. Moreover, biologists have found an abundance of other worms living in similar environments from various periods in history.
The Chinese team hope their latest discovery helps unlock some secrets related to the so-called Cambrian explosion - an evolutionary event that occurred around 540 million ago. It marks a kind of dividing line in evolutionary history between single-celled and multicellular organisms.
Some scientists believe this explosion of diverse life forms started with creatures showing more elaborate forms of body segmentation.
E. rarus had over 20 segments making up its body - twice as many as more modern worms in the same family.
Its highly segmented body suggests that animals in the early Cambrian period started to show signs of identical body parts repeated from the front to the rear of their bodies.
This would have given Mother Nature more freedom to “experiment” with different body plans during the process of evolution, as any single segment could have been turned into a specialised tool to serve a specific need.
The extraordinary diversification of the largest animal group around today - including centipedes, earthworms and humans - can all be traced back to the first worm that broke the mould by appearing in segmented form, according to previous studies.
Yet the latest finding is also expected to spur more debate among biologists over Darwin’s theory of natural selection.
Segmentation was regarded by some a result of convergent evolution, in which different animals acquired similar traits gradually as they lived in the same environment under the force of natural selection.
But other biologists argue that segmentation was produced by genetic mutation and had nothing to do with the change of environment.
Contemporary kinorhynchs - the generic name for the family that E. rarus belongs to - only show about half as many segments as their Cambrian ancestors.
Whether the reduction was a result of environmental change or genetic mutation remains a question to be answered by future scientific study.