An artist’s illustration of Eokinorhynchus rarus, one of
the oldest heavily armoured worms in the planet’s history. It lived on the
seabed and on beaches 535 million years ago, was smaller than a grain of rice,
and had a mouth full of teeth set on top of its head. Photo: Nanjing Institute
of Geology and Palaeontology
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.
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. South China Morning Post
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