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More than half a billion years ago, a worm-like creature stirred the last, creating a preserved fossil groove that offers new insights into some of the oldest movements in the world. # 39; animals.
The origins of movement in animal species remain quite dark, although there is evidence of a "directional movement" – as opposed to the winding drift of a jellyfish – there are already 560 million d & # 39; years.
But traces of such early movement are very rare, making a key discovery a series of fossils that provide evidence of the life and death of Yilingia spiciformis, similar to a worm.
Collected between 2013 and 2018 in southern China, the fossils represent a segmented creature that resembles a centipede that lived 550 million years ago, long before dinosaurs roamed the Earth.
And they include something even rarer: a fossilized "death march" or "mortichnium" – the trace produced by a Yilingia just before dying.
Fossils constitute the first "direct evidence to support" the first movements of a segmented animal, said AFP Shuhai Xiao, a professor in the Virginia Tech University Geosciences Department. .
Experts had long thought that segmented animals were able to move at that time, but there was no fossil evidence to support this idea.
"Yilingia spiciformis is up to now the oldest known segmented animal, capable of directional movement," Xiao added.
"We show that animal motility evolved nearly 550 million years ago, albeit rather modestly."
Experts generally believe that animals began to move during a period called the Ediacaran era, about 635 million to 540 million years ago.
But these animals left individual fingerprints or scratchy tooth marks as they passed over a surface.
"Yilingia is different because it has produced long, continuous streaks," Xiao said.
The animal that traced these long and continuous paths, which are regularly found in the fossil record of this time, was a mystery until the discovery of the mortichnium – which perfectly presented a Yilingia died at the end of the course.
The conclusions drawn by Xiao and his colleagues, published Thursday in the journal Nature, are due to the mortichnium, a discovery of a rare rarity in the world of fossils.
"Think of the number of footprints that a person would create during his lifetime," Xiao said.
"How lucky is this person to be fossilized with one of his fingerprints? Very thin."
The team examined other samples of Yilingia fossils that helped to better understand the creature, which seems to have made up to nearly half a meter (20 inches) long and lives in the sea.
And his discovery could also inform a long debate about whether segmentation in animals has evolved once or twice.
But there are still many questions to ask, including how and why Yilingia started to move.
"We would like to explore how animal locomotion behaviors may have responded to environmental changes and understand the role of animal motility – for example, looking for food, oxygen or partners, or Escape predators, "Xiao said.
Fossils could also give weight to the theory that animal segmentation in animals was linked to greater movement and maneuverability.
"The evolution of the segments may have led to a transformative innovation" in the animal movement that paved the way for an explosion of Cambrian life that followed, the newspaper said.
Rachel Wood, a professor at the Edinburgh School of GeoSciences, described the discovery as "a remarkable discovery of extremely significant fossils".
In a press release issued by Virginia Tech, she said the rare discoveries filled important gaps in understanding the movement of animals before the Cambrian period.
"Such preservation is unusual and provides considerable insight into a major stage in the evolution of animals," Wood said.
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