The discovery of traces of a worm 550 million years ago, key to understanding the evolution

When someone away from something, it loses its sharpness. This happens with the pictures of friends during night outings and with the study of the past. To find out what happened during the last US elections, you can access almost infinite direct and contemporary sources, but to revive Nero's reign, you must refer to the testimonies of some authors who wrote decades ago. after his death. In reconstructing the history of life on Earth, as progress progresses and hundreds of millions of years retreat to get closer to the origin, The pieces that complete the riddles are rare, precious and sometimes enigmatic.

On Wednesday, a team of Chinese scientists led by Shuhai Xiao, of Virginia Tech University in the United States, presented several of these articles stemming from a key milestone in the evolution of animals. In an article published in the magazine Nature, describe the discovery of several fossils of about 550 million years ago, found in the Dengying Formation, in the Yangtze Gorge, southern China, of worm-like beings, which would have bilateral symmetry, badociated with fossilized paths that might be theirs or similar living beings . In the case of one of them, the link between the worm and its track is clear, thus becoming one of the oldest examples of locomotion They know each other.

The period in which these worms lived is Ediacárico, a period in which, as far as we know, the first animals appeared. Their form was strange: they had neither bone nor shell, so they could not leave part of their fossilized body. What remains for posterity are its mussels preserved in the rock. This is how the Dickinsonia, who lived 560 million years ago, were known to have a symmetrical and oval body, one and a half meters long, which left traces suggesting that it could move. It seems that they crawled on the ground looking for microbes to feed themselves, but that they had neither mouth nor anus, which allowed them to feed themselves through the skin and they were really unicellular beings who grew up without measure in a world without predators.

Like Dickinsonia, the new inhabitants of Ediacárico that we know are now crawling on the ocean floor in search of food. Baptized as Yilingia spiciformis, They were up to 27 centimeters long and they have been divided into about 50 segments, which offers the first examples of the movement capacity offered by the first divided bodies. The discovery, according to the authors, also helps to identify the animals responsible for the large number of fossil trails and burrows found at that time.

Diego García Bellido, a fossil expert who works at the University of Adelaide in Australia, believes that the work of Xiao and his colleagues is valuable, even though he believes that it remains still mysteries to be solved. "I am very surprised that none of 35 copies keep both ends of the body and that makes me think that we still do not have all the information about this organism, "he says. The researcher is surprised that in these worms, the body is wider in the back, unlike those found in arthropods, such as ants, or annelids, such as worms. In the front, they house the senses and elements with which they can capture food and leave the bad area to evacuate waste. "That said, although they only have one copy, the link between the body and the trace seems authentic," he adds, though, he says, this trace is not "as complex as the one we have Kimberela, considered a "protomolusque" that has already recorded its ability to move four million before Yilingia spiciformis.

The new piece that Xiao and his team contribute to this story, in which, sometimes, between one witness and another, there is an abyss of millions of years, helps to understand how a key moment of animal evolution has been managed: the Cambrian explosion. A little more than 10 million years after the worms found in China left their traces deep in the sea, deposits from around the world show a creative impetus. gave birth to a world it's more familiar than Ediacara.

Virtually all the patterns recognized today in animals, including humans, appeared at that time. The ability to move is widespread, skeletons and shells appear, which would produce more abundant fossils and much more informative than those of the soft bodies of previous beings, and badual reproduction appears as a winning strategy for most species that we see without a microscope. Previously, most animals had a complexion other than those currently known. "Some had the form of a fractal" and others "looked like an eight-armed spiral galaxy," he says in The country Jochen Brocks, researcher at the National University of Australia.

Biologists do not know how to connect these animals, almost aliens, to current animals, but they do not have this problem with the fossils presented this Wednesday. The track of Yilingia It shows the way to structures that would allow targeted mobility or hunting as it is known today. The characteristics of this worm "are those found in a group of animals, a group that includes humans and most animals," says Xiao. In the fossils of the Yangtze Gorge, our history is also reconstructed.