The fossil, which is 500 million years old, is an extremely valuable find, as it contains the imprint of an animal that died literally on the go. The petrified "evidence" of his death is of exceptional interest. Mortichnia is a very rare find, since a living creature that leaves prints usually does not remain in place.
More than half a billion years ago, on the territory of modern South China, a worm similar to an ear of wheat crawled along the muddy bottom. Then he stopped and left a distinct imprint of the lower part of the body in the wet ground. Then he crawled a little more and died. Its segmented torso, about 18 centimeters long, has been turned into a fossil. As well as actually the last place where death overtook him. As a result, a trace of the last moments of the creature's life remained, that is, mortichnia was formed - an imprint of the body and traces of dying movements.
This happened at least 10 million years before the start of the Cambrian explosion, during which many of the existing groups of living organisms appeared, and more than 20 million years before the first dinosaurs appeared. The creature, which scientists named Yilingia spiciformis - after the Yiling region where it was discovered - was considered morphologically complex for the Ediacaran period: it was able to move, its body was bilaterally symmetrical, segmented, and each segment was divided into three lobes (which is typical for trilobites).
Plants had not yet colonized the Earth, but according to Rachel Wood, a geologist at the University of Edinburgh, "slime-covered living organisms" already existed on the shores of freshwater lakes.
The fossilized organism Yilingia spiciformis and traces of its dying movements became the subject of research, the materials of which were published Wednesday in the journal Nature. This "worm" is amazing in itself, but the petrified "evidence" of his death is of exceptional interest. Mortichnia is a very rare find, since a living creature that leaves prints usually does not remain in place. "It's kind of like a forensic examination," said Shuhai, a geobiologist at Virginia Polytechnic University and one of the study's authors. "You find a trail and you can probably say something about the suspect, but it's still better to film the suspect."
Dr. Wood, who analyzed the results of the study, compared mortihnia to "the last steps of a person who staggers and grabs onto everything in order not to fall." Better yet, she said, "to make the fossil prints large."
One or two other members of the Ediacaran fauna are known to have some of the Yilingia spiciformis traits, the study authors say, the horseshoe-headed Spriggina and the Marywadea, which resembled Spriggina "but had a crescent-shaped head."
These creatures were not trilobites, so they are not so closely related to living organisms that exist on Earth today. Other trilobites had a hardened skeleton, head, body, and tail. And the creature Yilingia spiciformis, as noted on the website of his group, Dr. Xiao, "had pronounced signs of a representative of the worm-like" with a soft, belt-like torso. In mortihnia of an earlier period, the imprints of the dying movements of organisms were more similar to the tracks that occur with intermittent movement, jumping, and they were characterized by one trace, or scratches, or teeth marks.
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Yilingia spiciformis, notes Dr. Xiao, "does not belong to the oldest segmented living organisms, nor to the most ancient mobile organisms, but today it is the oldest known segmented and mobile living organism capable of leaving long and continuous tracks." In other words, it is the most ancient creature that is most distinguished by the variety of signs - and mobility - in our understanding. Yilingia spiciformis is "an intermediate between two species (worm-like and arthropod)," says Dr. Wood.
Yilingia spiciformis was probably fed by microbial biomass - the notorious silt, says Dr. Xiao. It is possible that this creature died, being "buried" under a layer of bottom sediments. (By the way, "Mortichnium" / Mortichnium is also the name of the song of the little-known and obscure German black metal group LAM. Imagine for a moment how this creature Yilingia spiciformis, swallowing silt, crawls, exhausted, and dies on the dark seabed under rattle of this soundtrack).
Since Yilingia spiciformis consists of repeating symmetrical segments, it is closer to the form that contributed to the "explosion" of biodiversity, that is, in the process of evolution, led to the emergence of most living organisms on Earth, including humans. The segmentation contributed to the appearance of legs and wings. Modern living things are "real engines, passionaries," says Dr. Xiao, it is a "geological force" capable of erecting structures like termite mounds or the Great Wall of China. And we have this ability largely due to the fact that we can move.
We are still not indifferent to our worm-like ancestors and are crazy about them. The segmented, symmetrical, mobile centipede recently became famous online for a while when Twitter users posted a video of a worm-like arthropod and its shadow striding along the sidewalk. The centipede's shadow stretches upward, and it looks like a bus. You can see a thousand tiny legs, bouncing in pairs one after the other in time to the senseless, unpretentious tune of the song “You can, I'll go, let me go” (Send Me on My Way), which resembles the music of Kwela from South Africa, where the centipede is called Shongololo.
And the way worm-like moves inspire the creators of robots. In August, MIT engineers announced they had developed a "magnetically controlled filamentous robot" capable of moving inside arteries and blood vessels in the brain. The British magazine New Scientist called the invention a "robot worm". It is quite difficult to make a mistake when classifying this robot: it has a segment of the head, exactly the same as that of worm-like ones. When it hits an obstacle, for example, an angle, the "head" turns to the left and then to the right - like a caterpillar that has crawled to the very tip of the leaf and is looking for a new path on which there are no obstacles.
The last moments in the life of one of the oldest segmented animals, the oldest worm, shed light on phenomena that were likely harbingers of an explosion of biodiversity on Earth. The discovery of the fossil creature Yilingia spiciformis means that the beginning of the Cambrian period is beginning to lose shape, says Rachel Wood. “After that, as after all the most outstanding scientific discoveries, there are many more questions. Some of this discovery helps explain, but it entails new research in many interesting areas."
Helen Sullivan
