Precambrian creatures with three-beam symmetry could still crawl along the bottom

(ORDO NEWS) — Tribrachidium – an organism with an “extinct” three-beam type of symmetry – was distributed on Earth in the Ediacaran period, about 550 million years ago.

For a long time, he, along with relatives (other trilobozoans), was considered an immobile inhabitant of the seabed, but now paleontologists have discovered traces of his active movement.

The evolution of multicellular animals familiar to us started in the Cambrian period, which marked the beginning of the Paleozoic era about 541 million years ago. It was at this time that the so-called Cambrian explosion fell , when, in a very short time, evolution created many different systematic groups at once. Their numerous descendants thrive on Earth today.

However, life (including multicellular) existed even earlier, back in the Proterozoic. Paleontologists know dozens of different creatures from the last period of the Proterozoic era – the Ediacaran. Most of them looked so strange that they did not at all resemble other inhabitants of the Earth. They were proposed to be singled out as a special group of vendobionts (from “vends” – this is how the Ediacaran period is called in a different way).

The origin of the Vendobionts and their relationship to the later populations of the biosphere remain a matter of debate. These paradoxical life forms have been proposed to be attributed to sponges, coelenterates, “one-celled dinosaurs” (that is, huge, sometimes two-meter protozoa), fungi or lichens, and to something completely unknown. But the Cambrian period replaced the Ediacaran period, and the vendobionts completely died out , being “victims of the Cambrian explosion” – namely, competition with new, more successful life forms.

One of the biggest quirks of Ediacaran organisms is their special symmetry. The body organization of the Ediacarans is unparalleled among later organisms and most likely died out with them. For example, the so-called rangeomorphs (in particular, charnia Charnia ) had the form of a sheet of thin interlaced tubules.

Corresponding to each other “slices” of the left and right sides of the charnia were slightly shifted relative to each other. This is the “sliding reflection symmetry” characteristic, for example, of a three-strand pigtail.

A new article by Russian researchers is devoted to another group of inhabitants of the Ediacaran seas, which is no less strange and has its own alternative type of symmetry. Trilobozoans (or triradialomorphs) were round and consisted of three identical lobes, the so-called antimeres.

Scientists do not know of other creatures with full three-beam symmetry – neither on modern Earth, nor from fossils. Rare exceptions concern certain parts of the body of roundworms or extinct echinoderms. The same can be said about vendobionts with glancing reflection symmetry.

Precambrian creatures with three beam symmetry could still crawl along the bottom

Researchers from the Paleontological Institute. A. A. Borisyak of the Russian Academy of Sciences consider the most famous and widespread trilobozoic – the heraldic tribrachidium ( Tribrachidium heraldicum ). Its name comes from the Latin “three-handed”. The body of the tribrachidium really consists of three spirally twisted “arms” – wing-shaped antimers.

The surface of each is covered with grooves – it is believed that with their help the body directed the flow of water with nutrient particles. On many casts, a cavity is visible inside each of the lobes – perhaps food was digested in them. On the whole, the tribrachidium could have the shape of a hemisphere or completely correspond to the studied imprints and be flat.

The article also considers other trilobozoans, such as anfesta ( Anfesta ) and albumares ( Albumares ). All these prints were found on the coast of the White Sea, in one of the richest places on Earth with Ediacaran finds.

For a long time, it was believed that trilobozoans fed on the nutrient suspension of the ancient seas and were motionless. This is the way of life that we see in modern animals with a similar ecological niche. However, the new work suggests that Tribrachidium could independently move along the bottom.

This is eloquently evidenced by crawling traces ending in the place of death of the organism and its remains, imprinted in the rocks in the form of a “death mask”.

The new discovery has once again changed our understanding of the “difficult life” in the Ediacaran – presumably not for the last time. It allowed us to better understand what the Ediacarans were, and once again demonstrated that the diversity and ingenuity of living things far exceed our expectations.

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