Paleontologists have found the oldest representative of bilateria, which may have been the progenitor of this group. Recall that it includes 99% of described animal species, including all vertebrates, arthropods and worms.
Achievement is described in a scientific paper published in the journal PNAS.
Bilateria is dvustoronnesimmetrichnye beings. Their bodies are clearly divided into left and right halves, mirror mimic each other. In addition, for bilateral characterized by a clear distinction between the front end of the body where your mouth is, and back where is the anus.
Biologists believe that bilateria — treasure, that is, a group United by a common ancestor. It is obvious that the progenitor of the so far divergent lines lived a very long time. What looked like common ancestor of humans and flies?
Experts believe that it was a tiny creature that looks like a worm. The senses he had were in their infancy. Along the body from mouth to anus, which passed the digestive tract.
3D Laser scanning of the specimen shows the shape of the animal’s body.Illustration Droser Lab/UCR.
About 15 years ago there was reason to believe that bilateria were found among the ediacaran biota. Recall that this is one of the oldest communities of macroscopic animals on Earth that existed 570-540 million years ago. Experts are still arguing whether the “ediacaran” living descendants.
that in this oldest fauna was bilateria, testified the hole with a small diameter. They have been found in South Australia in the layer, which is 555 million years old.
by Studying these structures, experts have suggested that they created a worm-like animal. The front end of his body was noticeably different from the rear, and this, we recall a key symptom of bilateral. On the front end is the mouth, on the back of anal hole. Probably the “worm” ate onthe IR contained in the soil.
Also found in burrows ridges characteristic shape indicate that the creature was moving due to the wave-like muscle contractions throughout the body, like modern snake and worms.
Life in thin layers of sand on the seabed is required from this animal looking for food. So he had to be senses, though, and probably very primitive by today’s standards.
In General, burrowing “unknown little animals” was a typical bilateriya structure. She was very advanced compared to the typical “ediacaran” that do not have clearly defined organs and a suction nutrients through the body surface.
However, this attractive picture is obtained only if we assume that we have holes, that is the passages made by animals. Critics pointed out that fossil to give sufficient grounds for such a bold conclusion.
the surface of the stone, hiding a fossil.Photo Droser Lab/UCR.
And now a team of paleontologists found near the burrows of the remains of one who, probably, they dug.
Using three-dimensional laser scanning, the researchers discerned a cylindrical body with a pronounced “head” and “tail”. Length of the animal was 2-7 mm and a width of 1-2. 5 mm. The most noticeable thickening on the body of a worm fits perfectly to the diameter of the holes. Experts have distinguished between even traces of poorly developed musculature.
the New species was named Ikaria wariootia. It is easy to notice that it is strikingly similar to the ancestor of bilaterian what he sees specialists.
“Is that predicted evolutionary biologists — said the head of the research group Droser Mary (Mary Droser) of the University of California riverside. What we found, so exactly according to their forecast, that is really exciting”.
However, the fossilI record shows that many of the key breakthroughs occurred independently in different evolutionary branches. For example, life tried several times to become multicellular, and fish — to find the four limbs. So I. wariootia is not necessarily the ancestor of the present bilateral.
By the way, earlier “Conduct.Science” (nauka.vesti.ru) wrote that the most important events in the evolution of bilateria was linked to the massive loss of genes.