Paleoentomologists of the V. I. A. A. Borisyak RAS discovered the world's oldest worm-oligochaeta (Oligochaeta) in the recently discovered Early Triassic locality in the Orenburg region. The age of the fossil is about 248 million years, which is 100 million years older than all known fossil oligochaetes. An article describing the find was published in the journal Acta Palaeontologica Polonica.
Oligochaetes (small-bristle worms) descended from the ancient group of marine polychaete worms - polychaetes, which appeared at the beginning of the Cambrian period (it began about 540 million years ago and ended about 485 million years ago). There are few reliable finds of fossil oligochaetes, the oldest of them date back to the Cretaceous period; in the more ancient Mesozoic deposits, only their egg cocoons are found.
In the laboratory, when analyzing samples from the Orenburg region, scientists found an imprint that resembles a small worm, like the modern pipe worker, with which aquarists feed the fish. More precisely, half of the worm is the back and, apparently, most of it remained outside the found siltstone tile.
An imprint of an oligochaete from the Triassic of the Urals (above) and a tubifex from the Moscow region (below)
The print shows segmentation, thin secondary annularity, transverse ridges (in those places where there were rows of setae, the setae themselves are not preserved), a triangular head lobe and a transverse depression in the region of the 12th segment, where the genital organs are located in the tubule (oligochaetes - hermaphrodites). With the help of an electron microscope, it was possible to discern the layered wall of the body.
The genera and species of oligochaetes differ in the structure of the setae and internal genital organs; therefore, the new worm did not receive a Latin name. Perhaps he belongs to the same family as the tubifex.
"The similarity of the oldest oligochaete with the tubifex confirms the opinion that the increase in size and the transition to life in the soil in this group are secondary, and small-bristled worms came to land from fresh water bodies," the authors of the study conclude.