Scientists have discovered an intermediate link between asymmetrical flounders and their symmetrical ancestors. The eyes, which in flat animals moved to one half of the body, were still on different sides in their ancestor, but at unequal heights. The work was published in the Journal of Vertebrate Paleontology (the article was unavailable at the time of writing), and a brief description of it can be read on the website of the Society of Vertebrate Paleontology.

The remains of an extinct fish were found in the town of Bolca in northern Italy, where excavations had been going on for a long time. Here are deposits formed by prehistoric coral reefs. Like modern reefs, they contained a wide variety of animals.

The sample that became the object of research by scientists first ended up in the Vienna Museum, where it was kept unidentified for a long time until it was discovered by Oxford University professor Matt Friedman. He determined that the discovered fossils belonged to an ancient relative of modern flatfishes - flounder, saltfish, halibut and other flat fish. The species was named Heteronectes , that is, “swimming differently.”

The remains were perfectly preserved and allowed scientists to get a good look at the structure of the skeleton. The fish's left eye was much higher than its right eye, but they were still on different sides of the body. This means that the process of transformation of symmetrical fish into modern asymmetrical flatfishes took place gradually, and not in one jump.

Previously, scientists observed the process of migration of the eye to the other side of the body (in different flounders, both the left and right sides of the body become upper) only during the development of fry, but there was no paleontological evidence of this.

The find provides another argument for supporters of the greater importance of gradualism (gradualism) for the evolution of living things, as opposed to saltationism, which emphasizes sharp abrupt changes.

The migration route of the left eye of the flounder has been established