Scientists at the University of Arizona have discovered fossils of extinct creatures with well-preserved structures of an ancient brain. This is reported in an article published in the journal Current Biology.
The fossilized remains belonged to Leanchoiliidae — an extinct genus of arthropods that lived in the Cambrian period (541-485 million years ago). Experts have confirmed the presence of the extreme frontal region of the brain, which is not segmented and invisible in modern adult arthropods. As arthropods mature, it gives rise to several important neural centers in the brain involved in decision-making and memory formation.
Experts assumed that this frontal area, called prosocerebrum, differs from the anterior, middle, and posterior brains observed in modern arthropods. The finding proves that the anterior part of the brain existed half a billion years ago and was structurally different from the three-segmented ganglia that appeared later, which correspond to the anterior, middle, and posterior brains. These three ganglia form a solid mass, hiding their evolutionary origin as segmented structures.
Many arthropods, including insects and crustaceans, have a distinct pair of compound eyes and another set of more primitive, simple eyes. The simpler eyes correspond to the front eyes in Leanchoiliidae. The lateral eyes of Leanchoiliidae belong to the protocerebrum, the segmental ganglion that defines the forebrain of arthropods, lying just behind the prosocerebrum. In modern arthropods, the protocerebrum is a complex eye of insects and crustaceans. It “absorbed” the older prosocerebrum so that the latter can no longer be distinguished as a separate anatomical unit.