Scientists have found a 518-million-year-old "fish with four eyes"

New data from China hint: some of the earliest known vertebrates, who lived about 518 million years ago, could have not two, but four eyes at once - and the "extra pair" was located in the centre of the head.

We are talking about ancient fish from the group myllokunmingids (myllokunmingids ), whose fossils are found in the famous biota Chengjiang. The researchers studied 10 specimens (two forms of these early fish) and noticed a strange dark structure in the middle of the "face". Previously, it was considered something like a nasal sac, but now the team says: according to a set of features it looks more like ... another eye apparatus.

To understand, the scientists used electron microscopy (SEM and TEM) and found in the central structure of melanosomes - microparticles with melanin, characteristic of vertebrate eyes and associated with the pigment epithelium of the retina. In shape and size they turned out to be comparable to melanosomes in the lateral eyes of the same animals. This strengthened the theory that the "central spots" were not an olfactory organ but part of the visual system.

Most intriguingly, two oval "lenses" similar to a lens were noticed in these dark areas. The same structures are in the lateral eyes, which in these ancient fish worked on the "chamber" principle. If the interpretation is correct, the central organs may have been not just light-sensitive, but potentially capable of forming an image.

The authors link the finding to the pineal complex in modern vertebrates, a system of brain structures involved in the regulation of hormones and circadian rhythms (including melatonin production). In some reptiles, this complex includes a light-sensitive organ sometimes called the "third eye," although it doesn't see like normal eyes. The new study throws up a bold idea: perhaps in the earliest vertebrates, the pineal complex began as true "chamber" eyes, and then evolutionarily "simplified" and changed function.

Why might nature have needed such an "upgrade"? Researchers suggest that millocunmingids probably had to survive among the many Cambrian predators, and the extra eyesight may have increased the chances of spotting a threat and evading an attack. Over time, conditions may have changed - and the 'extra' eyes evolved into a more specialised system of light sensitivity and hormonal regulation.