It is revealed that they do not have two eyes, but at least five

It can be explained that it took a long time to discover those extra eyes. It is – in fossilized trilobites – more or less hidden.

About five million years ago, the oceans were teeming with trilobites. This is a well-known class of extinct arthropods that lived in the sea in ancient times. Trilobites, along with ammonites and dinosaurs, are undoubtedly among the best known fossils. But despite 150 years of research, the creature still has surprises waiting for us. For example, scientists have discovered extra eyes that have been ignored all along.

eyes
Arthropods usually have two types of eyes. First of all, they have a pair of compound eyes (they are also called compound eyes). These often consist of thousands of separate lenses. In addition, arthropods are also equipped with medium eyes. This is actually an extra set of single eyes, located in the middle of the forehead, between the compound eyes. Only trilobites, an important group of arthropods that lived during the Paleozoic Era, appear to lack mesial eyes.

Discovery
At least, that was the assumption until recently. Until researchers discover trilobites Olacoplura konenkifrom which part of the head was scraped off, and subjected them to close examination.

The team found three small, nearly identically shaped, dark, indistinct oval spots of the same size on the front of the head. These three structures run parallel to each other and are slightly spread out at the bottom. All three spots have a smooth, clear outline and a uniform dark brown colour. “These spots are clearly distinguished from spots caused by decomposition or fossilization,” explains researcher Brigitte Schoenemann. “Instead, it perfectly matches what a simple, medium eyeshadow looks like.”

average eye
This means that trilobites—like all other arthropods and many of their relatives—may have not only had compound eyes, but were also equipped with an extra set of eyes. “This finding supports the hypothesis that trilobites were originally meso-eyed,” Schuenemann concludes.

not noticed
It is remarkable that the trilobites managed to keep this secret for so long. As mentioned, trilobites have been studied extensively for over a century. Moreover, more than 22,000 species have already been discovered. Despite this, the mean eyes had gone unnoticed all this time. However, this can be explained. It is – in fossilized trilobites – more or less hidden.

handle
They explained that the scientists assumed that the intermediate eyes were a feature of the larval stage their studies Outside. In addition, they were located under a transparent layer of armor. However, during the fossilization process, this layer becomes opaque. “Both of these contributed to the fact that the discovery of the extra eye group was long anticipated,” said Schoenemann.

More about trilobites
Trilobites can be identified by a calcified exoskeleton on the back of the body. They had a crescent-shaped head similar to today’s horseshoe crab. Although the animals are now extinct, they were an evolutionarily successful species. They have survived for more than 250 million years; taller than dinosaurs.

This means that trilobites may have had several hidden eyes. When researchers discovered trilobites Cyclopegian Sibylla They also found three median eyes on the forehead, between the two compound eyes. In addition, these lenses are equipped with lenses similar to those in human eyes. This indicates that this trilobite may have had better eyesight than its closest relatives Olacoplura konenkiwhich – unlike Cyclopegian Sibylla – He just lived at the bottom.

uneven
In short, the results show that trilobites have many more eyes than previously thought. Maybe five at least! Although this number may also be varied. Researchers believe that arthropods had a different number of mesencephalons at different times of development. “The initial median number of eyes is two,” says Schuenemann. In addition, primitive arthropods probably had four. Modern animals, such as insects and crustaceans, are equipped with three intermediate eyes.

All in all, thanks to their sharp eye, researchers have been able to solve the mystery of the missing middle eyes in trilobites. But this not only expands our knowledge of these extinct prehistoric marine animals. The variation in the number of intermediate eyes in arthropods could facilitate the evolutionary classification of ancient arthropods. “Using the average number of eyes, we may now be able to locate arthropods in the evolutionary tree more easily,” concludes Schuenemann.