Median Eyes in Trilobites Found After 150 Years of Multiple Researches

After 150 years of study, scientists discovered trilobites had single median eyes.

According to new research by Brigitte Schoenemann from the University of Cologne and Professor Euan Clarkson from the University of Edinburgh, trilobites were ancient sea creatures that had single median eyes on their foreheads in addition to their compound eyes.

Single Median Eyes in Trilobites

All arthropods and numerous relatives of the extinct trilobites have single eyes like this.

After 150 years of research, the so-called median eyes, which are common to all arthropods, had not yet been identified in trilobites.

The researchers believe that the median eyes were typical of the animal's larval stage.

The carapace's transparent layer, which turned opaque during the fossilization process, covered the single eyes.

The ocelli were not found until now as a result of both situations.

Additionally, the scientists discovered median eyes in other, roughly 500 million-year-old arthropods.

These arthropods had varying numbers of median eyes according to their evolutionary stage.

In the future, it will be possible to categorize the evolutionary status of specific arthropod species using the number as well as the shape of the single eyes.

The study was recently published, along with the team's findings in the journal Scientific Reports.

The two types of eyes that arthropods typically have are compound eyes and what are known as "median eyes" or middle eyes.

The latter is situated between the compound eyes in the middle of the forehead.

150 Years Into Research

Only trilobites, a major group of Paleozoic arthropods, are thought to lack what appear to be median eyes.

This was the belief up until Schoenemann and Clarkson analyzed a trilobite specimen from Aulacopleura koninckii that had a portion of its head scraped off.

At the front of the head, they discovered three nearly identically shaped, small, oval, dark, and unnoticeable spots of the same size.

These three buildings are parallel to one another and slightly fan out on the underside.

Each of the three spots has a consistent, dark brownish color and a smooth, clear outline.

Mysterious Missing Median Eyes

Schoenemann explained that this structure's distinct, regular appearance sets it apart from the random formations left behind by decay or fossilization, and it is consistent with the expected remnants of simple, pigment-layered median eyes. Even though it is just one discovery, the University of Cologne claims that it supports the theory that trilobites primarily had median eyes.

Thus, the researchers have discovered the reason why trilobites lack middle eyes. According to Schoenemann, these cup eyes are descended from the primitive stump-footed animals, the tiny velvet worms. The modern, extremely conservative arachnids still have the original median eye count of 2, which is still the case. The modern-day, extremely conservative arachnids still have the original median eye count of 2, which is still the case.

There are four phylogenetic, extremely primitive arthropods, including Cindarella eucalla from the lower Cambrian of China. In contrast, there are only three contemporary animals like insects and crustaceans. There is now a crucial tool for determining an arthropod's position in the evolutionary tree thanks to the number of median eyes in an arthropod, PhysOrg reports.