New research suggests that extinct trilobites had a hidden third eye right in the middle of their foreheads.
Hidden Third Eye
Live Science reports that paleontologists are familiar with how these hard-shelled creatures had compound eyes that they used around 541 million to 252 million years ago, during the Paleozoic time.
The discovery of a hidden third eye is only recent. This eye was situated in the middle of their forehead, which is quite common among present-day arthropods. Findings were published in a Scientific Reports study.
When the researchers looked into an Aulacopleura koninckii specimen that had a missing part of its head, they discovered three tiny, inconspicuous, dark, and same-sized oval-shaped spots at the head's front.
Brigitte Schoenemann, the study's lead author and a substitute professor from the University of Cologne's Institute of Zoology, says that the regular and clear appearance of the feature distinguishes it from other formations that may have randomly formed due to fossilization or decay. It also corresponds with the expected relics of middle eyes that have a pigment layer. Schoenemann adds that, though this finding is singular, it supports the notion that ancient trilobites had median eyes on their foreheads.
Live Science also adds that, at varying evolution points, the creatures may have had one to multiple middle eyes. For instance, the scientists also discovered that the Cyclopyge sibilla trilobite had three median eyes that had lenses that were similar to human ones. The Cindarella ecualla, on the other hand, had four median eyes. Lately, most modern crustaceans and insects reportedly have three median eyes.
The study authors note that they now have a vital tool that can help in determining the position of the creatures in the evolutionary tree.
Trilobites
According to Oxford University's Museum of Natural History, trilobites are an extinct marine arthropod group that first showed up roughly 521 million years ago. Fossils of this arthropod group have been found across the globe.
Some of these creatures burrowed in the sediments, while others swam through open seas or crawled on the floor of the sea. Some trilobites could have also been predators, scavengers, or detritus feeders.
According to the Australian Museum, trilobites are the most species-rich arthropod group that is completely extinct. Among trilobites, its sturdy exoskeleton that covers the surface of its dorsal body and its "well-marked segmentation" are classic features of arthropods.
These creatures lived through almost the entire Palaeozoic Era for almost 300 million years. They became extinct by the end of the Permian period, which was roughly 251 million years ago. The Permian mass extinction event led to their eradication, as well as the deaths of over 90% of species across the globe.
