An article published in the journal “Scientific Reports” reports a study on the eyes of a fossil of Aulacopleura kionickii, a species of trilobite that lived about 429 million years ago, which offers evidence that it had a vision comparable to that of its distant modern cousins, insects but also crustaceans. Dr. Brigitte Schoenemann of the University of Cologne, Germany, and Euan Clarkson of the University of Edinburgh, Scotland, examined fossil eyes using digital microscopy to find in those compound eyes structures similar to those that exist today in bees, dragonflies, and many crustaceans with diurnal habits.
The available fossils are insufficient to reconstruct the origin of the eyes, but some very well preserved fossils show that compound eyes, still common today because they’re present in arthropods, already existed in the Cambrian period, during the greatest diversification ever seen in the history of life on the Earth. Brigitte Schoenemann and Euan Clarkson had previously researched this topic together with Helje Pärnaste, with results published in December 2017 in the journal “Proceedings of the National Academy of Sciences”. In that case, the research objects were trilobites that lived about 528-530 million years ago, in the new research the trilobite lived about 429 million years ago, in the Silurian period.
The fossil belonging to the species Aulacopleura koninckii is far from new as it was discovered in 1846 near Lodenice, in today’s Czech Republic. The extraordinary conservation allowed it to be subjected to new examinations using modern technologies that confirmed previous discoveries on trilobites’ compound eyes also offering new information about them.
The eyes of Aulacopleura koninckii have about 200 ommatidia, the elementary units typical of arthropods’ compound eyes, twice as many as those of the trilobites from the Cambrian period examined in the previous research. They’re still very far from the 30,000 ommatidia of dragonflies, but they allowed to perceive what could be obstacles or possible shelters and predator movements.
The examination of the fossil eyes allowed to find traces of the structures that make up the various ommatidia. Their lenses were very small, with a diameter of about 35 micrometers. This suggests that Aulacopleura koninckii lived in shallow, light-flooded, water, like some modern crabs that have similar eyes even if with many more ommatidia.
The researchers concluded that Aulacopleura koninckii had compound eyes with a structure similar to that of many modern arthropods, even though they had a limited number of ommatidia. The use of modern technologies continues to offer new information on old fossils. This offers hope that more trilobite fossils with very well-preserved eyes can be found to keep on reconstructing the evolution of compound eyes.
