An article published in the journal “Sciences Advances” reports a study on the eyes of Anomalocaris briggsi, a radiodon that lived about 515 million years ago, in the Cambrian period. Fossils discovered in the Emu Bay Shale, Australia, were so well preserved that they retained the their eye structure, which was found to be similar to that of their arthropod cousins and consisted of over 13,000 lenses. A team of researchers led by Dr. John Paterson of the University of New England, New South Wales, Australia, conducted a thorough examination of these fossil eyes. The conclusion is that Anomalocaris briggsi had excellent eyesight and that vision already played a crucial role in that ancient ecosystem.
Radiodonts are an order of extinct animals that lived during the Cambrian period. Their taxonomic classification is the subject of discussions because they have characteristics similar to those of arthropods but others that, according to some scientists, are sufficient to include them in another phylum, that of lobopods (Lobopodia). This is a recurrent problem in the classification of life forms from the Cambrian, a period during which the greatest differentiation of life forms on Earth occurred.
Among radiodonts, the anomalocarids, the species classified in the genus Anomalocaris, had similarities with today’s shrimp despite being much larger in size. They were top predators in their ecosystems, and thanks to the discovery of very well preserved fossils it was possible to ascertain that they had much better eyesight than that of their distant modern cousins with whom they have only a superficial resemblance.
The discovery of these very well preserved fossils of Anomalocaris briggsi in Emu Bay Shale was reported by a team of researchers, also led by Dr. John Paterson, in an article published in December 2011 in the journal “Nature” in which the acute sight of that radiodon was already stressed. Of that team, Gregory Edgecombe and Diego García-Bellido continued to work together with Dr. Paterson to study the animal’s eyes.
The examination of the fossils discovered in Emu Bay Shale made it possible to examine the details of their compound eyes. They were equipped with over 13,000 relatively large lenses that could perceive even the dim light present in the deep sea. The characteristics of the specimens also show that the lenses grew on their eyes’ edges, so their eyes grew along with the rest of the body. This is a mechanism that exists in modern arthropods.
According to the researchers, Anomalocaris briggsi’s excellent eyesight indicates that it played a crucial role in their hunting skills. Dr. John Paterson explained that the evolution of those eyes may have triggered a sort of arms race between predators and prey with eyesight as the primary weapon.
According to John Paterson, these animals were arthropods. Discussions about their classification will likely continue for a long time. The characteristics of Anomalocaris briggsi’s eyes are very similar to those of arthropods, including the ones existing today, so they’re likely to be at least closely related groups.
