A 429-million-year-old trilobite had eyes like those of modern bees

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Perfectly pristine fossils could make great museum centerpieces, but they’re not always the most informative for paleontologists. Some of the most salient secrets of ancient life are locked inside fossils and flukes can reveal internal details that might otherwise remain hidden. In the case of a 429-million-year-old trilobite — an extinct arthropod that looked like a large version of a woodlouse — a crack in the right place allowed paleontologists to see the world through the creature’s eyes.

Trilobites are one of evolution’s greatest achievements. These first animals, characterized by the “three lobes” of their exoskeletal body, first appeared around 521 million years ago, during the peak of biodiversity called the Cambrian explosion. They proliferated for millions more years, ranging from sizes smaller than a button to larger than a dinner plate, before disappearing about 252 million years ago. And given how common trilobites were in ancient seas, studying their evolutionary history can offer insight into life in our planet’s oceans.

“I have always loved these beautiful aulacopleure trilobites, with their big heads and big eyes,” says paleontologist Brigitte Schoenemann from the University of Cologne in Germany. “And so I bought one.” Perhaps the fossil would simply have been a collector’s item for someone else. But as an expert on the evolution of vision, Schoenemann noticed something unusual about it.

“I was very surprised to see that one eye was broken,” she said. The exposed inner surface revealed the animal’s lens, its receptor cells and other parts of its anatomy. Such detail is rare in the fossil record: the preservation of delicate cellular structures, especially in the eyes, often relies on rapid burial in oxygen-depleted environments. Places where this type of preservation occurs, such as the famous Cambrian Burgess Shale in British Columbia, are few and far between. (The circumstances in which Schoenemann aulacopleure specimen was buried are unclear.)

Exterior view of the trilobite Aulacopleura koninckiithe left eye. Credit: Brigitte Schoenemann

“For a long time it was thought that only bones, teeth and other hard objects could be kept in the fossil record,” she says. “Being able to distinguish cellular structures, especially in the eyes, is very, very rare and exceptional.”

Schoenemann and his co-author Euan Clarkson from the University of Edinburgh in Scotland published their analysis of the ancient eye on Thursday in Scientific reports. Although 429 million years old, the trilobite has a modern eye that resembles those of bees and dragonflies today. This type is called an appositional compound eye, which means that each lens acts independently to create a mosaic image of what a creature sees.

Examining the trilobite’s eye in detail helps track the evolution of eyes and vision in arthropods over time, says University of New England paleontologist John Paterson, who has no participated in the new study. “The take-home message seems to be that trilobites had developed appositional compound eyes during the early stages of group evolution and remained true to this design throughout their history.”

Drawing on previous studies of trilobite vision, the article also offers a window into the type of habitat aulacopleure prefer. The anatomy of the eye indicates that the trilobite lived in a bright, shallow environment. Given the relationship between lens size and availability of light dictated by physics, says Schoenemann, aulacopleureSmall lenses would have worked better in bright habitats. Thus, the animal was most likely active during the day.

The trilobite’s eye is very different from ours, Schoenemann notes, because it’s made up of dozens of facets that would have created a mosaic picture of the creature’s surroundings. “The eye has around 200 facets and is surely quite good at distinguishing between obstacles, dark and bright areas of the environment, shelters, shapes and other organisms,” she says, adding that organisms detected would include predatory cephalopods that probably ate trilobites. at the time. Like aulacopleure wandered around the ancient shallows, he certainly kept an eye out.

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