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The humble trilobite, a helmet-headed creature that swam the seas hundreds of millions of years ago, hid an extraordinary secret – a “hyper-eye” never before seen in the animal kingdom.
Looking at x-ray images, the researchers found that some species of trilobites – extinct arthropods distantly related to horseshoe crabs – had “hyper-compound eyes,” with hundreds of lenses, their own neural network to process and send. signals and multiple optic nerves. , according to a new study published on September 30 in the journal Scientific reports.
Related: Why did the trilobites disappear?
Today’s arthropods, like dragonflies and mantis shrimp, are also known for their powerful compound eyes, made up of a myriad of eye facets called ommatidia, each equipped with its own lens, like a disco ball.
But, according to new findings, the family’s trilobites Phacops had compound eyes that were much larger and more complex than their modern arthropod relatives. Each of their eyes (they had one on the left and one on the right) contained hundreds of lenses. At nearly a millimeter in diameter, these primary lenses were thousands of times larger than those of a typical arthropod. Tucked under them like bulbs in a car headlight were six (or more) faceted substructures similar to a typical compound eye. “So each of Phacopid’s large eyes is a hyper compound eye with up to 200 compound eyes each,” lead study author Brigitte Schoenemann, a paleontologist at the University of Cologne in Germany, told Live Science in an email.
Trilobites are creatures that lived from the early Cambrian Period (521 million years ago) to the late Permian (252 million years ago) on the ocean floor. Some may have been predators that hunted aquatic worms, although most were scavengers or plankton eaters. The remains are usually found in limestone rock from the Cambrian period. But despite their ubiquity in the fossil record, scientists still have questions about their physiology and evolutionary history.
To answer some of these questions, the researchers used photo enhancement techniques to examine dozens of archival photos, cross-checking them with recent findings. In the process, they also resolved a long-standing scientific debate: They confirmed that a mysterious series of “fibers” seen in x-ray images from over 40 years ago were in fact connected optic nerves. in the eyes of trilobites.
“It’s always difficult to infer the function of ancient and extinct organisms,” said Nigel Hughes, a trilobite expert at the University of California Riverside, who was not involved in the study. In fact, Hughes pointed out, even some strange features on living creatures escape explanation – for example, there is still debate about the function of the long, horn-shaped tooth of narwhals, according to the Smithsonian Institution.
However, eyes are a little easier to analyze than teeth or horns, Hughes said, because optical systems only have one function: sight. “We know it’s an eye of the structure,” he said, and so it makes sense that the attached filaments are nerves. “I think it’s pretty convincing in the newspaper.” Why a trilobite might need so much visual power remains a mystery.
The x-ray photos themselves were taken by Wilhelm Stürmer, a professional radiologist and amateur paleontologist from Siemens. In the 1970s, Stürmer mounted an X-ray probe inside his VW bus and created a new method for studying fossils: X-ray paleontology, which allowed him to look through solid rock on up and take some of the most sophisticated fossil photos of his day.
Examining the slate of Hunsrück, a fossil quarry a short drive from his home in Munich, Germany, Stürmer discovered a world of petrified creatures embedded in rock. Remarkably, these specimens – including the phacopid trilobites – were so well preserved that even their delicate soft tissues were visible. Stürmer and his collaborator Jan Bergström noted that the trilobites appeared to have fossilized “fibers” connected to their compound eyes, which they described in the June 1973 issue of the journal. Paleontological Journal.
Related: In pictures: a filtering Cambrian creature
But when Stürmer presented these findings to other paleontologists, “his colleagues in the scientific world laughed at him,” Schoenemann said. The prevailing wisdom at the time was that soft tissue, like nerves, simply did not fossilize. Stürmer must have confused gill filaments with optic nerve tissue, according to his detractors, according to Schoenemann. The radiologist, however, remained firm in his convictions.
“Stürmer believed in his theory until his death, filled with bitterness in 1986,” said Schoenemann. After nearly half a century, Schoenemann and his team feel they have finally justified their work.
Unfortunately, like Wilhelm Stürmer, the phacopid trilobites are no longer with us – they became extinct around 358 million years ago at the end of the devonian period, as well as about 75% of all life on Earth, Schoenemann said. “But surely not because of their sophisticated and highly adapted eyes.”
Originally posted on Live Science.
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