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Researchers examining decades-old x-rays of a 390-million-year-old trilobite fossil found that it had a very unique ocular structure made up of 200 large lenses in each eye.
Phacops geesops, a trilobite of the suborder Phacopina, lived in the Devonian, about 390 million years ago.
Under each optical lens in each of the eyes of the extinct arthropod, at least six facets are placed, each of them again forming a small compound eye, ”said zoologist Brigitte Schoenemann of the Institut de Didactique de la biology from the University of Cologne in a statement. .
“So we have about 200 compound eyes – one under each lens – in one eye. “
While the discovery was originally made by amateur paleontologist Wilhelm Stürmer in the 1970s, it wasn’t until Schoenemann and his team recently returned and reassessed x-rays – and confirmed them with CT scans – that Stürmer’s findings have been officially confirmed.
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The eyes of geesops phacops, a Devonian trilobite, have 200 lenses each, covering six small facets. Each facet forms another individual eye
Stürmer, a radiologist at German technology company Siemens, was an avid paleontologist, for decades driving his VW bus equipped with an x-ray station to the quarries of Hunsrück in central Germany in search of fossils.
When he examined the radiographs of p. geesops, he was sure they were showing fossilized eye nerves with a multitude of lenses.
At the time, however, Stürmer’s conclusions were dismissed by experts.
“The consensus was that only bones and teeth, the hard parts of living things, could be seen in fossils, but not the soft parts, like the intestines or nerves,” Schoenemann said.
X-rays of the 1970s first suggested p. geesops had this unique optical network, but the experts at the time rejected the idea. Pictured: Phacopid’s schizochroal eyes show a wider distance between lenses than most compound eyes
In the new study, published in Scientific Reports, Schoenemann and an international team of researchers verified Stürmer’s non-expert analysis.
They determined that trilobites of the suborder Phacopina had a unique optical lattice in the animal kingdom.
Each of their two eyes had 200 lenses, each measuring up to a millimeter.
Their sub-facets are arranged in one or two rings, under which there is a “moss-shaped nest,” said Schoenemann, who was likely a local neural network used to directly process information from the hyper-eye.
Recent CT scans of the trilobite fossil (above) confirmed the 50-year-old findings of amateur paleontologist Wilhelm Stürmer on the species’ hyper-compound eyes
They also found an optic nerve that allegedly carried information from the trilobite’s eye to the brain, just as Stürmer theorized.
Schoenemann had even found marks on Stürmer’s x-rays, labeling the six sub-facets.
“On an x-ray negative, there was a red pen arrow pointing to the structure of the six lower facets under a primary lens,” she said.
“This probably indicated that Stürmer had already recognized the hyper-compound eye.”
The team confirmed Stürmer’s findings with modern CT technology that was not available 40 years ago.
Trilobites dominated the world’s oceans from the beginning of the Cambrian Period, about 540 million years ago, until the end of the Permian period, about 250 million years ago.
Trilobites dominated the world’s oceans from the beginning of the Cambrian Period, about 540 million years ago, until the end of the Permian period, about 250 million years ago.
Most trilobites had compound eyes similar to those found in insects today – a large number of hexagonal facets forming an eye, with eight photoreceptors under each facet.
Drone bees have 8,600 facets, for example, while dragonflies have up to 10,000 facets.
In order to produce a consistent image, these facets must be very close to each other.
However, in the suborder Phacopinae Trilobites, the lenses visible from the outside of compound eyes are much larger and much further apart.
It didn’t work until Schoenemann looked at 50-year-old Stürmer’s x-rays and realized she was looking at a hyper-compound eye.
The “super-eye” could have been an evolutionary adaptation in order to see in low-light conditions, she said.
It is possible p. Geesops’ hyper-eye was designed to help him see in low light, the researchers said. Pictured: A rendering of a trilobite made in the 1880s
With his very complex visual apparatus, he could have been much more sensitive to light than a normal trilobite.
“It is also possible that the individual components of the eye perform different functions, allowing, for example, the enhancement of contrast or the perception of different colors,” said Schoeneman.
When Stürmer died in the mid-1980s, his heir donated his archives to the university, but researchers have only recently examined them in depth.
In 2017, Estonian paleontologists discovered an “exceptional” 530-million-year-old trilobite fossil containing what may be the oldest eye ever discovered.
The fossil’s right eye was partly worn out, giving researchers a clear view inside the organ, including details of its structures and functions.
Unlike Phacops geesops, this more primitive species, Schmidtiellus reetae, did not have a lens.
Its eye is made up of about 100 optical units, or ommatidia, which were located relatively far apart compared to contemporary compound eyes, the team said in a study published in the journal Proceedings of the National Academy of Sciences.
This is probably due to the fact that the species lacked the parts of the shell necessary for the formation of the lens.
“This exceptional fossil shows us how the first animals saw the world around them hundreds of millions of years ago,” geologist Euan Clarkson, co-author of the report, said at the time.
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