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A fossilized trilobite first studied by an amateur paleontologist half a century ago has provided researchers with a whole new way of seeing the world, in a very literal sense.
X-rays taken of the ancient arthropod in the early 1970s have been reexamined, revealing the structure of an eye that is unlike any other animal before or since.
As head of Siemens’ radiology department, Wilhelm Stürmer knew a thing or two about using x-rays to reveal hidden secrets. This was especially true when it came to studying fossils, a passion he fueled by fitting a minibus with x-ray equipment to take to paleontology sites.
Despite his expertise in radiology, Stürmer was not a paleontologist, so few claimed to have discovered optic nerves inside a 390 million year old body. Phacops geesops fossil seriously.
“At that time, 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,” says the paleontologist at the University of Cologne Brigitte Schoenemann.
In addition to the nerves, there was an arrangement of “fibers” that strangely resembled photoreceptor cells called ommatidia. Only in this case, they were strangely elongated, about 25 times their own diameter; far too long to sound plausible as a light collecting structure.
Much has changed since then. Today paleontologists are comfortable with the idea that soft tissue structures can leave a clear signature in fossilized materials. And super long ommatidia have since been found in the eyes made up of aquatic arthropods.
With that in mind, Schoenemann and his colleagues returned to Stürmer’s original footage for further examination. After rechecking the fossil with modern CT technology, they determined that the filaments he spotted were almost certainly optic nerve fibers after all.
But it was what the nest of moss-like fibers was connected to that really caught the researchers’ attention: what appeared to be two compound eyes were actually hundreds, split into left and right clusters.
“Each of these eyes consisted of around 200 lenses up to a millimeter in size,” says Schoenemann.
“Under each of these lenses, in turn, at least six facets are configured, each of which again constitutes a small compound eye. So we have about 200 compound eyes (one under each lens) in one eye.”
Trilobites have more or less dominated the oceans for hundreds of millions of years, adapting to fill a wide range of aquatic niches with a variety of weird and wonderful body planes.
One of their smartest inventions was a visual system of unprecedented complexity. While relatively straightforward in modern terms, their version of the eyes gave them the advantage of hunting or hiding and sensing the most subtle changes in light and movement.
Although the anatomy of their eyes comes in many forms, the most common structures would be easily recognizable to most zoologists today, consisting of a pattern of carefully arranged lenses working together to transform diffused light into a strongly pixelated map of their environment.
Modern insects and other arthropods continue to rely on compound eyes like these to great effect. What this pixelated view lacks in resolution is easily made up for in simplicity and adaptability, evolving to overcome limitations with a few anatomy tweaks.
Yet for the incredible diversity of the eyes of trilobites, those of some members of the suborder Phacopina have left paleontologists baffled.
In what’s called a schizochroal eye, each lens is a short distance from its neighbor, leaving a lot of empty space that could be used to catch more light.
We now know that what appears to be a single lens is, in fact, a single compound eye in two “hyper-eyes”.
While that doesn’t tell us why these eyes evolved, it does change the questions we need to ask ourselves about this unusual arthropod.
Rather than thinking about the waste of space between each lens, biologists can now speculate on the benefits hundreds of small eyes have in adapting to low light or responding to rapid changes in lighting conditions over an area. wider.
“It is also possible that the individual components of the eye perform different functions, allowing, for example, the improvement of contrast or the perception of different colors”, explains Schoenemann.
Stürmer must have known that there was something worth looking in the eye, having drawn an arrow in red pen pointing directly at the half-dozen veneers under one of the lenses.
Sadly, the radiologist passed away in the 1980s, long before his discovery received the validation it deserved.
Like the trilobite, Stürmer was clearly a visionary before his time.
This research was published in Scientific reports.
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