First studied by an amateur paleontologist half a century ago, a fossilized trilobite has opened up researchers a whole new way of seeing the world, literally.
Reviewing x-rays from this ancient arthropod in the early 1970s, researchers uncovered an eye structure not seen in any animal before or since.
Samples taken in the 1970s were reexamined
As head of Siemens’ radiology division, Wilhelm Stürmer had a wealth of knowledge in using X-rays to uncover hidden secrets. This was especially true when it came to examining fossils, a passion he fueled by packing a van with X-ray equipment to go to paleontology sites.
Despite his expertise in radiology, not many people took his claim that Stürmer had discovered optic nerves inside a 390-million-year-old Phacops geesops fossil because he was not a paleontologist. “At that time, there was consensus that only bones and teeth, that is, the hard parts of living things, could be seen in fossils, but not soft parts such as intestines or nerves,” said Brigitte Schoenemann, a paleontologist at the University of Cologne.
In addition to the nerves, there was also an arrangement of “fibers” resembling photoreceptor cells called ommatidia; but in this case, oddly enough, they were elongated to roughly 25 times their own diameter, far longer than would be reasonable for a light-gathering structure. Of course, a lot has changed since then. Today, paleontologists are aware that soft tissue structures can leave traces in fossils, and in addition, super-long ommatidia have been discovered in the compound eyes of aquatic arthropods.
Each eye consists of about 200 lenses
In light of this information, Schoenemann and his colleagues reworked Stürmer’s original images for further analysis. Researchers; After going over the fossil twice with modern CT technology, he determined that the detected filaments were almost certainly optic nerve fibers.
But what caught the researchers’ attention was what the foam-like loofah was connected to: What appeared to be two conjoined eyes were actually hundreds, divided into left and right clusters. “Under each of these lenses, in turn, there are at least six facets, each of which again forms a small compound eye. So there are about 200 compound eyes (one under each lens) in an eye,” Schoenemann said. He stated that it consists of about 200 lenses up to one millimeter.
Trilobites more or less dominated the oceans for hundreds of millions of years, adapting to populating a wide range of water niches with their various strange and wonderful bodies. One of the most wonderful inventions of the trilobites is; It was a visual system of unprecedented complexity. This system gave them an advantage when hunting or hiding, detecting the subtlest changes in brightness and movement.
Discovery; brought new questions
We now know that what appears to be a single lens is actually a single compound eye within two ‘hyper-eyes’. While this doesn’t give us any clue as to why these eyes evolved, it does change the questions we should ask about this unusual arthropod.
Biologists no longer think about wasting space between each lens; they can speculate on the benefits of hundreds of tiny eyes adapting to low light or responding to rapid changes in light conditions over a larger area. “It is also possible that the individual components of the eye perform different functions, for example, enhancing contrast or detecting different colors,” Schoenemann said.
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