Trilobites are segmented animals that existed during the Paleozoic Era. They have an elongated, flattened, oval body and a pair of eyes. Or so we thought. Analysis of X-ray evidence of a fossilized trilobite dating back 390 million years has revealed some disturbing secrets about these spectacular marine arthropods (reaching up to 70 centimeters long and 40 cm wide).
What appeared to be two distinct eyes of Phacops geesops, a trilobite of the suborder Phacopina, which lived during the Devonian (also known as the Age of Fish), some 390 million years ago, have actually turned out to be large systems of hundreds of individual eyes or “mini eyes”; in other words, these animals had hundreds and hundreds of eyes.
Behind each individual large eye they found a series of facets anchored by photoreceptors and a network of nerve cells, which captured the light from each before sending it down a central optic nerve to the brain, creating a completely unique way of seeing the world. The surprising finding has been published in the journal Scientific Reports.
“So we have about 200 compound eyes, one under each lens, in one eye,” explained zoologist Brigitte Schoenemann, from the Institute for Didactics of Biology at the University of Cologne (Germany), a co-author of the study.
The scientists, after identifying this discovery, officially confirmed it with CT scans, determining that the trilobites of the Phacopina suborder had a unique optical network in the animal kingdom.
Each of his two eyes had 200 tiny eyes, each up to a millimeter in size. Its sub-facets are arranged in a ring or two rings, below which is a “foam-like nest,” Schoenemann said, which was likely a local neural network used to process information from the hyper-eye directly.
“This rare fossil shows us how the first animals saw the world around them hundreds of millions of years ago,” said geologist Euan Clarkson, co-author of the report.
According to the team, the hypercomposite eyes of phacopid trilobites could have been the product of an evolutionary adaptation to life in low light conditions.
“With its highly complex visual apparatus, it may have been much more sensitive to light than a normal trilobite eye ,” says Schoenemann. “It is also possible that individual components of the eye perform different functions, allowing, for example, enhancement of contrast or the perception of different colors. Until now, that eye has only been found in the trilobite suborder Phacopina. In the course of evolution, this ocular system did not continue, since the trilobites of the Phacopina suborder became extinct at the end of the Devonian period 360 million years ago ”, clarifies the expert.
Trilobites more or less ruled the oceans for hundreds of millions of years, adapting to fill a wide range of water niches with a myriad of strange and wonderful body plans . Their ocular version, although present in many forms, gave them the advantage of hunting or hiding and detecting the most subtle changes in brightness and movement in the face of their prey or predators.
Reference: B. Schoenemann et al. 2021. A 390 million-year-old hyper-compound eye in Devonian phacopid trilobites. Sci Rep 11, 19505; doi: 10.1038 / s41598-021-98740-z
