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As big as a handwith pointed structures throughout his body and above all endowed with three bulging eyes: a specimen of Stanleycaris hirpex, predator that populated the shallow seas of the Cambrian geological period, approx 500 million years ago. This is what emerges from a study by the University of Toronto, Canada: researchers have collected more than 250 fossils exceptionally well preserved of these arthropods and have analyzed their characteristics, making them the most complete reconstruction ever done to date. From the results of the study, published in the journal Current Biology, it emerged that the animal probably possessed, in addition to the two eyes on each side of the head, a much larger third, in the middle, perhaps for chasing small, fast-moving prey.
Brains from 500 million years ago
Stanleycaris hirpex belonged to radiodonts, an extinct order of arthropods (the group of invertebrates including insects, arachnids and crustaceans) that lived during the Cambrian, about 500 million years ago. Variable in size, with an elongated body divided into segments and the eyes positioned on two lateral stem structures, radiodonts are the symbolic animals of this geological period. However, their importance goes far beyond the singular aspect: for paleontologists, in fact, they represent one great resourceas they offer crucial information onevolution of arthropods over millions of years, up to the present day.
Despite this, studying radiodontes is not easy: i fossils of these animals in fact they are difficult to trace and, when they are finally found, they often are badly preserved and fragmented. Yet there is one place that is a veritable goldmine for those who study prehistoric animals of the Cambrian period: the site of Burgess Shale, in British Columbia, Canada. It is a’area of clayey sediments in the Canadian Rockies, a Unesco World Heritage Site, where there is the largest number of Cambrian period fossils best preserved in the world.
The Canadian study began from this very place: the researchers collected and analyzed as many as 268 specimens of Stanleycaris hirpex from Burgess Shale, finding many of them exceptionally preservedwhich also had the soft tissues perfectly intact, including the brain and the nerve centers for processing the visual systems.
A ferocious predator
It is thanks to the perfect conservation of the fossils that the researchers were able to identify one characteristic of these arthropods never seen before: in addition to the pair of lateral eyes on the stem protrusions, the head of the Stanleycaris it housed, in the center and in the anterior position, a third Eye. Thanks to the fossils, the researchers have Brain subdivision observed for the first time of the arthropod and reconstructed his anatomy with great precision: Stanleycaris had the body, about 30 cm long, divided into seventeen segments, with two pairs of rigid blades in the lower region e pointed claws which probably had the purpose of dragging the prey directly to the jaws, equipped with sharp teeth. A experienced predator, in short. The third eye, according to the researchers, would also have played a crucial role in capturing the animals present in the surrounding environment.
The results obtained from the study have – it must be said – made us look at other arthropods of the same geological period with new eyes: for example, it is known that animals belonging to the genus Lyrarapaxradiodontes of 520 million years ago, had one on the anterior portion of the head structure similar to that found in the Stanleycaris. According to the authors of the study, therefore, also this arthropod, in profound evolutionary continuity with the Stanleycaris, he may have had a third eye. “These fossils are like a Rosetta stone, which help connect the traits of radiodonts and other primitive arthropods with their modern-day counterparts.“, concludes the researcher.
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