A fossil specimen of Burgess Shale’s Stanleycaris hirpex shows a strange-looking animal with three eyes that illuminate the evolution of the brain, vision, and head of modern insects and spiders. Jean-Bernard Caron / The Canadian Press
Research based on a collection of Burgess Shale fossils shows a strange-looking animal with three eyes that illuminates the evolution of the brain and head of insects and spiders.
The study, published in the journal Current Biology, looked at 268 specimens collected in the 1980s and 1990s from a site in Yoho National Park in British Columbia and stored at the Royal Ontario Museum in Toronto.
Dozens of these fossils contained the brain and nervous system of the half-million-year-old Stanleycaris, which was part of an ancient extinct branch of the arthropod evolutionary tree called Radiodonta, distantly related to modern insects and spiders. .
“It’s a unique type of discovery in life,” Joe Moysiuk, lead author of the study and a doctoral candidate in ecology and evolutionary biology at the University of Toronto, said in an interview this week.
“We have so much information that we couldn’t get from the ordinary fossil record, things like the characteristics of the brain. We can see how many segments this animal’s brain is made up of. We can see how the centers of visual information processing extend to eyes of the animal, giving us all sorts of information about the neuroanatomy of this extinct organism.
“This, in turn, helps us understand the evolution of the brain and nervous system of the group of modern animals we call arthropods, so it includes things like insects and spiders.”
The fossils show that the brain was composed of two segments, which he said have deep roots in the lineage of arthropods and that their evolution probably preceded the three-segment brain that characterizes today’s insects.
“We believe the third segment was added somewhere in this branch which is the tree of life between the divergence of velvet worms and modern arthropods,” Mr. Moysiuk.
Researchers, he said, were able to track how the brain segments evolved more than 500 million years ago.
“That’s pretty amazing when you think we’re looking at these fossils. You think fossils are mostly things like shells and bones, not things like brains.”
Mr. Moysiuk said proper conditions were needed to preserve the small, compressed fossils of an animal about 20 centimeters in size.
“The organisms were kept in these fast-flowing mud streams, so they were lying down and flattened in all sorts of orientations,” Moysiuk said, noting that most specimens were five inches or less.
“So when we looked at the different fossils we found from these different preservation orientations, we were able to reconstruct what the whole creature was like in three dimensions.”
The researchers found that the Stanleycaris, known as a predator in the Cambrian period, had an unexpectedly large central eye in front of its head, in addition to its pair of prickly eyes.
“It is noteworthy that these animals looked even stranger than we thought, but it also shows us that early arthropods had already developed a variety of complex visual systems like many of their modern relatives,” said Jean-Bernard Caron, Mr. Moysiuk. and curator of invertebrate paleontology at the Royal Ontario Museum, he said in a press release.
“Because most radiodonts are only known from scattered chunks, this discovery is a crucial leap forward in understanding how they were and how they lived.”
Mr. Moysiuk said the finding also shows the importance of fossil collections.
“There are a lot of treasures that can be found by tracing things that have been discovered a long time ago,” he said.
“We have this amazing collection of Burgess Shale fossils at the Royal Ontario Museum.”
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