Research based on a collection of fossils from the Burgess Shale shows a bizarre-looking animal with three eyes that sheds light on the development 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-billion-year-old Stanleycaris, which was part of an ancient, extinct offshoot of the evolutionary arthropod called Radiodonta, distantly related to modern insects and spiders.
“It’s a kind of once-in-a-lifetime discovery,” said Joe Moysiuk, lead author of the study and a doctoral student in ecology and evolutionary biology at the University of Toronto, in an interview this week.
“We get as much information as we could not get from the usual fossil document – things that function in the brain. We can see how many segments the brain of this animal consists of. We can see processing centers for visual information extend into the animal’s eyes,” which gives us all kinds of information about the neuroanatomy of this extinct organism.
“This in turn helps us understand the evolution of the brain and nervous system in the group of modern animals we call arthropods, so it includes things today such as insects and spiders.”
The fossils show that the brain was composed of two segments, which he said has deep roots in the arthropod line, and that its development probably preceded the three-segmented brain that characterizes today’s insects.
“We think the third segment was added somewhere along that branch that is the tree of life between the deviation of the velvet worms and the modern arthropods,” Moysiuk explained.
Scientists, he said, were able to trace how the evolution of brain segments occurred more than 500 million years ago.
“It’s pretty incredible when you think we’re looking at these fossils. You think of fossils as mostly things like shells and bones, not things like brains.”
Moysiuk said the right conditions were needed to preserve the small, compressed fossils of an animal about 20 centimeters in size.
“The organisms were preserved in these fast-flowing mudflows, so they tumbled around and flattened in all possible directions,” said Moysiuk, noting that most of the specimens were five centimeters or less.
“So, when we looked at the different fossils that we find from these different directions of conservation, we can piece together what the whole creature looked like in three dimensions.”
Researchers found that Stanleycaris, known as a predator during the Cambrian period, had an unexpectedly large central eye in front of its head in addition to its pair of stalked eyes.
“It emphasizes that these animals looked even more bizarre than we thought, but also shows us that the earliest arthropods had already developed a variety of complex visual systems like many of their modern relatives,” said Jean-Bernard Caron, Moysiuk’s supervisor and invertebrate curator. paleontology at the Royal Ontario Museum, said in a press release.
“Since most radio donors are known only from scattered pieces, this discovery is a crucial step forward in understanding what they looked like and how they lived.”
Moysiuk said the find also shows the importance of fossil collections.
“There are many treasures that can be found by conjuring things that have been discovered long ago,” he said.
“We have this incredible collection of Burgess Shale fossils at the Royal Ontario Museum.”
– Colette Derworiz, Canadian Press
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