Research based on a collection of fossils from the Burgess Shale shows a bizarre-looking animal with three eyes that sheds light on 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 those fossils contained the brain and nervous system of the half-billion-year-old Stanleycaris, which was part of an ancient, extinct offshoot of the arthropod evolutionary tree called Radiodonta, distantly related to modern insects and spiders.
“It’s a once-in-a-lifetime kind of discovery,” Joe Moysiuk, lead author of the study and a PhD candidate in ecology and evolutionary biology at the University of Toronto, said in an interview this week.
“We get so much information that we couldn’t get from the ordinary fossil record — things like features of the brain. We can see how many segments the brain of this animal is made up of. We can see the processing centres for visual information extending into the eyes of the animal, giving us all kinds of information about the neuroanatomy of this extinct organism.
“That, in turn, helps us to understand the evolution of the brain and nervous system of the group of modern animals we call the arthropods, so that includes things today like insects and spiders.”
The fossils show the brain was composed of two segments, which he said has deep roots in the arthropod lineage and that its evolution likely preceded the three-segmented brain that characterizes present-day insects.
“We think that third segment was added somewhere along that branch that is the tree of life between the divergency of the velvet worms and the modern arthropods,” explained Moysiuk.
Researchers, he said, were able to trace how the evolution of the brain segments occurred more than 500 million years ago.
“That’s pretty incredible when you think we are looking at these fossils. You think of fossils as being 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 that was about 20 centimetres in size.
“The organisms were preserved in these fast-flowing mudflows, so they were tumbling around and flattened in all kinds of orientations,” said Moysiuk, noting most of the specimens were five centimetres or less.
“So, when we looked at the different fossils that we find from these different orientations of preservation, we are able to piece back together what the whole creature looked like in three dimensions.”
Researchers found that the Stanleycaris, known as a predator in the Cambrian period, had an unexpected large central eye in front of its head in addition to its pair of stalked eyes.
“It emphasizes that these animals were even more bizarre-looking than we thought, but also shows us that the earliest arthropods had already evolved a variety of complex visual systems like many of their modern kin,” Jean-Bernard Caron, Moysiuk’s supervisor and curator of invertebrate paleontology at the Royal Ontario Museum, said in a news release.
“Since most radiodonts are only known from scattered bits and pieces, this discovery is a crucial jump forward in understanding what they looked like and how they lived.”
Moysiuk said the finding also shows the importance of fossil collections.
“There’s a lot of treasures that can be found by trolling through things that have been discovered a long time ago,” he said.
“We have this incredible collection of Burgess Shale fossils at the Royal Ontario Museum.”
– Colette Derworiz, The Canadian Press