Research based on a collection of fossils from the Burgess Shale reveals a strange-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 British Columbia’s Yoho National Park and housed 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 branch of the arthropod evolutionary tree called Radiodonta, distantly related to modern insects and spiders.
“This is a once-in-a-lifetime discovery,” Joe Moysiuk, the study’s lead author and a doctoral student in ecology and evolutionary biology at the University of Toronto, said in an interview this week.
“We’re getting so much information that we couldn’t get from regular fossils — things like brain features. We can see how many segments the brain of this animal consists of. We can see the visual information processing centers extending into the animal’s eyes, giving 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 of the group of modern animals we call arthropods, so that includes things today like insects and spiders.”
The fossils show that the brain was composed of two segments, which he says have deep roots in the arthropod lineage, and that its evolution probably preceded the three-segmented brain that characterizes modern insects.
“We think the third segment was added somewhere along this branch, which is the tree of life between the divergence of velvet worms and modern arthropods,” explained Moysiuk.
The researchers, he said, were able to trace how the evolution of brain segments occurred more than 500 million years ago.
“It’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.
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 rolled around and flattened out in all sorts of orientations,” Moysiuk said, noting that most of the specimens were five centimeters or less.
“So when we looked at the different fossils that we’re finding from these different storage orientations, we’re able to piece together what the whole creature looks like in three dimensions.”
The researchers found that Stanleycaris, known as a predator during the Cambrian period, had an unexpectedly large central eye at the front of its head in addition to a pair of stalked eyes.
“This highlights that these animals look even stranger than we thought, but also shows us that the earliest arthropods had already developed different complex visual systems like many of their modern relatives,” Jean-Bernard Caron, head and Moysiuk Curator of Invertebrate Paleontology at the Royal Ontario Museum, said in a news release.
“Since most radiodonts are known only from scattered pieces, this discovery is a crucial leap forward in understanding what they looked like and how they lived.”
Moysiuk said the find also shows the importance of fossil collections.
“There’s a lot of treasure that can be found by trolling in things that were discovered a long time ago,” he said.
“We have this incredible collection of fossils from the Burgess Shale at the Royal Ontario Museum.”
– Colette Derworiz, The Canadian Press
Add Comment