Fossils of ancient three-eyed predators shed light on insect evolution

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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 brains and heads of insects and spiders.

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 brains and heads of insects and spiders.

The study, published in the journal Current Biology, examined 268 specimens collected in the 1980s and 1990s from a site in Yoho National Park in British Columbia and held at the Royal Ontario Museum in Toronto.

Dozens of these fossils contained the half-billion-year-old brain and nervous system of Stanleycaris, which was part of an ancient extinct offshoot of the arthropod evolutionary tree called Radiodonta, distantly related to insects. and modern spiders.

“This is a once-in-a-lifetime discovery,” said Joe Moysiuk, the study’s lead author and doctoral candidate in ecology and evolutionary biology at the University of Toronto, in an interview this week.

“We get 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 the information processing centers visuals extending into the 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, which today includes things like insects and spiders.”

The fossils show that the brain was made up of two segments, which he says has deep roots in arthropod lineage and that its evolution likely predated 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 velvet worm divergence and modern arthropods,” Moysiuk explained.

Researchers, he said, were able to trace how the evolution of brain segments happened more than 500 million years ago.

“It’s pretty amazing when you think we look 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 around 20 centimeters in size.

“Organisms were preserved in these fast-flowing mudslides, so they tumbled and flattened in all sorts of orientations,” Moysiuk said, noting that most specimens were five centimeters or smaller.

“So when we looked at the different fossils that we find in these different preservation orientations, we’re able to piece together what the whole creature looked like in three dimensions.”

The researchers found that the Stanleycaris, known as a predator in Cambrian times, had an unexpectedly large central eye in front of its head in addition to its pair of stalked eyes.

“This highlights that these animals had an even more bizarre appearance than we thought, but also shows us that early arthropods had already evolved a variety of complex visual systems, like many of their modern relatives,” said Jean-Bernard Caron. , supervisor and curator of Moysiuk. of Invertebrate Paleontology at the Royal Ontario Museum, said in a news release.

“Since most radiodonts are only known from scattered fragments, this discovery is a crucial leap forward in understanding what they looked like and how they lived.”

Moysiuk said the discovery also shows the importance of fossil collections.

“There are a lot of treasures that can be found by browsing things that were discovered long ago,” he said.

“We have this incredible collection of Burgess Shale fossils at the Royal Ontario Museum.”

This report from The Canadian Press was first published on July 8, 2022.

Colette Derworiz, The Canadian Press

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