‘Amazing’ fossilized brains dating back 500 million years prompt a rethinking of the evolution of insects and spiders

An ancient three-eyed predator reveals key information about the evolution of the body plan of arthropods.

New research is based on a cache of fossils containing the brain and nervous system of a half-billion-year-old marine predator from the Burgess Shale called Stanley Karis Unveiled by the Royal Ontario Museum (ROM). It belongs to an ancient, extinct branch of the arthropod evolutionary tree called Radiodonta, Stanley Karis It is closely related to modern insects and spiders. These findings shed light on arthropod brain development, vision, and head structure.

“The details are so clear it’s like we’re looking at an animal that died yesterday.”

– Joseph Moiseuk

The results were announced in the research paper, “Three-eye radiographs with fossil neuroanatomy inform arthropod head origin and segmentation,” published July 5, 2022, in the journal Science. current biology.

Pair of fossil specimens of Stanleycaris hirpex, specimen ROMIP 65674.1-2. Image source: Jean-Bernard Caron, © Royal Ontario Museum

What interests scientists the most is what’s inside Stanley Karis‘ head. The remains of the brain and nerves are still preserved after 506 million years in 84 fossils.

“While fossilized brains from the Cambrian period are not new, this discovery stands out for the amazing quality of preservation and the large number of specimens,” said Joseph Moisiuk, lead author of the research and University of Toronto (U of T). PhD candidate in Ecology and Evolutionary Biology, at the Royal Ontario Museum. “We can even provide fine details such as the visual processing centers that serve the large eyes and traces of nerves entering the appendages. The details are so clear as if we were looking at an animal that died yesterday.”

Turntable animation of Stanleycaris hirpex, including transparency to show internal organs. Credit: Animation by Sabrina Cappelli © Royal Ontario Museum

New fossils reveal that the brain Stanley Karis It consisted of two parts, the protocerebrum, attached to the eyes, and the deutocerebrum, attached to the front claws.

“We conclude that the two-part head and brain have deep roots in the arthropod lineage and that its evolution likely preceded the three-section brain that characterizes all living organs in this diverse animal phylum,” Moiseuk added.

In present-day arthropods such as insects, the brain consists of protocerebrum, deutocerebrum, and tritocerebrum. While the difference in the clip may not seem like a game-changer, it actually has drastic scientific implications. Because repetitive copies of many arthropod members can be found in their segmented bodies, knowing how the parts lined up between different species is key to understanding how these structures varied across the group.

“Like the Rosetta Stone, these fossils help link traits in radiators and other early arthropods with their counterparts in surviving groups.”

Reconstruction of a pair of Stanleycaris hirpex; The upper individual has an increased external transparency to show the internal organs. The nervous system is shown in light beige and the digestive system in dark red. Credit: Illustration by Sabrina Cappelli © Royal Ontario Museum

Plus a pair of stalking eyes, Stanley Karis He possesses a large central eye in the front of his head, a feature not previously observed in radiology. Having a huge third eye in Stanley Karis It was unexpected. It confirms that these animals looked more exotic than we thought, but also shows us that the earliest arthropods actually evolved as diverse as many complex visual systems as many of their modern relatives,” said Dr. Jean-Bernard Caron, Richard Ivey of ROM. Curator of Invertebrate Paleontology. and Moysiuk’s PhD supervisor. Karon, who is also an associate professor at U of T, added, in ecology, evolution and earth sciences.

Paper summary, illustrating the interpretation of the nervous system from the Stanley Karis fossils and its implications for understanding arthropod brain development. The brain is represented in red and the nerve cords in purple. Image source: Jean-Bernard Caron © Royal Ontario Museum

In the Cambrian period, Radiodonts included some of the largest animals found around, with their famous “strange wonders” anomalocaris It reaches a length of at least one meter. with a length of not more than 20 cm, Stanley Karis It was small for its range, but at a time when most animals were no larger than a human finger, it would have been an impressive predator. Stanley KarisWell-developed sensory and nervous systems would have enabled them to select small prey efficiently in the dark.

Reconstruction of the Stanleycaris hirpex. Image Credit: Art by Sabrina Cappelli © Royal Ontario Museum

With large compound eyes, a wonderful-looking round mouth lined with teeth, front claws with an impressive set of spines, and a flexible body divided by a series of swimming flaps on either side, Stanley Karis It would have been the stuff of nightmares for any little inhabitant at the bottom unlucky enough to cross his path.

About Burgess Shell

For this research, Moysiuk and Caron studied a previously unpublished set of 268 samples of Stanley Karis. Fossils were collected primarily in the 1980s and 1990s from layers of rock above the famous Walcott Quarry site in the Burgess Shale in Yoho National Park, British Columbia, Canada, and are part of the extensive collection of Burgess Shale fossils found in ROM.

Burgess Shale fossil sites are located within Yoho and Kootenay National Parks and are managed by Parks Canada. Parks Canada is proud to work with leading scientific researchers to expand knowledge and understanding of this key period in Earth’s history and to share these sites with the world through award-winning walking tours. The Burgess Shale was designated a UNESCO World Heritage Site in 1980 due to its outstanding universal value and is now part of the largest World Heritage Site for the parks of the Canadian Rockies.

fossils Stanley Karis It can be seen by the audience in the new Burgess Shale fossil show at Wellner Madge Gallery, Dawn of Life in ROM.

Reference: “Tri-ocular radiation with fossilized neuroanatomy tells of arthropod head origin and segmentation” by Joseph Moisiuk and Jean-Bernard Caron, July 8, 2022, current biology.
DOI: 10.1016 / j.cub.2022.06.027

Major research funding support came from the National Council for Scientific and Engineering Research in Canada, through the Vanier Canada Graduate Grant to Moysiuk and the Discovery Grant (No. 341944) to Caron.