Stanley Karis’s 500-million-year-old brains prompt a rethink of the evolution of insects and arachnids

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. Image Credit: Sabrina Cappelli, © Royal Ontario Museum

The Royal Ontario Museum has revealed new research based on a cache of fossils containing the brain and nervous system of a half-billion-year-old marine predator from Burgess Rock called Stanley Cares. Stanleycaris belongs to an ancient, extinct branch of an arthropod evolutionary tree called Radiodonta, closely related to modern insects and spiders. These findings shed light on arthropod brain development, vision, and head structure. The results were announced in the research paper published in the journal titled: “Three ray eyes with fossilized neuroanatomy tell us about the origin and segmentation of the arthropod head.” current biology.

It’s what’s inside Stanley Karis’ head that interests researchers the most. In 84 fossils, remains of the brain and nerves are still preserved after 506 million years.

“Although 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). Ph.D. Candidate in Ecology and Evolutionary Biology, based 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

The new fossils show that the brain of stanlikaris was composed of two parts, the primary brain and the microcerebellar, connected to the eyes and front claws, respectively. “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 part difference 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.”

Stanley Karis's 500-million-year-old brains prompt a rethink of the evolution of insects and arachnids

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

In addition to a pair of stalking eyes, Stanleycaris has a large central eye on the front of its head, a feature not previously observed in radio-rays. “The presence of a huge third eye in Stanleycaris was unexpected. It confirms that these animals were more exotic in appearance than we thought, but also shows us that the first arthropods did indeed evolve as diverse as many complex visual systems as many modern visual systems are,” said Dr. Jean-Bernard Caron, Richard Ivey curator of invertebrate fossils at ROM, and Moysiuk’s PhD supervisors added Caron, who is also an associate professor at U of T, in ecology, evolution and earth sciences.

In the Cambrian period, radio beams included some of the largest animals found around, with the famous “strange wonder” Anomalocaris reaching a length of at least one meter. Stanley Karis was no more than 20 cm in length, and was small for his group, but at a time when most animals were no larger than a human finger, he would have been an impressive predator. Stanley Karis’ sophisticated sensory and neural systems would have enabled her to select small prey efficiently in the dark.

With large compound eyes, a wonderfully round, tooth-lined mouth, front claws with an impressive set of spines, and a flexible, segmented body with a series of swimming flaps on either side, Stanley Cares was the stuff of nightmares for anyone unfortunate enough to cross his path.

  • Stanley Karis's 500-million-year-old brains prompt a rethink of the evolution of insects and arachnids

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

  • Stanley Karis's 500-million-year-old brains prompt a rethink of the evolution of insects and arachnids

    Fossil specimen of Stanleycaris hirpex. Dark matter within the head is remnant of nervous tissue, sample ROMIP 65674.2. Credit: Jean-Bernard Caron © Royal Ontario Museum

About Burgess Shell

For this research, Moysiuk and Caron studied a previously unpublished set of 268 samples of Stanleycaris. 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.

  • Stanley Karis's 500-million-year-old brains prompt a rethink of the evolution of insects and arachnids

    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. Credit: Jean-Bernard Caron © Royal Ontario Museum

  • Stanley Karis's 500-million-year-old brains prompt a rethink of the evolution of insects and arachnids

    Fossil specimen of Stanleycaris hirpex. Dark matter inside the head is a remnant of nervous tissue, sample ROMIP 65674.1. Credit: Jean-Bernard Caron © Royal Ontario Museum

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.

The public can see Stanleycaris fossils in the new Burgess Shale fossil display at Willner Madge Gallery, Dawn of Life at ROM.


New gigantic animal species discovered in the half-billion-year-old Burgess Shale


more information:
Joseph Moisiuk, three-eyed ray with a fossilized neuroanatomy, tells us about the origin of the arthropod’s head and segmentation, current biology (2022). DOI: 10.1016/j.cub.2022.06.027. www.cell.com/current-biology/f… 0960-9822 (22) 00986-1

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the quote: Stanley Karis’s 500-million-year-old brains spur rethinking of the evolution of insects and arachnids (2022, July 8) Retrieved on July 8, 2022 from https://phys.org/news/2022-07-million-year-old brains petrified- stanleycaris-prom.html

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