The 505 million-year-old fossil hints at what sea life was like in the Cambrian era
By ELIZABETH HLAVINKA
PUBLISHED AUGUST 2, 2023
When a group of paleontologists dusted off a group of fossils that had been sitting on the shelf at the Royal Ontario Museum in Toronto, Canada since the 1980s, they uncovered a spooky organism with a bell-shaped body and about 90 stubby tentacles extending out from its rim.
The 505 million-year-old fossil revealed the oldest known species of swimming jellyfish, which the research team named Burgessomedusa phasmiformis, according to a study published today in the Proceedings of the Royal Society B.
"That [name] means 'the Burgess Shale jellyfish with a ghost-like form,'" study author Joseph Moysiuk, a Ph.D. candidate at the University of Toronto, told Salon. "We gave it that name because its overall body shape looks a little bit like the ghost from Pacman."
Only a handful of jellies have ever been discovered in fossils, (without bones, it's hard to fossilize), including one 2007 discovery in Utah also tracing back to the Cambrian time period, when most animal groups were born. However, Moysiuk says these might have been comb jellies from the Ctenophora phylum, rather than the Cnidaria phylum which includes jellyfish, corals and sea anemones. Although they are similar, the latter is more predatory and mobile.
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"We gave it that name because its overall body shape looks a little bit like the ghost from Pacman."
The fossils examined by Moysiuk and his team showed the bulbous body of the jellyfish extending up to 20 centimeters, with dozens of flexible tentacles it would have used to swim. Although B. phasmiformis has a box shape similar to one of the most venomous types of jellyfish, it also has a ring of tentacles similar to a group called true jellyfish, Moysiuk said. These traits that resemble many different kinds of modern-day jellyfish provide a glimpse into how the species evolved.
"I think what's neat about this mix of characteristics is it's probably suggesting to us that Burgessomedusa diverged from the line quite deep in that group's history," Moysiuk said. "It's telling us a little bit about the ancestry of the group of jellyfish as a whole."
A jellyfish begins its life cycle as an anemone-like creature on the sea floor before undergoing a metamorphosis and sprouting into a recognizable medusa — that Pacman ghost shape we're all familiar with. Jellyfish have also been identified in fossils in this time period in these earlier forms, suggesting this transformation began at the species level at least 505 million years ago.
The Anomalocaris canadensis, a long arthropod with spiny claws resembling a shrimp, is thought to have been a major predator during the Cambrian era. But in one fossil Moysiuk's team worked with, they discovered evidence that suggested the Burgessomedusa phasmiformis might have given it some competition as an ancient predator underwater.
Within the bell shape of one fossil, researchers found additional fossils from relatives of modern-day crustaceans and spiders. Although this was only found in one sample, the presence of these critters suggests this ancient creature was carnivorous, like jellyfish that feed on plankton and crustaceans today.
The presence of these critters suggests this ancient creature was carnivorous, like jellyfish that feed on plankton and crustaceans today.
"It's possible this represents some kind of predatory interaction preserved in the fossil," Moysiuk said. "But since we only have one specimen, we can't be certain that it's not just a chance occurrence."
The fossil was uncovered from a region known as the Burgess Shale, a designated UNESCO World Heritage Site in Yoho National Park in British Columbia, where fossils of arthropods, predators and even some of the oldest human ancestors have been found.
Typically, jellyfish are uncommon in the fossil record because squishy, soft materials like jellies don't preserve as well as hard materials like bones. Because of the conditions in the Burgess Shale, which was likely buried rapidly in an underwater mudslide, many soft tissues like brains, eyes and digestive organs were preserved.
It's there that B. phasmiformis swam among the shrimp-like Anomalocaris canadensis (and other creatures we've yet to discover) that paved the way for life as we know it today.
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"Jellyfish have been so elusive in the Cambrian fossil record, and yet we think jellyfish are one of the earliest groups of animals to diverge," Moysiuk said. "This discovery helps fit that final piece in and complete our picture of how much animal diversity was already existing in the Cambrian period."
Royal Ontario Museum researchers identify oldest known species of swimming jellyfish
505-million-year-old swimming jellyfish from the Burgess Shale highlights diversity in Cambrian ecosystem.
Peer-Reviewed PublicationIMAGE: ARTISTIC RECONSTRUCTION OF A GROUP OF BURGESSOMEDUSA PHASMIFORMIS SWIMMING IN THE CAMBRIAN SEA view more
CREDIT: RECONSTRUCTION BY CHRISTIAN MCCALL. © CHRISTIAN MCCALL
Royal Ontario Museum (ROM) announces the oldest swimming jellyfish in the fossil record with the newly named Burgessomedusa phasmiformis. These findings are announced in the journal Proceedings of the Royal Society B.
Jellyfish belong to medusozoans, or animals producing medusae, and include today’s box jellies, hydroids, stalked jellyfish and true jellyfish. Medusozoans are part of one of the oldest groups of animals to have existed, called Cnidaria, a group which also includes corals and sea anemones. Burgessomedusa unambiguously shows that large, swimming jellyfish with a typical saucer or bell-shaped body had already evolved more than 500 million years ago.
Burgessomedusa fossils are exceptionally well preserved at the Burgess Shale considering jellyfish are roughly 95% composed of water. ROM holds close to two hundred specimens from which remarkable details of internal anatomy and tentacles can be observed, with some specimens reaching more than 20 centimetres in length. These details enable classifying Burgessomedusa as a medusozoan. By comparison with modern jellyfish, Burgessomedusa would also have been capable of free-swimming and the presence of tentacles would have enabled capturing sizeable prey.
“Although jellyfish and their relatives are thought to be one of the earliest animal groups to have evolved, they have been remarkably hard to pin down in the Cambrian fossil record. This discovery leaves no doubt they were swimming about at that time,” said co-author Joe Moysiuk, a Ph.D. candidate in Ecology & Evolutionary Biology at the University of Toronto, who is based at ROM.
This study, identifying Burgessomedusa, is based on fossil specimens discovered at the Burgess Shale and mostly found in the late 1980s and 1990s under former ROM Curator of Invertebrate Palaeontology Desmond Collins. They show that the Cambrian food chain was far more complex than previously thought, and that predation was not limited to large swimming arthropods like Anomalocaris (see field image showing Burgessomedusa and Anomalocaris preserved on the same rock surface).
“Finding such incredibly delicate animals preserved in rock layers on top of these mountains is such a wonderous discovery. Burgessomedusa adds to the complexity of Cambrian foodwebs, and like Anomalocaris which lived in the same environment, these jellyfish were efficient swimming predators,” said co-author, Dr. Jean-Bernard Caron, ROM’s Richard Ivey Curator of Invertebrate Palaeontology. “This adds yet another remarkable lineage of animals that the Burgess Shale has preserved chronicling the evolution of life on Earth.”
Cnidarians have complex life cycles with one or two body forms, a vase-shaped body, called a polyp, and in medusozoans, a bell or saucer-shaped body, called a medusa or jellyfish, which can be free-swimming or not. While fossilized polyps are known in ca. 560-million-year-old rocks, the origin of the free-swimming medusa or jellyfish is not well understood. Fossils of any type of jellyfish are extremely rare. As a consequence, their evolutionary history is based on microscopic fossilized larval stages and the results of molecular studies from living species (modelling of divergence times of DNA sequences). Though some fossils of comb-jellies have also been found at the Burgess Shale and in other Cambrian deposits, and may superficially resemble medusozoan jellyfish from the phylum Cnidaria, comb-jellies are actually from a quite separate phylum of animals called Ctenophora. Previous reports of Cambrian swimming jellyfish are reinterpreted as ctenophores.
The 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 of Earth history and to share these sites with the world through award-winning guided hikes. The Burgess Shale was designated a UNESCO World Heritage Site in 1980 due to its outstanding universal value and is now part of the larger Canadian Rocky Mountain Parks World Heritage Site.
Visitors to ROM can see fossils of Burgessomedusa phasmiformis on display in the Burgess Shale section of the recently opened Willner Madge Gallery, Dawn of Life.
Slab showing one large and one small (rotated 180 degree) bell-shaped specimens with preservation of tentacles. ROMIP 65789
CREDIT
Photo by Jean-Bernard Caron © Royal Ontario Museum
Field images of Burgessomedusa phasmiformis jellyfish specimens (middle right ROMIP 65789 – see close up images) and of the top arthropod predator Anomalocaris canadensis preserved on the same rock surface. Hammer for scale.
Detail of previous image showing Burgessomedusa phasmiformis jellyfish specimens (middle right ROMIP 65789) and of the top arthropod predator Anomalocaris canadensis.
CREDIT
Photo by Desmond Collins. © Royal Ontario Museum
ROM Burgess Shale fieldwork site in Yoho National Park, BC Raymond Quarry, in 1992.
CREDIT
Photo by Desmond Collins. © Royal Ontario Museum
Display of Burgessomedusa phasmiformis in the Burgess Shale section of ROM Willner Madge Gallery, Dawn of Life.
CREDIT
Photo by David McKay. © Royal Ontario Museum
JOURNAL
Proceedings of the Royal Society B Biological Sciences
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
A macroscopic free-swimming medusa from the middle Cambrian burgess shale
ARTICLE PUBLICATION DATE
2-Aug-2023
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