505-Million-Year-Old Jellyfish Fossils May Be the Oldest Ever Found

Jellyfish have been floating around the Earth’s oceans for what seems like an eternity. But the exact origins of these fluffy sea creatures, some of the earliest complex animals, are difficult to determine. Jellyfish rarely appear in the fossil record because they are 95% water and subject to rapid decomposition.

“If you find a jellyfish out in the water, a few hours later it’s just a ball of slime,” said Jean-Bernard Caron, a paleontologist at the Royal Ontario Museum in Toronto.

But Dr. Caron and other scientists recently reported that they have discovered an unlikely route to preservation in a archive of Cambrian jellyfish fossils. In a paper published Wednesday in the journal Proceedings of the Royal Society B, scientists say these 505 million-year-old animals are among the oldest swimming jellyfish known to science. claims.

“These new fossils present the most convincing evidence for a Cambrian jellyfish to date,” said David Gold, a paleontologist at the University of California, Davis, who was not involved in the new study. .

The jellyfish specimen was discovered in the Burgess Shale, a fossil-rich site in the Canadian Rockies that offers a glimpse of life during Earth’s Cambrian explosion. Like other soft-bodied creatures found at this site, the gelatinous jellyfish are preserved in amazing detail. Most still have more than 90 finger-like tentacles that protrude from their bell-shaped bodies like strings at the end of a tassel rug. Some retain their stomach contents and gonads.

Back in the 1990s, researchers at the Royal Ontario Museum unearthed more than 170 jellyfish fossils from the Raymond Quarry in British Columbia. Dr. Caron and his PhD students recently examined the specimen and realized that the fossil was a new species, which they named Burgessomedusa phasmiformis.

This species is part of a diverse group called Mesozoa, thought to have originated at least 600 million years ago, and still swims in the same oceans we know today. However, evidence of their rise is scant. Most pre-Cambrian fossils are microscopic or only faint traces, making it difficult to infer how these ancestral jellyfish lived.

Over the past two decades, paleontologists have discovered several well-preserved jellyfish-like fossils from sites in Utah and China that are similar in age to the Burgess Shale. However, the true identity of these creatures is still up for debate. In a new paper, Dr. Caron and his colleagues show that fossils discovered in Utah and China show that true jellyfish are closely related to another group of gelatinous animals, ancient ctenophores. Or proposed that it represents a comb jellyfish.

Not all researchers are convinced by this reclassification. Bruce Lieberman, a paleontologist at the University of Kansas who studied the Utah fossil, said the new paper lacks strong evidence linking the early fossils to comb jellyfish. Rather, he thinks Bergesomedusa may have joined the swarms of jellyfish that patrolled the Cambrian seas. “This adds to a compelling body of evidence that the mesozoans, a clade of great importance in today’s oceans, were already established by the Cambrian.” said Dr. Lieberman.

Researchers believe adding jellyfish to the Burgess Shale’s miniature zoo adds further complexity to the Cambrian ecosystem. Growing to nearly 8 inches long, Burgesomedusa was one of the larger creatures around.

Dr. Gold said Burgesomedusa’s bell-like shape is reminiscent of modern-day box jellyfish, powerful predators with deadly stings. “Box jellyfish are active hunters, using their bells to aggressively turn and gain great speed in pursuit of prey,” Dr. Gold said. However, Burgessomedusa appears to lack some sensory structures found in modern jellyfish. “We don’t know if modern box jellyfish had eyes that were used for hunting,” Gold said.

Even without eyes, Burgesomedusa may have been an apex predator. Like modern jellyfish, they probably specialized in small fish. However, it seems that they also had the ability to hunt relatively large prey. One specimen of Burgesomedusa studied in the paper was preserved with a trilobite inside its bell.

Despite being composed almost entirely of water, jellyfish are able to capture prey while floating through the ocean, making them the ocean’s most persistent predators.

“Bergesomedusa shows how little the basic jellyfish body has changed,” Dr. Gold said. “They have survived with little change for hundreds of millions of years.”

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