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Researchers at the Royal Ontario Museum (ROM) and the University of Toronto have discovered evidence of the oldest swimming jellyfish in the fossil record, .

A study, , documented the finding of 182 fossils in the Burgess Shale, a deposit in B.C.’s Rocky Mountains known for its rich preservation of the explosion of life during the Cambrian period.

Researchers found that the fossils belong to a newly identified species of jellyfish that swam in the Earth’s oceans 505 million years ago, CNN reported. Given that jellyfish are 95 per cent water, it is a remarkable and rare fossil find.

“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,” Joe Moysiuk, a PhD candidate in the Faculty of Arts & Science’s department of ecology and evolutionary biology, who is based at the ROM, quoted by CNN. “This discovery leaves no doubt they were swimming about at that time.”

Co-author Jean-Bernard Caron, an associate professor in ecology and evolutionary biology and the ROM’s Richard Ivey Curator of Invertebrate Palaeontology, adds that the discovery the new species – called the Burgessomedusa phasmiformis – enriches our understanding of the complexity of Cambrian food webs, noting that these jellyfish were efficient swimming predators.

The discovery was covered by outlets around the world, including , and . Visitors can see fossils of Burgessomedusa phasmiformis at the ROM’s .