Researchers identify oldest known species of swimming jellyfish

(CN) — Researchers in Canada have discovered the oldest swimming jellyfish in the fossil record at a hot spot of the fossil world: the Burgess Shale in southeast British Columbia.

The new species, Burgessomedusa phasmiformis — a name which means Burgess Shale jellyfish with a ghostly form — was swimming about the water some 500 million years ago, according to co-author of the study, Joe Moysiuk, a Ph.D. candidate in ecology and evolutionary biology at the University of Toronto.

The “ghostly form” part of the jellyfish’s name is in reference to the creature’s body, which resembles a shape similar to the little ghosts in the old video game Pac-Man.

Reached by phone Monday from his office at the Royal Ontario Museum in Toronto, Moysiuk said the Burgess Shale is world famous because of its “incredibly well-preserved” fossils. It’s not just bones that are fossilized; the area’s unique features allows researchers a look at soft tissue, such as eyes, nervous systems and stomachs still containing the last meals of animals.

“The site really gives us unparalleled insight into what was going on during this time period in history,” said Moysiuk, whose interest in fossils began as a youngster while exploring ravines in Toronto.

The Burgess Shale was discovered around 100 years ago and researchers are still making new discoveries today. It’s like a prized gold mine that continues to produce.

Although Moysiuk and his colleagues don’t know everything about the Burgess Shale, they figure that sediment covered organisms quickly.

“It definitely required rapid burial of the organisms, and we think that all of these organisms were living on the sea floor 500 million years ago. Then they were caught up in mudslides that trapped them and covered them in a layer of sediment, and in doing so quickly sealed off the environment from bacteria that might have decayed away the organic remains and allowed those soft tissues to be preserved,” Moysiuk said.

That time period is of extreme importance to researchers.

“The Cambrian Explosion is this time in history when we see the first appearances of essentially all major modern groups of animals,” Moysiuk said.

“So we think that this is a pivotal moment in the evolution of life on Earth," he added. "The jellyfish discovery is the oldest known large-bodied jellyfish that we have in the fossil record. It has filled in one more piece in this growing picture of how much of the Earth’s diversity of life had already arisen by the Cambrian period.”

The study identifying Burgessomedusa is based on fossil specimens mostly found in the late 1980s and 1990s under Desmond Collins, former Royal Ontario Museum curator of Invertebrate Palaeontology.

“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 food webs, and like Anomalocaris which lived in the same environment, these jellyfish were efficient swimming predators,” study co-author Jean-Bernard Caron, Royal Ontario Museum's Richard Ivey curator of invertebrate palaeontology, said in a statement.

“This adds yet another remarkable lineage of animals that the Burgess Shale has preserved chronicling the evolution of life on Earth," he added.

Jellyfish belong to medusozoans, which are part of one of the oldest groups of animals to have existed, called Cnidaria. That group also includes corals and sea anemones.

Moysiuk said the jellyfish spent the first part of their life in a body form known as polyps that looks like little coral or anemones that live stuck to the sea floor. Then, at some point, the jellyfish would go through a metamorphosis and turn into the swimming jellyfish.

It wasn’t clear until now that these large, swimming jellyfish had evolved by the Cambrian era and went into this metamorphosis, said Moysiuk.

“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 Moysiuk.

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