500-million year old jellyfish fossil discovered Burgess Shale after century-long search

• Fossils of any type of jellyfish are extremely rare, according to the study.
• The new study helps underscore the Cambrian period as a critical time for jellyfish evolution. Jellyfish and their relatives are thought to be one of the earliest animal groups to have evolved.
• According to Royal Ontario Museum, 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, a group which also includes corals and sea anemones.

A 508-million-year-old fossil discovered in the mountains of British Columbia has been dubbed the oldest adult swimming jellyfish ever found by paleontologists looking to understand soft-bodied animals’ relationship to the ancient past.

A new paper published this week in Proceedings of the Royal Society B details Burgessomedusa phasmiformis, a newly named animal and the first jellyfish species discovered in Canada's Burgess Shale, located in Yoho National Park. Paleontologists found 182 fossils of Burgessomedusa between the late 1980s and 1990s only in a spot called Raymond Quarry.

Considered by UNESCO to be one of the most important in the world, Burgess Shale preserves fossils that offer a glimpse of early life on Earth during the Cambrian, a period when animal diversity exploded more than half a billion years ago, according to the National Museum of Natural History. 

Burgess Shale fossils were first found in 1909 by Charles D. Walcott, then Secretary of the Smithsonian Institution, but Burgessomedusa have eluded detection for reasons that are still unclear, according to Smithsonian Magazine's Riley Black. 

Royal Ontario Museum paleontologist and study author Joseph Moysiuk said paleontologists who first saw the ancient jellyfish fossils decades ago knew almost immediately that it was an early jellyfish, but it took years before a formal description of the fossils was undertaken, according to Smithsonian Magazine.

Burgessomedusa’s mix of traits may indicate that it was a close relative of the common ancestor from which modern jellies diverged, according to paleontologists from the study. With more than 90 short, “finger-like” tentacles dangling from the nearly seven-inch umbrella-like animal, the fossil confirms that prehistoric jellies floated over reefs where their tentacles could capture prey, just like jellyfish spotted today. 

According to the National Museum of Natural History, the diverse group of Burgess Shale fossils, which range in shape and size, are remarkably preserved and significant to researchers for several reasons:

• Burgess Shale fossils of soft-bodied animals from a time when creatures were just beginning to evolve are so well-preserved because an underwater avalanche of fine mud buried them. 
• Only hard parts are preserved in most other Cambrian deposits, which limits our understanding of the geologic record.
• Some fossilized specimens appear to be early ancestors of higher forms like algae and chordates (a major group of animals that includes human primates) while others appear unrelated to any living forms.

“Finding such incredibly delicate animals preserved in rock layers on top of these mountains is such a wonderous discovery,” said study co-author Jean-Bernard Caron. “This adds yet another remarkable lineage of animals that the Burgess Shale has preserved chronicling the evolution of life on Earth.”

Paleontologists debate possible cases of mistaken jellyfish identify

Researchers of fossils found in Utah and South China have also claimed the discovery of medusa jellyfishes in recent years, however, Moysiuk claims those animals are likely comb jellies, which belong to a different phylum of animals called Ctenophora. Comb jellies are similar to jellyfish and just as old, but the two animals belong in distinct taxonomic classifications, Moysiuk said. Comb jellies push themselves through the water with hundreds of tiny cilia, whereas free-swimming jellyfish pump a large bell-shaped body. 

The co-author of a 2007 paper which describes a medusa jellyfish from Utah said he disagrees with some claims made in the newer study, Smithsonian Magazine reported. 

In the 2007 paper, University of Kansas researcher Bruce Lieberman described a medusa jellyfish from the 505-million-year-old Marjum Formation. Although Moysiuk and colleagues say that previous finds, including Lieberman’s, were cases of mistaken jellyfish identity,  the researcher maintained that these specimens are in fact jellyfish, according to Smithsonian Magazine.  

“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, a Ph.D. candidate in Ecology & Evolutionary Biology at the University of Toronto, in a press release.