The oldest swimming jellyfish are 505 million years old and are preserved in rocks in Canada
95% of its body is made up of water and in addition to being one of nature's most unusual creatures, it is also one of the most successful despite its apparent fragility.. The next time you come across a jellyfish, think that they have been cruising the oceans for hundreds of millions of years.. At least, from 505 million years ago, since that is the dating of the oldest fossils of swimming jellyfish discovered so far.
This is confirmed by a team of scientists from the Royal Ontario Museum, in Canada, who unknowingly guarded in their collection such ancient fossils of a hitherto unknown species of jellyfish that has been named Burgessomedusa phasmiformis.. Although jellyfish and their relatives are thought to be one of the earliest animal groups to evolve, it has been difficult to place them in the Cambrian fossil record (a period that spans from 539 million years to 485 million years ago).
Artist's reconstruction of 'Burgessomedusa phasmiformis'
As Jean-Bernard Caron, co-author of the study and curator of Invertebrate Paleontology at the Royal Ontario Museum, explains to this newspaper, the Burgess Shale site was discovered in 1909, but these jellyfish fossils were collected almost 80 years later by the Royal Museum from Ontario under Parks Canada research and collecting permits. “Although these fossils were discovered decades ago, they had never been formally described or studied,” adds his colleague Joe Moysiuk, co-author of this study published this week in the Proceedings of the Royal Society B Biological Sciences, via email.. “There's always a conflict between needing to wait to see if more fossils can be discovered and just doing the job.. After all this time, it's exciting to finally give these fossils the attention they deserve.”
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According to the dating carried out, they would be the oldest confirmed swimming jellyfish: “Apart from Burgessomedusa, the next oldest definitive large jellyfish comes from the late Cambrian period, and is about 10 million years younger. These fossils are just impressions, so they provide very little detail.. There are also some slightly older fossils of microscopic larval forms that suggested that this group of animals might have an earlier origin, but now we have conclusive proof,” Moysiuk says.
Caron admits, however, that the fossil record of jellyfish is controversial: “Prior to the Burgessomedusa discovery, the oldest published jellyfish body fossil was a fragmentary, poorly preserved specimen from 518 million years ago found at the Chinese Jellyfish site. Chengjiang biota. We reinterpret this fossil as an organism resembling a ctenophore (or comb jellyfish), a different group of animals unrelated to jellyfish.. Younger fossils found in Utah (USA), and approximately the same age as the Burgess Shale site (505 million years), were also redescribed as ctenophore-type fossils in our article.. Some older microscopic fossils from China, from 535 million years ago, probably did not swim,” he reviews.
“The key point here is that Burgessomedusa unequivocally represents the oldest macroscopic swimming jellyfish in the fossil record.. The term 'swim' here is critical,” says Caron.
Poison
Regarding Burgessomedusa's resemblance to modern jellyfish, Joe Moysiuk notes that “it shares characteristics with several modern groups, but does not fit neatly into any of them.”. For example, its cubic shape resembles that of modern box jellyfish (or sea wasps), some of which are famous for their deadly stings.. The arrangement of the tentacles around the entire bell-shaped body margin is most similar to modern members of the true jellyfish group, such as moon jellyfish.. Although we're pretty sure Burgessomedusa is a member of the Medusozoa, we're not so sure which group of jellyfish it's most closely related to.”
Excavations at the Burgess Shale site in 1992
Was it a poisonous jellyfish? The authors of the discovery suspect so but are not sure. As Caron explains, “jellyfish belong to the cnidarians, which also includes corals and sea anemones.. Cnidarians are united by having stinging cells, called cnidocytes, however such cells are not preserved in fossils and can only be inferred.”
“While they primarily use this venom to catch smaller prey, in some species it can be powerful enough to kill much larger organisms, including people.”. We strongly suspect that Burgessomedusa would have had venom based on its relationship to modern jellyfish.. However, we don't know how powerful it would have been,” admits Moysiuk.
Regarding its possible prey, the researcher states that they have a specimen in which two different arthropods (related to modern spiders and crabs) are apparently preserved inside the Burgessomedusa bell: “However, we are not sure if this is evidence of predatory interaction or a random association. Arthropods and their larvae would have been the most abundant potential prey at this site.”
Fossils found in Canada that preserve jellyfish from 500 million years ago
As Jean-Bernard Caron details, the size of the jellyfish specimens found vary in size and range from a couple of centimeters to more than 20 centimeters: “Given that most of the animals in the Burgess Shale site are smaller than an adult finger, the largest jellyfish specimens were gigantic compared to other organisms living at the same time in that community. The groups of small and large specimens are reminiscent of jellyfish swarms in modern oceans.”
For Caron, this scientific find made from a museum archive “exemplifies the important role of new field research and collections in increasing our knowledge of the diversity of life that existed after the appearance of animals during the so-called explosion. Cambrian”.