# Burgessomedusa
**Burgessomedusa** is an extinct genus of medusozoan cnidarian known from a single species, *Burgessomedusa phasmiformis*, a large free-swimming jellyfish that lived about 505 million years ago during the middle Cambrian period. Described in *Proceedings of the Royal Society B* on 2 August 2023 by Justin Moon, Jean-Bernard Caron, and Joseph Moysiuk of the [Royal Ontario Museum](https://www.edgepedia.org/royal-ontario-museum) and [University of Toronto](https://www.edgepedia.org/university-of-toronto), it is the oldest unequivocal macroscopic free-swimming medusa in the fossil record.[1](https://doi.org/10.1098/rspb.2022.2490) • [2](https://www.rom.on.ca/news-releases/royal-ontario-museum-researchers-identify-oldest-known-species-swimming-jellyfish)
| Key fact | Detail |
|---|---|
| Classification | Medusozoan cnidarian; phylogenetic analysis recovers it as a stem-group cubozoan (box jellyfish relative) with moderate support, 66% of trees[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC10394413/) |
| Age | Approximately 505 million years old, middle Cambrian (Wuliuan), Burgess Shale Formation[1](https://doi.org/10.1098/rspb.2022.2490) • [4](https://burgess-shale.rom.on.ca/science/the-burgess-shale/geological-background/how-old-is-the-burgess-shale/) |
| Fossil material | 182 exceptionally preserved body fossils from the Raymond Quarry, Burgess Shale, British Columbia, Canada[5](https://pubmed.ncbi.nlm.nih.gov/37528711/) |
| Size and form | Cuboidal, lampshade-shaped umbrella up to 20 centimeters (7.9 inches) high, fringed by more than 90 short, finger-like tentacles[6](https://www.guinnessworldrecords.com/world-records/756586-earliest-jellyfish) |
| Significance | Oldest known swimming jellyfish; shows large medusae had evolved by the middle Cambrian[2](https://www.rom.on.ca/news-releases/royal-ontario-museum-researchers-identify-oldest-known-species-swimming-jellyfish) • [3](https://pmc.ncbi.nlm.nih.gov/articles/PMC10394413/) |
| Ecology | Efficient swimming predator, likely among the largest predators of its ecosystem[2](https://www.rom.on.ca/news-releases/royal-ontario-museum-researchers-identify-oldest-known-species-swimming-jellyfish) • [6](https://www.guinnessworldrecords.com/world-records/756586-earliest-jellyfish) |
## Fossil discovery
The specimens that became the basis of the species were collected at the [Burgess Shale](https://www.edgepedia.org/burgess-shale), mostly in the late 1980s and 1990s under Desmond Collins, then the Royal Ontario Museum's Curator of Invertebrate Palaeontology.[2](https://www.rom.on.ca/news-releases/royal-ontario-museum-researchers-identify-oldest-known-species-swimming-jellyfish) The Burgess Shale, in the Canadian Rockies of Yoho National Park, British Columbia, is a Cambrian deposit famous for preserving soft-bodied animals in fine mud, and its fossils date to between 505 and 510 million years ago.[4](https://burgess-shale.rom.on.ca/science/the-burgess-shale/geological-background/how-old-is-the-burgess-shale/) The ROM holds close to two hundred *Burgessomedusa* specimens, some more than 20 centimeters long, with observable details of internal anatomy and tentacles.[2](https://www.rom.on.ca/news-releases/royal-ontario-museum-researchers-identify-oldest-known-species-swimming-jellyfish)
Preservation of a jellyfish is rare because living medusae are roughly 95% water.[2](https://www.rom.on.ca/news-releases/royal-ontario-museum-researchers-identify-oldest-known-species-swimming-jellyfish)
## Anatomy and classification
Each specimen resembles a cuboidal umbrella or lampshade up to 20 centimeters high, with a fringe of more than 90 short, finger-like tentacles around its edge.[6](https://www.guinnessworldrecords.com/world-records/756586-earliest-jellyfish) The cuboidal shape and tetraradial symmetry of the umbrella are reminiscent of living cubozoans (box jellies), but a definite cubozoan affinity cannot be established because key diagnostic features, such as pedalial tentacle bases, a velarium, frenula, and developed rhopalia for vision and balance, are not preserved.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC10394413/)
A constrained Bayesian phylogenetic analysis recovered Burgessomedusa as a stem cubozoan in 66% of trees, with the next most strongly supported placements in the stem groups of Acraspeda (9%) or of the clade combining Cubozoa and [Scyphozoa](https://www.edgepedia.org/scyphozoa) (7%). Only a small fraction of trees (4% assuming the cubic shape interpretation) placed it in the medusozoan stem group, so the authors regard it with confidence as a crown-group medusozoan, most likely a stem-group cubozoan or stem-group acraspedan.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC10394413/) Its tentacle shape and placement along the oral umbrella margin are more comparable to those of living scyphozoans and hydrozoans, while the lack of a stalk and clustered tentacles rules out a stauromedusan affinity.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC10394413/)
## Significance for medusozoan evolution
Burgessomedusa unambiguously shows that large, swimming jellyfish with a typical bell-shaped body had already evolved more than 500 million years ago.[2](https://www.rom.on.ca/news-releases/royal-ontario-museum-researchers-identify-oldest-known-species-swimming-jellyfish) The fossil record of jellyfish is otherwise sparse: earlier putative Cambrian medusae have been reinterpreted, with previous reports of Cambrian swimming jellyfish now regarded as ctenophores (comb jellies), a separate animal phylum, and other early medusozoan fossils consisting mainly of microfossils and tubular forms.[2](https://www.rom.on.ca/news-releases/royal-ontario-museum-researchers-identify-oldest-known-species-swimming-jellyfish) • [5](https://pubmed.ncbi.nlm.nih.gov/37528711/) Even older sessile cnidarian ancestors are known, such as the 560-million-year-old *Auroralumina attenboroughii* from the [Ediacaran](https://www.edgepedia.org/ediacaran) period, but whether such anchored animals later had a free-swimming stage cannot yet be established.[6](https://www.guinnessworldrecords.com/world-records/756586-earliest-jellyfish)
The discovery supports a growing number of studies indicating an early evolutionary diversification of [Medusozoa](https://www.edgepedia.org/medusozoa), including of the crown group, during the late [Precambrian](https://www.edgepedia.org/precambrian) to Cambrian transition, and provides a minimum age constraint for the evolution of large swimming medusae by at least the middle Cambrian.[5](https://pubmed.ncbi.nlm.nih.gov/37528711/) • [3](https://pmc.ncbi.nlm.nih.gov/articles/PMC10394413/)
## Ecology of the Cambrian sea
By comparison with modern jellyfish, Burgessomedusa would have been capable of free swimming, and its tentacles would have enabled it to capture sizeable prey.[2](https://www.rom.on.ca/news-releases/royal-ontario-museum-researchers-identify-oldest-known-species-swimming-jellyfish) It is likely to have been one of the top predators of its time.[6](https://www.guinnessworldrecords.com/world-records/756586-earliest-jellyfish) The finding shows that Cambrian pelagic ecosystems were not uniquely dominated by large arthropod predators such as *Anomalocaris* and *Titanokorys*, but also harbored a diversity of other predators including chaetognaths, ctenophores, and jellyfish.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC10394413/)
## References
1. [Moon, J., Caron, J.-B., and Moysiuk, J. (2023). A macroscopic free-swimming medusa from the middle Cambrian Burgess Shale. Proceedings of the Royal Society B, 290(2004), 20222490.](https://doi.org/10.1098/rspb.2022.2490)
2. [Royal Ontario Museum Researchers Identify Oldest Known Species of Swimming Jellyfish, ROM news release, 2 August 2023](https://www.rom.on.ca/news-releases/royal-ontario-museum-researchers-identify-oldest-known-species-swimming-jellyfish)
3. [A macroscopic free-swimming medusa from the middle Cambrian Burgess Shale, PMC full text](https://pmc.ncbi.nlm.nih.gov/articles/PMC10394413/)
4. [How Old is the Burgess Shale, The Burgess Shale (ROM/Parks Canada)](https://burgess-shale.rom.on.ca/science/the-burgess-shale/geological-background/how-old-is-the-burgess-shale/)
5. [A macroscopic free-swimming medusa from the middle Cambrian Burgess Shale, PubMed abstract](https://pubmed.ncbi.nlm.nih.gov/37528711/)
6. [Earliest jellyfish, Guinness World Records](https://www.guinnessworldrecords.com/world-records/756586-earliest-jellyfish)
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*Topic: Encyclopedia › Life and health › Animals › Invertebrates › Other invertebrate lineages › Cnidarians and ctenophores › Medusozoans (jellyfish classes) › True jellyfish (Scyphozoa) › Scyphozoan orders and genera › Fossil and prehistoric scyphozoans*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license