The Royal Ontario Museum (ROM) announces the oldest swimming jellyfish in the fossil record with the newly named Burgessomedusa phasmiformis. These findings are announced in the journal Proceedings of the Royal Society B.
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, called Cnidaria, a group which also includes corals and sea anemones.
Burgessomedusa fossils are exceptionally well preserved at the Burgess Shale considering jellyfish are roughly 95% composed of water. ROM holds close to 200 specimens from which remarkable details of internal anatomy and tentacles can be observed, with some specimens reaching more than 20 centimeters in length.
“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 co-author Joe Moysiuk, a Ph.D. candidate in Ecology & Evolutionary Biology at the University of Toronto, who is based at ROM.
This study, identifying Burgessomedusa, is based on fossil specimens discovered at the Burgess Shale and mostly found in the late 1980s and 1990s under former ROM Curator of Invertebrate Paleontology Desmond Collins. They show that the Cambrian food chain was far more complex than previously thought, and that predation was not limited to large swimming arthropods like Anomalocaris (see field image showing Burgessomedusa and Anomalocaris preserved on the same rock surface).
Slab showing one large and one small (rotated 180 degree) bell-shaped specimens with preservation of tentacles. ROMIP 65789. Credit: Jean-Bernard Caron © Royal Ontario Museum
Cnidarians have complex life cycles with one or two body forms, a vase-shaped body, called a polyp, and in medusozoans, a bell or saucer-shaped body, called a medusa or jellyfish, which can be free-swimming or not. While fossilized polyps are known in ca. 560-million-year-old rocks, the origin of the free-swimming medusa or jellyfish is not well understood.
Fossils of any type of jellyfish are extremely rare. As a consequence, their evolutionary history is based on microscopic fossilized larval stages and the results of molecular studies from living species (modeling of divergence times of DNA sequences).
The Burgess Shale fossil sites are located within Yoho and Kootenay National Parks and are managed by Parks Canada. Parks Canada is proud to work with leading scientific researchers to expand knowledge and understanding of this key period of Earth history and to share these sites with the world through award-winning guided hikes. The Burgess Shale was designated a UNESCO World Heritage Site in 1980 due to its outstanding universal value and is now part of the larger Canadian Rocky Mountain Parks World Heritage Site.