The Royal Ontario Museum (ROM) has announced the discovery of the oldest known swimming jellyfish in the fossil record, named Burgessomedusa phasmiformis. This newly discovered species provides evidence that large, swimming jellyfish with a bell-shaped body existed over 500 million years ago.
Jellyfish are part of the ancient animal group called Cnidaria, which also includes corals and sea anemones. Burgessomedusa is a definitive indication that this group had already evolved in the Cambrian period.
The Burgessomedusa fossils were exceptionally well preserved in the Burgess Shale, despite jellyfish being primarily composed of water. The ROM holds close to two hundred specimens, allowing scientists to observe remarkable details of their internal anatomy and tentacles. Some specimens are over 20 centimeters long, enabling the classification of Burgessomedusa as a medusozoan.
According to co-author Joe Moysiuk, these fossils provide clear evidence that jellyfish were swimming in the Cambrian sea. The discovery of Burgessomedusa adds complexity to our understanding of the Cambrian food chain and demonstrates that predation was not limited to large arthropods like Anomalocaris.
The evolution of medusozoans, the group to which jellyfish belong, is not well understood. While fossils of polyps, the non-swimming form of jellyfish, have been found in rocks dating back 560 million years, the origin of free-swimming jellyfish remains elusive. The discovery of Burgessomedusa provides valuable insights into the evolution of these ancient creatures.
The Burgess Shale fossil sites, where the Burgessomedusa fossils were found, are located within Yoho and Kootenay National Parks and are managed by Parks Canada. These sites are an important part of Earth’s history, and scientific research continues to expand knowledge and understanding of life during the Cambrian period.
