Scientists identified the oldest known species of swimming jellyfish

505-million-year-old swimming jellyfish from the Burgess Shale highlights diversity in Cambrian ecosystem.

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True jellyfish, stalked jellyfish, box jellies, and hydroids are medusozoans or invertebrates that produce medusae. The group of animals known as Cnidaria, including corals and sea anemones, is one of the earliest animal groups ever lived. This group contains medusozoans.

The newly described Burgessomedusa phasmiformis has been named the oldest swimming jellyfish in the fossil record by the Royal Ontario Museum (ROM).

Burgessomedusa demonstrates that giant swimming jellyfish with a typical saucer or bell-shaped bodies evolved more than 500 million years ago.

Field images of Burgessomedusa phasmiformis jellyfish specimens (middle right ROMIP 65789 – see close up images) and of the top arthropod predator Anomalocaris canadensis preserved on the same rock surface. Hammer for scale
Field images of Burgessomedusa phasmiformis jellyfish specimens (middle right ROMIP 65789 – see close up images) and of the top arthropod predator Anomalocaris canadensis preserved on the same rock surface. Hammer for scale. Credit: Desmond Collins. © Royal Ontario Museum

Since jellyfish comprise about 95% water, the Burgess Shale’s Burgessomedusa fossils are extraordinarily well preserved. Nearly 200 specimens are kept in the ROM, some of which are over 20 centimeters long and exhibit extraordinary interior anatomical intricacies and tentacle characteristics.

Burgessomedusa can be categorized as a medusozoan because of these features. Burgessomedusa would have been similar to modern jellyfish in that it would have been able to swim freely and that would have had the ability to catch large prey because of its abundance of tentacles.

Co-author Joe Moysiuk, a Ph.D. candidate in Ecology & Evolutionary Biology at the University of Toronto, who is based at ROM, said, “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.”

Slab showing one large and one small (rotated 180 degree) bell-shaped specimens with preservation of tentacles. ROMIP 65789
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

Despite being one of the earliest animal groups to have emerged, jellyfish and its cousins have proven extraordinarily difficult to identify in the Cambrian fossil record. This finding dispels any doubt that they were swimming around at the time.

Co-author Dr. Jean-Bernard Caron, ROM’s Richard Ivey Curator of Invertebrate Palaeontology, said, “Finding such incredibly delicate animals preserved in rock layers on top of these mountains is such a wonderous discovery. Burgessomedusa adds to the complexity of Cambrian food webs, and like Anomalocaris, which lived in the same environment, these jellyfish were efficient swimming predators.”

“This adds yet another remarkable lineage of animals that the Burgess Shale has preserved, chronicling the evolution of life on Earth.”

Journal Reference:

  1. A macroscopic free-swimming medusa from the middle Cambrian Burgess Shale, Proceedings of the Royal Society B: Biological Sciences (2023). DOI: 10.1098/rspb.2022.2490

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