Jellyfish are among the most ancient and fascinating animals on Earth, but their evolutionary history is shrouded in mystery. How did these soft-bodied creatures, composed of mostly water, evolve and diversify over hundreds of millions of years? A recent discovery of some exceptionally well-preserved fossils may shed some light on this question.
A new species from the Burgess Shale
Scientists have identified a new species of jellyfish that lived about 505 million years ago, during the Cambrian period, based on nearly 200 fossil specimens found at the Burgess Shale fossil site in Canada. The site is famous for preserving a remarkable diversity of soft-bodied animals that would otherwise be lost to the fossil record.
The new species, named Burgessomedusa phasmiformis, belongs to a group of animals called medusozoans, which includes modern-day box jellies, hydroids, and true jellyfish. Medusozoans have an umbrella-shaped body with stinging tentacles, like the mythical snake-haired Medusa.
The fossils of Burgessomedusa phasmiformis show that it had a large bell-shaped body, up to 20 centimeters in length, with four clusters of tentacles around the mouth. The fossils also reveal details of the internal anatomy, such as the digestive system and the radial canals that distribute nutrients and oxygen throughout the body.
The oldest swimming jellyfish
The discovery of Burgessomedusa phasmiformis is significant because it represents the oldest known example of a swimming jellyfish. Previous fossil evidence of medusozoans was limited to polyps, which are vase-shaped and usually attached to the seafloor. Polyps are one of the possible body forms within the life cycle of medusozoans, along with medusas, which are free-swimming.
The researchers believe that Burgessomedusa phasmiformis was capable of swimming by contracting its bell and using its tentacles to capture prey. This suggests that some of the key features of modern jellyfish, such as their typical saucer or bell-shaped body, had already evolved by the Cambrian period.
“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 doctoral candidate in ecology and evolutionary biology at the University of Toronto, in a statement.
Implications for the Cambrian food web
The discovery of Burgessomedusa phasmiformis also has implications for understanding the complexity of the food web in the Cambrian oceans. The Cambrian period was a time of rapid diversification and innovation among animal life forms, but the role of predation and competition is still debated.
The researchers suggest that Burgessomedusa phasmiformis was a predator that fed on other animals, such as worms and arthropods. This indicates that predation was not limited to large swimming arthropods, such as trilobites and anomalocarids, but also involved soft-bodied animals like jellyfish.
The presence of large swimming jellyfish may have also influenced the evolution of other animals, such as their potential prey or competitors. For example, some animals may have developed defensive strategies, such as armor or spines, to avoid being stung or eaten by jellyfish.
A wonderous discovery
The discovery of Burgessomedusa phasmiformis is a testament to the power and beauty of paleontology, which allows us to glimpse into the ancient past and uncover secrets that would otherwise remain hidden. Finding such delicate and ephemeral animals preserved in rock layers is a wonderous discovery that enriches our knowledge of the history of life on Earth.
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