500 Million Years Ago, Jellyfish Left Their Mark in Fine Sea Sediments

The Cambrian fossil jellyfish, left, shows similarity to the modern jellyfish.

Henry Fountain - The New York Times, Your average jellyfish washed up on a beach is hardly recognizable — just an amorphous blob, fast decomposing in the sun. (They don’t call them jellyfish for nothing.)

Which makes the discovery in Utah of four types of well-preserved fossil jellyfish from the Middle Cambrian period, half a billion years ago, all the more remarkable.

In a paper in the open-access online journal PLoS ONE, Paulyn Cartwright of the University of Kansas and colleagues report that these are the oldest jellyfish fossils yet described, by about 200 million years.

The fossils were found in the Marjum Formation in the west-central part of the state. During the Cambrian period, what is now Utah was covered in warm shallow seas, so fossils of many ancient marine organisms are found there. But such well-preserved specimens of soft creatures like jellyfish are uncommon. What helped in this case was that they were compressed into very fine sediment, preserving images of what appear to be tentacles and even some internal features.

Some of those features, the researchers say, are comparable to modern ones, suggesting that jellyfish had already diversified greatly by 500 million years ago. It is not known whether they diversified quickly or got their start long before the Middle Cambrian.

SOURCE : The New York Times