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The dying jellyfish swallowed sand

Science / A cluster of jellyfish fossils was discovered that washed ashore in a storm about half a billion years ago

Photo: IP Hagadorn holding one of the fossils. Within a few hours the jellyfish were buried in the sand

The thousands of fossilized rings of jellyfish, some of which reach almost a meter in diameter, were discovered in a quarry in the state of Wisconsin in the USA, in what scientists say is one of the largest finds of its kind in the world.

About 510 million years ago, the jellyfish were washed into a small lagoon, after being washed ashore by extreme tides or a storm, and were buried in the sand only a few hours later." Preservation of soft-bodied creatures is extremely rare, but finding an entire layer of such creatures is like finding A gold treasure," said James Hagadorn, a scientist at the California Institute of Technology (Caltech) and one of the partners in writing an article reporting the discovery in the February issue of the journal "Geology

Jellyfish, which have no body parts that can be preserved, became accustomed during the Cambrian period, when the oceans were teeming with an unusual range of life forms.

Dan Damrow, a fossil dealer who also co-wrote the article, discovered the jellyfish about four years ago in a quarry in Mossin, Wisconsin, about 320 km northwest of Milwaukee. In the quarry, there are strips of sandstone, piled up in orderly horizontal layers. These layers are excellent for use as paving stones and for other commercial purposes. "They could eventually become the floor of someone's bathroom, or the flooring in their garden," Hagadorn said.

The Gadorn said that they found fossilized jellyfish in seven layers in the quarry, trapped in a rock at a height of about 3.7 meters - which records a time interval of about a million years. The rock layers also record the fine water marks that streaked the ocean floor in what was probably shallow water near the shore.

"It gives you the feeling that you are in that moment," said Damro, "at the exact time when this beach was created."

The circular rings indicate where each jellyfish washed ashore, most likely during a storm caused by high tides, Hagadorn said. Each fossil usually features a concave circular shape, which records the tiny dimple created by the pumping action of the bell-shaped jellyfish as it attempted to swim to deeper water.

This ring is surrounded at its edge by a higher layer of rock, which is actually composed of the sand that was washed by the tidal waves and covered the dead or dying jellyfish on the beach. The tiny piles in the center are likely sand swallowed by the jellyfish as it struggled for its life, Hagadorn said.

The fossil jellyfish are similar in size and characteristics to their modern sisters, but it was not possible to determine what their specific biological species was.

Today, jellyfish washed ashore fall victim to predators, such as birds and curious children. But during the Cambrian period, there were very few predators and scavengers that could disturb the creatures once they reached the shore and were buried, Hagadorn said. This fact, and the speed with which the jellyfish were buried in the sand, explains their survival as fossils that record history.

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