The fossil remains of fragile jellyfish that lived some 505 million years ago have been discovered in the rocks of a Utah mountainside that once lay at the bottom of a shallow tropical sea.
The ancient fossils are strikingly similar to modern jellyfish. The remains are of unequalled clarity, and their discoverers at the University of Kansas and the University of Utah say they’re guessing that the ancient ones were at least closely related to common jellies today.
The fossils are more than 200 million years older than any scientists have found before. They clearly reveal their bell-shaped umbrellas, wavering tentacles and even the animals’ gonads.
But researchers say the creatures were unusually tiny, most barely a quarter-inch in diameter — or about the same size as the tip of a pencil eraser. The modern jellies often run five times that size, said Kevin Raskoff, a marine biologist who teaches at Monterey Peninsula College.
The fossils were found by a team headed by Bruce Lieberman, senior curator of invertebrate paleontology at the University of Kansas. His group’s report appears in the current issue of PLoS One, an international online scientific journal published by the Public Library of Science in San Francisco.
The jellyfish appear to have been living in a very shallow sea, Raskoff said, whereas the modern kind they resemble are known to occur in large numbers at far lower ocean depths — anywhere from 600 to 6,000 feet, he said.
Because jellyfish have soft bodies, they rarely become fossilized. According to Lieberman, the ones his group found must have sunk onto the bed of a shallow sea and then lay there as tiny particles of sand buried them to preserve their delicate imprints.
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