LAWRENCE, Kan., Oct. 31 (UPI) -- U.S. biologists have discovered rock-etched fossils of a 500 million-year-old jellyfish -- the oldest definitive jellyfish fossil ever found.

University of Kansas researchers said the specimens found in Utah are about 200 million years older than the oldest previously discovered jellyfish fossils.

"The fossil record is full of circular shaped blobs, some of which are jellyfish,” said Assistant Professor Paulyn Cartwright, one of the study's authors. "That’s one of the reasons the fossils we describe are so interesting, because you can see a distinct bell-shape, tentacles, muscle scars and possibly even the gonads."

The jellyfish left behind a film in fine sediment that resembles a picture of the animal. Most jellyfish don't leave such a clear impression because they are often preserved in coarse sand, Cartwright said.

Cartwright, Professor Bruce Lieberman, postdoctoral researcher Jonathan Hendricks and colleagues at the University of Utah, University of San Paulo, and the Smithsonian Institution report their research in the online journal PLoS One.