October 31, 2007—They didn't have any bones to leave behind, but ten fossilized jellyfish recently discovered in Utah have made an impression in more ways than one.
At half a billion years old, the fossils represent the oldest jellyfish ever found and push back the known existence of jellies 205 million years, scientists say.
The newfound fossils also offer much greater detail than more recent specimens, which has allowed researchers to link the ancient animals to types of jellyfish living today.
"The fossil record is full of circular-shaped blobs, some of which are jellyfish," Paulyn Cartwright, a University of Kansas biologist who was on the research team, said in a press statement.
"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."
Cartwright and her colleagues studied these anatomical features and found that the fossils may represent early ancestors of three modern jellyfish groups. The researchers liken the two fossils pictured here to living species from the genus Cunina (top) and Periphylla (bottom).
If verified, these connections would suggest that jellies either evolved into their current, complex form very quickly around 500 million years ago, or they evolved slowly and have existed much longer than has been estimated.
Cartwright's team reports its findings today in the online journal PLoS One.
—Blake de Pastino
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