BEIJING, Oct. 31 (Xinhuanet) -- Soft-bodied animals
don't often leave a fossil record behind, yet jellyfish fossils more than 500
million years old have been found in rocks in Utah, a new study reports.
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Jellyfish swim in a fish tank at Palma
aquarium in Palma de Mallorca on the Spanish island of Mallorca July 16,
2007.(Xinhua/Reuters Photo)
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"The fossil record is biased against soft-bodied life
forms such as jellyfish, because they leave little behind when they die," said
study member Bruce Lieberman of the University of Kansas.
These jellyfish left their lasting imprint because
they were deposited in fine sediment, rather than coarse sand. The film that the
jellyfish left behind shows a clear picture, or "fossil snapshot," of the
animals.
"You can see a distinct bell-shape, tentacles, muscle
scars and possibly even the gonads," said study team member Paulyn Cartwright,
also of KU.
The exquisite detail of the fossils allowed the team
to compare the cnidarian (the phylum to which jellyfish, coral and sea anemones
belong) fossils to modern jellyfish. The comparison confirmed that the fossils
were jellyfish and pushed the earliest known occurrence of definitive jellyfish
back from 300 million to 505 million years ago.
The fossils also offer insights into the rapid
species diversification that occurred during the Cambrian radiation, which began
around 540 million years ago and when most animal groups start to show up in the
fossil record, Lieberman said.
The complex makeup of these early jellyfish seems to
suggest that either the complexity of modern jellyfish developed rapidly about
500 million years ago, or that jellyfish are even older and developed long
before that time.
(Agencies)
