Friday, November 16, 2007

Jellyfish - 500 million years old

University of Kansas researchers used recently discovered "fossil snapshots" found in rocks from 500 million years ago to identify the oldest definitive jellyfish ever found. In a new article researchers describe four types of cnidarian fossils preserving traits that allow them to be related to modern orders and families of jellyfish. The specimens 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 Paulyn Cartwright, KU assistant professor of ecology and evolutionary biology and one of the article'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."

A film left behind by the jellyfish in the fine sediment resembles a picture of the animal. Often being preserved in coarse sand, jellyfish don't leave behind such a clear impression. Lieberman said the jellyfish the group describes, found in Utah, offer insights into the puzzle of rapid species diversification and development that occurred during the Cambrian radiation, a time when most animal groups appear in the fossil record, beginning roughly 540 million years ago. This record reveals more about the early evolution and origin of animals with hard shells or bones, and very little on jellyfish.

"The fossil record is biased against soft-bodied life forms such as jellyfish, because they leave little behind when they die," Lieberman said. "That means that we are still working to solve the evolutionary development of many soft-bodied animals."

With the discovery of the four different types of jellyfish in the Cambrian, however, the researchers said that there is enough detail to assert that the types can be related to the modern orders and families of jellyfish. The specimens show the same complexity. That means that either the complexity of modern jellyfish developed rapidly roughly 500 million years ago, or that the group is even older and existed long before then.

Cartwright said the jellyfish described in the article are also unique because they push the known occurrence of definitive jellyfish back from 300 million to 505 million years, a huge jump, and show more detail than anything previously described that is younger.

Since we are learning about invertebrates in class, including jellyfish, I thought this article to be interesting and relevant. Fossils allow us to research and determine the origin and evolution of many species, found years ago and found recently.

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Dominic B. said...

Nice way to connect the first part of the class (fossils and evolution) with the last one...vertebrates. It is quite rare to find soft structures is quite difficult to mineralize a structure that does not last long enough! Good blog post!