February 17, 2011

Fossils Of 600 Million Year Old Worm-Like Animals Found

Scientists have discovered that a community of seaweeds and worm-like animals lived in a quiet deep-water niche under the sea about 600 million years ago near what is now Lantian, which is a small village in Anhul Province of South China.

The scientists identified about 15 different species at the site, in addition to the ancient versions of algae and worms.

The researchers said that the fossils suggest that morphological diversification of macroscopic eukaryotes may have occurred only tens of millions of years after the snowball earth event that ended 635 million years ago. 

Their presence in the highly organic-rich black shale suggests that brief oxygenation of the oceans did come and go.

"So there are two questions," said Shuhai Xiao, professor of geobiology in the College of Science at Virginia Tech. "Why did this community evolve when and where it did? It is clearly different in terms of the number of species compared to biotas preserved in older rocks."

Xiao said in a press release the team was examining the black shale rocks because, although they were laid down in waters that were not good for oxygen-dependent organisms, "they are known to be able to preserve fossils very well."

"In most cases, dead organisms were washed in and preserved in black shales. In this case, we discovered fossils that were preserved in pristine condition where they had lived "“ some seaweeds still rooted."

Xiao said that the conclusion that the environment would have been poisonous is derived from geochemical data, "but the bedding surfaces where these fossils were found represent moments of geological time during which free oxygen was available and conditions were favorable. They are very brief moments to a geologist."

"But long enough for the oxygen-demanding organisms to colonize the Lantian basin and capture the rare opportunities."

The scientists suggest that the Lantian basin was largely without oxygen but was punctuated by brief oxic episodes that were opportunistically populated by complex new life forms, which were subsequently killed and preserved when the oxygen disappeared.

"Such brief oxic intervals demand high-resolution sampling for geochemical analysis to capture the dynamic and complex nature of oxygen history in the Ediacaran Period," lead author Xunlai Yuan, professor of palaeontology with the Chinese Academy of Sciences, said in a press release.

The team said that more research is still required.

"We will need to sample each layer to see whether there is any difference in oxygen contents between layers with fossils and those without" co-author Chuanming Zhou, professor of palaeontology with the Chinese Academy of Sciences, said in a press release.

The researchers reported their discovery of the fossils and they mystery in the February 17 issue of Nature.


Image 1: Seaweed holdfast, a 600 million-year-old fossil from the Lantian Formation in China. Credit: Zhe Chen and Xunlai Yuan

Image 2: A cluster of fossils from the Lantian area, preserved and unearthed in very high densities. Credit: Zhe Chen and Xunlai Yuan

Image 3: A treasure trove of fossils was found at this excavation site near Lantian village. Credit: Zhe Chen and Xunlai Yuan


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