Oldest Fossils of Large Seaweeds, Possible Animals Tell Story About Oxygen in an Ancient Ocean
ScienceDaily (Feb. 19, 2011) — Almost 600 million years ago, before the rampant evolution of diverse life forms known as the Cambrian explosion, a community of seaweeds and worm-like animals lived in a quiet deep-water niche under the sea near what is now Lantian, a small village in Anhui Province of South China. Then they simply died, leaving some 3,000 nearly pristine fossils preserved between beds of black shale deposited in oxygen-free waters.
These images are part and counterpart of a macroscopic Lantian fossil, probably a seaweed, with differentiated morphologies including a distinct root-like holdfast to secure the organism on sea bottom, a conical stem, and a crown of ribbon-like structures. Scale bar is 1 centimeter. (Credit: Photo by Zhe Chen)
Scientists from the Chinese Academy of Sciences, Virginia Tech in the U.S., and Northwest University in Xi'an, China report the discovery of the fossils and the mystery in the Feb. 17 issue of Nature.
In addition to perhaps ancient versions of algae and worms, the Lantian biota -- named for its location -- included macrofossils with complex and puzzling structures. In all, scientists identified about 15 different species at the site.
The fossils suggest that morphological diversification of macroscopic eukaryotes -- the earliest versions of organisms with complex cell structures -- may have occurred only tens of millions of years after the snowball earth event that ended 635 million years ago, just before the Ediacaran Period. And their presence in the highly organic-rich black shale suggests that, despite the overall oxygen-free conditions, brief oxygenation of the oceans did come and go.
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An early Ediacaran assemblage of macroscopic and morphologically differentiated eukaryotes
Xunlai Yuan, Zhe Chen, Shuhai Xiao, Chuanming Zhou & Hong Hua
Received 15 August 2010 Accepted 07 January 2011 Published online 16 February 2011
Abstract
The deep-water Avalon biota (about 579 to 565 million years old) is often regarded as the earliest-known fossil assemblage with macroscopic and morphologically complex life forms1. It has been proposed that the rise of the Avalon biota was triggered by the oxygenation of mid-Ediacaran deep oceans2. Here we report a diverse assemblage of morphologically differentiated benthic macrofossils that were preserved largely in situ as carbonaceous compressions in black shales of the Ediacaran Lantian Formation (southern Anhui Province, South China). The Lantian biota, probably older than and taxonomically distinct from the Avalon biota, suggests that morphological diversification of macroscopic eukaryotes may have occurred in the early Ediacaran Period, perhaps shortly after the Marinoan glaciation, and that the redox history of Ediacaran oceans was more complex than previously thought.
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