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Status of most celebrated Ediacaran fossils to be revoked?


In “Terminal Developments in Ediacaran Embryology” (Science, 23 December 2011) , Cambridge’s N. J. Butterfield (Earth Sciences) tells us,

Ever since Darwin there has been a disturbing void, both paleontological and psychological, at the base of the Phanerozoic eon. If his theory of gradualistic evolution be true, then surely the pre-Phanerozoic oceans must have swarmed with living animals—despite their conspicuous absence from the early fossil record. Thus, the 1998 report of fossilized animal embryos in the early Ediacaran Doushantuo Formation of South China (1) [635 million years (mya) to 551 mya, approx] was met with almost palpable relief. It was indeed the fossil record that had let us down, not the textbooks, and certainly not the exciting new insights from molecular clocks. All was not as it seemed, however, and new data from Huldtgren et al. on page 1696 of this issue (2) look set to revoke the status of these most celebrated Ediacaran fossils.

Here’s an abstract offering an original claim:

Macroscopic algae widely lived in the Doushantuo-period sea of the Ediacaran in the Yangtze region, South China. They have successfully laid down an essential basis in a new environment and an ecosystem chain for the evolution and the development of the metazoan. The Wenghui biota, which is found in the Ediacaran Doushantuo Formation in Northeast Guizhou, is composed mainly of macroalgae (18 species of 15 genera, one unnamed macroalgae, and macroalgal holdfast forms described herein), and contains macroscopic metazoan, putative metazoan and trace fossils. This biota not only contains some elements of the Miaohe biota from West Hubei, the Lantian flora from South Anhui, the Ediacara fauna in Australia, and the White Sea biota in Russia, but also has its own characters to distinguish other Ediacaran biota. The diverse macroalgae of the Wenghui biota clearly show organic and functional differentiations with some exhibiting a relationship with higher plants. The Wenghui biota lived in the euphotic zone of shallow sea with lower-energy and poor oxygen. Numerous macroalgae settled on the deposits by their holdfasts, and their semi-floating bodies erected on sea floors. They advanced the photosynthetic efficiency and increased oxygen in water. In addition, the macroalgae served as a primary producer in the paleoecosystem to provide an alternative food for the metazoan. Therefore, the appearance of macroscopic algae not only improved the environment and played an essential support for the growth and propagation of the metazoan which depended on oxygen, but also provided a new food source that served as a new basis in the ecosystem for metazoan’s evolution and development. Moreover, prosperous macrobiota not only increased the productivity of organic matter but also favored the sedimentation and the preservation of organic carbon.

– Yue Wang, Xunlian Wang, Yuming Huang, Macroscopic algae from the Ediacaran Doushantuo Formation in Northeast Guizhou, South China, Earth Science Journal of China University of Geosciences (2007)

You missed the conclusion.... Wherever the Doushantuo fossils eventually end up, it will clearly not be within “crown-group” Metazoa. Does this then mean there were no early Ediacaran animals? Not at all. No fossil assemblage, however well preserved, provides a full account of past diversity, particularly when the local conditions are so extraordinary as to fossilize nuclei and other intracellular constituents. The “exceptional” fossil record is, by any measure, woefully unrepresentative and incomplete (15). When it comes to assessing the first appearance of early, difficult-to-preserve animals, the most reliable signal will be found in the conspicuous coevolutionary features that they have induced in other organisms with higher preservation potential (16). Early Ediacaran microfossils—with or without included “embryos”—may no longer include animals, but their dramatic radiation clearly marks the arrival of this revolutionary new clade.Lij
January 1, 2012
12:50 AM

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