Wednesday, November 12, 2008

New and unusual Ediacaran fossil

Recent news report of an unusual fossil from the 'home' of pre-Cambrian biota, the Ediacaran Hills (in the Flinders Ranges) in South Australia.

In the fifty years since this fossil period was confirmed, the Hills have been well scoured. But fossil finds are often enough a matter of luck, and this species, called Eoandromeda octobrachiata was not discovered until recently.

There are several odd aspects about this discovery. Firstly, it has eight arms; the discoverer, Dr Jim Gehling of the South Australian Museum, referred to it as having eight-fold symmetry, which is rare.

But a few months after the discovery, Gehling went to China, and opened up his laptop to show the fossil to Maoyan Zhu, of the Nanjing Institute of Geology. Zhu opened his laptop and - snap! - an identical discovery made at roughly the same time in China.

Further, the two rock types preserving the specimens were quite different: sandstone in South Australia, and black shale in China.

From my perspective, I didn't even know there were any Ediacarans with arms (let alone eight). That's a good deal more sophistication than was originally thought for the period: time was, Ediacarans were thought to be sponge-like intermediaries between plants and animals (as we know them). Again (viz Richard Dawkins), this would make the Cambrian explosion somewhat less explosive than thought, in terms of sudden evolution of radically new and varied body shapes (phyla). That would make sense.

(Thanks to Mark for the tip.)

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