Chinese Ediacarans

[Joe Botting]

Ediacarans are among the most fascinating of fossils. They are found worldwide in the uppermost Precambrian, just before the first animals with skeletons apear in the 'Cambrian Explosion', 540 million years ago.

A large part of their appeal stems from their peculiarity. They are almost invariably preserved in sandstones (often beach-like deposits), with a very strange form of mouldic preservation - google for 'Ediacaran faunas' for more information. They have been interpreted as early members of living animal groups, as ancestral/ intermediate examples of these, or as a separate group of organisms entirely. A large proportion of Ediacarans appear to be 'quilt-like' and were interpreted by Dolf Seilacher as Vendobionts - an independent form of life probably separate from animals.
The Vendobiont hypothesis has been losing favour over the past years, as alternative interpretations of the fossils emerge; perhaps they include sea pens, sponges, jellyfish and primitive molluscs. Many of the quilted forms are more difficult to squeeze into living groups, but many believe they will be eventually. Now, new fossils from Dengying, China (described by Dong Xiping et al. show three-dimensional preservation of some of these quilted organisms. The internal structure is consistent with them being vendobionts after all...

There's also some 3D preservation from the White Sea of Russia that I've been shown by Dima Grazhdankin. In this case it's a sea pen-like form with pyritised tubes... and it also looks nothing like the structure of a sea pen. So, it seems Seilacher's vendobionts may be making a comeback. What remains unresolved about this intrepretation, however, is:

What on Earth were they?!?


Joe

[hallucygenia]

Here's the link for the new Chinese ediacarans:

www.pnas.org/cgi/content/abstract/0502176102v1

And I'm off to have a look at it - I couldn't find the paper on the site earlier.

[hallucygenia]

I've had a look - interesting! I think I want to read the whole paper, rather than just the abstract, which is all I can get at home. I can't see the pictures here either, which I'd like to.

The authors of the new Chinese forms say that the fossil consists of a series of tubes with two side walls, a floor and a roof, and an open end. I think from what they say that the tubes are stacked on top of each other in two rows - this is where a picture would be really helpful!

Obviously this means that the new fossils aren't consistent with Ediacarans being microbes - bacteria don't form open-ended tubes, not on that scale anyway. It's certainly consistent with Ediacarans, or this one at least, being vendobionts. However, it would be fair to describe a diplograptid graptolite as a series of tubes with vertical side walls, a floor and a roof, with the tubes stacked on top of each other in two rows, and a graptolite certainly isn't a vendobiont! So this doesn't prove that this fossil is a vendobiont.

There's always a temptation with the Ediacarans to put them all into the same box - they must all be vendobionts, or cnidarians, or lichens... This almost certainly isn't true, as I think all palaeontologists realise. A modern seafloor is unlikely to contain only one type of organism, and there's no reason to think that Precambrian seafloors were any different.