Ediacarans Not Related to Cambrian Animals

Posted on December 16, 2012 in Darwin and Evolution, Fossils

Two surprises come from a re-analysis of classic Ediacaran fossils from Australia: they’re unrelated to Cambrian animals, and they may have lived on land.

Dr. Gregory Retallack (University of Oregon), a native Australian, examined the rocks in south Australia containing fossil Ediacaran organisms.  According to Astrobiology Magazine, Retallack now believes the creatures were not ancestors of ancient marine multicellular life, but instead represent “remnants of land-dwelling lichen or other microbial colonies.”  His conclusion may or may not affect classification of Ediacarans from other parts of the world.

Retallack used state-of-the-art techniques to examine the rock, and found that its “old elephant skin” appearance resembles crusty sandstone or microbial soil crusts in modern deserts. Below the sand in which they were buried he found evidence of fossil soils.

This discovery has implications for the tree of life, because it removes Ediacaran fossils from the ancestry of animals,” said Retallack, professor of geological sciences and co-director of paleontological collections at the UO’s Museum of Natural and Cultural History. His evidence, mostly gathered from a site in the Flinders Ranges, is presented in a paper placed online ahead of print by the journal Nature.

These fossils have been a first-class scientific mystery,” he said. “They are the oldest large multicellular fossils. They lived immediately before the Cambrian evolutionary explosion that gave rise to familiar modern groups of animals.”

In the paper, Retallack wrote, “Newly documented palaeosols in the Ediacara Member of the Rawnsley Quartzite in South Australia now call for a re-evaluation of its famous fossils, widely considered evolutionary predecessors of the Cambrian explosion of marine animal phyla.”  He also noted, “Most Ediacaran fossils have no clear relationship with modern animals.

If not sea creatures, what are they?  Retallack suggested they could be “lichens, other microbial consortia, fungal fruiting bodies, slime molds, flanged pedestals of biological soil crusts, and even casts of needle ice.”  In the paper and the press release, he had very little to say about evolution, except that the Ediacarans represent “an independent evolutionary radiation of life on land that preceded by at least 20 million years the Cambrian evolutionary explosion of animals in the sea.”

So much for pointing to multicellular precursors to the Cambrian explosion.  Retallack mistakenly called it the “Cambrian evolutionary explosion.”  He should have said “Cambrian explosion demolishing evolution.”  See the documentary Darwin’s Dilemma for reasons why.

 

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