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Life forms that remain unclassified

In “Enigmatic fossils are neither animals nor bacteria” (Nature, 22 December 2011), Matt Kaplan reports that “Scanning techniques reveal detailed cell structure of debated relics”:

The unusually complex appearance of a group of 570-million-year-old fossils from Doushantuo, China, has sparked debate among palaeontologists. Researchers haven’t been able to decide whether the remains come from animals, bacteria or close relatives of animals that thrived at the dawn of animal evolution. But a team has now used three-dimensional scanning techniques to take a closer look at the fossils — and has decided that in fact, they are none of these.

Some thought they might be giant bacterium thiomargarita, still very much with us, but they had cell nuclei.

When the researchers took a closer look, they noticed that specimens which seemed to be in later stages of development contained hundreds of thousands of tiny cells, and that the outer envelopes of these specimens had partly burst open. On the basis of this observation, Donoghue and Bengtson suggest that the creatures are similar to modern mesomycetozoeans, single-celled microorganisms that are neither animals nor bacteria.

They reproduce by keeping their spores in a thick cell wall. But some wonder if they are a fungus.

“What isn’t widely appreciated is that the Doushantuo rock formation contains billions of microfossils, many of which have no traits that are diagnostic of any living group and contain features that are not of biological origin,” says Jake Bailey, a geobiologist at the University of Minnesota in Minneapolis. “We are still far from understanding the origins of these enigmatic microfossils.”

Sounds like we’ll be there for some time.

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