Outcompeted (Image: CC BY 2.5)

Strange and largely immobile organisms made of tubes were the first complex life on Earth. Appearing 579 million years ago, they thrived on the seafloor for some 37 million years, then vanished – becoming a curiosity we know only from faint impressions in the sandstone fossil record.

What made them die out? New fossil evidence from Namibia suggests that the Ediacarans, as these creatures are known, had their world turned upside by an explosion of life forms at the beginning of the Cambrian period 541 million years ago. Some of these may have evolved to eat their enigmatic predecessors and to bioengineer the environment in ways that left little hope for the passive Ediacarans.

If so, the very first mass extinction of complex life forms had a biological cause, unlike the big five mass extinctions which are thought to be environmentally driven – kicked off by widespread volcanic eruptions that poisoned the oceans or a massive meteorite strike, for example.


The disappearance of the Ediacarans from the fossil record has long troubled biologists. Leading theories are a catastrophic mass extinction, that Ediacarans got eaten or had their habitat destroyed by newly evolved animals, or no longer left fossils because of a change in ocean conditions.

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But a careful search by Marc Laflamme of the University of Toronto in Mississauga and colleagues threw up no geochemical signatures of low-oxygen conditions or other turmoil to support the idea of an environmentally driven mass extinction. And given that soft-bodied Cambrian animals are fossilised within rocks like the famed Burgess Shale, it seems unlikely that the conditions simply didn’t allow any surviving Edicaranas to leave a fossil trace in the Cambrian period.

That suggests that by the time the Cambrian explosion of species reached full force, the Ediacarans were gone, says Simon Darroch of the Smithsonian Institution in Washington DC. He will detail the team’s evidence next week at the Joint Assembly of the American Geophysical Union in Montreal, Canada.

Their search took them to southern Namibia, where outcrops stretching over a large area expose fossils covering the crucial few million years when the Ediacarans disappeared and the new animals of the Cambrian appeared.

The deposits showed a vastly increased number of trace fossils from Cambrian animals, showing they had already evolved and were breaking up sediment and disturbing the Ediacaran environment.

Eco engineers

“Modern animals are ecosystem engineers. They alter the environment, burrow into sediments and prey on each other,” says Darroch. So he looked for interactions between the two groups.

If these animals wiped out the Ediacarans, Darroch reasoned, fossils of the most recent Ediacaran communities should hint that they were struggling. By a number of measures, such as low species richness, he found the Namibian fossil communities did indeed “look very stressed”. For example, he found traces in the latest Ediacaran fossils very similar to those left by sea anemones, which are predatory. “So there probably were predators in the late Ediacaran,” he says.

All of this adds up to pretty robust evidence, he says, that the new species ate the old ones or destroyed their habitat.

However there was no cold, hard stop for everything Ediacaran, says Jim Gehling of the South Australian Museum in Adelaide, who has been studying Australian deposits of the same age.

“Clearly there was an extinction of the big fleshy things stuck on the seafloor,” he says.

But he adds that although many of those Ediacarans were so strange that their biology makes little sense to us today, there is evidence that some of them did evolve movement and ways of ingesting food like modern animals, so may have given rise to life forms that evolved later.