Our slimy relatives

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Sohail Wasif/UCR

Palaeontologists have discovered our earliest ancestor—a tiny, bug-like creature that burrowed in the mud half a billion years ago. It is the first known bilatarian—an animal that’s largely symmetrical and has a front and a back, with a mouth at one end and an anus at the other. This body type turned out to be a successful innovation. It’s the shape sported by most animals today.

“We now have evidence of the origin of groups of animals which went on to conquer the Earth,” says James Gehling from the Australian Museum, co-author of a paper describing the new species. It was named Ikaria wariootia.

Until now, palaeontologists traced our ancestry to the explosion of marine lifeforms in the Cambrian period, which began 541 million years ago. It was thought that fossils from the earlier Ediacaran period represented some of evolution’s failed experiments—dead ends on the family tree. But this discovery, made in South Australia’s Flinders Ranges, shows that our lineage dates all the way back to the Ediacaran.

The Ediacaran was “a very weird world”, says Gehling. “Little bugs like the Ikaria were ploughing through thin layers of sand, eating microbial mats. The world was really one of slime. We have nothing equivalent to it today. You’ve got to think as though you’re on a different planet.”

The name acknowledges the Adnyamathanha, the indigenous custodians of the land on which the fossils were found. Ikaria is a nod to Ikara, the Adnyamathanha word for meeting place, while the species name comes from nearby Warioota Creek.

There’s still so much we don’t know about these ancient animals and their strange home, says Gehling. “But whatever they were, life expands after that point and changes the planet—and that interaction between life and environment is something that indigenous people have always thought about. What we’re doing here is acknowledging that we scientists aren’t the first people that needed to understand origins.”

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