Scientists have discovered a fossil of our earliest ancestor: a tiny, wormlike creature that lived about 555 million years ago, according to a new study. 

“It’s the earliest ‘bilaterian’ …. which is an organism with a front and back, two symmetrical sides and openings at either end connected by a gut,” scientists from the University of California–Riverside said in a statement.

“It’s the oldest fossil we get with this type of complexity,” UCR geologist and study co-author Mary Droser said. The tiny fossil, about as big as a grain of rice, was discovered in Australia. 

Evidence for these early fossils is rare, scientists say. Most studies rely on trace fossils, or the tracks they left behind, rather than preservation of the small, soft-bodied organisms themselves.

With the help of high-tech 3D laser scanning, scientists were able to locate fossils of the distinct tubelike organisms in a former seabed in present-day South Australia.

“Bilateral symmetry,” as its known, was a critical step in the evolution of animal life, UCR reported. It gave organisms the ability to move purposefully as well as a common, yet successful way to organize their bodies.

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An artist's rendering of Ikaria wariootia, likely the oldest animal ancestor yet discovered.
An artist’s rendering of Ikaria wariootia, likely the oldest animal ancestor yet discovered.

“A multitude of animals, from worms to insects to dinosaurs to humans, are organized around this same basic body plan,” according to the UCR statement.

The tiny animal likely spent its life burrowing through layers of sand on the ocean floor, looking for any organic matter on which it could feed, the BBC said. 

The creature was given the Latin name Ikaria wariootia, after Ikara, an indigenous Australian word for “meeting place,” and Warioota, the name of a local creek.

Droser said the discovery is “what evolutionary biologists predicted. It’s really exciting that what we have found lines up so neatly with their prediction.”

The study was published Monday in the peer-reviewed journal Proceedings of the National Academy of Sciences.

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This article originally appeared on USA TODAY: Oldest animal ancestor: A 555-million-year-old wormlike creature



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