Worm-Like Creature Ancestor of Humans and Most Modern Animals

(CN) – A team of geologists revealed Monday the discovery of the ancestor of most familiar modern animals, including humans.

In a paper published in Proceedings of the National Academy of Sciences, researchers from the University of California, Riverside described the Ikaria wariootia as a “tiny, wormlike creature.”

The geologists said it is the “earliest bilaterian, or organism with a front and back, two symmetrical sides, and openings at either end connected by a gut.”

Artist’s rendering of Ikaria wariootia. (Courtesy of Sohail Wasif/UCR)

Researchers said it was the development of this bilateral symmetry that represented a significant step in the evolution of life, giving animals “the ability to move purposefully and a common, yet successful way to organize their bodies.” Such organisms include worms, insects, dinosaurs and humans.

The discovery is the result of a 15-year-old mystery of ancient burrows found in Nilpena, South Australia. Scientists presumed the burrows were made by a bilaterian organism, but they could not find fossils of the elusive creature.

It wasn’t until researchers examined the area with a three-dimensional laser scanner that they could identify the animal just 2 to 7 millimeters long and 1 to 2.5 millimeters wide.

“We thought these animals should have existed during this interval, but always understood they would be difficult to recognize,” said Scott Evans, a recent doctoral graduate from UC Riverside. “Once we had the 3D scans, we knew that we had made an important discovery.”

Mary Droser, professor of geology at the university, said the creature’s 555 million-year-old burrows are unique due to the depth in which they’re found.

“Burrows of Ikaria occur lower than anything else. It’s the oldest fossil we get with this type of complexity,” Droser said. “Dickinsonia and other big things were probably evolutionary dead ends. We knew that we also had lots of little things and thought these might have been the early bilaterians that we were looking for.”

The shape of the burrows suggest the organism moved via contracting muscles, much like a worm.

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

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