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550 million years ago, a worm squirmed toward death, and evolution leaped forward


This image shows a fossilized worm.

More than half a billion years ago, an ancient worm squirmed. Trails were created. And animal mobility was born.

That’s the conclusion of researchers at Virginia Tech, who discovered the fossilized remains of what may well be the first ever animal trails on Earth’s surface.


These worms predated the dinosaurs, according to a statement from the researchers. They existed, and died out, long before the Pangea supercontinent was even a thing.

“This discovery shows that segmented and mobile animals evolved by 550 million years ago,” said lead author Shuhai Xiao, a professor of geosciences with the Virginia Tech College of Science, in a statement. “Mobility made it possible for animals to make an unmistakable footprint on Earth, both literally and metaphorically. Those are the kind of features you find in a group of animals called bilaterans. This group includes us humans and most animals. Animals and particularly humans are movers and shakers on Earth. Their ability to shape the face of the planet is ultimately tied to the origin of animal motility.”

This miracle animal was much like a millipede, the researchers said. Between one-quarter inch and an inch wide, and up to 4 inches long, the worm “alternately dragged its body across the muddy ocean floor and rested along the way, leaving trails as long as 23 inches,” the research team explained. It had 50 body segments, a head and tail, and a back and belly.

The evolution of bilaterians represents a “monumental event in early animal evolution,” the statement said. Xiao’s team’s discovery is the first physical evidence of something that has been surmised to have occurred during the Ediacaran Period, which was 635 to 539 million years ago.

This one is named the spiky Yiling bug, to tag the district in China where it was found, and the trail it left was actually its “death march” — its last, lurching movements on this Earth. While other animals have been motile like this, and segmented, it is the oldest one carrying both traits to produce such long, unbroken trails.

“As such, it has important implications for the early evolution of animal segmentation and motility,” Xiao wrote on his research website. “The origin of segmentated and motile animals is a monumental innovation that shaped the Earth’s surface environment.”