Scientists Uncover 550 Million-Year-Old Fossils of Bug Trails

A fossil of Yilingia spiciformis and the track it left as it moved. (Z. Chen et al. / Nature)

(CN) – In a shattering evolutionary revelation, scientists in China have discovered fossils of an ancient bug and the trails – likely the oldest ever found – stamped onto Earth’s surface more than a half-billion years ago, according to a study released Wednesday.

The team of researchers co-led by Virginia Tech geoscientist Shuhai Xiao dug into multiple layers of ancient rock near Yiling, a city located on the banks of China’s Yangtze River, for years beginning in 2013.

In the rocky gorges near the Yangtze, Xiao and other scientists discovered the footpaths and fossilized remains of the Yilingia spiciformis, an ancient spiky bug that lived between 635 and 539 million years ago, according to the study published Wednesday in Nature.

The bug – which resembled a millipede 4 inches long and an inch wide – dates to the Ediacaran Period, an era well before the age of dinosaurs and even the existence of the Pangaea supercontinent, the study said.

The long, narrow creature had a head and a tail and likely dragged its belly across the muddy floor of Earth’s ancient oceans, leaving behind trails 23 inches long.

Scientists believed that the evolution of bilaterally symmetrical animals – bilaterans – such as the Yilingia spiciformis occurred in the Ediacaran Period but had no evidence before this discovery to support that theory.

Xiao said in a statement Wednesday that the discovery of the nearly 550 million-year-old fossils is evidence of the origin of animal mobility.

“Mobility made it possible for animals to make an unmistakable footprint on Earth, both literally and metaphorically,” Xiao said in the statement. “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.”

The study said the fossilized bug, and the trail it produced, were found together.

Interestingly, the fossils showed signs of movement toward or away from something, perhaps evidence of the bug’s decision-making process and the first-known indication of an animal’s sophisticated central nervous system.

Xiao said in the statement that the ancient bug’s movement led to the “Cambrian substrate and agronomic revolutions” and other ecological developments by later species.

“We are the most impactful animal on Earth,” said Xiao. “We make a huge footprint, not only from locomotion, but in many other and more impactful activities related to our ability to move. When and how animal locomotion evolved defines an important geological and evolutionary context of anthropogenic impact on the surface of the Earth.”

Rachel Wood of the University of Edinburgh, a geoscientist not involved with the study, said in a statement Wednesday that the study’s findings are paramount.

“We now have evidence that segmented animals were present and had gained an ability to move across the sea floor before the Cambrian, and more notably we can tie the actual trace-maker to the trace,” Wood said. “Such preservation is unusual and provides considerable insight into a major step in the evolution of animals.”

The study was backed by the Chinese Academy of Sciences, the National Natural Science Foundation of China, the U.S. National Science Foundation, and the National Geographic Society.

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