500 million year old worm fossil discovered on the floor of an ancient sea

The worms were found hiding in the ocean sediments. They even left their own footprints, with tiny “tunnels” as evidence.

Traces of these fossilized “tunnels” have been found in rocks collected decades ago from Canada’s Mackenzie Mountains in the Northwest Territories. But scientists only recently reanalyzed them and found the “mini-tunnels.”

Research by scientists has shed light on the region's ocean ecosystems during the Cambrian period (543 million to 490 million years ago), suggesting these environments may have contained more oxygen and more life.

The tunnels the worms leave in weathered rock are invisible to the naked eye and were discovered entirely by accident, said lead study author Brian Pratt, a professor of geosciences at the University of Saskatchewan in Canada.

Pratt and co-author Julien Kimmig, invertebrate paleontology collection manager at the Biodiversity Institute and Natural History Museum at the University of Kansas, found the tunnels while collaborating on another 2018 study.

Pratt and Kimmig were preparing samples for the 2018 study, sawing and grinding rocks, when they discovered something they had never seen before.

The preserved tunnel shapes are well-defined and have not collapsed, suggesting that the sediment around them was solid and "undisturbed," the study authors write.

The tunnels, which measured between 0.5 and 15 millimeters wide, were made by worms that ranged from about a millimeter to the size of a finger, according to the study. Most of the burrows were tiny, dug by worms scouring ocean sediments for organic matter to eat.

In addition, the researchers found preserved worm bodies that were not burrowing worms, but contained pieces of body tissue that likely belonged to other worms.