A team of scientists led by Shuhai Xiao at Virginia Tech College of Science have discovered the oldest known footprint ever found.

The footprint is estimated to be 540 million to 550 million years old.

The tiny tracks were found in a small sediment rock in China and were made by an unknown bug-like creature no bigger than a thumb.

Science Advances published the ancient footprint in its latest issue in hopes to help scientist determine when and how legs and limbs evolved.

“We were trying to answer the question ‘when did animals began to have appendages, such as legs and leglike structures?,’ ” said Xiao, a professor in the Department of Geosciences.

Xiao and his colleagues from the Nanjing Institute of Geology and Paleontology and Center for Excellence in Life and Paleoenvironment, discovered the fossils in the Yangtze Gorges area of South China.

The new fossils found are up to 10 million years older than previously known footprints.

“We only found the footprints,” said Xiao. “We have not yet found the animals that made the footprints. Unlike many modern animals that have hard skeletons, these early animals did not yet evolve hard skeletons, so their likelihood of being preserved is slim.”

Xiao and his team believe the crawler may have had legs similar to a bumble bee or a bristle worm, as evidence by the width and gait of the tracks.

The trackways are about half an inch in width and a few inches in length.

The rock with the foot imprints was formed from sediments deposited in a shallow sea bottom that was covered by microbial mats similar to pond scums.

“Oddly, the tracks sometimes transition into tunnels, suggesting that the animals occasionally dug into the microbial mat,” added Xiao.

Scientists believe that the animals may have dug into the microbial mats to mine oxygen and food.

The microbial mats, constructed by a group of photosynthetic bacteria known as cyanobacteria that produced oxygen as a side product, were a reliable source of oxygen and food for early animals.

Several different groups funded the study including the National Geographic Society.