Scientists in China believe tracks left by tiny animals that crawled in sea-shore mud around 550 million years ago are the oldest footprints on Earth.
Previously, scientists had discovered footprints as old as 530-540m years, but none predating the Cambrian period, which also began at this time and marked an explosion in the diversity and complexity of life on Earth.
"We do not know exactly what animals made these footprints, other than that the animals must have been bilaterally symmetric because they had paired appendages", said Chen.
"If an animal makes footprints, the footprints are depressions on the sediment surface, and the depressions are filled with sediments from the overlying layer".
Researchers on the study came from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences, and Virginia Tech in the United States. The trackways are somewhat irregular, consisting of two rows of imprints that are arranged in series or repeated groups.
Prof Shuhai Xiao, a geobiologist at Virginia Tech University and senior author of the research, said the finding brings scientists closer to understanding what creatures were the first to evolve pairs of legs. They are one of the most diverse animal groups in existence today.
By looking at the ancient trackway - of which The Guardian has made an animation of, that you can watch below - the team was able to determine that this prehistoric creature had multiple paired feet that raised its body above the ocean floor. Until the current discovery, however, no fossil record of animal appendages had been found in the Ediacaran Period.
This is a group of animals characterised by having paired appendages - in this case, perhaps, paired legs.
The researchers speculate that the same creature left both the tracks and the burrows, suggesting an animal that scurried and tunneled its way across the ground.
Still, due to the proximity of the track marks to fossilised burrows discovered nearby, the researchers hypothesise the creature may have exhibited "complex behaviour", such as periodically digging into sediments to mine oxygen and food among its riverbed habitat.
While bilaterian animals - including arthropods and annelids - were suspected to have first stretched their innovative legs prior to the Cambrian explosion, in what's called the Ediacaran Period, before now there was no evidence for it in the fossil record.