Created before the Cambrian Explosion-a sudden burst in animal diversity that took place about 541 million years ago-scientists think these are the oldest trackways ever discovered on Earth.
Researchers from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences and Virginia Tech studied ancient trackways and burrows found in the Yangtze Gorges area of South China. They published their findings Wednesday in the journal Science Advances.
Researchers believe they may have been a type of arthropod - the family of animals with jointed limbs that includes insects and crustaceans, or something akin to a legged worm.
Researchers have unearthed the almost 600 million years old fossil footprints of animals, considered to be the earliest record, in China. That's hundreds of millions of years before dinosaurs started roaming Earth, about 245 million years ago.
"Previously identified footprints are between 540 and 530 million years old".
"If an animal makes footprints, the footprints are depressions on the sediment surface, and the depressions are filled with sediments from the overlying layer".
"It is important to know when the first appendages appeared, and in what animals, because this can tell us when and how animals began to change to the Earth in a particular way", Xiao said. "The new fossils are probably up to 10 million years older".
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.
"The footprints are organized in two parallel rows, as expected if they were made by animals with paired appendages".
Trackways and burrows excavated in situ from the Ediacaran Dengying Formation.
Bilaterians are one of the most common body types in the world, now and throughout history, but previous fossil evidence for them only goes back as far as the Cambrian. Maybe they were never preserved.