An international team of scientists has reported the discovery of oldest footprints ever found on Earth, which was left behind by a mysterious animal that roamed our planet sometime between 541 and 551 million years ago — way before many known animals, including dinosaurs, thrived and became extinct.

The Ediacaran-era (541– 635 million years ago) prints were found by researchers from Chinese Academy of Sciences’ Nanjing Institute of Geology and Palaeontology and Virginia Tech in the United States during a study of tracks and burrows spotted at the Dengying Formation, a fossil-rich site near the Yangtze Gorges area of southern China.

They took a close look at the irregular trackways and witnessed two parallel rows of footprints, which appeared to have been arranged in a series or repeated groups.

"If an animal makes footprints, the footprints are depressions on the sediment surface, and the depressions are filled with sediments from the overlying layer,” Shuhai Xiao told the Independent while speaking of the finding. "This style of preservation is distinct from other types of trace fossils, for example, tunnels or burrows, or body fossils.

Ancient animal foorprint
Trackways and burrows excavated in situ from the Ediacaran Dengying Formation. Nanjing Institute of Geology and Palaeontology

As the researchers noted, this was the first evidence of animal footprints from the time before Cambrian explosion – the evolutionary event that occurred 510 to 540 million years ago and marked a major surge in Earth’s diversity.

It is believed most major animals capable of leaving footprints appeared during and after this event, but many have suspected there might be some more ancient fossils that could reveal the evolutionary ancestry of the animals that thrived later. This discovery proves that idea; however, according to the researchers, the information collected from the observation is not enough to determine which animal left these marks.

All that the prints suggest was they were formed by some kind of bilaterian animal which had multiple paired appendages, like arthropods and annelids, to raise its body above the water-sediment interface. Among other things, it is also worth noting the trackways appear connected to the burrows, something that indicated the animals probably dug into the sediments in order to consume food or oxygen.

"We explicitly stated in the paper that 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," Xiao added.

As modern arthropods and annelids served as appropriate analogs for the interpretation of this fossil, the researchers posit the animal in question could be the ancestor of either of the two groups. But, as there are no body fossils next to the prints to validate the theory, it cannot be said for sure. The fossil of the animal has not been found or maybe it never got preserved.

The study entitled "Late Ediacaran trackways produced by bilaterian animals with paired appendages" was published June 6 in the journal Science Advances.