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When Did Animals Leave Their First Footprint On Earth?

08 June 2018

The footprints, belonging to an unknown invertebrate, date back to around 541 million years ago.

Previously, it was believed animals with pairs of legs capable of leaving such footprints first appeared during the "Cambrian Explosion" about 541 to 510 million years ago. The research was published in Science Advances on June 6, 2018.

Further, the footprints left behind by its multiple feet suggest that this sea-dwelling animal had paired appendages that raised its body above the ocean floor.

This means that the symmetrical creature appeared before the Cambrian Period, Chen noted. The newfound trace fossils are some of the earliest known evidence for animal appendages on record.

Mystery surrounds the one-millimetre long creatures that made the prints, since no trace of their bodies has been found.

The presence of paired appendages (a primitive version of legs and arms) in the anatomy of this prehistoric creature is mirrored in the way the fossil footprints are laid out, Xiao explains.

It also seems that the tracks are somehow connected to the burrows, suggesting that whichever animal this might have been, they had a tendency of digging into sediments and microbial mats, most probably in order to search for food and oxygen. While scientists are not sure exactly which beast made the footprints, the fossils have been estimated to be around 551 million years old.

The tracks are only a few millimeters in diameter and dot the soft gray limestone found in the Yangtze Gorges region of China.

While the researchers are unable to identify the animal behind the footprints, there are three types of living animals with paired appendages: arthropods such as bumble bees, annelids such as bristle worms, and tetrapods which include humans.

Researchers do not know what animals made the footprints but have interpreted the two parallel rows of dots as rows of tracks.

"Together, these trackways and burrows mark the arrival of a new era characterized by an increasing geobiological footprint of bilaterian animals", the researchers point out.

'Arthropods and annelids, or their ancestors, are possibilities.

Now, the discovery of the trackways and burrows shows that animals with appendages lived during the Ediacaran period, the researchers said.

The fossil trackways-preserved between two ancient layers of rock-are very narrow, measuring about half an inch in width.

When Did Animals Leave Their First Footprint On Earth?