When did animals leave their first footprint on Earth?

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"If an animal makes footprints, the footprints are depressions on the sediment surface, and the depressions are filled with sediments from the overlying layer".

Although it's not clear what animal left these ancient tracks behind - since only the trace fossils (evidence that an animal has been there) were discovered, and not the fossils themselves - the footprints date back 551 million to 541 million years ago, to the Ediacaran Period.

The research by a Chinese team appears in Science Advances journal. This is considered the earliest animal fossil footprint record.

These trackways, preserved near burrows, were discovered in Dengying Formation - a rich fossil preserve in China's south - and constitute the first evidence confirming that an ancient group of animals called bilateria actually pre-dates the Cambrian explosion.

This places them perhaps even 10 million years before the "Cambrian Explosion" (roughly 541 million years ago), the moment in time which sparked the incredible evolution of life that led to the wonderful diversity of species that we see today.

In other words, this prehistoric critter wasn't a biped like you or me, but perhaps something with multiple paired legs - such as a spider, or a centipede - although given we have so little to go upon, the researchers emphasise it's impossible to know for sure what specific form this early walker embodied.

So, what type of creature has left behind its mark all those 550 million years ago in China?

Team-members are unclear whether the creature had two legs or several. The new findings suggest animals evolved primitive "arms" and "legs" earlier than previously thought.

Bilaterian animals such as arthropods and annelids have paired appendages and are among the most diverse animals today and in the geological past.

"Animals use their appendages to move around, to build their homes, to fight, to feed, and sometimes to help mate", Xiao told The Guardian.

'At least three living groups of animals have paired appendages (represented by arthropods such as bumble bees, annelids such as bristle worms, and tetrapods such as humans)', said Dr Chen.

The trackways' characteristics indicate that a bilaterian animal - that is, a creature with bilateral symmetry that has a head at one end, a back end at the other, and a symmetrical right and left side - made the tracks.

"Previously identified footprints are between 540 and 530 million years old".

The trackways are irregular, the scientists found, with two rows of imprints that suggest they were created by a bilaterian animal whose appendages raised it above the ground.

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

The animal appears to have paused from time to time, since the trackways seem to be connected to burrows that may have been dug into the sediment, perhaps to obtain food.

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