When did animals leave their first footprint on Earth?

When did animals leave their first footprint on Earth?

The oldest known footprints on Earth, left by an ancient creepy-crawly more than 500 million years ago, have been discovered in China.

The odd-looking prehistoric trackways show two rows of imprints that resemble a series of repeated footprints, the researchers said.

Their fossilised trackways and burrows were discovered in the Yangtze Gorges area of south China in a rock formation dating back between 541 and 551 million years.

The Chinese and American team led by Dr Shuhai Xiao, from Virginia Tech in the United States, wrote in the journal Science Advances: "The irregular arrangement of tracks in the trackways may be taken as evidence that the movement of their trace maker's appendages was poorly coordinated and is distinct from the highly coordinated metachronal (wave-like) rhythm typical of modern arthropods".

Scientists believe the tiny parallel footprints - which are only a few millimetres across - were left by an early ancestor of modern-day insects or worms. This critter was roaming the planet millions of years before the first mammals, the first dinosaurs, and even the first fish.

They said they don't know exactly what species the footprints belong to, but described the creature as a bilaterian animal, like an arthropod. The new findings suggest animals evolved primitive "arms" and "legs" earlier than previously thought.

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.

The fossil tracks offer "some of the earliest known evidence for animal appendages and extend the earliest trace fossil record of animals with appendages from the early Cambrian (485 million to 541 million years ago) to the late Ediacaran period".

"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)". Take that, rest of the pre-Cambrian life forms!

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

"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 the Earth in a particular way."

"Previously identified footprints are between 540 and 530 million years old", Dr Zhe Chen from the Nanjing Institute of Geology and Palaeontology told MailOnline. The trackways also appear to be connected to burrows, suggesting the creatures periodically tunnelled down into the sediments, perhaps to mine oxygen and microbes as food.

This is a sign of "complex behavior involving both walking and burrowing", the team argues in the paper.

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