Oldest fossil footprints on Earth discovered in China

Christopher Davidson
June 8, 2018

Animals with bilaterally paired appengages are assumed to have appeared during the Cambrian Explosion, but now their ancestry may be traceable to even further back in history.

They are often assumed to have appeared and radiated suddenly during the "Cambrian Explosion" about 541-510 million years ago, although it has always been suspected that their evolutionary ancestry was rooted in the Ediacaran Period.

Previously no evidence of limbed animals has been found that pre-dates the "Cambrian Explosion", the sudden surge in diversity that occurred on Earth about 510 to 541 million years ago.

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.

Unearthed in Southern China, the footprints are no more than a few millimeters wide, notes Science Alert, and were found in the Dengying Formation, a rich fossil site in the Yangtze Gorges area.

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". The new findings suggest animals evolved primitive "arms" and "legs" earlier than previously thought.

"The rock that contains the fossil has been very well dated between 551 and 541 million years old", study author Zhe Chen, a researcher at the Chinese Academy of Sciences, told AFP in an email.

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This remarkable discovery is hailed in a study, published yesterday in the journal Science Advances by a research team from Virginia Tech University in the USA and the Nanjing Institute of Geology and Palaeontology (NIGP) of the Chinese Academy of Sciences.

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

These legs raised the animal's body above the sediment it was moving across.

No body fossils for these animals have been found yet, however, and the scientists believe such remnants may not have been preserved.

The researchers speculate that the same creature left both the tracks and the burrows, suggesting an animal that scurried and tunneled its way across the ground. In fact, the China discovery represents one of the earliest known records of animals evolving appendages.

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

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