The oldest known animal ‘footprints’ on Earth, left by bilaterian animals with paired appendages about 545 million years ago, have been discovered in the Yangtze Gorges area of South China.

“Bilaterian animals, such as arthropods and annelids, have paired appendages, and are among the most diverse animals today and in the geological past,” said co-lead author Dr. Zhe Chen from the Nanjing Institute of Geology and Palaeontology and colleagues.

“They are often assumed to have appeared and radiated suddenly during the ‘Cambrian explosion,’ about 541-510 million years ago, although it has long been suspected that their evolutionary ancestry was rooted in the Ediacaran period (635-541 million years ago).”

“Until our discovery, however, no fossil record of animal appendages had been found in the Ediacaran.”

Dr. Chen and co-authors studied trace fossils from the Ediacaran Shibantan Member (551-541 million years old) of the Dengying Formation in the Yangtze Gorges area, China.

These trace fossils include burrows and trackways that are preserved in close proximity and are apparently connected.

The trackways are somewhat irregular, consisting of two rows of imprints that are arranged in series or repeated groups.

They were probably made by millimeter-sized bilaterian animals with paired appendages that raised the animal body above the water-sediment interface.

“These trace fossils represent some of the earliest known evidence for animal appendages and extend the earliest trace fossil record of animals with appendages from the Early Cambrian to the Late Ediacaran period,” the paleontologists said.

“The body fossils of the animals that made these traces, however, have not yet been found. Maybe they were never preserved.”

The study was published in the June 6, 2018 issue of the journal Science Advances.

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Zhe Chen et al. 2018. Late Ediacaran trackways produced by bilaterian animals with paired appendages. Science Advances 4 (6); doi: 10.1126/sciadv.aao6691