Oldest animal fossil footprint on record discovered in China

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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.

Previously, scientists had discovered footprints as old as 530-540m years, but none predating the Cambrian period, which also began at this time and marked an explosion in the diversity and complexity of life on Earth.

Because the footprints are trace fossils, not fossils of the animal itself, it's going to be hard to credit a particular branch of the Tree of Life with the title of "First to Develop Limbs".

In a release put out by the Chinese Academy of Sciences- Nanjing Institute of Geology and Palaeontology, researchers noted that the fossils were from the Ediacaran Period- about 635-541 million years ago. "This style of preservation is distinct from other types of trace fossils, for example, tunnels or burrows, or body fossils". "Late Ediacaran trackways produced by bilaterian animals with paired appendages".

The Cambrian Explosion, around 541 million years ago, was a period when a wide variety of animals burst onto the evolutionary scene.

The team from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences and Virginia Tech in the USA discovered two rows of imprints that are arranged in a series or repeated groups in irregular trackways and burrows.

While the footprints were well-preserved, scientists don't know exactly what animal made the tracks since there were no body fossils found in the site.

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The study is published June 6 in the journal Science Advances.

Bilaterian animals such as arthropods and annelids have paired appendages or "legs" and are among the most diverse animals today and in the geological past. "They consist of two rows of imprints arranged in poorly organized series or repeated groups", the researchers wrote in their paper.

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.

Both the footprints and the borrows are known as "trace fossils", a term that refers to fossilized remnants that animals leave behind, such as fossilized poop, rather than fossils of the animals themselves.

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.

Senior author Shuhai Xiao, who is a geobiologist at the Virginia Tech University, says that the new discovery is a crucial step in identifying the first ever animal that grew a pair of legs.

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