Earliest animal footprints found in China

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Soft tissues aren't prone to fossilisation, since they degrade quickly after death, so scientists have only a shady conception of what some of our planet's earliest animals were like.

The authors can't tell exactly what kind of animal made the tracks, but they can narrow it down to something with pairs of matching legs.

"Although the exact identity of the trace maker of the Shibantan trackways is hard to determine in the absence of body remains at the end of the trackways, we suggest that the trace maker was probably a bilaterian animal with paired appendages", the authors reported.

It is believed most major animals capable of leaving footprints appeared during and after this event, but many have suspected there might be some more ancient fossils that could reveal the evolutionary ancestry of the animals that thrived later.

Still, this discovery means that paleontologists will have to revise their vision of how life developed in Earth's primordial oceans.

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

"The newly found pieces are the oldest existing animal footprint fossils to date", said Chen Zhe, one of the Chinese researchers, before adding that they think the animal is similar to the modern-day shrimp.

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The areas, called frontier counties, had a suicide rate of 25.9 per 100,000 people, compared to a rate of 17.8 among all counties. That number has remained steady over recent decades, she said. "If they did, we would all respond, but that isn't how it works".

The fossils, which were found in the Yangtze Gorges area of south China, lie between two rock layers that have been radiocarbon-dated to 551m and 541m years old, meaning the footprints were made sometime between these dates.

Trackways and burrows excavated in situ from the Ediacaran Dengying Formation.

In a press release about the survey, Dr. Shuhai Xiao of Virginia Tech conveys, "If an animal makes footprints, the footprints are depressions on the sediment surface, and the depressions are filled with sediments from the overlying layer."This style of preservation is distinct from other types of trace fossils, for example, tunnels or burrows, or body fossils".

The research by a Chinese team appears in Science Advances journal.

"At least 3 living groups of animals have paired appendages (represented by arthropods such as bumble bees, annelids such as bristle worms, and tetrapods such as humans)". The trackways are somewhat irregular, consisting of two rows of imprints that are arranged in series or repeated groups.

'Arthropods and annelids, or their ancestors, are possibilities. The trackways also indicate a connection to burrowing, suggesting that whatever animal made the tracks might have had a habit of digging into sediments. Maybe they were never preserved, the researchers said.