World's Oldest Footprints Discovered on Ancient Seafloor

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.

"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.

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.

Scientists have found what they think is the oldest animal footprint in the fossil record, uncovering incredibly ancient track marks imprinted in the dirt as far back as 550 million years ago.

The presence of paired appendages (a primitive version of legs and arms) in the anatomy of this prehistoric creature is mirrored in the way the fossil footprints are laid out, Xiao explains.

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

An worldwide team of scientists, including researchers from the Nanjing Institute of Geology and Palaeontology, and Virginia Tech in the United States, conducted the study.

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Prof Shuhai Xiao, a geobiologist at Virginia Tech University and senior author of the research, said the finding brings scientists closer to understanding what creatures were the first to evolve pairs of legs.

Prior to this, animal life on Earth consisted of simpler, single-celled or multicellular organisms, but the Cambrian Period gave rise to more complex creatures of a kind we recognise today, including bilaterian animals, who exhibited the first bilateral symmetry. "Also, they are organized in repeated groups, as expected if the animal had multiple paired appendages". Until the current discovery, however, no fossil record of animal appendages had been found in the Ediacaran Period.

Animals use their appendages or outgrowths to move around, make their homes, feed, and find mates.

While the researchers are unable to identify the animal behind the footprints, there are three types of living animals with paired appendages: arthropods such as bumble bees, annelids such as bristle worms, and tetrapods which include humans.

"The trackways appear to be connected to burrows, suggesting that the animals may have periodically dug into sediments and microbial mats, perhaps to mine oxygen and food".

"Together, these trackways and burrows mark the arrival of a new era characterized by an increasing geobiological footprint of bilaterian animals", the researchers point out.

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