An international team of scientists has recently uncovered what they believe are the earliest animal fossil footprints on record, Phys.org reports.
Although it’s not clear what animal left these ancient tracks behind — since only the trace fossils (evidence that an animal has been there) were discovered, and not the fossils themselves — the footprints date back 551 million to 541 million years ago, to the Ediacaran Period.
This places them perhaps even 10 million years before the “Cambrian Explosion” (roughly 541 million years ago), the moment in time which sparked the incredible evolution of life that led to the amazing diversity of species that we see today.
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. 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 U.S. and the Nanjing Institute of Geology and Palaeontology (NIGP) of the Chinese Academy of Sciences.
“These trace fossils represent the earliest known trackways. They consist of two rows of imprints arranged in poorly organized series or repeated groups,” the researchers wrote in their paper.
So, what type of creature has left behind its mark all those 550 million years ago in China? Well, the team has it narrowed down to a bilaterian animal — a creature with bilateral symmetry, that has a head at one end and the back end at the other, as well as a symmetrical right and left side, Live Science explains.
“We do not know exactly what animals made these footprints, other than that the animals must have been bilaterally symmetric because they had paired appendages,” study co-author Shuhai Xiao, a geobiologist from Virginia Tech, told the Independent.
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 footprints are organized in two parallel rows, as expected if they were made by animals with paired appendages. Also, they are organized in repeated groups, as expected if the animal had multiple paired appendages.”
According to the researchers, this is the first evidence that bilaterian animals existed before the “Cambrian Explosion.” As the Inquisitr previously reported, up until that historic event, which lasted for 20-25 million years and gave rise to most of the major animal groups on the planet, animal life on Earth was limited to simpler, single-celled or multicellular organisms.
Yet the bilaterian that left behind the Earth’s oldest footprints were spectacularly evolved for creatures living during the Ediacaran Period (about 635-541 million years ago), reveals the study. In fact, the China discovery represents one of the earliest known records of animals evolving appendages.
By looking at the ancient trackway — of which The Guardian has made an animation of, that you can watch below — the team was able to determine that this prehistoric creature had multiple paired feet that raised its body above the ocean floor. Take that, rest of the pre-Cambrian life forms!
“Animals use their appendages to move around, to build their homes, to fight, to feed, and sometimes to help mate,” Xiao told The Guardian.
As Xiao explains, knowing when the first legged animal appeared on Earth is a crucial detail, considering that the movement of sediments triggered by that first walking creature as it trotted over our planet’s surface could have had a major impact on the Earth’s geochemical cycles and climate.
“It is important to know when the first appendages appeared, and in what animals, because this can tell us when and how animals began to change the Earth in a particular way.”
While science has previously recorded that bilaterian animals, such as arthropods and annelid worms, first emerged during the “Cambrian Explosion” (541 to 510 million years ago), this finding proves that these creatures actually evolved earlier, confirming the suspicion shared by some researchers.
Near the ancient footprints, the team found fossilized burrows, which suggests that the animal might have been periodically tunneling into sediments and microbial mats, either in search of food or perhaps to mine for oxygen.
This is a sign of “complex behavior involving both walking and burrowing,” the team argues in the paper.
“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.