A team of researchers from the University of Alberta and the Universidad de la República in Uruguay has uncovered physical proof that animals existed 585 million years ago, 30 million years earlier than all previous established records show.
Image shows tracks of the earliest animal life form ever discovered. Bilaterians, centimetre-long slug-like animals, left their mark 585 million years ago in shallow-water silt in what is now Uruguay. The find predates all previous evidence of "first" animal life on Earth by 30 million years (Richard Siemens)
The researchers discovered fossilized tracks of a centimeter long, slug-like animal left behind 585 million years ago in a silty sediment.
They determined that the tracks were made by a primitive animal called a bilaterian, which is distinguished from other non-animal, simple life forms by its symmetry-its topside is distinguishable from its bottom side-and a unique set of ‘footprints’.
The team suggests the fossilized tracks indicate the soft-bodied animal’s musculature enabled it to move through the sediment on the shallow ocean floor. The pattern of movement indicates an evolutionary adaptation to search for food, which would have been organic material in the sediment.
The precise age of the tracks was calculated by dating the age of an igneous rock that intruded into the siltstone in the area where the tracks were found. It took more than two years for the researchers to satisfy themselves and a panel of peer review scientists that the age of 585 million years is accurate.
The dating process included a trip back to Uruguay to collect more samples of the fossilized rock and multiple sessions of mass spectrometry analysis.
“When it comes to soft-bodied animals and their tracks it’s not unusual for the animal’s body to disappear but its tracks become fossilized,” said Dr Murray Gingras, a paleontologist at the University of Alberta and senior author of a paper published in the journal Science.
Prior to the discovery and age confirmation, the oldest sign of animal life was dated at 555 million years ago from a find made in Russia.
“The team’s discovery will prompt new questions not only about the timing of animal evolution, but also the environmental conditions under which they evolved,” said study co-author Dr Kurt Konhauser, a geomicrobiologist at the University of Alberta.
Dr Konhauser explained that the challenge now is “to find out how these animals evolved to the point where they were able to move about and hunt for food.”
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Bibliographic information: Pecoits E et al. 2012. Bilaterian Burrows and Grazing Behavior at >585 Million Years Ago. Science 29 June 2012: vol. 336, no. 6089, pp. 1693-1696; doi: 10.1126/science.1216295
