Earth's oldest 'footprints' found
2008-10-06 08:50
Washington - US scientists have found the oldest fossilised tracks of a tiny legged animal, from 570 million years ago, that push back the advent of more complex creatures on Earth by some 30 million years, a report said on Sunday.
The fossilised trails, thought to belong to a centipede or a leg-bearing worm that lived in the water, were found in sedimentary rocks in the US state of Nevada, said Ohio State University geology professor and the study's chief author Loren Babcock.
The finding, as reported to the Geological Society of America meeting on Sunday in Houston, Texas, shatters the belief that pre-Cambrian life on Earth was restricted to microbes and simple, multi-cellular organisms.
The tracks, two parallel rows of small dots, each about two millimetres in diameter, date back some 570 million years, to the Ediacaran period (630-542 million years ago).
They suggest that animals walked using legs at least 30 million years earlier than had been thought.
The Cambrian period (543-490 million years ago) saw an evolutionary explosion that produced most of the major animal groups we know today.
Evidence
"We keep talking about the possibility of more complex animals in the Ediacaran - soft corals, some arthropods, and flatworms - but the evidence has not been totally convincing," Babcock said.
"But if you find evidence, like we did, of an animal with legs - an animal walking around - then that makes the possibility much more likely," he added.
He said he was "reasonably certain" the trails were made by a centipede-like arthropod or a leg-bearing worm with a centimetre-wide body.
A fossil of the actual animal would be more definitive, so Babcock said he would continue searching the area of Nevada that was covered by a shallow sea 570 million years ago, where the "accidental discovery" of the ancient trails was made.
He said other potential sites for similar Eciacaran fossils include the White Sea area of Russia, South Australia, Newfoundland and Namibia.
In 2002, other researchers found a similar fossil trail from Canada that dated back to the middle of the Cambrian period, about 520 million years ago.
Another set of tracks found in South China date back to 540 million years ago