The fossilized trail of an aquatic creature suggests that animals walked using legs at least 30 million years earlier than had been thought.
The tracks -- two parallel rows of small dots, each about 2 millimeters in diameter -- date back some 570 million years, to the Ediacaran period.
The Ediacaran preceded the Cambrian period, the time when most major groups of animals first evolved.
Scientists once thought that it was primarily microbes and simple multicellular animals that existed prior to the Cambrian, but that notion is changing, explained Loren Babcock, professor of earth sciences at Ohio State University.
"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," he 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."
Soo-Yeun Ahn, a doctoral student at Ohio State, presented the discovery in a poster session at the Geological Society of America meeting Sunday in Houston. Coauthors included Margaret Rees of the University of Nevada, Las Vegas, and J. Stewart Hollingsworth of the Institute for Cambrian Studies.
If the disccovery holds up, this trace fossil has some profound implications. It'd do a mighty blow to the multiple origination hypothesis of complex life.