Slug-Like Animal Resets Date of Animal Life

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Researchers have found the first physical proof that animals existed 585 million years ago, which is 30 million years earlier than previously documented, according to a new paper in the journal Science.

The proof isn't much to look at for the untrained eye. It resembles a mark left behind by someone dragging a stick across the ground. But the above image actually shows a fossilized track of a primitive slug-like animal, University of Alberta geologists Ernesto Pecoits and Natalie Aubet conclude. The animal measured about 1/4 of an inch long.

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The pattern of the track indicates that the prehistoric slug-ish species likely was searching for organic material to eat in silty sediment. This sediment was at the bottom of a shallow ocean in what is now Uruguay

The primitive creature was a bilaterian. These animals are bilaterally symmetrical, with their top side  distinguishable from the bottom side.

The track was dated by studying an igneous rock that intruded into siltstone in the area where the tracks were found. Studying the track itself wasn't too complicated, but the dating process took more than two years and involved feedback from a bunch of peer review scientists. The researchers even had to travel back to Uruguay to collect additional samples of the fossilized rock. A technique called mass spectrometry permitted its analysis.

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Most early animal life is known to us through such tracks, since the soft bodies of most creatures would long have eroded away.

Kurt Konhauser, a U of A geomicrobiologist, said in a press release that 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. 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."

(Image courtesy of Ernesto Pecoits and Natalie Aubet)

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