Evidence of billion-year-old worm-like animals found in rock

September 30, 1998 - AP

Researchers say they have found tiny tunnels preserved in rock in India that were dug by burrowing, worm-like creatures more than a billion years ago. The finding indicates complex animals may have evolved far earlier in Earth's history than previously believed. The tunnels, about the size of a soda straw, are thought to be the oldest trace fossil ever found and probably were carved by worms that lived under the muck at the bottom of a shallow sea, Adolph Seilacher of Yale University said Wednesday.

Multicellular animals made a dramatic appearance in the fossil record about 540 million years ago at the beginning of what is called the Cambrian period. Animals then developed skeletons, shells and mineralized bodies that were preserved in the fossils.

Before that, it has been believed, life consisted of primitive, soft-bodied organisms that left no trace in the fossil record. Scientists generally believed that life started some 4 billion years ago with simple, single-celled creatures that crept slowly up the evolutionary ladder until there was an explosion of new, complex life forms during the Cambrian.

But Seilacher, a professor emeritus at the University of Tubingen in Germany, said that discovery of the worm tunnels in India shows that there were multicellular animals, with complicated and intricate lifestyles, more than a half-billion years before the Cambrian. "This means that the birth of multicellular animals was at least twice as long ago as we thought," he said. The announcement, made at a German news conference, met with immediate skepticism among some paleontologists.

Seilacher and his colleagues found the tunnels, now eroded to mere meandering grooves, in sandstone in northern India. The rock was formed from sand that once was the floor of a shallow sea. Seilacher said he believes the worm-like creatures lived in the sand and fed on a mat of decaying organic matter that coated the sea floor. The organic matter, he said, probably was the bodies of microorganisms and algae that lived in the water, died and sank to the bottom.

Seilacher said the path of the tunnels seems to purposely follow the contours of the sea floor, as if the animals were feeding from below on the organic debris. Some of the tunnels have branches, he said, suggesting that the animals sometimes dug forward and then backed out to take a new burrowing path. This suggests a complex life form that had nerves, instincts and senses. The shape of the tunnels, said Seilacher, suggests the animals moved by a wavelike action and could have been coated with a mucous that eased the passage through the sand.

Seilacher said the sand containing the tunnels hardened over time to become rock and this preserved the impressions of the tunnels. In recent geologic times, the rock has been lifted up and layers eroded away, revealing the tunnels as grooves in the soft stone. Runnegar said a troubling element of Seilacher's conclusion is that there is a 400 million-year gap in the fossil record between the worm tunnels and the hard-bodied fossils of animals from the Cambrian period.