These findings add a new perspective to origin of animals. They were thought to have begun with a sudden explosion during the early Cambrian period, about 540 million years ago.

But researchers from the University of Tübingen and Yale University, as well as Jadavpur University in Calcutta, have found tunnels that may be burrows left behind as ancient worm-like animals wriggled through sand beds underneath a shallow sea covering what is now Central India.

Left behind by a worm?

These structures, known as "trace fossils", were preserved when the beds solidified into rock 1.1 billion years ago. Before this discovery, the oldest known fossil evidence of multicellular animals was 580 million years old.

The Cambrian period is often thought to have been the "big bang" of animal evolution, a time when a wide variety of organisms originated and left their mark on the fossil record.

An important argument for this idea has been that no multicellular organisms have been found in rocks older than the Cambrian.

However, some molecular studies have suggested that soft-bodied animals arose well before the Cambrian, perhaps as much as one billion years ago.

The trace fossils are preserved in so-called Chorhat Sandstone, which contains sand beds that built up during storms. The tops of many sand beds were covered with a blanket of microbes that protected the sand below from any disturbances above.

The ancient worm-like animals may have wiggled through the sand just below the microbes, using them as a source for food and oxygen since the water within the sand layers was probably poor in oxygen.

According to the researchers the Chorhat findings are best explained as the products of burrowing animals.

They point out that diameters vary from tunnel to tunnel but remain constant along each individual tunnel. The tunnels also do not resemble the structures commonly caused by physical processes and are similar to younger trace fossils known to be produced by worms.