According to a new study, the 'biomats' of photosynthetic bacteria that save oxygen-rich sediment in a hostile environment for small organisms, may have triggered the evolution of animals capable of moving.

"Slug and worm-like animals lived on, within and immediately beneath the mat," said lead author Murray Gingras of the University of Alberta, Canada, which "served as a food and oxygen resource for the early animals".

Gingras said that the team aims to find out how animals evolved during ancient period when mobile animals first evolved, called Ediacaran, by studying modern day lagoons.

Animals with complex bio-structures first evolved between 635 and 542 million years ago, which was the time when oceans were just becoming oxygenated.

The oxygen level might have been a tenth of the level of today, which is too low to support energetic life. Gingras and his team studies modern-day, low-oxygen lagoons in the Los Roques archipelago, Venezuela.

He found that the microbial mats on the lagoon floors contained four times oxygen than the water above. He said that the burrows left by these animals are similar to those found in the 600-million-year-old rocks.