Major fossil study sheds new light on emergence of early animal life 540 million years ago
(PHYSorg.com Archaeology & Fossils)

All the major groups of animals appear in the fossil record for the first time around 540-500 million years ago-an event known as the Cambrian Explosion-but new research from the University of Oxford in collaboration with the University of Lausanne suggests that for most animals this `explosion` was in fact a more gradual process.