Newly discovered fossils from China seem to be the oldest multi-celled animals yet found that were complex enough to have a two-sided body plan rather than a round one. The report on the creatures, published online Friday by the journal Science, is the latest in a series of fossil finds that downplays a supposed surge of species and diversity in body styles believed to have happened rather suddenly 540 million years ago. The episode, known as the Cambrian explosion, has been generating controversy for more than a century because it marked the point in pre-history where fossils for virtually all...