550 million years: animals

A fossil of Yilingia spiciformis and the track it left as it moved. (Z. Chen et al./Nature)

Ancient worm rolls back animal origins The fossil of a bizarre-looking worm-like creature — and the exceptionally rare remains of the trail it left behind — is revising our understanding of when and how animals evolved. The fossil formed some time between 551 million and 539 million years ago, in the Ediacaran period. It joins a growing body of evidence that challenges the idea that animal life on Earth burst onto the scene during the ‘Cambrian explosion’, which began about 539 million years ago. Nature | 4 min read