dramatically. It was the time of the Cambrian Explosion, an eruption of life when Earth’s very first animals began appearing in the fossil record — the ancestors of all major animal groups ...

The Cambrian Explosion saw an incredible diversity of life emerge, including many major animal groups alive today. Among them were the chordates, to which vertebrates (animals with backbones ...

This animation created for Evolution: "Great Transformations" depicts creatures whose fossils were found at the Burgess Shale. As alien as these creatures seem, they are also surprisingly familiar.

Worminess wasn’t the only factor that brought oblivion to the Ediacarans and triggered the Cambrian explosion—there also were changes in ocean chemistry that allowed animals to acquire hard ...