Chengjiang fossils: Early animals were preserved by sediment from a river delta

The Cambrian animals preserved at the Chengjiang fossil site in China lived in a shallow sea close to a river delta – a changeable environment that might have driven rapid evolution

By Michael Marshall

Some of the first complex animals lived in a shallow sea near the mouth of a river delta about 518 million years ago. The changeable environment, which was prone to violent floods, may have helped drive the evolution of early animals, including some of the first worms and animals with hard shells.

The Cambrian period, from 541 to 485 million years ago, saw a great flowering of animal life, dubbed the Cambrian explosion. A number of major animal groups originated …