The oldest fossilised remains of complex animals appear suddenly in the fossil record, and as if from nowhere, in rocks that are 538 million years old.
The very oldest of these are simple fossilised marks (called Treptichnus) made by something worm-like with a head and a tail. A host of other animals appear rapidly, ancestors of the diverse animal groups we know today: ancient crab-like arthropods, shelled molluscs and the forebears of starfish and sea urchins.
