Many spectacular animals that lived over 500 million years ago are now extinct. The Burgess Shale Fauna fossils, discovered in Canada at the start of the twentieth century, were preserved in mud that retained remarkable detail of both hard and soft parts of a variety of sea creatures.
The Burgess Shale animals lived on a muddy sea floor in shallow water. A mudslide probably swept them into deeper waters, where they were buried alive in oxygen-starved sediments.
Parts of Anomalocaris were at first thought to be three separate animals.