Burgess Shale animals. Illustration of some of the animals from the Cambrian Period, identified from fossils in the Burgess Shale site (508 million years old) in British Columbia, Canada. The main predatory animal at centre is Anomalocaris. At top left is a free-swimming Pikaia. At bottom left (spiky) are two specimens of Hallucigenia. The worm-like animal in the burrow at lower right is Aysheaia. The swimming arthropods (five specimens shown here) are Marrella. The Burgess Shale fossil site records a key moment in Earth's history, the Cambrian Explosion, when an unprecedented period of evolution produced a wide diversity of body types, including those of today's animals.