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The fossils of the Burgess Shale, like the Burgess Shale itself, formed around in the Mid Cambrian period. They were discovered in Canada in 1886, and Charles Doolittle Walcott collected over 60,000 specimens in a series of field trips up from 1909 to 1924. After a period of neglect from the 1930s to the early 1960s, new excavations and re-examinations of Walcott's collection resumed and paleontologists continue to discover new species. These fossils have been preserved in a distinctive style known as Burgess shale type preservation, which preserves fairly tough tissues such as cuticle as thin films and soft tissues as solid shapes.

In the 1970s and early 1980s the Burgess fossils were largely regarded as evidence that the familiar phyla of animals appeared very rapidly in the Early Cambrian, in what is often called the Cambrian explosion. This view was already known to Charles Darwin, who regarded it as one of the greatest difficulties for the theory of evolution he presented in The Origin of Species. However, from the early 1980s the cladistics method of analysing "evolutionary family trees" has persuaded most researchers that many of the Burgess Shale's "weird wonders", such as Opabinia and Hallucinogenia, were evolutionary relatives of modern animal groups rather than a rapid proliferation of separate phyla, some of which were short-lived. Nevertheless, there is still debate, sometimes vigorous, about the relationships between some groups of animals. (see more...)