The Smithsonian's fourth Secretary Charles D. Walcott discovered the Burgess Shale deposit in British Columbia in 1909. It provided the first evidence regarding the diversity of ancient soft - bodied organisms. Some of the specimens contained in it are so unique that all efforts to link them with other known animals have failed.

The deposit formed as mud and silt periodically fell to the base of an underwater cliff, forming clouds of fine particles that trapped animals and plants. In an environment free from scavengers, the organisms remained preserved.