The Burgess Shale is not merely a collection of rocks; it is the “Rosetta Stone” of evolutionary history—capturing a moment 508 million years ago when the blueprint for complex animal life was being drawn, erased, and redrawn in a frenzy of biological creativity. A UNESCO World Heritage Site in Yoho National Park, it preserves soft-bodied Cambrian organisms in exceptional detail; eyes, guts, and gills fossilized in fine silt when jellyfish and worms normally vanish without a trace.

Discovery. In 1909, Charles Doolittle Walcott—Secretary of the Smithsonian—discovered the first fossils above Emerald Lake near Field. The legendary story that his horse stumbled on a slab of shale is likely apocryphal but endures. Walcott opened the original Walcott Quarry, a small depression on Fossil Ridge between Wapta Mountain and Mount Field that yielded over 65,000 specimens. He initially shoehorned these bizarre creatures into modern taxonomic groups, missing their revolutionary significance. CPR workers had already found “stone bugs” (trilobites) on Mount Stephen in the 1880s; the Mt. Stephen Trilobite Beds are part of the same formation. Access to fossil beds is restricted; guided tours (Parks Canada, Burgess Shale Geoscience Foundation) or research permits required.

Geology of preservation. How does a jellyfish fossilize? Usually it doesn’t. The Burgess Shale is a Lagerstätte—a storage place of exceptional preservation. The key was the Cathedral Escarpment, a massive underwater submarine cliff (the Cathedral Mountain formation). Turbidity currents—undersea mudslides—swept animals living at the cliff base into deep, oxygen-starved (anoxic) water, instantly burying them in fine silt. That rapid burial preserved not just shells, but soft tissues in microscopic detail.

The “weird wonders.” The shale’s icons include Anomalocaris—the “odd shrimp,” a metre-long apex predator with circular jaws; Opabinia, with five eyes and a vacuum-cleaner-like nozzle, so strange that the audience laughed when it was first presented at a scientific conference; Hallucigenia, a worm originally reconstructed upside down (walking on its spines) before researchers realized which end was up; Marrella, the “lace crab,” the most common fossil in the shale yet not a true crab; and Pikaia, a small swimming worm with a notochord—the probable ancestor of all vertebrates. See Waptia fieldensis for another iconic Burgess arthropod.

Modern research. Paleontology did not stop in the 20th century. The Marble Canyon site, discovered in 2012, revealed a new trove of fossils 40 km away. Recent finds include Mosura fentoni (the “Sea Moth”), a three-eyed radiodont that illuminates arthropod segmentation. Elemental mapping and scanning electron microscopy now image fossilized brains and nervous systems of creatures dead for half a billion years.