A slab of alien life
On August 30, 1909, paleontologist Charles Doolittle Walcott struck a block of shale high in the Canadian Rockies and discovered one of the most important fossil fields in the world. The site, now known as the Walcott Quarry, contained exceptionally preserved soft-bodied animals from the Middle Cambrian period, around 508 million years ago. Before this, the fossil record of the era consisted almost entirely of hard shells and bones. The Burgess Shale, as the formation is known, displayed the full diversity of an ancient marine ecosystem.
The creatures were buried by a catastrophic underwater mudflow. This event swept them from their habitat at the base of a 160-meter-tall limestone cliff into a deep basin with low oxygen, burying them instantly. This rapid entombment in fine-grained mud, combined with the unique seawater chemistry of the Cambrian period, prevented decay and preserved delicate tissues like gills, guts, and even primitive nervous systems. Between 1910 and 1924, Walcott and his family excavated over 65,000 specimens from this single quarry.
Among the finds were animals that are difficult to classify. Opabinia regalis was a creature with five stalked eyes, a backward-facing mouth, and a long, flexible proboscis ending in a claw. Hallucigenia, named for its "dream-like" appearance, was a worm-like animal with stilt-like spines on one side and tentacles on the other; it was initially reconstructed upside down. The ecosystem's top predator was Anomalocaris canadensis, a segmented animal that could reach up to a meter in length and had two large, spiked appendages for grasping prey.
Rewriting the tree of life
Walcott initially attempted to classify all his bizarre finds within existing modern animal groups. The fossils were treated as curiosities and largely remained in drawers at the Smithsonian Institution for decades. A thorough re-examination began in the 1960s, led by paleontologist Harry Whittington and his students, Simon Conway Morris and Derek Briggs. Their work revealed that many of the Burgess Shale animals were strange and represented entire evolutionary lineages.
Many of these organisms could not be placed in any modern phylum, suggesting that the diversity of fundamental body plans during the Cambrian Explosion was far greater than it is today. The discovery showed that life's early history was not a simple, linear march toward modern forms. It was a period of wild experimentation, with many unique lineages ultimately going extinct. This view was famously popularized by Stephen Jay Gould's 1989 book, "Wonderful Life."
The quarry is located within Yoho National Park and is part of the Canadian Rocky Mountain Parks UNESCO World Heritage Site, a designation it received in 1980. Access to the fossil beds is highly restricted to prevent damage and looting, and the quarry can only be visited on guided hikes. These restrictions ensure the preservation of this record of early animal evolution.