The Burgess Shale formation contains a vitally important collection of fossils. They are significant because of their age, about 505 million years old; because of their fine detail, which preserves the soft parts of ancient organisms; and because some of them are the remains of creatures that contributed no descendants to the modern world.
The formation is located in southeastern British Columbia near the small town of Field, about 90 km from the resort town of Banff, in Yoho National Park. Mountain-building forces moved these ocean deposits to a high ridge that is now a World Heritage Site. Because treasures have been unearthed here, fossil gathering is prohibited. However, public tours are readily available, for those with the stamina to hike to the quarries where the fossils lie.
They were deposited at the base of an escarpment, an underwater cliff, in a warm shallow sea. The land was barren then, though life abounded in the seas. Animals lived on and around a carbonate reef, the Cathedral Escarpment, on the edge of what would become western North America. Canada was then located just below the equator, on the continent of Laurentia.
The wall at the edge of the reef was about two hundred meters high. Periodically, mudslides carried primitive animals down this cliff. They were buried there, sealed up, some scientists believe, by tiny particles of clay that penetrated their every feature, and kept out oxygen that would have contributed to their decay. Other scientists believe that chemicals in each animal’s gut helped form films that preserved their features.
The fossils are wonderfully preserved. Some are images on fine-grained shale. (Shale is hardened mud.) Some are mineralized remains. All draw paleontologists a vivid picture of life in the Cambrian era, right after what is called the Cambrian Explosion.
In the Cambrian Explosion, major groups of complex animals suddenly appeared, about 530 million years ago. At the same time, other groups of organisms suddenly diversified, producing many new species. Suddenly, in geologic time, means during a period of 70 or 80 million years. The Cambrian Explosion is a major topic in paleontology, and the Burgess Shale provides evidence about the period.
R.G. McConnell of the Geological Survey of Canada was the first scientist to gather fossils at the site, in1886. Railroad workers in the area also collected fossil remains, and Charles Walcott, head of the U.S. Smithsonian Institution heard about them. He came to the site in 1907, and published reports about it in 1908.
From 1910 to 1917, he worked with his family every summer at what is now called the Walcott Quarry. He sent 65,000 specimens to the U.S. His work at the remote site was meticulous and well documented. However, later paleontologists would say he misclassified some of what he saw.
In 1930, Percy Raymond of Harvard worked in the Burgess Shale. He reopened the Walcott Quarry, and opened a new one, higher on the mountain, now called the Raymond Quarry.
In 1966-67, the Geological Survey of Canada reopened both quarries, and documented odd new forms. Their discoveries led to a new investigation of the site by Harry Blackmore Whittington, a brilliant paleontologist, professor at Harvard and Cambridge, and an expert on trilobites. He was assisted by Derek Briggs and Simon Conway Morris.
Whittington, Briggs, and Conway Morris published papers beginning in 1971 about the Burgess Shale. Using Walcott’s notes and photographs, combined with their own finds, the scientists revealed startling new information about the site, the Cambrian Explosion, and, probably, about the nature of evolution.
Many of the fossils of the Burgess do not fit in any existing classification of animals. They have no descendants. There seems to have been a greater diversity of animal forms in the Cambrian era than exists now.
This, for many, destroys the idea of evolution as a constant climb towards a more adapted, more evolved, higher, life form. As paleontologist Stephen J. Gould said in Wonderful Life, his popular 1989 book about the Burgess Shale, “Life is a copiously branching bush, continually pruned by the grim reaper of extinction, not a ladder of predictable progress.” Gould argues for contingency, the idea that if we did it all over (somehow) it would come out different.
Simon Conway Morris, now a Cambridge Professor of Earth Science, does not entirely agree with what Stephen J. Gould had to say. His book, The Crucible of Creation: The Burgess Shale and the Rise of Animals, includes an engrossing time-travel section that brings the period to vivid life. He also argues that convergence plays a larger role in evolution than contingency does, and that some of the Burgess creatures that seem to be without descendents are in fact ancestors.
These scientists disagree about some of the mechanisms of evolution, and take as their battleground the Burgess Shale. They do not question Darwin’s great insight. They elaborate upon it; to enrich his theory and carry it forward, as scientists who come after them will build upon their work, perhaps correcting it in detail but respecting its contributions to an evolving understanding of the world.
