Walcott’s Discovery and Early Studies
Charles Walcott visited Yoho National Park in British Columbia in 1907, prospecting for the Smithsonian. There he discovered the earliest forms of the basic categories of organism we know today. The sheer scale of the find was extraordinary: unlike most fossils, soft body parts had been preserved. The mountain range, then submarine, deposited sediments in the form of landslides, burying animals instantly, leaving no chance for decomposition to set it.
Cambridge, Ontario and New Discoveries
Harry Whittington of Cambridge, Desmond Collins of the Royal Ontario Museum, and other scientists have continued studying and formally describing the fauna of the Burgess Shale, and establishing their place on the tree of evolution. More fossils of the same era have been discovered in China and in Greenland, where rocks of the right age are accessible.
Ediacaran Precursors
The earliest forms of visible life, the Ediacaran fauna, were simple, sea-filtering organisms reminiscent of slugs or sea pens which, to the untrained eye, all look much the same. However, the Cambrian Explosion, 550 to 485 million years ago, was a proliferation, not just of species, but more importantly of body plans.
Burgess Shale Fauna
Organisms in the Burgess Shale include Trilobites, a common arthropod in the oceans until the rise of the Dinosaurs; Santacaris, an arthropod thought to be the ancestor of insects, spiders and scorpions; and most crucially, Pikia, arguably the most unremarkable-looking animal in Cambrian Fauna - rather like a swimming worm – had the first known chordate structure (a body supported by a central cord-like structure). This makes this humble worm the ancestor of dinosaurs, lizards, whales and human beings, and every other being in the chordate phylum.
Classification Conundrums
Having said that, some creatures in the Cambrian Explosion era conform to no known classification. Opabinia, arguably the most bizarre organism in the Burgess Shale, has five eyes, a segmented body with banks of oar-like fins and a long trunk it uses to pass food to its mouth. It is an not clearly an arthropod, an annelid, or any other phylum known today. Some, like Nectocaris, has in appearance the body of an eel and the head of a shrimp. To add to the confusion of totally new phyla come organisms like Nectocaris that seem to be halfway between one phylum and another.
Effect on Evolutionary Theory
The importance of the Burgess Shale and other Cambrian fossils to the understanding of our origins is crucial; we see in it the dawn of many of the creatures we know today, ourselves included. Furthermore, the discovery of the Cambrian Explosion has done much to affect our perception of how evolution works. Whereas evolution was long perceived as a gradual, continuous process of the tree of life branching and advancing with occasional pruning, the perception has been revised to depict massive proliferations, where every conceivable ecological niche (and a few more inconceivable ones) is filled, and then all compete to most effectively use the world around them. Hosts of unknown phyla and hybrid phyla existed at no other time than the Cambrian explosion, and many more died out than persist today, making the world as we now recognize it.
Significance
Stephen Jay Gould postulates that if the history of life were restarted, every probability recalculated, then all it would take would be one epidemic disease, one natural disaster, and the whole history of life would be redrawn. The dominant species on Earth might have five eyes and dozens of legs. The Burgess Shale is a tribute to the variety and potential of life, as well as the incredible luck it took to get us where we are.
Bibliography
Stephen Jay Gould, Wonderful Life: The Burgess Shale and the Nature of History, W.W. Norton & Company, 1989.
Simon Conway Morris, The Crucible of Creation: The Burgess Shale and the Rise of Animals, Oxford University Press, 1998.
“Ancient Oceans,” Planet of Life. Narrated by Stacy Keach. Discovery Channel, 1998.
Desmond Collins, “Misadventures in the Burgess Shale,” in Nature, Vol 460, Part 20, August 2009.
