What made the creatures seem new is they have no living descendants. The first European to see a kangaroo could not have been more surprised. But decades later, when the Cambridge geologist Harry Whittington and his colleagues took another look, they realized that the Burgess Shale contained not just unique species, but entire phyla (the broadest classification of animals) new to science. Walcott conservatively tried to place the creatures into groups that were known from other fossils, or living descendants.
How to classify this trove has been a contentious question. Cambrian fossils are known from many sites, but usually only from remains of shells and other hard parts here, owing to some accident of geology, entire organisms were preserved with eyes, tissue and other soft parts visible. This was the full flowering of the “Cambrian explosion,” the sudden appearance of a vast new panoply of life-forms-creeping, burrowing and swimming through seas that had held nothing like them in the previous three billion years.
They include Opabinia, a five-eyed creature with a grasping proboscis, whose presentation at a scientific conference was regarded at first as a practical joke Hallucigenia, a marine worm that earned its name when it was originally reconstructed upside-down, so that it appeared to ambulate on seven pairs of stiltlike spines and Pikaia, an inch-and-a-half-long creature with a spinal rod called a notochord, the earliest known chordate-the group of animals that would later evolve into vertebrates. Some were well known, such as the segmented arthropods known as trilobites, others completely novel.
Whether or not it happened that way-Gould argued against it-Walcott knew he had found something special, and returned the following year, assembling the nucleus of a collection now numbering some 65,000 specimens representing about 127 species. One tale is that a horse ridden by Walcott’s wife, Helena, slipped, overturning a slab of rock that revealed the first astonishing specimens. It was late August 1909, and an expedition led by the Smithsonian’s longtime Secretary, Charles D. The discovery of the Burgess Shale fossils, high on a mountainside in the Canadian Rockies, is shrouded in legend. For decades they have fired the passions of researchers, fueling one of the great scientific controversies of the 20th century, a debate about the nature of life itself. Their very names- Hallucigenia, Anomalocaris-testify to their strangeness. They are, in the opinion of no less an authority than the paleontologist Stephen Jay Gould, “the world’s most important animal fossils”-not Tyrannosaurus rex, not Lucy, but a collection of marine invertebrates mostly a few inches in size, dating from the very dawn of complex life on earth more than 500 million years ago.
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