Seldom does a work on paleontology appeal to a large audience, for the field today is limited to a small number of academic specialists who publish their findings in articles and monographs directed toward fellow specialists. While the study of fossils was an early and influential element in the development of evolutionary theory, in recent times biochemistry and microbiology have made stronger contributions to scientific understanding of the development of life. To be sure, the discoveries of Louis and Mary Leakey were highly significant for anthropology, but their value was restricted to their contribution to understanding the development of early man. In Wonderful Life, Stephen Jay Gould traces the discovery and scientific study of the Burgess Shale formation and explores its significance for the entire field of evolution, thus reaffirming the significance of paleontology for a large readership.
The Burgess Shale, a formation approximately eight feet thick and one city block long, is located in the Canadian Rockies in Yoho National Park, British Columbia. It was discovered in 1909 by Charles D. Walcott, an eminent American paleontologist and secretary of the Smithsonian Institution. He recognized its importance at once, for it contained a rich harvest of fossil life more varied than any other known source of a similar date. By virtue of scientific custom and tradition, Walcott retained proprietary interest in his discovery for the remainder of his life.
The deposit dates from the Cambrian period, 530 million years ago, when an explosion of life-forms occurred from apparently meager beginnings. The multi-celled animals, the primary focus of Gould’s book, are better preserved than most fossil remains, because of the unusual way that the deposit was formed. A mudslide trapped numerous creatures in a limited space, and, unlike most other fossil remains, they became hardened without having been pressed completely flat. As a result, scientists have been able to study the interior body cavities and organs and reconstruct them in three-dimensional illustrations.
For the nonspecialist, a firsthand view of the Burgess Shale is offered at the National Museum of Natural History in Washington, D.C., where ninety-five fossils collected from the site are on display. To compare it with the fauna from the Ediacaran formation, on display a few feet away in the museum, is instructive. The Ediacaran exhibit, formed from deposits laid down 570 million years ago, shows that animal life was dominated by simple organisms such as jellyfish. Forty million years later, life had evolved into an extraordinary variety of animals dominated by mollusks, arthropods, and brachiopods. Perhaps the most interesting part of the exhibit, however, lies in the explanatory notes on the fossils. For eight of the
creatures on display—including Opabinia regalis, Hallucigenia sparsa, Wiwaxia corrugata, and Aysheaia peduculata—the explanatory note reads, “Relationship to living organisms unknown.”
The Burgess animals themselves are for the most part small marine creatures ranging from about one-fourth of an inch to six inches long, though one exceptional species, Anomalocaris, reached two feet in length. Among them is Pikaia, the earliest known representative of the phylum Chordata, which includes all mammals. Many resemble commonly found crustaceans, such as shrimp or the various marine worms known today, but some have unusual anatomical features that make classification difficult. Opabinia, a segmented creature with five eyes atop its head, possesses a feeding nozzle that extends frontally for approximately a third of its body length. Wiwaxia, a bottom feeder shaped something like a pancake, features a top covered with scales and two rows of fins that resemble fronds growing from a base. Odaraja, a thick-bodied creature with a heavy exoskeleton, possesses a three-pronged tail that resembles a three-bladed propeller.
From his discovery of the deposit in 1909 until his death in 1927, Walcott had exclusive rights to study and classify the findings, but because of his burdensome administrative duties, he found his time for the Burgess Shale severely limited. He made several expeditions to the site and collected an impressive number of samples for storage in Washington, publishing monographs and articles on the animals. At his death, he left voluminous notes that make it plain that he had difficulty placing some specimens into a known phylum, yet in 1912 he had placed...
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