The suddenness of this "Cambrian Explosion" has become, since, the subject of numerous papers in academic circles as well as a prong in the intelligent design argument against evolution. It has since become clear to all working in this period that, while it occurred comparatively rapidly, the diversification of organisms can be perfectly explained using evolutionary theory. As Kenneth Miller writes:
Beavering away at the Sedgwick Museum of Geology at Cambridge, they patiently reconstructed the fossils in three-dimensional form, revealing a weird bestiary so different from anything now living that 15 to 20 organisms might rank as separate trunks of the evolutionary tree.
The most common organism, Marrella splendens, the subject of Whittington’s first report, published in 1971, had been identified by Walcott as a trilobite. Whittington saw that while it was clearly an arthropod, it was not a member of any known arthropod class. Organisms such as the five-eyed Opabinia and spiny, slug-like Wiwaxia were so different from anything else known that Whittington’s team assumed they must represent different phyla, only distantly related — if at all — to anything known today.
The implications of the Burgess Shale were colossal and disturbing, particularly as most of these creatures became victims of a mass extinction soon after, and such a prolific evolutionary flowering has never been repeated in nature. What became known to scientists everywhere as the “Cambrian explosion” raised the possibility that evolution may have worked by different rules at different times in Earth’s history.
The Cambrian was actually not an explosion at all, but a 30-million year period of body plan experimentation and diversification that led to most of the major groups of animals alive today. But even the richly populated world of the Cambrian was not today’s world. There were no insects, no modern fish, no land plants, no flowers, no birds, and not a reptile, a dandelion, or a frog. All of that was to come. (p. 123)1To put this into perspective, thirty million years ago, the largest primates were the size of house cats, whales were just beginning to take to the ocean and the Mediterranean Sea didn't exist. It is a long time.
1Miller, K. (2009). Only a theory: Viking.
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