Bowring does radiometric dating, so that reference is not directly relevant to the fossils. He (and others) found that the base of the Cambrian is only about 540 million and also refined dates within the Cambrian, so that a high diversity was found to be present within about 10 million years of the base of the Cambrian. However, this does not address what was going on during the late Precambrian.
I think Gould overemphasizes the Cambrian radiation in an effort to emphasize the randomness and contingency of evolution as he sees it. It seems ironically appropriate that this has been seized upon so much by young earth or ID advocates as evidence of the opposite.
Numerous evolutionary mechanisms have been proposed for generating rapid diversification, including key innovations (eyesight, predation, planktivory, hard skeletons, etc.) and environmental factors (global warming, increased oxygen levels, etc.). Conversely, various factors have been suggested as constraining later evolution, including the filling of niches and increased genomic integration and stability.
Dr. David Campbell
NEW ADDRESS AS OF 8/21/00
Saint Mary's College of Maryland
18952 E. Fisher Road
St. Mary's City, MD 20686-3001 USA
email@example.com, 301 862-0372 Fax: 301 862-0996
"He had discovered an unknown bivalve, forming a new genus"-E. A. Poe, The Gold Bug
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