The charge that the construction of the geologic scale involves circularity has a certain amount of validity. ...Thus, the procedure is far from ideal and the geologic ranges are constantly being revised (usually extended) as new occurrences are found.
David M. RaupThere are about 250,000 different species of fossil plants and animals known . . In spite of this large quantity of information, it is but a tiny fraction of the diversity that [according to the theory] actually lived in the past. There are well over a million species living today and . . [it is] possible to predict how many species ought to be in our fossil record. That number is at least 100 times the number we have found.
David M. RaupA large number of well-trained scientists outside of evolutionary biology and paleontology have unfortunately gotten the idea that the fossil record is far more Darwinian than it is. This probably comes from the oversimplification inevitable in secondary sources: low-level textbooks semipopular articles, and so on. Also, there is probably some wishful thinking involved. In the years after Darwin, his advocates hoped to find predictable progressions. In general. these have not been found-yet the optimism has died hard and some pure fantasy has crept into textbooks.
David M. RaupIn the beginning, there were bacteria.... [A] nearly universal assumption is that all subsequent life descended from the original life form through a continuous chain of ancestor-descendant pairs. This assumption looks good because all living organisms share biochemical traits. It is conceivable, of course, that life originated more than once on the early earth but that all except one life form died out early, leaving a single lineage as the ancestor of life as we know it. If this did happen, it was the first important species extinction.
David M. Raup