The jump from the simpler Precambrian organisms (further explored in the next chapters) to the radically different Cambrian forms appears to occur far too suddenly to be readily explained by the gradual activity of natural selection and random variations. Neither the Burgess Shale nor any other series of sedimentary strata known in Walcott’s day recorded a pattern of novel body plans arising gradually from a sequence of intermediates. Instead, completely unique organisms such as the bizarre arthropod Opabinia (see Fig. 2.9)—with its fifteen articulated body segments, twenty-eight gills, thirty
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