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At the beginning of the Cambrian period, about 545 million years ago, almost all the main types of animals that are still dominant today suddenly emerge in the fossil record. But was there a Cambrian "explosion" that saw accelerated evolution, or was there an extended period of evolutionary genesis in the Precambrian that did not leave a trace in the fossil record? In his Perspective, Fortey discusses recent support for the second hypothesis, highlighting in particular the report by Siveter et al. on a crustacean-like fossil from the early Cambrian.