Precambrian trace fossils and the rise of bilaterian animals

In this attempt to synthesize present knowledge into a coherent story, the Cambrian explosion is interpreted to represent a true adaptive radiation, an event similar to Phanerozoic radiation events in principle but unique in its possibilities. A model of bilaterian evolution helps explain how this particular event involved the sudden initiation of major coelomate phyla. In many of these groups, preservable skeletons are part of the basic body plan. Biochemical‐sequence analyses indicate that acoelomates and pseudocoelomates branched off long before the coelomate radiation. The great differences between Vendian and Cambrian ichnofaunas, therefore, may be the result of a major shift in composition from Vendian acoelomate‐pseudocoelomate‐procoelomate faunas to Phanerozoic faunas dominated by new coelomate groups.