Cambrian explosion

"The key element in deciphering the Cambrian explosion (11) is to integrate the expanding insights of molecular phylogeny (12) and developmental biology with the totality of paleontological evidence, including the Ediacaran assemblages. Somewhere, and this is the tricky point, in the Ediacaran assemblages are animals that may throw particular light on key transitions. Of these, the most significant are those between sponges and diploblasts, cnidarians and triploblasts, as well as the early evolution of the three superclades of triploblast (deuterostomes, ecdysozoans, and lophotrochozoans) (Fig. 1). The overall framework of early metazoan evolution comes from molecular data, but they cannot provide insights into the anatomical changes and associated changes in ecology that accompanied the emergence of bodyplans during the Cambrian explosion. The fossil record provides, therefore, a unique historical perspective."
Simon Conway Morris The Cambrian "explosion": Slow-fuse or megatonnage? PNAS April 25, 2000 vol. 97 no. 9 4426-4429