The Cambrian explosion is late in this game; this would be about the emergence of the Ediacaran biota (largely fractal-like body plans, followed by organisms with more specialised structural groups and less-local symmetries) and simpler aggregate colony organisms like sponges, which seemed to come out of nowhere quickly after the Cryogenian. The Cambrian explosion seems to have been mostly about riffing on the bilateral symmetry lick.