- rapid diversification of multicellular animal life ~541 million years ago
- most major animal phyla appeared within a ~25 million year window
- origin of eyes, shells, exoskeletons, predation, bilateral symmetry
- preceded by the Ediacaran biota: soft-bodied, sessile organisms
- triggers: rising oxygen levels, calcium availability, ecological arms races
- first appearance of arthropods, mollusks, chordates, echinoderms
- the Burgess Shale and Chengjiang fossil beds preserve this radiation
- deepest example of an epoch boundary driven by innovation cascades
- analogous to the Information Age explosion of digital complexity