The Great Ordovician Biodiversification Event
Marine diversity triples without a single new body plan — evolution filling in rather than inventing.
- When
- —
- Duration
- 18 million years
- Known to
- ± 5 million years
- Era
- Ordovician, Paleozoic
Over roughly thirty million years the number of marine genera rises threefold or more, as brachiopods, bryozoans, crinoids, corals, cephalopods and graptolites radiate into every available niche. Unlike the Cambrian explosion it produced no new phyla: this was diversification within existing designs, building the complex tiered ecosystems that characterise the rest of the Paleozoic. Its cause is contested — rising oxygen was long favoured, but uranium isotopes suggest oxygenation came after the steepest diversity rise rather than before it.