|A diorama portraying the seas of the Ordovician Period (from the Exhibit Museum, University of Michigan)|
When did it happen?
Around 445-440 million years ago, possibly in 2 phases
What went extinct?26% of all marine families, 60% of all genera, an estimated 82-88% of all species.
Although no major groups were completely lost, many sea creatures suffered substantial losses. These included nautiloids (cousins of today's squid and cuttlefish), which were the top marine predators of the time, as well as brachiopods, corals, bryozoans, echinoderms, graptolites and eel-like conodonts. Over 90% of trilobite species disappeared.
|Nautiloids are a large and diverse group of marine cephalopods (Mollusca) belonging to the subclass Nautiloidea that began in the Late Cambrian|