What really caused the Late Ordovician Mass Extinction? What can brachiopod tell us about this event?

The Late Ordovician mass extinction was the first mass extinction in Phanerozoic life history. This mass extinction Eliminated 49-60% of marine genera and nearly 85% of marine species. More than 50% of the brachiopods and bryozoans in North America were wiped out and biodiversity recovered rapidly in the Early Silurian. Brachiopods became extinct at the onset of the Hirnantian glaciation (casualties of the first extinction pulse). The latest Ordovician Mass Extinction is partly the result of a mass dying of the epicontinental marine fauna that evolved during the great Late Ordovician marine transgression (just before the latest Ordovician glaciation)