The Late Ordovician Mass Extinction

TLDR

The Late Ordovician mass extinction eliminated about 85 % of marine species, ending a long period of ecological stasis and prompting surviving faunas to adapt to a new environment, a pattern that contrasts with other events that killed fewer species but caused greater long‑term ecological change. A brief glacial episode triggered two extinction pulses: the first at glaciation onset, when sea‑level fall and harsh climates drove deep‑ocean currents that aerated and possibly released toxins, and the second after rapid sea‑level rise, when cooling subsided and circulation stagnated. Recovery from the event took several million years, but the resulting fauna had ecological patterns similar to the fauna that had become extinct.

Abstract

▪ Abstract Near the end of the Late Ordovician, in the first of five mass extinctions in the Phanerozoic, about 85% of marine species died. The cause was a brief glacial interval that produced two pulses of extinction. The first pulse was at the beginning of the glaciation, when sea-level decline drained epicontinental seaways, produced a harsh climate in low and mid-latitudes, and initiated active, deep-oceanic currents that aerated the deep oceans and brought nutrients and possibly toxic material up from oceanic depths. Following that initial pulse of extinction, surviving faunas adapted to the new ecologic setting. The glaciation ended suddenly, and as sea level rose, the climate moderated, and oceanic circulation stagnated, another pulse of extinction occurred. The second extinction marked the end of a long interval of ecologic stasis (an Ecologic-Evolutionary Unit). Recovery from the event took several million years, but the resulting fauna had ecologic patterns similar to the fauna that had become extinct. Other extinction events that eliminated similar or even smaller percentages of species had greater long-term ecologic effects.