Life › Seas, forests & the move to land
Late Devonian extinction
pulses c. 372 and 359 million years ago· Extinction or crisis· Earth, climate & extinctions
Well establishedStrong fossil, genetic or geological evidence.
One of the 'Big Five' mass extinctions, striking in pulses about 372 and 359 million years ago and devastating reefs and fish.
See it on the Life map →What happened
The Late Devonian crisis was a series of blows over millions of years. The Kellwasser events, about 372 million years ago, spread oxygen-poor water through the seas and destroyed vast coral-and-sponge reefs. The Hangenberg event, about 359 million years ago, ended the armored placoderms and hit early tetrapods and ammonoids. Estimates vary, but roughly 70% or more of marine species disappeared over the whole interval.
Why it matters
It ended the 'Age of Fishes', cleared the way for sharks and ray-finned fish, and left reef ecosystems diminished for millions of years.
The evidence (fossils, genes, rocks)
Black, oxygen-poor shale layers such as the Kellwasser beds in Germany, carbon and oxygen isotope shifts, and fossil counts showing pulsed losses in dated marine rocks.
Still debated
The cause is debated: nutrient runoff from new forests, global cooling, volcanic eruptions, ozone loss and even a nearby supernova have all been proposed.
Connections (4)
▸First trees & forests may have helped cause Late Devonian extinctionDebated
The connection
Deep tree roots broke up rock and built soil, releasing extra nutrients such as phosphorus that washed into the seas. That could have fed algal blooms that used up oxygen as they decayed, creating dead zones. Forests also drew down carbon dioxide, cooling the climate. Both effects line up with Late Devonian ocean crises.
When and how
Proposed by Thomas Algeo and colleagues in the 1990s; forests spread from about 390 to 360 million years ago.
How sure are we?
Uncertain: the timing broadly fits and black shales record oxygen loss, but tying forest spread to specific extinction pulses is hard.
Debates and open questions
Volcanism, cooling, ozone loss and sea-level change are rival or additional causes; how much the forests mattered is debated.
▸Late Devonian extinction wiped out Placoderms: armored fishWell established
The connection
Placoderms were the most varied fish of the Devonian, but they suffered in the Kellwasser crisis about 372 million years ago and vanished in the Hangenberg event at the end of the Devonian, about 359 million. Sharks and ray-finned fish, which survived, then took over their roles.
When and how
Oceans and rivers worldwide, about 372–359 million years ago; the turnover was analyzed by Lauren Sallan and Michael Coates in 2010, among others.
The evidence
No placoderm fossils occur in rocks after the end of the Devonian despite good fish records, and fossil counts show the sharp turnover.
Debates and open questions
Why placoderms died out while sharks and ray-finned fish survived: size, habitat, slow reproduction or simple bad luck.
▸Late Devonian extinction set back Vertebrates move onto land (tetrapods)Strong evidence
The connection
Early tetrapods lived in shallow coastal and river waters hit by the Hangenberg event, about 359 million years ago, and most Devonian tetrapod lineages disappeared. Afterward comes 'Romer's Gap', some 15 million years with few tetrapod fossils, before survivors spread across land in the Carboniferous.
When and how
End of the Devonian, about 359 million years ago; studied by Jennifer Clack, Lauren Sallan and colleagues.
How sure are we?
Fossil counts show many tetrapod and fish lineages vanishing at the boundary; recent finds in Scotland partly fill Romer's Gap.
Debates and open questions
Whether Romer's Gap reflects a real collapse or a shortage of fossil-bearing rock; recent Scottish finds suggest the record is partly to blame.
▸Late Devonian extinction is one of the Big Five in Extinction & mass extinctionsWell established
The connection
The Late Devonian saw two main crises, about 372 and 359 million years ago, that devastated reefs, armored fish and many marine groups; roughly 70–80% of species vanished overall, estimates vary. It made the Big Five list in 1982, though the drop may reflect fewer new species appearing as much as more dying.
When and how
The Kellwasser (372 million years ago) and Hangenberg (359 million) events, named after German rock layers; counted in Raup and Sepkoski's 1982 tally.
The evidence
Black, oxygen-poor shale layers, carbon-isotope shifts and fossil counts show the losses; dating ties them to the end of two Devonian stages.
Debates and open questions
Causes are unclear: oxygen loss as land plants flushed nutrients into seas, volcanic eruptions, cooling, or several combined. Whether it was a true mass extinction is also argued.