The Late Devonian crises

Two clocks

The late part of the Devonian period saw two major extinction pulses: one at the Frasnian–Famennian boundary about 374 million years ago, and the Hangenberg event about 359 million years ago.

What the evidence shows

• A survey of more than 1,250 kinds of vertebrates found that the Hangenberg event hit them hardest, with long-term losses of over half their diversity, in both marine and freshwater faunas.
• Afterwards, groups that had been scarce, including four-limbed animals, ray-finned fish and sharks, diversified and came to dominate.
• Geochemical evidence indicates that oxygen-free, sulfide-rich water reached the sunlit upper ocean during the Hangenberg crisis.

What is uncertain

• The ocean chemistry evidence comes from marine settings. It does not establish conditions in every river or lake.

Sources

• Sallan & Coates 2010. End-Devonian extinction and a bottleneck in the early evolution of modern jawed vertebrates. PNAS. (opens the publisher’s site)

  What it supports: Two Late Devonian extinction pulses (about 374 and 359 million years ago) and the heavy losses among vertebrates at the second, the Hangenberg event.

• Wang et al. 2025. Photic-zone euxinia had a major role in the Devonian-Carboniferous boundary mass extinction. Communications Earth & Environment. (opens the publisher’s site)

  What it supports: Evidence that oxygen-free, sulfide-rich water reached the sunlit upper ocean during the Hangenberg crisis. It concerns marine settings, not every river or lake.

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