Extinction rates appear to have been higher than the background rate for an extended period lasting the last 20–25 million years of the Devonian.During this period, about eight to ten distinct events can be seen, of which two stand out as particularly severe.
The surviving taxa show morphological trends through the event.
The continent of Siberia occupied the Northern Hemisphere, while an equatorial continent, Laurussia (formed by the collision of Baltica and Laurentia), was drifting towards Gondwana, closing the Iapetus ocean.
The Caledonian mountains were also growing across what is now the Scottish Highlands and Scandinavia, while the Appalachians rose over America. Plants, which had been on land in forms similar to mosses, liverworts, and lichens since the Ordovician, had just developed roots, seeds, and water transport systems that allowed them to survive away from places that were constantly wet—and consequently built huge forests on the highlands.
The brims are thought to have served a respiratory purpose, and the increasing anoxia of waters led to an increase in their brim area in response.
The shape of conodonts' feeding apparatus varied with δ 97 per cent of vertebrate species disappeared, with only smaller forms surviving.