<P> 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 Kellwasser event was preceded by a longer period of prolonged biodiversity loss . The fossil record of the following first 15 million years of the Carboniferous is largely void of terrestrial animal fossils, likely related to losses during the end - Devonian Hangenberg event . This period is known as Romer's gap . </P> <P> The Kellwasser event, named for its locus typicus, the Kellwassertal in Niedersachsen, Germany, is the term given to the extinction pulse that occurred near the Frasnian--Famennian boundary . Most references to the "Late Devonian extinction" are in fact referring to the Kellwasser, which was the first event to be detected based on marine invertebrate record . There may in fact have been two closely spaced events here as shown by the presence of two distinct anoxic shale layers . </P> <P> The Hangenberg event sits on or just below the Devonian--Carboniferous boundary and marks the last spike in the period of extinction . It is marked by an anoxic black shale layer and an overlying sandstone deposit . Unlike the Kellwasser event, the Hangenberg event affected marine and terrestrial habitats . </P> <P> The extinction events were accompanied by widespread oceanic anoxia; that is, a lack of oxygen, prohibiting decay and allowing the preservation of organic matter . This, combined with the ability of porous reef rocks to hold oil, has led to Devonian rocks being an important source of oil, especially in the USA . </P>

What plants and animals survived after the late devonian