dwindle when the crisis subsided and other groups recovered.Their prosper-
ity during the late Devonian signifies that less fortunate species had suc-
cumbed to the effects of climatic cooling. Large numbers of brachiopod
families also died out at the end of the period.
The extinction did not identically affect all species that shared the same
environments, however. Many Gondwanan fauna survived the onslaught due to
the scarcity of reef builders and other warm-water species prone to extinction.Figure 98A collection of
ammonoid shells from a
formation in Arkansas.
(Photo by M. Gordon Jr.,
courtesy USGS)
Historical Geology