rebound after a mass extinction than their more sensitive neighbors. Never-
theless, both groups declined considerably. However, the unbuffered organisms
were the hardest hit, losing 90 percent of their genera compared with 50 per-
cent for the buffered group.
Surviving crinoids and brachiopods, which were highly prolific in the
Paleozoic, were relegated to minor roles during the succeeding Mesozoic era.
The spiny brachiopods, which were plentiful in the late Paleozoic seas, van-
ished entirely without leaving any descendants. The trilobites, which were
extremely successful during most of the Paleozoic, suffered final extinction
when the era ended. A variety of other crustaceans, including shrimps, crabs,
crayfish,and lobsters, occupied habitats vacated by the trilobites. The sharks,
regaining ground lost by the great extinction, continued to become the suc-
cessful predators they are today.
Figure 128Marine flora
and fauna of the Permian.
(Courtesy Field Museum of
Natural History)PERMIAN REPTILES