Paleozoic.It also explains why the reptiles, which adapt readily to hot, dry cli-
mates, replaced the amphibians as the dominant land animals.
The sea level lowered dramatically during the formation of Pangaea,
which drained the interiors of the continents (Fig. 129).The drop in sea level
caused the inland seas to retreat, producing a continuous, narrow continental
margin around the supercontinent Pangaea.This, in turn, reduced the amount
of shoreline, confining marine habitats to nearshore environments.This had a
major influence on the extinction of marine species. Moreover, unstable
nearshore conditions resulted in an unreliable food supply. Many marine
species unable to cope with the limited living space and food supply died out
in tragically large numbers.
The extinction was particularly devastating to Permian marine fauna.
Half the families of aquatic organisms, 75 percent of the amphibian families,
andover 80 percent of the reptilian families, representing more than 95 per-
cent of all known species, abruptly disappeared. In effect, the extinction left
Figure 129The
paleogeography (ancient
landforms) of the upper
Paleozoic in North
America.PERMIAN REPTILESPanthalassa
SeaPanthalassa
Sea
LAURENTIA
Acadian MountainsAcadian Mountains