however. The relatively low extinction rates were probably due to a limited
number of extinction-prone species following the late Devonian extinction.
When the glaciers departed, the first reptiles emerged to displace the
amphibians as the dominant land vertebrates. The climate of the tropics
became more arid, and the swamplands began to disappear. Land once cov-
ered with great coal swamps began to dry out as the climate grew colder.PANGAEA
Between 360 and 270 million years ago, Gondwana and Laurasia converged
into the supercontinent Pangaea (Fig. 115), whose name comes from Greek
meaning “all lands.” The massive continent had an area of about 80 million
square miles and covered 40 percent of Earth’s surface. It straddled the equa-
tor and extended practically from pole to pole, with an almost equal amount
of land in both hemispheres. Today, in contrast, two-thirds of the continents
lie north of the equator.A single great ocean called Panthalassa stretched unin-
terrupted across the planet, with all the continents huddling to one side. Over
the ensuing periods, smaller parcels of land continued to collide with the
supercontinent until it reached its peak size at the end of the Triassic about
210 million years ago.Figure 115The
supercontinent Pangaea
250 million years ago.
Historical Geology
PANGAEAPangaeaPangaea Tethys