Historical Geology Understanding Our Planet\'s Past

edge of Gondwana and located on the Antarctic Circle. A later collision

between North America and Gondwana near the end of the Cambrian about

500 million years ago created an ancestral Appalachian range that continued

into western South America long before the Andes formed. North America

then broke away from Gondwana and linked with Greenland and Eurasia to

form Laurasia about 400 million years ago. Eurasia, the largest modern conti-

nent, assembled from about a dozen individual continental plates that welded

together at the end of the Proterozoic.

A preponderance of evidence for the existence of Gondwana includes

fossilized finds of a mammal-like reptile called Lystrosaurus in the Transantarc-

tic Range of Antarctica. They indicate a commonality with southern Africa

and India, the only other known sources of Lystrosaurus fossils.A fossil of a

South American marsupial in Antarctica, which acted as a land bridge between

the southern tip of South America and Australia, lends additional support to

the existence of Gondwana. Further evidence for Gondwana includes fossils

of a reptile called Mesosaurus in eastern South America and South Africa.

After discussing life in the Cambrian, the next chapter takes a look at the

early vertebrate life-forms of the Ordovician period.

Figure 59During the
Paleozoic, the southern
continents combined into
Gondwana.

Historical Geology

AFRICA

SOUTH AMERICA

ANTARCTICA

AUSTRALIA

INDIA