Great%20American%20Interchange

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Great American Interchange
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The isthmus of Panama connects the North American
and South American continents.
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It became a complete land bridge for the first
time about 3,000,000 years ago, in the Middle
Pliocene.
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At the same time, the Andes Mountains were
undergoing their final uplift, which doubled
their height from 2000 to 4000 meters. This
led to dramatic climatic changes in South America
at exactly the time that significant faunal
exchanges were occurring between the two
continents.
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Before this exchange, which has come to be known
as the Great American Interchange, each continent
had 26 families of land mammals. About 16
families from each dispersed to the other
continent during the interchange. Of the North
American mammals, 26 genera dispersed southward,
mainly in the Late Pliocene/Early Pleistocene
(about 2.5 million years ago). At the same time,
12 genera of South American mammals dispersed
northward.
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The fauna that was exchanged between NA and SA
was one that was adapted to a savanna type
community. This suggests that this must have
been the environment of the isthmus when the
exchange took place.
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Although the percentages of dispersing mammals
was similar for the two continents, the North
American mammals fared better in South America
than their South American counterparts did in
North America. In South America, 50 of the
living land mammal genera are descended from
North American immigrants. The corresponding
figure for South American descendants among North
American mammals is only 29.1.
Great American Interchange migrants. Those with
a cross by their name became extinct in their new
continent.
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What was the reason for the greater success of
the immigrants from North America?
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It has also been suggested that the North
American mammals may have been shaped by millions
of years of competition between mammal groups in
the Northern Hemisphere, while South American
mammals had been protected in a relatively
isolated environment. It appears that size may
have played a role. Larger species were more
likely to go extinct, and South American species
were larger than North American ones.
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Other notable factors All 13 species of endemic
South American ungulates went extinct, probably
because they were unable to cope with North
American carnivores or with competition from
North American ungulates.
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An interesting result. Tapirs and llamas
originally dispersed from North America. They
later became extinct here, but survived in South
America. As a result, both groups show a disjunct
distribution in which their surviving relatives
are found in Asia.