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From an evolutionary standpoint, Amazonian fish
species come from an ancient line of groups that were already established
nearly 60 million years ago (they have changed little since that time). The
most commonly accepted theory regarding the existence of most Amazon species
is that their precursors evolved during a period when what is now South
America, Africa, southern Asia and Australia were a single continent called
Gondwanaland.
Upon the separation of these continents, these mutual ancestors
then evolved independently. Today, although the remnant of this relationship
between the Amazonian, African and Australian fish remains evident, their
modern descendents have speciated into thousands of endemic varieties.
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