Five Mass Extinctions

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Five mass extinctions in history of life (sixth starting now):  250 million years ago (Permian) was the greatest.  Gases . . . temperatures soared, seas stagnated then died.  Two lines of reptiles survived:  tuatara and dinosauroids.

When North and South America were connected:  armadillos, anteaters, possums went north; dogs, bears, cats wet south.  Three million years later . . . the dodo—killed off by Dutch sailors and especially their monkeys and pigs.  Single egg.

Since then, alien invaders have been causing extinctions at an ever increasing rate, especially on islands.  On Guam the brown tree snake, a nocturnal bird-hunter, was introduced from New Guinea and wiped out the birds, causing the populations of insects and spiders to increase dramatically.

Not all islands are at sea—Amazonian forest being fragmented into islands.  Experiment in various patches.  Trees at edge were killed by wind and drying.  Birds, monkeys, and insects dropped.  Some local extinctions caused by domino effect; some species are “key”, e.g. peccaries that make wallows used by frogs.

Earth’s forest reduced to one-tenth—therefore possibly fifty percent of species gone.  As always, the specialists are the most vulnerable (e.g. the panda).

Black bears are generalists:  worms, grubs, ants.  Ag com. Now as prehistorically in America, thanks to dumps.