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1 A change of direction, usually by 180°. It commonly refers to a change of polarity of the geomagnetic field.

2 A form of homoplasy; resemblance between two taxa because one of them has gained a new character, then lost it again, and the other taxa has never gained it. Reversal by character loss is common; there is much doubt about whether it ever occurs by regaining a lost character.

Subjects: Earth Sciences and Geography.

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