Most saltwater fish may have evolved from a freshwater ancestor, according to a new study that traces the family tree of both marine and freshwater fish.
The finding may seem topsy-turvy given that life originated in the oceans, but the results could help explain why the sea is relatively low in diversity compared with the land. The ocean takes up 70 percent of the Earth's surface, but contains only 15 percent to 25 percent of the Earth's total estimated species.
"It's a striking pattern that we haven't really explained yet," said study researcher John Wiens, a professor of ecology and evolution at Stony Brook University in New York.
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