By CARA GIAIMO New York Times
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Put a dolphin’s front flipper in an X-ray machine, and you will see a surprise: an arc of humanlike finger bones. The same goes for a sea turtle, a seal, a manatee and a whale. All of these animals had four-legged ancestors that lived on land. As their various lineages adapted to life in the water, what had been multidigit limbs slowly transformed into flippers.