Assertion: blue whale's tail | /r/CapableOf | evolve into two rubbery flukes
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text: Its forelimbs had become stiff flippers, its trunk was elongated, its hind limbs were virtually non-existent and its tail had evolved into two rubbery flukes, which propelled the animal forward through the water as they were wafted up and down, rather than the side-to-side motion of a fish’s tail.