Assertion: dugong's fin | /r/CapableOf | use up-and-down motion
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Source sentences:
text: When the Dugongidae appeared at this time, sirenians had evolved the characteristics of modern variety, including an aquatic streamlined body with flipper-like front legs with no hind limbs, and a powerful tail with horizontal caudal fins which uses an up-and-down motion to move them through the water.