鳍状肢可能确实是水生生物的必要反应，海龟、鲸鱼和儒艮也有鳍状肢。
Flippers may indeed be a necessary response to aquatic life, turtles, whales, and dugongs also have them.
它们向我们展示了进化过程中半成品的样貌，而完全进化的结果是鲸鱼和儒艮。
They show us what the intermediates might have been like, on the way to extreme cases such as whales and dugongs.
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