因为它们是两足动物，它们的手臂可以自由地进化出拍打的翅膀，这在当时的爬行动物中是不可能的。

Because they were bipedal, their arms were free to evolve flapping flight, which cannot be said for other reptiles of their time.

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从那以后，科学家们已对许多深层同源性的案例有了更为详细的认识。 比如卡洛尔博士和他的同事们最近就弄清楚了果蝇翅膀上的斑点是如何通过模块功能置换而进化出来的。

Dr. Carroll and his colleagues, for example, recently figured out how the spots on a fly’s wing evolved through rewiring modules.

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现在问题来了，为什么在庞大的恐龙族谱中，有这样一个分支会先进化出如此古怪的外表而不是翅膀呢？

That did raise the question, though, of why one twig of the great dinosaur tree had developed such strange outer vestments, even before it developed wings.

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