对龙翼的描述基本上有两种-一对连接在脊椎上的第三肢，或者是蹼状的前肢。
Dragon wings are usually depicted in one of two ways-a third pair of limbs connected to the backbone, or webbed forearms.
事实上，海洋无脊椎动物不变的外壳是通过1亿年前的沉积物发现的。
Indeed, unaltered shells of marine invertebrates are known from deposits over 100 million years old.
事实上，关于脊椎存在的目的有很多的猜测。
In fact, speculation abounds about what purpose the spines serve.
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