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To prove it they thought they needed just two fossils.
他们认为证明这一观点只需要两块化石
They needed the first tetrapod, the very first land walking creature with four legs with five toes
他们需要找到第一只四足动物，第一只具备四肢和五趾的陆行动物
and they needed the fish from which it came, a fish that could grow legs.
他们还需要找到它起源的那条鱼，一条能长出腿的鱼
Find these two fossils, compare them and in the differences between them
找到这两块化石，对它们进行比较，根据它们之间的区别
we would learn the reason why a fish had developed legs.
我们就能了解鱼进化出腿的原因
They had one huge clue to set them off:
有一条重要线索引导科学家进行探寻
they knew this evolution must have happened 400 million years ago, in the Devonian era.
他们知道这一进化过程肯定发生在4亿年前的泥盆纪
The Devonian is so long ago that barely any rock can now be found from it, let alone fossils,
泥盆纪距今甚为久远，如今那个时代的岩层已难觅踪迹，更不用说化石了
but academics knew that before it nothing walked and after it everything did,
不过学者们知道，在此之前没有能行走的动物，而这之后却是谁都能行走
so the evolution of legs must have happened then and they thought they knew something else.
所以腿的进化必然发生在那个年代，而且他们还了解别的情况
Textbooks said it was a time of blistering heat when almost nothing could live on the land, not even plants.
教科书中记载当时的气候酷热难耐，任何生物都无法在陆地上生存，甚至连植物也不例外
It meant most life survived not on land but in the water.
也就是说大部分生物并非生活在陆地上，而是呆在水中
This was the age of fish and one of them, the one with the beginning of legs, was the first fossil they needed to find.
那是鱼的时代，而其中一条鱼拥有腿的雏形，那就是他们要找的化石。
