And occasionally we still find whales with the vestiges of tiny hind limbs.

并且我们偶尔仍能发现鲸鱼残留着微型后肢。

Eventually, their front limbs became flippers and their hind limbs became weak and unnecessary.

最终，它们的前肢变成了鳍状肢，而它们的后肢变得虚弱和多余。

Now, this can be a little confusing because both types have three claws on their hind limbs.

现在，这可能有点混乱，因为这两种类型树懒的后肢上都有三个爪子。

Snake embryos, for example, sprout hind limb buds.

比如说，蛇的胚胎萌发了后肢芽。

Birds only use their hind limbs, their legs, for walking on the ground.

鸟类只用它们的后肢， 它们的腿，在地上行走。

Another major category in differences in dinosaurs is in the hind limbs.

恐龙差异的另一个主要类别是后肢。

But if the hind limbs couldn't do the same thing, what did they do?

但如果后肢不能做同样的事情，它们会做什么呢？

JACQUES GAUTHIER: What's this dinosaur doing with these aerodynamic feathers coming off their hind limbs?

JACQUES GAUTHIER：这只恐龙用后肢上脱落的空气动力羽毛做什么？

If Microraptor couldn't splay its hind limbs, how did it use its leg feathers in flight?

如果小盗龙无法张开后肢，它是如何利用腿部羽毛来飞行的呢？

GAUTHIER: They certainly can't flap with their hind limbs.

高希尔：它们当然不能用后肢拍打。