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SSS 2009-01-13

时间:2010-05-17 02:35来源:互联网 提供网友:木渐浅。   字体: [ ]
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    (单词翻译:双击或拖选)

This is Scientific American's 60-Second Science. I'm Karen Hopkin. This will just take a minute.

A bird in flight is a thing of beauty. Even their takeoffs and landings usually look effortless. But pterodactyls? Well, that’s another story. Scientists have long assumed that pterodactyls, also called pterosaurs, flew just like birds, and launched themselves using their hind1 legs. Now a biologist at Johns Hopkins says that can’t be true. Instead, he says that pterosaurs needed all four limbs for liftoff.

Modern birds use their legs to launch and their wings to stay aloft. Once they’re in the air, their hind limbs are essentially2 payload, carried along for the ride. That arrangement presents a problem. A bird’s legs have to be muscular enough to get Tweety off the ground, but not so big that they drag him down. That limits how big a bird can be. Some pterosaurs, on the other hand, were the size of a giraffe. And looking at the bones of three different pterodactyl species, the Hopkins scientist concludes that there’s no way those legs were strong enough to get that bulk airborne. Instead, he says a pterosaur used all four limbs, leapfrogging forward on its knuckles3, to propel itself into the air. Maybe not a thing of beauty. But it must have been something to see.

Thanks for the minute for Scientific American's 60-Second Science. I'm Karen Hopkin.


点击收听单词发音收听单词发音  

1 hind Cyoya     
adj.后面的,后部的
参考例句:
  • The animal is able to stand up on its hind limbs.这种动物能够用后肢站立。
  • Don't hind her in her studies.不要在学业上扯她后腿。
2 essentially nntxw     
adv.本质上,实质上,基本上
参考例句:
  • Really great men are essentially modest.真正的伟人大都很谦虚。
  • She is an essentially selfish person.她本质上是个自私自利的人。
3 knuckles c726698620762d88f738be4a294fae79     
n.(指人)指关节( knuckle的名词复数 );(指动物)膝关节,踝v.(指人)指关节( knuckle的第三人称单数 );(指动物)膝关节,踝
参考例句:
  • He gripped the wheel until his knuckles whitened. 他紧紧握住方向盘,握得指关节都变白了。
  • Her thin hands were twisted by swollen knuckles. 她那双纤手因肿大的指关节而变了形。 来自《简明英汉词典》
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TAG标签:   SSS  pterodactyl
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