英语听力：2013-07-14 《恐龙的战争》3 顽强防御—13

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If you look at the size of their brain, you actually have to kind of wonder how these animals managed.

 

But they did manage. Physical size makes up for every other shortcoming. Surviving for 15 million years, these mammoth² creatures spread out across the globe onto every continent except Antarctica. But there’s another dinosaur³ that doesn’t rely on size. It uses an even more unusual trick to stay alive, the most sophisticated communication system ever developed in the prehistoric⁴ world. 

 

It’s one vegetarian⁵ that lacks any obvious weaponry. A Parasaurolophus is a duckbill.

 

Named for its ducklike beak⁶, weighing in at almost four tons, it’s not tiny, but taking on a seven-ton predator⁷ like a T-Rex would be suicide. 

 

They have no fangs⁸, no armor at all, no spikes⁹ or horns anywhere on the body. They seem to be large, vulnerable targets. 

 

Parasaurolophus range across a vast area more than 160,000 square kilometers from Alberta, Canada, to New Mexico, a region with more than its fair share of vicious predators¹⁰. 

 

What has puzzled all of us is, how did they protect themselves? 

 

The most important clue to this mystery is buried inside their skull¹¹. Parasaurolophus has the biggest brain of all herbivores and one part of that brain is abnormally large—the area responsible for hearing … 

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