英语听力：2013-07-24 《恐龙的战争》3 顽强防御—17

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One of the curious things about sauropods is that they did have a swelling⁴ in the spinal⁵ cord in the neighborhood of their pelvis. It is sort of like a second brain to help control the back half of the body.

 

It’s called the sacro-lumbar expansion, a bundle of nerves which acts like a primitive⁶ brain controlling the movements of the legs and tail. The brain in a Sauroposeidon’s head is simply too small and far away to coordinate⁷ its front and back legs. So a second brain operates the back end of the animal. 

 

The reason why animals like Sauroposeidon have an enlargement in their hip⁸ is because there’s actually a lot going on back there. There are lots of muscles that are in the legs, and also muscles that are going through the tail. 

 

The primitive brain in its pelvis keeps Sauroposeidon’s legs and tail in sync with its body. Without it, they could never have grazed over such large territories or possibly, they wouldn’t have even been able to walk at all. This tiny bundle of nerves weighing just a few grams allows herds⁹ of Sauroposeidon to rule the great plains of the southern Midwest of America for almost 15 million years. 

 

Another plant eater couldn’t appear more different. It’s small, weak, and highly intelligent. But like Sauroposeidon, Parasaurolophus live in herds. They stick together and are constantly on the lookout¹⁰ for threats. But for Parasaurolophus, there’s a problem. Their eyes …

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