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托福听力TPO10原文 Lecture 1-智课教育旗下智课教育
下面就让小编来为大家介绍一下托福听力TPO10原文中Lecture 1的文本内容吧，大家要好好把握，这些都是非常有价值的材料，同时，大家也可以登录智课教育论坛进行TPO练习辅导，希望能够给准备托福听力的同学带来帮助。
TPO 10 Lecture 1Marine BiologyNarrator
Listen to part of a lecture in a Marine Biology ClassProfessor
We know whales are mammals and that they evolved fromland creatures. So the mystery is figuring out how they becameocean dwellers. Because until recently there was no fossil recordof what we call “the missing link”- that is evidence of speciesthat show the transition between land-dwelling mammals andtoday’s whales. Fortunately, some recent fossil discoveries havemade the picture a little bit clearer.
For example, a few years back in Pakistan, they found theskull of a wolf-like creature. It was about 50 million years old.Scientists had seen this wolf-like creature before, but this skullwas different. The ear area of the skull had characteristics seenonly in aquatic mammals, specifically whales.
Uh, well, then also in Pakistan they found a fossil of anothercreature, which we call Ambulocetus Natans. That’s a mouthful,eh? The name Ambulocetus natans comes from Latin of course,and means “walking whale that swims”. It clearly had fourlimbs that could have been used for walking. It also had a longthin tail, typical of mammals, something we don’t see in
today’s whales. But, it also had a long skeletal structure. Andthat long skeletal structure suggests that it was aquatic.
And very recently in Egypt, they found a skeleton of
Basilosaurus. Basilosaurus was a creature that we’ve alreadyknown about for over a hundred years. And it has been linked tomodern whales because of its long whale-like body. But this newfossil find showed a full set of leg bones, something we didn’thave before. The legs were too small to be useful. They weren’teven connected to its pelvis and couldn’t have supported itsweight. But it clearly shows Basilosaurus’s evolution from landcreatures. So that’s a giant step in the right direction. Even
better, it establishes Ambulocetus natans as a clear link betweenthe wolf-like creature and Basilosaurus.
Now these discoveries don’t completely solve the mystery. Imean, Ambulocetus is a mammal that shows a sort of bridgebetween walking on land and swimming. But it also is verydifferent from the whales who know today. So really we areworking just a few pieces of a big puzzle.
Um…a related debate involved some recent DNA studies.Remember, DNA is the genetic code for any organism. And whenthe DNA from two different species is similar, it suggests thatthose two species are related. And when we compared somewhale DNA with DNA from some other species, we got quite asurprise. The DNA suggests that whales are descendants of thehippopotamus. Yes, the hippopotamus! Well, it came as a bit of ashock. I mean, that a four-legged land and river dweller could bethe evolutionary source of a completely aquatic creature up to 25times its size? Unfortunately this revelation about the
hippopotamus apparently contradicts the fossil record, whichsuggests that the hippopotamus is only a very distant relative ofthe whale, not an ancestor. And of course as I mentioned, thatwhales are descended not from hippos but from that distantwolf-like creatures.
