Part I
Professor: We know whales are mammals and that they evolved from land creatures. So the mystery is figuring out how they became ocean dwellers. Because until recently there was no fossil record of what we call “the missing link” – that is evidence of species that show the transition between land-dwelling mammals and today's whales. Fortunately, some recent fossil discoveries have made the picture a little bit clearer.
For example, a few years back in Pakistan, they found the skull of a wolf-like creature. It was about 50 million years old. Scientists had seen this wolf-like creature before, but this skull was different. The ear area of the skull had characteristics seen only in aquatic mammals, specifically whales. Uh, well, then also in Pakistan, they found a fossil of another creature, which we call Ambulocetus Natans.
这个头骨的耳朵区域具有仅见于水生哺乳动物，特别是鲸鱼的特征。
1. mammal 哺乳动物，rodent 啮齿动物，amphibian 两栖动物，reptile 爬行动物，mollusk 软体动物，arthropod 节肢动物
2. dweller|ˈdwelə(r)|
noun. a person or an animal that lives in the particular place that is mentioned 居民；居住者；栖身者
E.g.: But in some respects cave dwellers were far cleverer than us.
但是在某些方面穴居人要比我们聪明得多。
3. the missing link
something, such as a piece of information, that is necessary for sb to be able to understand a problem or in order to make sth complete （理解问题或使事物完整的）必要的环节，不可缺少的一环
E.g.: The missing link is action on trade talks.
目前缺失的一环是贸易谈判方面的行动。
4. aquatic |əˈkwætɪk|
adj. growing or living in, on or near water 水生的；水栖的
E.g.: The pond is quite small but can support many aquatic plants and fish.
池塘虽小，但能为许多水生植物和鱼类提供足够的养分。
5. Ambulocetus Natans
Ambulocetus is a genus of early amphibious cetacean from the Kuldana Formation in Pakistan, roughly 48 or 47 million years ago during the Early Eocene 走鲸属于早期两栖鲸类，大约在始新世早期的4800或4700万年前，是已知的最完整的始新世鲸类动物之一，有助于研究鲸类动物的进化和从陆地到海洋的过渡。
Part II
That's a mouthful, eh? The name Ambulocetus Natans comes from Latin of course, and means “walking whale that swims”. It clearly had four limbs that could have been used for walking. It also had a long thin tail, typical of mammals, something we don't see in today's whales. But, it also had a long skeletal structure. And that 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 had already known about for over a hundred years. And it has been linked to modern whales because of its long whale-like body. But this new fossil find showed a full set of leg bones, something we didn't have before.
The legs were too small to be useful. They weren't even connected to its pelvis and couldn't have supported its weight. But it clearly shows Basilosaurus's evolution from land creatures. So that's a giant step in the right direction. Even better, it establishes Ambulocetus as a clear link between the wolf-like creature and Basilosaurus.
因为它有长长的鲸鱼般的身体，所以它被认为与现代的鲸鱼有关系。
1. mouthful |ˈmaʊθfʊl|
adj. a word or a phrase that is long and complicated or difficult to pronounce 又长又拗口的词（或短语）
E.g.: It's called the Pan-Carib-bean Disaster Preparedness and Prevention Project, which is quite a mouthful.
它被称为 the Pan-Caribbean Disaster Preparedness and Prevention Project（泛加勒比备灾防灾项目），名称相当冗长拗口。
2. limb|lɪm|
noun. an arm or a leg; a similar part of an animal, such as a wing 肢；臂；腿；翼；翅膀
E.g.: For a while, she lost the use of her limbs.
好一会儿她四肢都动弹不得。
3.skeletal |ˈskelətl|
adj. connected with the skeleton of a person or an animal 骨骼的
E.g.: the skeletal remains of seven adults
7 具成人遗骸
4. Basilosaurus
noun. Basilosaurus (meaning "king lizard") is a genus of large, predatory, prehistoric archaeocete whale from the late Eocene, approximately 41.3 to 33.9 million years ago. 龙王鲸，又名械齿鲸，已经绝种的古代海洋哺乳动物，现代鲸鱼的近亲，是鲸下目中的一个属，生存于4,000万至3,500万年前的始新世晚期。龙王鲸刚开始被误认为是巨大的海洋爬虫类的化石，所以被命名为帝王蜥蜴。
5. pelvis|ˈpelvɪs|
noun. the wide curved set of bones at the bottom of the body that the legs and spine are connected to 骨盆
E.g.: Your hips or pelvis is made up of 5 bones.
你的屁股/骨盆是由5块骨头构成的。
Part III
Now these discoveries don't completely solve the mystery. I mean, Ambulocetus is a mammal that shows a sort of bridge between walking on land and swimming. But it also is very different from the whales who know today. So really we are working with 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 when the DNA from two different species is similar, it suggests that those two species are related. And when we compared some whale DNA with DNA from some other species, we got quite a surprise. The DNA suggests that whales are descendants of the hippopotamus. Yes, the hippopotamus!
我的意思是，Ambulocetus作为一种哺乳动物，它似乎将在陆地上行走和水中游泳连接起来。
1. bridge |brɪdʒ|
noun. a thing that provides a connection or contact between two different things 起联系作用的事物；桥梁；纽带
E.g.: Cultural exchanges are a way of building bridges between countries.
文化交流是各国之间建立联系的纽带。
2. piece of the puzzle
part of the solution to a question or problem; a piece of information that helps you to understand part of a difficult question or mystery 理解或解决问题的部分办法、部分信息
E.g.: Researchers are close to finding a solution, but they haven't found the final pieces of the puzzle.
研究人员几乎可以找到解决方案了，但就差最后几条线索了。
3. genetic |dʒəˈnetɪk|
adj. connected with genes (= the units in the cells of a living thing that control its physical characteristics) or genetics (= the study of genes ) 基因的；遗传学的
E.g.: The offspring contain a mixture of the genetic blueprint of each parent.
子女身上遗传了父母双方的基因型板。
4. descendant |dɪˈsendənt|
noun. something modern which developed from an older thing can be called a descendant of it 派生物;衍生物;后代产物
E.g.: They are the descendants of plants imported by the early settlers.
它们是早期移民带来的一些植物的后代。
5. hippopotamus |ˌhɪpəˈpɒtəməs|
noun. a large heavy African animal with thick dark skin and short legs, that lives in rivers and lakes 河马
E.g.: A hippopotamus surfs the waves off the coast of Gabon.
一头河马在加蓬的海岸附近冲浪。
Part IV
Well, it came as a bit of a shock. I mean, that a four-legged land and river dweller could be the evolutionary source of a completely aquatic creature up to 25 times its size?Unfortunately, this revelation about the hippopotamus apparently contradicts the fossil record, which suggests that the hippopotamus is only a very distant relative of the whale, not an ancestor. And of course as I mentioned, that whales are descended not from hippos but from that distant wolf-like creature.
So we have contradictory evidence. And more research might just raise more questions and create more controversies. At any rate, we have a choice. We can believe the molecular data, the DNA, or we can believe the skeleton trail, but unfortunately, probably not both.
我的意思是，一个四足的可以同时生活在陆地和河流的动物，居然可能是一个体型比它大25倍的完全水生生物的进化源头？
1. up to
as far as a particular number, level, etc. 到达（某数量、程度等）；至多有
E.g.: The temperature went up to 35˚C.
气温上升到了35摄氏度。
2. revelation |ˌrevəˈleɪʃn|
noun. a fact that people are made aware of, especially one that has been secret and is surprising 被暴露的真相；被曝光的内情
E.g.: The book includes many shocking/startling revelations about the mayor's personal life.
这本书包括许多关于市长个人生活的令人震惊/惊人的内情。
3. be descended from
to be related to sb who lived a long time ago 是某人的后裔
E.g.: He claims to be descended from a Spanish prince.
他声称是一位西班牙王子的后裔。
4. controversy |ˈkɑ:ntrəvɜ:rsi|
noun. public discussion and argument about sth that many people strongly disagree about, disapprove of, or are shocked by （公开的）争论，辩论，论战
E.g.: The President resigned amid considerable controversy.
总统在一片争论声中辞职。
5. at any rate
used to say that a particular fact is true despite what has happened in the past or what may happen in the future （强调事情的真实性）无论如何，不管怎样
E.g.: I may be away on business next week but at any rate I'll be back by Friday.
我下周可能要出差，但无论如何，我最晚星期五回来。
6. molecule |ˈmɒlɪkju:l|
noun. the smallest unit, consisting of a group of atoms, into which a substance can be divided without a change in its chemical nature 分子
E.g.: A molecule of water consists of two atoms of hydrogen and one atom of oxygen.
水分子由两个氢原子和一个氧原子构成。
7. trail |treɪl|
noun. a long line or series of marks that is left by sb/sth 痕迹，踪迹，足迹
E.g.: The hurricane left a trail of destruction behind it.
飓风过后满目疮痍。
Part V
Um...and there have been some other interesting findings from DNA research. For a long time, we assumed that all whales that had teeth including sperm whales and killer whales were closely related to one another. And the same for the toothless whales, like the blue whale and other baleen whales, we assumed that they be closely related.
But recent DNA studies suggest that that's not the case at all. The sperm whale is actually closely related to the baleen whale, and it's only distantly related to the toothed-whales. So that was a real surprise to all of us.
抹香鲸实际上与须鲸关系密切，与齿鲸的关系较远。
1. sperm whale 抹香鲸, killer whale 虎鲸, blue whale 蓝鲸, baleen whale 长须鲸
2. the case
the true situation 实情；事实
E.g.: It is simply not the case that prison conditions are improving.
监狱条件得到改善的情况绝非事实。
