托福 新托福 02 - The Origins of Cetaceans
题目
1 2 3 4 5 6 7 8 9 10
4.Pakicetus and modern cetaceans have similar
  • A.Hearing structures
  • B.Adaptations for diving
  • C.Skull shapes
  • D.Breeding locations
  • 正确答案:
    答案解析:
    答题统计
    答题统计

    登录 后才可以查看答案解析,还没有账号?

    还没有账号?马上 注册 >>

    阅读原文 中文译文

    It should be obvious that cetaceans-whales, porpoises, and dolphins-are mammals. They breathe through lungs, not through gills, and give birth to live young. Their streamlined bodies, the absence of hind legs, and the presence of a fluke1 and blowhole2 cannot disguise their affinities with land dwelling mammals.However, unlike the cases of sea otters and pinnipeds (seals, sea lions, and walruses, whose limbs are functional both on land and at sea), it is not easy to envision what the first whales looked like. Extinct but already fully marine cetaceans are known from the fossil record. How was the gap between a walking mammal and a swimming whale bridged? Missing until recently were fossils clearly intermediate, or transitional, between land mammals and cetaceans.

    Very exciting discoveries have finally allowed scientists to reconstruct the most likely origins of cetaceans. In 1979, a team looking for fossils in northern Pakistan found what proved to be the oldest fossil whale. The fossil was officially named Pakicetus in honor of the country where the discovery was made. Pakicetus was found embedded in rocks formed from river deposits that were 52 million years old. The river that formed these deposits was actually not far from an ancient ocean known as the Tethys Sea.

    The fossil consists of a complete skull of an archaeocyte, an extinct group of ancestors of modern cetaceans. Although limited to a skull, the Pakicetus fossil provides precious details on the origins of cetaceans. The skull is cetacean-like but its jawbones lack the enlarged space that is filled with fat or oil and used for receiving underwater sound in modern whales. Pakicetus probably detected sound through the ear opening as in land mammals. The skull also lacks a blowhole, another cetacean adaptation for diving. Other features, however, show experts that Pakicetus is a transitional form between a group of extinct flesh- eating mammals, the mesonychids, and cetaceans. It has been suggested that Pakicetus fed on fish in shallow water and was not yet adapted for life in the open ocean. It probably bred and gave birth on land.

    Another major discovery was made in Egypt in 1989. Several skeletons of another early whale, Basilosaurus, were found in sediments left by the Tethys Sea and now exposed in the Sahara desert. This whale lived around 40 million years ago, 12 million years after Pakicetus. Many incomplete skeletons were found but they included, for the first time in an archaeocyte, a complete hind leg that features a foot with three tiny toes. Such legs would have been far too small to have supported the 50-foot-long Basilosaurus on land. Basilosaurus was undoubtedly a fully marine whale with possibly nonfunctional, or vestigial, hind legs.

    An even more exciting find was reported in 1994, also from Pakistan. The now extinct whale Ambulocetus natans ("the walking whale that swam") lived in the Tethys Sea 49 million years ago. It lived around 3 million years after Pakicetus but 9 million before Basilosaurus. The fossil luckily includes a good portion of the hind legs. The legs were strong and ended in long feet very much like those of a modern pinniped. The legs were certainly functional both on land and at sea. The whale retained a tail and lacked a fluke, the major means of locomotion in modern cetaceans. The structure of the backbone shows, however, that Ambulocetus swam like modern whales by moving the rear portion of its body up and down, even though a fluke was missing. The large hind legs were used for propulsion in water. On land, where it probably bred and gave birth, Ambulocetus may have moved around very much like a modern sea lion. It was undoubtedly a whale that linked life on land with life at sea.

    1. Fluke: the two parts that constitute the large triangular tail of a whale

    2.Blowhole: a hole in the top of the head used for breathing


    众所周知,鲸类动物是哺乳动物,如鲸鱼、鼠海豚和海豚。它们用肺呼吸,而不是鳃,属于胎生。鲸类动物呈流线型的身体,后腿的消失,尾片和气孔的出现,这些特征都不能掩饰它们和陆生哺乳动物的相似之处。然而,想知道世上第一只鲸长什么样并非易事,不像还原海獭及鳍足类动物(四肢水陆两用如海豹,海狮,海象)的原貌那么简单。一些完全水生的鲸类动物虽然已经灭绝,但仍可通过化石来对它们进行考察。陆栖哺乳动物和海洋鲸类之间有何联系?近期发现的化石已经可以很清晰地帮助人们了解这个问题,以及他们之间的过渡关系。 科学家们通过一些令人振奋的发现重现了鲸类动物几近真实的起源。1979年,在巴基斯坦北部,一个寻找化石的考察队发掘到了最古老的鲸鱼化石。这块化石被官方命名为Pakicetus,以纪念人们发现它的地方。这块化石是在一条河的沉积岩中发现的,这条河有5200万年的历史,离古地中海不远。 Pakicetus包括一个完整原始动物的头盖骨,它的主人是现代鲸类的祖先。尽管只是个头盖骨,但它却提供了研究原始鲸类动物起源的珍贵信息。这个头盖骨和鲸类动物的很像,但它的下颌骨和现代鲸类略有不同,现代鲸类动物的下颌骨中含有额外的空间储存脂肪或者油脂来吸收水下的声音。Pakicetus的主人可能会像陆生哺乳动物那样通过张开的耳朵来探测声音。另外,这个头盖骨没有呼吸孔,而鲸类动物有,这便是鲸类动物为了适应水生环境的另一种适应性表现。然而,专家认为Pakicetus的其它特征表明它们是已灭绝的食肉哺乳动物(中兽科动物)和鲸类动物的过渡型。有人认为Pakicetus靠吃浅水的鱼类为生,未能适应在辽阔的大海里生活。它们很有可能在陆地进行生育繁殖。 1989年,在埃及有了另一个重大发现。人们在古地中海残留的沉积物中发现了另一类早期鲸鱼Basilosaurus的一些骨骸,这些骨骸如今暴露在撒哈拉大沙漠上。Basilosaurus生活在大约4000万年前,比Pakicetus鲸鱼晚了1200万年。尽管发现的这些骨骼并不完整,但这是专家们第一次在原始动物身上发现完整的后肢,它有三个小脚趾作为的足部特征。可这些后肢还太小,远无法支撑50英尺长的Basilosaurus在陆地行走。因此,Basilosaurus必定是完全水生的鲸鱼,它们的后肢已经不起任何作用,或者说已经退化。 1994年,巴基斯坦报道了一个更令人兴奋的发现。目前已经灭绝的鲸鱼Ambulocetus natans(可以步行的鲸类)4900万年前曾在古地中海生活过。比Pakicetus晚大约300万年,比Basilosaurus早900万年左右。幸运的是,被发现的Ambulocetus natans保留着完整的后肢。它的后肢很强壮,底部有长足,非常像现在的鳍足类动物。这些后肢使得他们既能在陆地行走又能在海里游行。虽然Ambulocetus natans保留了尾巴,但它们缺少现代水生鲸类动物用于行动的主要身体部位——尾片。不过,从Ambulocetus的脊椎结构上可以看出,即使缺少尾片,它们也能像现代鲸鱼那样通过身体背部的上下摆动来游走。大的后肢通常被当作是水中前行的发动机。在它们可能交配繁殖的陆地上,Ambulocetus行动起来非常像现代海狮。毫无疑问,鲸鱼是连接着陆地生命和海洋生命的物种。

    留言区中有很多我们对问题的解答喔, 登录后可以查看

    还没有账号?马上 注册 >>

    最新提问
    • wx_6697
      觉得B C 意思一样,不知道选哪个
    • wx_5576
      这道题C为什么对,E为什么不对?
    • wx_5576
      B为什么不能选啊?
    • wx_6697
      TPO30 passage 2 Q5我选的 D,不明白为啥不对?
    • wx_6697
      鑫哥,TPO6passage3Q5 答案是给错了吗?好多人都选A
    • wx_6697
      这题也很容易选错选成了D
    • wx_6697
      这道题A为什么错了
    • 芊儿
      为什么这道题不选c??a中的variety不是应该对应文中的differentiating 吗??求解!
    • wx_1000
      这道题不选E是因为太细节了吗
    • 王金阁
      这个题为什么不选C啊。。。
    • 芊儿
      这道题的D选项不是和文中的better able to reproduce in open settings相对应么??
    • 风荨火
      有大佬解释一下这个为啥选D嘛?
    • 以沫
      请问这个D 在哪里提现?为什么D错?
    • 芊儿
      第六题 的C选择为什么不对,感觉A是明显驳斥啊...
    • wx_6697
      鑫哥,这道题D是从哪里看出来的
    • wx_6697
      这题选的A,根据是Joly’s calculations clearly supported those geologists who insisted on an age for Earth far in excess of a few million years.想问鑫哥为啥不选A
    • wx_6697
      这题我选的是C依据是into a new habitat outside of its natural range, it may adapt to the new environment and leave its enemies behind.C为啥错了呢?鑫哥
    • wx_8861
      F选项的weather-related destruction在哪里体现了呢?原文最后一段的开头Among the costs里的costs是不是打错了?应该是coast?
    • wx_6697
      求问这道题B为啥不选,原文依据:viable seeds of pioneer species can be found in large numbers on some forest floors.
    • 与托福的斗争史
      与托福的斗争史 去解答 去解答
      这题为什么选C?
    • 小雨淅沥哗啦的下
      小雨淅沥哗啦的下 去解答 去解答
      B哪里错了
    • 小雨淅沥哗啦的下
      小雨淅沥哗啦的下 去解答 去解答
      B为啥不对
    • 李浩然
      B选项错误,是因为残缺么?
    • wx_100
      请问在做题的时候如何排除c呢。看了答案,感觉是该选a的,但是当时做题脑子一热,就特别钟爱c,也没看其他选项。。求敲醒。。
    • wx xxxxx
      请问鑫哥,这段开头有写As one pesticide replaces another为什么不是对应a new pesticide is developed?
    • wx_7695
      鑫哥,从哪里看出来这个masks 不是use呀,原文说了wear呀
    • haiyuqiao
      @鑫哥,这题the damage will continue 不应该对应前面的 the target species evolves resistance to it,然后As one pesticide replaces another,不应该是结束了time cycle 吗
    • wx_2065
      鑫哥,想知道E错在哪里?
    • wx_7695
      鑫哥,B选项 cannot extended to earlier geological periods. 原文说的意思是后来的进化无法估计吧
    • wx_2163
      B为什么不选
    • wx_7780
      鑫哥,这个哪里看不use了。BD是修饰错,C是无中生有,怎么能直接选出A?
    • 100
      看到第一句话,以为是中心句就选了A... 为什么不能选A呢
    • 100
      为什么选b?
    • gu33
      请问下 这里选D的原因是 因为 evolutionary approach 对应着 原文的 Rates of evolution 嘛? 这里我选了C。。不是很懂 插入句和 D的关系 求解答
    • 我是啦啦啦
      我是啦啦啦 去解答 去解答
      这个题A哪里错了?是因为主语不对吗?这个C比A多一步推理啊
    • haiyuqiao
      鑫哥,D选项里的19世纪出现了很多假设,原文中并没有提到啊
    • wx_7060
      为什么选a 呢。我觉得a是细节。F哪错了?
    • wx_1105
      我想问一下,这道题为什么不能选A呢?
    • wx_8122
      D为什么不选
    • wx_1655
      f选项哪里说了
    • chaulaw
      鑫哥,原文是below经济损害水平,D是一触发经济损害就用,这也对吗?
    • chaulaw
      interclan婚姻是对的吗?不是只在自己的family结婚扩大家族吗?
    • wx_6697
      鑫哥,这道题答案是不是错了,好多人选D 我也选的D求解答
    • wx_6697
      这道题应该是一道易错题,每个选项的都有,然而我选的A错了,求解
    • wx_6697
      鑫哥,这题的C是怎么得到的?B也没有找到啊?难道不是应该选B
    • wx_6697
      鑫哥,还有这个,好多人选A答案是不是错了
    • wx_6697
      求问D是从哪里得出来的,我选的B呀哎呀
    • wx_4185
      it is difficult to say how far they were intended to be portraits rather than generalized images 这句话怎么理解呢
    • 此楠楠
      请问下这个插入题怎么选的呢?
    • 此楠楠
      求鑫哥讲解下A选项。。。 Even though in error, Joly’s calculations clearly supported those geologists who insisted on an age for Earth far in excess of a few million years.