托福阅读：TPO2(The Origins Of Cetaceans)原文及答案

　　参考答案

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　　文章逐句翻译

　　第一段：

　　It should be obvious that cetaceans-whales, porpoises, and dolphins-are mammals.

　　显而易见，鲸目动物，鲸鱼，鼠海豚，和海豚等属于哺乳动物。

　　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.

　　他们通过肺部，而不是鳃呼吸，并且直接生育有生命的下一代。流线型的身体，退化的后足，以及fluke和气孔的存在不能掩盖它们和陆生哺乳动物的亲缘关系。

　　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. 然而，跟海獭和鳍足类动物(海豹，海狮和海象等四肢都在陆地和海上)的情况不同，很难想象最初的鲸类动物的模样。

　　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.

　　灭绝的完全海洋鲸类已经在化石记录中被发现。鲸鱼是如何从陆生哺乳动物过渡进化到海生哺乳动物的?直到最近，清晰表现鲸鱼在从陆生哺乳动物到海生哺乳动物过渡时期的化石才被发现。

　　第二段：

　　Very exciting discoveries have finally allowed scientists to reconstruct the most likely origins of cetaceans.

　　这项非常令人兴奋的发现终于使科学家们能够重建鲸目动物最有可能的起源。

　　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.

　　1979年，一个小组在巴基斯坦北部地区找到了被证明是最古老的鲸鱼的化石。该化石被正式命名为Pakicetus，以纪念化石被发现所在的国家。

　　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.

　　Pakicetus被发现时被嵌在已有5200万年历史的河流沉积物形成的岩石中。形成这些沉积物的河流实际上离一个古海洋不远，那个古海洋即是特提斯海。

　　第三段：

　　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.

　　化石包括一具archaeocyte(现代鲸类动物的祖先的已灭绝的一种)的完整头骨。虽然仅是一具头骨，化石Pakicetus为鲸类动物的起源提供了珍贵的细节。

　　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.

　　头骨是鲸类动物的头骨，但是与现代鲸类动物的头骨相比，其颚骨缺乏用于接收水下声音的充满脂肪或油的扩大的空间

　　Pakicetus probably detected sound through the ear opening as in land mammals. The skull also lacks a blowhole, another cetacean adaptation for diving.

　　Pakicetus可能是开放的耳朵来侦测声音，正如陆生哺乳动物那样。头骨也缺乏一个气孔，而气孔是又一个鲸类动物用于潜水的适应性进化。

　　Other features, however, show experts that Pakicetus is a transitional form between a group of extinct flesh-eating mammals, the mesonychids, and cetaceans.

　　但是，专家发现，其他特征显示Pakicetus是一种介于中爪兽(一种已灭绝的食肉哺乳动物)和鲸类动物的过渡形式。

　　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.

　　这已经暗示，Pakicetus是以浅水鱼为食并且尚未适应开放海洋的生活。它可能在陆地上繁殖和生育。

　　第四段：

　　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.

　　另一个重大发现发生于1989年的埃及。几块龙王鲸(另一种早期鲸鱼)的骨骼被发现于特提斯海遗留下的沉积物中，并且现在在撒哈拉沙漠暴露出来。

　　This whale lived around 40 million years ago, 12 million years after. 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.

　　这种鲸鱼生活在大约4千万年前，比Pakicetus晚了1200万年。许多不完整的骨骼被发现，但其中包括一个在archaeocyte中首次发现的一个带有三个微小脚趾的起脚的作用的完整的后腿。

　　Such legs would have been far too small to have supported the 50-foot-long Basilosaurus on land.

　　这样的腿本来太小，远不足以支撑生活在陆地上的的50英尺长的龙王鲸。

　　Basilosaurus was undoubtedly a fully marine whale with possibly nonfunctional, or vestigial, hind legs.

　　龙王鲸是无疑是一个具有可能无功能的，或者说退化后肢的完全海洋鲸鱼。

　　第五段：

　　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.

　　一个更令人激动的发现是在1994年报道的，也来自巴基斯坦。已灭绝的走鲸(“会游泳的走动鲸鱼”) 生活在四千九百万年前的特提斯海洋。它生活在Pakicetus之后约3百万年的时期，但是比龙王鲸早9百万年。

　　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.

　　幸运的是，化石包括了后腿的一个完好部分。这些腿很强壮并且有着长脚，这和现代鳍足类动物很像。

　　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.

　　这些腿肯定在陆地及海里都能发挥作用。这种鲸鱼保留了尾巴(现代鲸类动物运动的主要结构)，但是没有fluke。

　　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.

　　但是，脊椎的结构显示，即使缺少fluke，走鲸通过上下移动其身体后部游动，这一点类似于现代鲸类动物。

　　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

　　巨大的后腿被用于在水中推进。在它们可能繁殖及生育的陆地上，走鲸可能生活得很像现代的海狮了。这无疑是联系陆生生命与海生生命的一种鲸鱼。