1. Their streamlined bodies, the absence of hind legs, and the presence of a fluke and blowhole cannot disguise their affinities with land dwelling mammals.
短語：cannot disguise their affinities with：不能掩蓋它們與…的姻親關(guān)系
land dwelling mammals：陸棲哺乳動物
釋義：鯨類動物的流線型身體，后肢的缺少，三角狀尾鰭的存在以及頭頂?shù)某鰵饪祝ㄒ陨隙际堑湫偷暮Ｑ髣游锾攸c(diǎn)）并不能掩蓋它們與陸棲哺乳動物的姻親關(guān)系。
2. 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.
短語：unlike the case of:與…的情況不同
it is not easy to envision:很難想象…的樣子
釋義：與海獺和其他鰭足動物不同，人們很難想象最初鯨類的模樣。邏輯轉(zhuǎn)換：人們很難想象最初鯨類動物的模樣，但與之相反，設(shè)想海獺等動物的原始樣貌應(yīng)較為容易。
3. How was the gap between a walking mammal and a swimming whale bridged?
釋義：本段主旨句，提出文章所討論的中心問題：從陸棲哺乳動物到水生鯨類之間到底是如何進(jìn)化的？
4. Pakicetus was found embedded in rocks formed from river deposits that were 52 million years old. 分句：“formed from river deposits that were 52 million years old”：形成于距今52 million年前的河流沉積物中，修飾rocks釋義：化石P被發(fā)現(xiàn)鑲嵌在巖石中，該巖石從距今52 million年前的河流沉積物中演化而來。
5. The fossil consists of a complete skull of an archaeocyte, an extinct group of ancestors of modern cetaceans.
短語：a complete skull：完整的頭骨
分句：“an extinct group of ancestors of modern cetaceans”修飾archaeocyte,即archaeocyte是鯨類動物的一種已滅絕的祖先
釋義：此句為事實(shí)1，化石P具有一個完整的鯨類始祖archaeocyte的頭骨。
6. 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. 分句：“that is filled with fat or oil and used for receiving underwater sound in modern whales”部分修飾enlarged space釋義：化石P的顎骨（jawbones）缺少現(xiàn)代鯨類具有的擴(kuò)大性空間，這部分空間通常由脂肪和油脂填充并用來收聽水下聲音。此句為事實(shí)2。
7. Pakicetus probably detected sound through the ear opening as in land mammals.
釋義：注意probably,此句為猜測1，化石P可能和陸棲動物一樣通過耳孔來接受聲音。
8. The skull also lacks a blowhole, another cetacean adaptation for diving.
釋義：此句為事實(shí)3，P頭骨缺少氣孔，該氣孔是鯨類適應(yīng)潛水活動的結(jié)構(gòu)。
9. Other features, however, show experts that Pakicetus is a transitional form between a group of extinct flesh-eating mammals, the mesonychids, and cetaceans.
分句：“a group of extinct flesh-eating mammals”修飾“the mesonychid”，即M動物是一類已滅絕的食肉哺乳動物
主干：Pakicetus is a transitional form between the mesonychids and cetaceans
釋義：此句指明化石P正是食肉哺乳動物M與鯨類的過渡階段形態(tài)，為本段結(jié)論。
10.It has been suggested that Pakicetus fed on fish in shallow water and was not yet adapted for life in the open ocean.
短語：fed on fish：以魚為食shallow water：淺水區(qū)
釋義：注意suggested,此句為猜測2，即化石P可能生前靠淺水區(qū)魚類為食并尚未適應(yīng)海洋生活。
11. It probably bred and gave birth on land.
釋義：“it”指代化石P，此句為猜測3，指出Pakicetus可能在陸地繁殖。
12. Several skeletons of another early whale, Basilosaurus, were found in sediments left by the Tethys Sea and now exposed in the Sahara desert.
詞匯：exposed意為“暴露在”，此處指“處于，位于”。
分句：“l(fā)eft by the Tethys Sea”修飾sediments,即B骨架發(fā)現(xiàn)于T海遺留的沉積物中
釋義：人們在Tethys海遺留的沉積物中發(fā)現(xiàn)了若干Basilosaurus的骨架，這些骨架現(xiàn)在位于撒哈拉沙漠中。
13. This whale lived around 40 million years ago, 12 million years after Pakicefus.
釋義：此句為事實(shí)1，即Basilosaurus生活于40 million年前，比化石P晚12 million年。
14. 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.
分句：“a complete hind leg that features a foot with three tiny toes”即B具有完全的后肢，包括包括一只腳和三個腳趾
釋義： 此句為事實(shí)2。注意archaeocyte是鯨類動物的一種已滅絕的祖先（已在上段中指出），由此可知原始鯨類Basilosaurus也是archaeocyte進(jìn)化過程中的階段性形態(tài)。
15.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.
短語：“nonfunctional, or vestigial, hind legs”：無實(shí)用作用的，退化了的后肢。
分句：“would have been too small to have supported the 50-foot-long Basilosaurus on land”:（這后肢）太小以至于不可能支撐50英尺長的Basilosaurus在陸地活動
釋義：此句為本段結(jié)論，即Basilosaurus絕對已是（undoubtedly）完全的海洋鯨類。
16. The now extinct whale Ambulocetus natans lived in the Tethys Sea 49 million years ago. It lived around 3 million years after Pakicetus but 9 million before Basilosaurus.
主干：Ambulocetus natans lived after Pakicetus but before Basilosaurus
釋義：此句為事實(shí)1。指出Ambulocetus natans生活于49million年前的Tethys海中，它晚于Pakicetus 3million 年，但早于Basilosaurus 9 million年。
17.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.
短語：a good portion of:很完好的一部分
be ended in：末端是…
分句：“ended in long feet very much like those of a modern pinniped”：實(shí)際為“ended in long feet (which is)very much like those of a modern pinniped”,修飾long feet
釋義：此處為事實(shí)2。A化石具有完好的后肢，后肢很強(qiáng)壯且足部很長，如同現(xiàn)代鰭足動物（如海獅）一樣，能夠同時在陸地和海洋活動。
18. 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.
分句：“the major means of locomotion in modern cetaceans”修飾fluke,即現(xiàn)代鯨類在水中前進(jìn)時所依靠的是其三角狀尾鰭
主干：the structure of the backbone shows that Ambulocetus swam like modern whales
釋義：此處為事實(shí)3。說明A化石缺少三角狀尾鰭，但既便如此它仍能像現(xiàn)代鯨類一樣游泳。
19. On land, where it probably bred and gave birth, Ambulocetus may have moved around very much like a modern sea lion.
釋義：注意probably和may,此為猜測，即Ambulocetus可能在陸地繁殖后代，并且它在陸地運(yùn)動時類似現(xiàn)代海獅。
20. It was undoubtedly a whale that linked life on land with life at sea.
釋義：此句為本段結(jié)論，即通過上文描述A兼具海洋動物和陸地哺乳動物的特點(diǎn)得出它毫無疑問正是陸地哺乳動物到海洋鯨類過渡過程中的海陸兩棲動物。
短語：cannot disguise their affinities with：不能掩蓋它們與…的姻親關(guān)系
land dwelling mammals：陸棲哺乳動物
釋義：鯨類動物的流線型身體，后肢的缺少，三角狀尾鰭的存在以及頭頂?shù)某鰵饪祝ㄒ陨隙际堑湫偷暮Ｑ髣游锾攸c(diǎn)）并不能掩蓋它們與陸棲哺乳動物的姻親關(guān)系。
2. 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.
短語：unlike the case of:與…的情況不同
it is not easy to envision:很難想象…的樣子
釋義：與海獺和其他鰭足動物不同，人們很難想象最初鯨類的模樣。邏輯轉(zhuǎn)換：人們很難想象最初鯨類動物的模樣，但與之相反，設(shè)想海獺等動物的原始樣貌應(yīng)較為容易。
3. How was the gap between a walking mammal and a swimming whale bridged?
釋義：本段主旨句，提出文章所討論的中心問題：從陸棲哺乳動物到水生鯨類之間到底是如何進(jìn)化的？
4. Pakicetus was found embedded in rocks formed from river deposits that were 52 million years old. 分句：“formed from river deposits that were 52 million years old”：形成于距今52 million年前的河流沉積物中，修飾rocks釋義：化石P被發(fā)現(xiàn)鑲嵌在巖石中，該巖石從距今52 million年前的河流沉積物中演化而來。
5. The fossil consists of a complete skull of an archaeocyte, an extinct group of ancestors of modern cetaceans.
短語：a complete skull：完整的頭骨
分句：“an extinct group of ancestors of modern cetaceans”修飾archaeocyte,即archaeocyte是鯨類動物的一種已滅絕的祖先
釋義：此句為事實(shí)1，化石P具有一個完整的鯨類始祖archaeocyte的頭骨。
6. 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. 分句：“that is filled with fat or oil and used for receiving underwater sound in modern whales”部分修飾enlarged space釋義：化石P的顎骨（jawbones）缺少現(xiàn)代鯨類具有的擴(kuò)大性空間，這部分空間通常由脂肪和油脂填充并用來收聽水下聲音。此句為事實(shí)2。
7. Pakicetus probably detected sound through the ear opening as in land mammals.
釋義：注意probably,此句為猜測1，化石P可能和陸棲動物一樣通過耳孔來接受聲音。
8. The skull also lacks a blowhole, another cetacean adaptation for diving.
釋義：此句為事實(shí)3，P頭骨缺少氣孔，該氣孔是鯨類適應(yīng)潛水活動的結(jié)構(gòu)。
9. Other features, however, show experts that Pakicetus is a transitional form between a group of extinct flesh-eating mammals, the mesonychids, and cetaceans.
分句：“a group of extinct flesh-eating mammals”修飾“the mesonychid”，即M動物是一類已滅絕的食肉哺乳動物
主干：Pakicetus is a transitional form between the mesonychids and cetaceans
釋義：此句指明化石P正是食肉哺乳動物M與鯨類的過渡階段形態(tài)，為本段結(jié)論。
10.It has been suggested that Pakicetus fed on fish in shallow water and was not yet adapted for life in the open ocean.
短語：fed on fish：以魚為食shallow water：淺水區(qū)
釋義：注意suggested,此句為猜測2，即化石P可能生前靠淺水區(qū)魚類為食并尚未適應(yīng)海洋生活。
11. It probably bred and gave birth on land.
釋義：“it”指代化石P，此句為猜測3，指出Pakicetus可能在陸地繁殖。
12. Several skeletons of another early whale, Basilosaurus, were found in sediments left by the Tethys Sea and now exposed in the Sahara desert.
詞匯：exposed意為“暴露在”，此處指“處于，位于”。
分句：“l(fā)eft by the Tethys Sea”修飾sediments,即B骨架發(fā)現(xiàn)于T海遺留的沉積物中
釋義：人們在Tethys海遺留的沉積物中發(fā)現(xiàn)了若干Basilosaurus的骨架，這些骨架現(xiàn)在位于撒哈拉沙漠中。
13. This whale lived around 40 million years ago, 12 million years after Pakicefus.
釋義：此句為事實(shí)1，即Basilosaurus生活于40 million年前，比化石P晚12 million年。
14. 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.
分句：“a complete hind leg that features a foot with three tiny toes”即B具有完全的后肢，包括包括一只腳和三個腳趾
釋義： 此句為事實(shí)2。注意archaeocyte是鯨類動物的一種已滅絕的祖先（已在上段中指出），由此可知原始鯨類Basilosaurus也是archaeocyte進(jìn)化過程中的階段性形態(tài)。
15.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.
短語：“nonfunctional, or vestigial, hind legs”：無實(shí)用作用的，退化了的后肢。
分句：“would have been too small to have supported the 50-foot-long Basilosaurus on land”:（這后肢）太小以至于不可能支撐50英尺長的Basilosaurus在陸地活動
釋義：此句為本段結(jié)論，即Basilosaurus絕對已是（undoubtedly）完全的海洋鯨類。
16. The now extinct whale Ambulocetus natans lived in the Tethys Sea 49 million years ago. It lived around 3 million years after Pakicetus but 9 million before Basilosaurus.
主干：Ambulocetus natans lived after Pakicetus but before Basilosaurus
釋義：此句為事實(shí)1。指出Ambulocetus natans生活于49million年前的Tethys海中，它晚于Pakicetus 3million 年，但早于Basilosaurus 9 million年。
17.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.
短語：a good portion of:很完好的一部分
be ended in：末端是…
分句：“ended in long feet very much like those of a modern pinniped”：實(shí)際為“ended in long feet (which is)very much like those of a modern pinniped”,修飾long feet
釋義：此處為事實(shí)2。A化石具有完好的后肢，后肢很強(qiáng)壯且足部很長，如同現(xiàn)代鰭足動物（如海獅）一樣，能夠同時在陸地和海洋活動。
18. 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.
分句：“the major means of locomotion in modern cetaceans”修飾fluke,即現(xiàn)代鯨類在水中前進(jìn)時所依靠的是其三角狀尾鰭
主干：the structure of the backbone shows that Ambulocetus swam like modern whales
釋義：此處為事實(shí)3。說明A化石缺少三角狀尾鰭，但既便如此它仍能像現(xiàn)代鯨類一樣游泳。
19. On land, where it probably bred and gave birth, Ambulocetus may have moved around very much like a modern sea lion.
釋義：注意probably和may,此為猜測，即Ambulocetus可能在陸地繁殖后代，并且它在陸地運(yùn)動時類似現(xiàn)代海獅。
20. It was undoubtedly a whale that linked life on land with life at sea.
釋義：此句為本段結(jié)論，即通過上文描述A兼具海洋動物和陸地哺乳動物的特點(diǎn)得出它毫無疑問正是陸地哺乳動物到海洋鯨類過渡過程中的海陸兩棲動物。