2024年6月11日发(作者：雍安南)
新托福TPO2阅读原文(一):The Origins of Cetaceans
TPO-2-1：The Origins of Cetaceans
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.
译文：TPO-2-1 鲸类的起源
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
2024年6月11日发(作者：雍安南)
新托福TPO2阅读原文(一):The Origins of Cetaceans
TPO-2-1：The Origins of Cetaceans
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.
译文：TPO-2-1 鲸类的起源
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